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CN 11-2282/P
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Volume 49,2023 Issue 2
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2023,49(2):129-145, DOI: 10.7519/j.issn.1000-0526.2022.100301
Abstract:
The downburst is the outburst of divergent flow on or near the ground induced by a strong convective downdraft. A single downburst affects a small area of several kilometers, and the downburst cluster can extend over several hundreds of kilometers resulting in many noncontinuous surface damaging gusts. Its enhancing mechanism may not be limited to the strong downdraft divergent outflow. This article reviews the definition of downburst, and dicusses downbursts under two different situations. One is the downburst induced by isolated storms and the other is the downbursts embedded in mesoscale convective systems, including the formation processes of downburst and warning technology of downburst based on Doppler weather radar. On the basis of the above review, the formation mechanism of downburst and the difficulties of warning are discussed, and the much-needed issues related to downburst are listed.
The downburst is the outburst of divergent flow on or near the ground induced by a strong convective downdraft. A single downburst affects a small area of several kilometers, and the downburst cluster can extend over several hundreds of kilometers resulting in many noncontinuous surface damaging gusts. Its enhancing mechanism may not be limited to the strong downdraft divergent outflow. This article reviews the definition of downburst, and dicusses downbursts under two different situations. One is the downburst induced by isolated storms and the other is the downbursts embedded in mesoscale convective systems, including the formation processes of downburst and warning technology of downburst based on Doppler weather radar. On the basis of the above review, the formation mechanism of downburst and the difficulties of warning are discussed, and the much-needed issues related to downburst are listed.
2023,49(2):146-156, DOI: 10.7519/j.issn.1000-0526.2022.022301
Abstract:
Based on the principle of the melting layer detection algorithm (MLDA) from National Severe Storms Laboratory, some detection tests are carried out using S-band dual-polarization radar volume data from Jinan and Qingdao radar stations in July and August 2020. According to the test results, some improvement measures such as radial continuity check, increasing the range of scan elevation and adjusting the threshold of total radar bin number for identifying the melting layer are integrated into the MLDA, and the recognition effect of MLDA on the melting layer before and after improvement are compared and the conclusions are as follows. The melting layer could be identified by the MLDA, but the mean absolute error of the top height of the melting layer is large and the melting layer bottom height is too low. After the radial continuity check is integrated into the MLDA (MLDA-R1), the mean absolute error of the top height of the melting layer gets smaller obviously, the temperature of the bottom height and the thickness of the melting layer are within a reasonable range, but the number of the test not having detected the melting layer increases markedly. On the basis of the MLDA-R1, 3.3° elevation is added to the scanning area (MLDA-R2) and the threshold of total number of radar bin for recognizing the melting layer is adjusted (MLDA-R3). Then, the number of the test not having detected the melting layer is significantly reduced, and the identification effect of the height information of the melting layer is improved. Some areas containing precipitation echo and non-precipitation echo could be falsely detected as the melting layer by MLDA after improvement so that the recognition effect of the melting layer is influenced. In general, MLDA after the improvement is more applicable to S-band dual-polarization radar in China and it can be utilized to support the radar hydrometer classification and quantitative precipitation estimation.
Based on the principle of the melting layer detection algorithm (MLDA) from National Severe Storms Laboratory, some detection tests are carried out using S-band dual-polarization radar volume data from Jinan and Qingdao radar stations in July and August 2020. According to the test results, some improvement measures such as radial continuity check, increasing the range of scan elevation and adjusting the threshold of total radar bin number for identifying the melting layer are integrated into the MLDA, and the recognition effect of MLDA on the melting layer before and after improvement are compared and the conclusions are as follows. The melting layer could be identified by the MLDA, but the mean absolute error of the top height of the melting layer is large and the melting layer bottom height is too low. After the radial continuity check is integrated into the MLDA (MLDA-R1), the mean absolute error of the top height of the melting layer gets smaller obviously, the temperature of the bottom height and the thickness of the melting layer are within a reasonable range, but the number of the test not having detected the melting layer increases markedly. On the basis of the MLDA-R1, 3.3° elevation is added to the scanning area (MLDA-R2) and the threshold of total number of radar bin for recognizing the melting layer is adjusted (MLDA-R3). Then, the number of the test not having detected the melting layer is significantly reduced, and the identification effect of the height information of the melting layer is improved. Some areas containing precipitation echo and non-precipitation echo could be falsely detected as the melting layer by MLDA after improvement so that the recognition effect of the melting layer is influenced. In general, MLDA after the improvement is more applicable to S-band dual-polarization radar in China and it can be utilized to support the radar hydrometer classification and quantitative precipitation estimation.
2023,49(2):157-169, DOI: 10.7519/j.issn.1000-0526.2022.061801
Abstract:
To reduce the deviation between radar rainfall field and surface rainfall observations, this paper proposes calibrating the radar rainfall field with surface microwave links including the variational calibration method, the Kalman filter calibration method, the mean calibration method and the Kriging calibration method. The rainfall rates retrieved by two microwave links are used to calibrate the S band radar rainfall field in two precipitation cases of different types. The calibration results are then compared with the measurements of rain gauges. The conclusions are as follows. Firstly, all the four calibration methods are proved effective to reduce the bias between the radar based rainfall estimates and the gauge measured rainfall. The problems of the underestimation of heavy precipitation in precipitation Case Ⅰ and the overestimation of weak precipitation in Case Ⅱ are both partly solved. The statistical errors including mean absolute error (MAE)， mean error (ME) and root mean square error (RMSE) are all significantly lowered after calibration. The improvement degrees of the statistical errors from high to low are ME, RMSE and MAE. Secondly, the effectiveness of the Kriging calibration method is the best among the four methods. The performances of the variational calibration method and the mean calibration method are better than that of Kalman filter calibration method. The Kriging calibration method is the most effective to reduce ME and RMSE and the variation method is most effective for MAE. Thirdly, the Kriging calibration method and the variational calibration method can derive calibration factor fields which vary with time and spatial position, while the mean calibration method and Kalman filter method can only obtain a mean calibration factor for each time. These results suggest that microwave link can be an effective alternative to calibrate the radar rainfall field.
To reduce the deviation between radar rainfall field and surface rainfall observations, this paper proposes calibrating the radar rainfall field with surface microwave links including the variational calibration method, the Kalman filter calibration method, the mean calibration method and the Kriging calibration method. The rainfall rates retrieved by two microwave links are used to calibrate the S band radar rainfall field in two precipitation cases of different types. The calibration results are then compared with the measurements of rain gauges. The conclusions are as follows. Firstly, all the four calibration methods are proved effective to reduce the bias between the radar based rainfall estimates and the gauge measured rainfall. The problems of the underestimation of heavy precipitation in precipitation Case Ⅰ and the overestimation of weak precipitation in Case Ⅱ are both partly solved. The statistical errors including mean absolute error (MAE)， mean error (ME) and root mean square error (RMSE) are all significantly lowered after calibration. The improvement degrees of the statistical errors from high to low are ME, RMSE and MAE. Secondly, the effectiveness of the Kriging calibration method is the best among the four methods. The performances of the variational calibration method and the mean calibration method are better than that of Kalman filter calibration method. The Kriging calibration method is the most effective to reduce ME and RMSE and the variation method is most effective for MAE. Thirdly, the Kriging calibration method and the variational calibration method can derive calibration factor fields which vary with time and spatial position, while the mean calibration method and Kalman filter method can only obtain a mean calibration factor for each time. These results suggest that microwave link can be an effective alternative to calibrate the radar rainfall field.
2023,49(2):170-177, DOI: 10.7519/j.issn.1000-0526.2022.080301
Abstract:
In order to study the cloud characteristics of the southeast coast of China, a laser ceilometer CL5 by Vaisala was used to detect cloud characteristics in Xiamen from 1 January 2016 to 31 December 2020. By using the time proportion algorithm to calculate the cloud fraction, this paper analyzes the distributions of cloud layers, cloud-base height and cloud fraction via data analysis method. The results show that the cloud structure in the southeast coast of China is dominated by single-layer clouds (43.59%), supplemented by double-layer clouds (16.42%), and the probability of occurrence of clouds with more than three layers is rare (5.25%). During the observation period, there were mainly low- and mid-level clouds. Compared with that in other seasons, the concentration of cloud distribution density in summer is smaller, and the cloud-base height difference between the lowest layer cloud and the highest layer cloud is larger. High clouds are more likely to occur between 18:00 BT and 06:00 BT, especially in summer, showing the characteristics of obvious diurnal variation.
In order to study the cloud characteristics of the southeast coast of China, a laser ceilometer CL5 by Vaisala was used to detect cloud characteristics in Xiamen from 1 January 2016 to 31 December 2020. By using the time proportion algorithm to calculate the cloud fraction, this paper analyzes the distributions of cloud layers, cloud-base height and cloud fraction via data analysis method. The results show that the cloud structure in the southeast coast of China is dominated by single-layer clouds (43.59%), supplemented by double-layer clouds (16.42%), and the probability of occurrence of clouds with more than three layers is rare (5.25%). During the observation period, there were mainly low- and mid-level clouds. Compared with that in other seasons, the concentration of cloud distribution density in summer is smaller, and the cloud-base height difference between the lowest layer cloud and the highest layer cloud is larger. High clouds are more likely to occur between 18:00 BT and 06:00 BT, especially in summer, showing the characteristics of obvious diurnal variation.
2023,49(2):178-187, DOI: 10.7519/j.issn.1000-0526.2022.050601
Abstract:
By using the ground-based vertical remote sensing equipment constructed by the Beijing National Comprehensive Meteorological Observation and Test Base for the Super-Large City Observation Test, and the observation data of radiosonde, laser aerosol radar, microwave radiometer and wind profiler radar from May to August 2021, and according to different detection advantages of the equipment and the diurnal variation of the boundary layer, this paper performs the joint inversion to the observation data of laser aerosol radar, microwave radiometer, and wind profiler radar to obtain the all-weather atmospheric boundary layer height. The comparison of the height of the boundary layer obtained from the joint inversion with the height of the all-weather atmospheric boundary layer provided by the sounding data calculation and the ERA5 reanalysis data suggests that the joint inversion boundary layer height is in good agreement with the atmospheric boundary layer height provided by the ERA5 data. The laser aerosol radar is suitable for the observation of the convective boundary layer during the daytime, and the microwave radiometer is suitable for the observation of the stable boundary layer at night. The use of microwave radiometer and wind profiler radar to jointly retrieve the height of the atmospheric boundary layer can improve the performance of a single device during rainfall. The joint inversion of the atmospheric boundary layer height result and the single device inversion of the atmospheric boundary layer height are in line with the diurnal variation of the atmospheric boundary layer. The joint inversion of boundary layer height obtained in this article is compared with the height difference of the atmospheric boundary layer from the sounding data, and their standard deviation is 62 m. Compared with the average value of the atmospheric boundary layer height in a certain range provided by the ERA5 data, the joint inversion of the boundary layer height could more accurately reflect the atmospheric boundary layer height in a smaller range.
By using the ground-based vertical remote sensing equipment constructed by the Beijing National Comprehensive Meteorological Observation and Test Base for the Super-Large City Observation Test, and the observation data of radiosonde, laser aerosol radar, microwave radiometer and wind profiler radar from May to August 2021, and according to different detection advantages of the equipment and the diurnal variation of the boundary layer, this paper performs the joint inversion to the observation data of laser aerosol radar, microwave radiometer, and wind profiler radar to obtain the all-weather atmospheric boundary layer height. The comparison of the height of the boundary layer obtained from the joint inversion with the height of the all-weather atmospheric boundary layer provided by the sounding data calculation and the ERA5 reanalysis data suggests that the joint inversion boundary layer height is in good agreement with the atmospheric boundary layer height provided by the ERA5 data. The laser aerosol radar is suitable for the observation of the convective boundary layer during the daytime, and the microwave radiometer is suitable for the observation of the stable boundary layer at night. The use of microwave radiometer and wind profiler radar to jointly retrieve the height of the atmospheric boundary layer can improve the performance of a single device during rainfall. The joint inversion of the atmospheric boundary layer height result and the single device inversion of the atmospheric boundary layer height are in line with the diurnal variation of the atmospheric boundary layer. The joint inversion of boundary layer height obtained in this article is compared with the height difference of the atmospheric boundary layer from the sounding data, and their standard deviation is 62 m. Compared with the average value of the atmospheric boundary layer height in a certain range provided by the ERA5 data, the joint inversion of the boundary layer height could more accurately reflect the atmospheric boundary layer height in a smaller range.
2023,49(2):188-200, DOI: 10.7519/j.issn.1000-0526.2022.081001
Abstract:
In this paper, radar extrapolation and high-resolution numerical weather prediction (NWP) are blended to get a 6 h quantitative precipitation forecast for the Yangtze River Delta Region of China. The method used here is based on a mainstream blending framework, and modifications and calibrations are conducted done to both the extrapolation and NWP to improve the result. The traditional COTREC extrapolation is extended by using a mosaic system of 11 radars within the region and NWP data. Intensity and position calibration for the NWP are conducted based on Weibull function fitting and object recognition. A weighted blending of extrapolation and NWP is then carried out based on scale and forecast time. Finally, real-time Z-R relation conversion is performed. The results show that the blending method can extend forecast time of the extrapolation forecast, and calibrate the intensity and position bias of NWP, thus making a better result as a whole.
In this paper, radar extrapolation and high-resolution numerical weather prediction (NWP) are blended to get a 6 h quantitative precipitation forecast for the Yangtze River Delta Region of China. The method used here is based on a mainstream blending framework, and modifications and calibrations are conducted done to both the extrapolation and NWP to improve the result. The traditional COTREC extrapolation is extended by using a mosaic system of 11 radars within the region and NWP data. Intensity and position calibration for the NWP are conducted based on Weibull function fitting and object recognition. A weighted blending of extrapolation and NWP is then carried out based on scale and forecast time. Finally, real-time Z-R relation conversion is performed. The results show that the blending method can extend forecast time of the extrapolation forecast, and calibrate the intensity and position bias of NWP, thus making a better result as a whole.
2023,49(2):201-212, DOI: 10.7519/j.issn.1000-0526.2022.090601
Abstract:
On 22 June 2017, an extreme warm-sector rainfall event hit the western coastal area of South China, during which Jinjiang Station observed a maximum cumulative rainfall of 562.5 mm in 24 hours which broke many local historical records. This paper analyzes the synoptic background, synoptic-scale triggering and maintenance mechanisms as well as evolution of the precipitation characteristics in this extreme rainfall event by using the NCEP/NCAR reanalysis data and multi-source observations. The results show that this extreme rainfall occurred under the condition of the low-level warm and humid southerly airflow. The updraft movement caused by the double low-level jets was the main synoptic-scale triggering mechanism. The upper-level jet also provided favorable unstable energy and water vapor. The outflow boundary generated by weak cold pool maintained for a long time at the same place and continuously lifted the warm and humid unstable air, resulting in extreme cumulative rainfall. During the whole rainfall process, the convective structure showed a low centroid. In the mature stage of convection, the average particle sizes of near-surface in the Jinjiang and Gangmei areas were relatively alike. The rainfall efficiency of Jinjiang was higher than that of Gangmei, which was mainly reflected in the larger number concentration of raindrops.
On 22 June 2017, an extreme warm-sector rainfall event hit the western coastal area of South China, during which Jinjiang Station observed a maximum cumulative rainfall of 562.5 mm in 24 hours which broke many local historical records. This paper analyzes the synoptic background, synoptic-scale triggering and maintenance mechanisms as well as evolution of the precipitation characteristics in this extreme rainfall event by using the NCEP/NCAR reanalysis data and multi-source observations. The results show that this extreme rainfall occurred under the condition of the low-level warm and humid southerly airflow. The updraft movement caused by the double low-level jets was the main synoptic-scale triggering mechanism. The upper-level jet also provided favorable unstable energy and water vapor. The outflow boundary generated by weak cold pool maintained for a long time at the same place and continuously lifted the warm and humid unstable air, resulting in extreme cumulative rainfall. During the whole rainfall process, the convective structure showed a low centroid. In the mature stage of convection, the average particle sizes of near-surface in the Jinjiang and Gangmei areas were relatively alike. The rainfall efficiency of Jinjiang was higher than that of Gangmei, which was mainly reflected in the larger number concentration of raindrops.
2023,49(2):213-223, DOI: 10.7519/j.issn.1000-0526.2022.072201
Abstract:
Based on the NCEP FNL (1°×1°) global analysis data and surface meteorological observations, the spatio-temporal characteristics of the 70 hailstorms in Tianjin from 2009 to 2019 are statistically analyzed, and the fusion sounding data are constructed to calculate the environmental parameters for hailstorms. Additionally, the environmental conditions for hailstorms in different months, different circulation patterns and different sizes are compared, and the corresponding prediction indices are given. The results show that the hailstorm in Tianjin mainly occurs from April to September, especially the hail and big hail days in June account for 49.4% and 60.0%, and the probability of hail and big hail from 12:00 BT to 20:00 BT account for 74.8% and 100%, 〖JP2〗respectively. Besides, the environmental parameters for hailstorms, such as convective available potential energy (CAPE), lift index (LI) , vertical wind shear (SHR), wet bulb 0℃ layer height (HWBZ) and total precipitable water (TPW), have obvious monthly variations and they should be noted significantly as prediction indicators. In April and September, the hailstorms mostly occur in low CAPE and high SHR conditions, but in July and August, the hailstorms often occur in medium-high CAPE and low SHR conditions. Additionally, the average HWBZ is 0.4-0.9 km lower than dry bulb 0℃ layer height (HDBZ), except that a very small number of hail in July and August HWBZ is in the range of 4.0-4.2 km. The other hails always occur in HWBZ<3.9 km conditions. The environmental conditions of cold vortex pattern and northwest flow pattern are not significantly different, but they are obviously different from the western trough pattern. The hailstorms of〖JP2〗 cold vortex pattern and northwest flow pattern usually occur under SHR>12 m·s-1, HWBZ<3.6 km and TPW>27 kg·〖JP〗m-2, while hailstorms of the western trough pattern mostly occur under SHR>9 m·s-1, HWBZ<3.9 km and TPW>36 kg·m-2. As for the hail, it is closely related to HWBZ and SHR. Take June as example. Small hails generally occur under HWBZ<3.9 km and SHR>9 m·s-1, while big hails appear under HWBZ<3.5 km and SHR>11 m·s-1.
Based on the NCEP FNL (1°×1°) global analysis data and surface meteorological observations, the spatio-temporal characteristics of the 70 hailstorms in Tianjin from 2009 to 2019 are statistically analyzed, and the fusion sounding data are constructed to calculate the environmental parameters for hailstorms. Additionally, the environmental conditions for hailstorms in different months, different circulation patterns and different sizes are compared, and the corresponding prediction indices are given. The results show that the hailstorm in Tianjin mainly occurs from April to September, especially the hail and big hail days in June account for 49.4% and 60.0%, and the probability of hail and big hail from 12:00 BT to 20:00 BT account for 74.8% and 100%, 〖JP2〗respectively. Besides, the environmental parameters for hailstorms, such as convective available potential energy (CAPE), lift index (LI) , vertical wind shear (SHR), wet bulb 0℃ layer height (HWBZ) and total precipitable water (TPW), have obvious monthly variations and they should be noted significantly as prediction indicators. In April and September, the hailstorms mostly occur in low CAPE and high SHR conditions, but in July and August, the hailstorms often occur in medium-high CAPE and low SHR conditions. Additionally, the average HWBZ is 0.4-0.9 km lower than dry bulb 0℃ layer height (HDBZ), except that a very small number of hail in July and August HWBZ is in the range of 4.0-4.2 km. The other hails always occur in HWBZ<3.9 km conditions. The environmental conditions of cold vortex pattern and northwest flow pattern are not significantly different, but they are obviously different from the western trough pattern. The hailstorms of〖JP2〗 cold vortex pattern and northwest flow pattern usually occur under SHR>12 m·s-1, HWBZ<3.6 km and TPW>27 kg·〖JP〗m-2, while hailstorms of the western trough pattern mostly occur under SHR>9 m·s-1, HWBZ<3.9 km and TPW>36 kg·m-2. As for the hail, it is closely related to HWBZ and SHR. Take June as example. Small hails generally occur under HWBZ<3.9 km and SHR>9 m·s-1, while big hails appear under HWBZ<3.5 km and SHR>11 m·s-1.
2023,49(2):224-234, DOI: 10.7519/j.issn.1000-0526.2022.110401
Abstract:
China Meteorological Administration (CMA) is one of the data exchange centers of global ensemble forecasting system. Global ensemble forecast systems (GEFS), including the European Center for Medium-Range Weather Forecasts (ECMWF), and the National Centers for Environmental Prediction (NCEP) have been used in real-time operation of the National Meteorological Centre (NMC) of CMA since 2010. The application of multi-model has promoted the progress of tropical cyclone forecasting operation of CMA. Based on the data of ECMWF and NCEP ensemble models from 2010 to 2019, we evaluate the performance and systematic deviation of their track forecast performance in following aspects: intensity, moving speed, month, ocean area, landing and turning. The ensemble mean forecast errors of the two models generally show a downward trend, and their systematic deviations are almost in the opposite directions. Separately, ECMWF ensemble forecast has a southwest bias, while NCEP ensemble tends to be northeastward, and is larger than the former in number. At present, the track prediction performance of ECMWF ensemble model is better than that of NCEP, especially for weak TCs and landing TCs. The results of the performance evaluation and deviation analysis could also provide a reference for actual TC forecasts when there are obvious differences between the products of the two ensemble models.
China Meteorological Administration (CMA) is one of the data exchange centers of global ensemble forecasting system. Global ensemble forecast systems (GEFS), including the European Center for Medium-Range Weather Forecasts (ECMWF), and the National Centers for Environmental Prediction (NCEP) have been used in real-time operation of the National Meteorological Centre (NMC) of CMA since 2010. The application of multi-model has promoted the progress of tropical cyclone forecasting operation of CMA. Based on the data of ECMWF and NCEP ensemble models from 2010 to 2019, we evaluate the performance and systematic deviation of their track forecast performance in following aspects: intensity, moving speed, month, ocean area, landing and turning. The ensemble mean forecast errors of the two models generally show a downward trend, and their systematic deviations are almost in the opposite directions. Separately, ECMWF ensemble forecast has a southwest bias, while NCEP ensemble tends to be northeastward, and is larger than the former in number. At present, the track prediction performance of ECMWF ensemble model is better than that of NCEP, especially for weak TCs and landing TCs. The results of the performance evaluation and deviation analysis could also provide a reference for actual TC forecasts when there are obvious differences between the products of the two ensemble models.
2023,49(2):235-248, DOI: 10.7519/j.issn.1000-0526.2022.110801
Abstract:
Using the spatial-temporal verification method of precipitation process, this paper evaluates the prediction effect of non-typhoon hourly precipitation in warm season (April to September of 2019-2020) of Hainan Island by Guangdong rapid update assimilation numerical prediction system (3 km resolution, CMA-GD), Shanghai numerical prediction system (CMA-SH9) and mesoscale weather numerical prediction system (CMA-MESO) of China Meteorological Administration. 〖JP2〗The results show that the three models 〖JP〗all can capture the spatial distribution of precipitation and the diurnal variation of precipitation under different flow field conditions. However, the frequency and intensity of precipitation in CMA-GD and CMA-SH9 are generally more and stronger, of which the frequency of precipitation in CMA-GD is more than 10%, the average hourly rainfall intensity of CMA-SH9 is nearly 4 mm·h-1 stronger. The precipitation intensity above 5 mm·h-1 of CMA-MESO is mostly distributed in the southwestern and central mountainous areas, which is quite different from the observed spatial distribution. The easiest precipitation start time and precipitation peak time of the three models are 1-3 h earlier than the observation, and the easiest precipita-tion end time is 1-3 h later than the observation; The predicted values of dew point temperature and unstable energy in the upper atmosphere of the model are too large, unstable energy appears earlier, the characteristic prediction of the near-surface inversion layer is distorted, the start time of precipitation forecast tends to be earlier, and the precipitation duration is too long. The sea-land wind convergence zone along the northern coast of Hainan Island is predicted to be strong in the daytime by the three models, especially CMA-SH9, which is consistent with obvious strong precipitation intensity of the model’s output. The forecast position of the sea-land wind convergence zone along the southern coast of CMA-GD at night is westward, which corresponds to the higher frequency of precipitation along the southwestern coast of the model. CMA-MESO has strong wind speed convergence in the southwestern and central mountainous areas of Hainan Island, and the corresponding precipitation forecast intensity is stronger than the observation.
Using the spatial-temporal verification method of precipitation process, this paper evaluates the prediction effect of non-typhoon hourly precipitation in warm season (April to September of 2019-2020) of Hainan Island by Guangdong rapid update assimilation numerical prediction system (3 km resolution, CMA-GD), Shanghai numerical prediction system (CMA-SH9) and mesoscale weather numerical prediction system (CMA-MESO) of China Meteorological Administration. 〖JP2〗The results show that the three models 〖JP〗all can capture the spatial distribution of precipitation and the diurnal variation of precipitation under different flow field conditions. However, the frequency and intensity of precipitation in CMA-GD and CMA-SH9 are generally more and stronger, of which the frequency of precipitation in CMA-GD is more than 10%, the average hourly rainfall intensity of CMA-SH9 is nearly 4 mm·h-1 stronger. The precipitation intensity above 5 mm·h-1 of CMA-MESO is mostly distributed in the southwestern and central mountainous areas, which is quite different from the observed spatial distribution. The easiest precipitation start time and precipitation peak time of the three models are 1-3 h earlier than the observation, and the easiest precipita-tion end time is 1-3 h later than the observation; The predicted values of dew point temperature and unstable energy in the upper atmosphere of the model are too large, unstable energy appears earlier, the characteristic prediction of the near-surface inversion layer is distorted, the start time of precipitation forecast tends to be earlier, and the precipitation duration is too long. The sea-land wind convergence zone along the northern coast of Hainan Island is predicted to be strong in the daytime by the three models, especially CMA-SH9, which is consistent with obvious strong precipitation intensity of the model’s output. The forecast position of the sea-land wind convergence zone along the southern coast of CMA-GD at night is westward, which corresponds to the higher frequency of precipitation along the southwestern coast of the model. CMA-MESO has strong wind speed convergence in the southwestern and central mountainous areas of Hainan Island, and the corresponding precipitation forecast intensity is stronger than the observation.
2023,49(2):249-256, DOI: 10.7519/j.issn.1000-0526.2023.013001
Abstract:
The main characteristics of the general atmospheric circulation in November 2022 are as follows. There were two polar vortex centers in the Northern Hemisphere. The East Asian trough and the southern branch trough were weaker than in the same period of normal years. The western Pacific subtropical high was stronger during this month. The monthly mean precipitation across China was 26.9 mm, which is 33.2% more than normal (20.2 mm). The monthly average temperature was 4.8℃, 1.5℃ higher than the temperature (3.3℃) in the same periods of normal years. The cold and warm temperatures fluctuated greatly during the month. The cold air was not so active in the early and mid dekads. Accordingly, the temperature was higher and the precipitation was less in most of China. However, in the later period, affected by the strong cold air and the active southern branch trough, the temperature dropped sharply and precipitation increased significantly. In addition, there were one nationwide cold wave process and two widespread persistent fog-haze weather processes.
The main characteristics of the general atmospheric circulation in November 2022 are as follows. There were two polar vortex centers in the Northern Hemisphere. The East Asian trough and the southern branch trough were weaker than in the same period of normal years. The western Pacific subtropical high was stronger during this month. The monthly mean precipitation across China was 26.9 mm, which is 33.2% more than normal (20.2 mm). The monthly average temperature was 4.8℃, 1.5℃ higher than the temperature (3.3℃) in the same periods of normal years. The cold and warm temperatures fluctuated greatly during the month. The cold air was not so active in the early and mid dekads. Accordingly, the temperature was higher and the precipitation was less in most of China. However, in the later period, affected by the strong cold air and the active southern branch trough, the temperature dropped sharply and precipitation increased significantly. In addition, there were one nationwide cold wave process and two widespread persistent fog-haze weather processes.
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Available online: March 24, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.021701
Abstract:
Abstract：Using the precipitation data of intensive automatic weather station, ERA5 reanalysis data and radar data, a local rainstorm process influenced by the parallel ridge-valley topography in western Chongqing from 16 to 17 June 2020 is analyzed. The results show that the rainstorm process is happened under the combined influence of the stable low vortex shear formed by the southwest warm and humid low-level airflow around the subtropical high and the northward air flow intruding into the Sichuan Basin under the guidance of the high trough in western Chongqing, and the maintaining mesoscale convergence line under the influence of the parallel ridge-valley topography. From 00:00 to 03:00 UTC 17 June, there are obvious moisture convergence, ascending motion and strong instability center in the boundary layer below 850 hPa in the ridge-valley region, which result in local heavy rainfall. Under the influence of the ridge-valley topography, the cold front and the convergence center moving northward along the convergence line lifts on the windward slope, which strengthen the vertical ascending motion that increase the vertical circulation wind speed in front of the front, which is an important reason for the rainstorm amplification in the southern end of Huaying Mountain and the eastern transition area of wide valleys and hills. The development and evolution of the mesoscale convective systems are closely related to the postion change of the surface convergence line. The convergence listing of the parallel ridge-valley makes the mesoscale convective systems stagnate near the Huaying Mountain and develop and strengthen twice at its southern end.
Abstract：Using the precipitation data of intensive automatic weather station, ERA5 reanalysis data and radar data, a local rainstorm process influenced by the parallel ridge-valley topography in western Chongqing from 16 to 17 June 2020 is analyzed. The results show that the rainstorm process is happened under the combined influence of the stable low vortex shear formed by the southwest warm and humid low-level airflow around the subtropical high and the northward air flow intruding into the Sichuan Basin under the guidance of the high trough in western Chongqing, and the maintaining mesoscale convergence line under the influence of the parallel ridge-valley topography. From 00:00 to 03:00 UTC 17 June, there are obvious moisture convergence, ascending motion and strong instability center in the boundary layer below 850 hPa in the ridge-valley region, which result in local heavy rainfall. Under the influence of the ridge-valley topography, the cold front and the convergence center moving northward along the convergence line lifts on the windward slope, which strengthen the vertical ascending motion that increase the vertical circulation wind speed in front of the front, which is an important reason for the rainstorm amplification in the southern end of Huaying Mountain and the eastern transition area of wide valleys and hills. The development and evolution of the mesoscale convective systems are closely related to the postion change of the surface convergence line. The convergence listing of the parallel ridge-valley makes the mesoscale convective systems stagnate near the Huaying Mountain and develop and strengthen twice at its southern end.
Available online: March 24, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.012901
Abstract:
Urban ventilation corridor is an effective measure to alleviate urban heat island and improve urban wind environment, which is helpful to improve the air circulation and micro-climate environment in urban areas, creating a "breathing city" and improve the comfort of urban living. Taking the main urban area of Hefei as an example, this paper uses multiple data, such as meteorological observation data, satellite remote sensing data, geographic information data, etc., and grades the ventilation potential of the main urban area of Hefei by calculating a series of urban ecological parameters, such as sky openness and surface roughness. Results show that the heat island effect of the Jingkai and Shuangfeng development zone in the main urban area of Hefei was serious. Hefei city center area of the sky openness is low, most of the area under 0.5, the surface roughness of Nanfei river, but it’s both sides of the surface roughness are higher. The surface ventilation potential of most areas is general, but the southeast side near Chao lake and Nanfei river had higher ventilation potential. The construction area and northwest sides had poor ventilation potential. Based on the wind direction rose diagram and the analysis of urban space thermal environment, six ventilation corridors with four longitudinal and two horizontal lines was preliminarily constructed.
Urban ventilation corridor is an effective measure to alleviate urban heat island and improve urban wind environment, which is helpful to improve the air circulation and micro-climate environment in urban areas, creating a "breathing city" and improve the comfort of urban living. Taking the main urban area of Hefei as an example, this paper uses multiple data, such as meteorological observation data, satellite remote sensing data, geographic information data, etc., and grades the ventilation potential of the main urban area of Hefei by calculating a series of urban ecological parameters, such as sky openness and surface roughness. Results show that the heat island effect of the Jingkai and Shuangfeng development zone in the main urban area of Hefei was serious. Hefei city center area of the sky openness is low, most of the area under 0.5, the surface roughness of Nanfei river, but it’s both sides of the surface roughness are higher. The surface ventilation potential of most areas is general, but the southeast side near Chao lake and Nanfei river had higher ventilation potential. The construction area and northwest sides had poor ventilation potential. Based on the wind direction rose diagram and the analysis of urban space thermal environment, six ventilation corridors with four longitudinal and two horizontal lines was preliminarily constructed.
Available online: March 21, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.010901
Abstract:
Coastal offshore observation stations are rare, while coastal land observation stations are relatively dense. Carrying out research on the characteristics of land-sea wind speed difference caused by land-sea distribution and realizing the estimation of sea surface wind speed from land observation wind speed is helpful to improve the service ability of sea surface wind forecast. In this paper, the hourly mean wind speed and gust speed data of two groups of buoys and their adjacent land observation stations in the north coast of China from 2016 to 2020 are used to statistically analyze the characteristics and regularity of the difference between sea surface wind speed and land wind speed. And the support vector machine method is used to build the sea surface wind speed estimation model based on the land mean wind speed, land gust speed, distance between land-sea stations, month and hour. The estimation model is tested by using the observation data of the other two groups of land-sea observation stations in 2021. The results show that for the mean wind speed above scale 5 and gust wind speed above scale 6, the model has a high estimation accuracy and is superior to ERA5. The root mean square error of the mean wind speed (gust speed) of the two groups estimated by the model is 2.40 m·s-1 (3.20 m·s-1) and 2.35 m·s-1 (3.20 m·s-1 and 2.57 m·s-1), respectively. Compared with ERA5, it decreased by 24% (14%) and 23% (14% and 20%) respectively. In a strong wind process jointly affected by an extratropical cyclone and cold air, the mean absolute errors of the mean wind speed (gust speed) estimated by the model for the two test groups are 1.6 m·s-1 (2.3 m·s-1) and 1.1 m·s-1 (2.3 m·s-1 and 1.5 m·s-1) respectively, and the mean wind speed (gust speed) errors at the extreme moment are -1.3 m·s-1 (-0.6 m·s-1) and -1.2 m·s-1 (-0.6 m·s-1 and -3.1 m·s-1) respectively, which are better than that of ERA5. The sea surface wind speed estimation model based on support vector machine can estimate accurate heavy sea surface wind speed using the land observation wind speed, which can reduce the impact of insufficient sea observation data, and has a certain application prospect.
Coastal offshore observation stations are rare, while coastal land observation stations are relatively dense. Carrying out research on the characteristics of land-sea wind speed difference caused by land-sea distribution and realizing the estimation of sea surface wind speed from land observation wind speed is helpful to improve the service ability of sea surface wind forecast. In this paper, the hourly mean wind speed and gust speed data of two groups of buoys and their adjacent land observation stations in the north coast of China from 2016 to 2020 are used to statistically analyze the characteristics and regularity of the difference between sea surface wind speed and land wind speed. And the support vector machine method is used to build the sea surface wind speed estimation model based on the land mean wind speed, land gust speed, distance between land-sea stations, month and hour. The estimation model is tested by using the observation data of the other two groups of land-sea observation stations in 2021. The results show that for the mean wind speed above scale 5 and gust wind speed above scale 6, the model has a high estimation accuracy and is superior to ERA5. The root mean square error of the mean wind speed (gust speed) of the two groups estimated by the model is 2.40 m·s-1 (3.20 m·s-1) and 2.35 m·s-1 (3.20 m·s-1 and 2.57 m·s-1), respectively. Compared with ERA5, it decreased by 24% (14%) and 23% (14% and 20%) respectively. In a strong wind process jointly affected by an extratropical cyclone and cold air, the mean absolute errors of the mean wind speed (gust speed) estimated by the model for the two test groups are 1.6 m·s-1 (2.3 m·s-1) and 1.1 m·s-1 (2.3 m·s-1 and 1.5 m·s-1) respectively, and the mean wind speed (gust speed) errors at the extreme moment are -1.3 m·s-1 (-0.6 m·s-1) and -1.2 m·s-1 (-0.6 m·s-1 and -3.1 m·s-1) respectively, which are better than that of ERA5. The sea surface wind speed estimation model based on support vector machine can estimate accurate heavy sea surface wind speed using the land observation wind speed, which can reduce the impact of insufficient sea observation data, and has a certain application prospect.
Available online: March 17, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.030702
Abstract:
In this paper, based on two commonly used aircraft icing diagnostic indices and using ERA5 reanalysis data as the atmospheric environmental field for icing occurrence, an aircraft icing diagnosis and forecasting method is constructed and back-calculated for 25 collected spring icing cases over eastern China. The spatial and temporal distribution characteristics of aircraft icing occurrence over typical cities at different latitudes in China are calculated separately, and the spatial and temporal distribution of icing areas over Xinchang, Zhejiang Province during one cold air activity case is simulated. Several application scenarios of aircraft icing forecasting methods are proposed. The results indicate the following. Among the selected icing cases, the diagnosis accuracy of icing index (IC) method is 80%, while that of the false frost point temperature empirical (TF) method is 92%. The effect of aircraft flight speed and power warming are taken into account by TF method, which has better correlation with water particle concentration and cloud volume in medium and low clouds. But the predicted icing intensity is not accurate enough without the real airspeed of the aircraft, and there are more error reports above 400hPa altitude. Both the IC method and TF method can effectively diagnose the icing-prone altitude layer and the icing-prone time, and can effectively forecast the distribution of high-altitude ice accumulation intensity at a certain station. In addition, TF method can calculate the icing critical flight speed of the aircraft.
In this paper, based on two commonly used aircraft icing diagnostic indices and using ERA5 reanalysis data as the atmospheric environmental field for icing occurrence, an aircraft icing diagnosis and forecasting method is constructed and back-calculated for 25 collected spring icing cases over eastern China. The spatial and temporal distribution characteristics of aircraft icing occurrence over typical cities at different latitudes in China are calculated separately, and the spatial and temporal distribution of icing areas over Xinchang, Zhejiang Province during one cold air activity case is simulated. Several application scenarios of aircraft icing forecasting methods are proposed. The results indicate the following. Among the selected icing cases, the diagnosis accuracy of icing index (IC) method is 80%, while that of the false frost point temperature empirical (TF) method is 92%. The effect of aircraft flight speed and power warming are taken into account by TF method, which has better correlation with water particle concentration and cloud volume in medium and low clouds. But the predicted icing intensity is not accurate enough without the real airspeed of the aircraft, and there are more error reports above 400hPa altitude. Both the IC method and TF method can effectively diagnose the icing-prone altitude layer and the icing-prone time, and can effectively forecast the distribution of high-altitude ice accumulation intensity at a certain station. In addition, TF method can calculate the icing critical flight speed of the aircraft.
Available online: March 15, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.030302
Abstract:
Based on automatic weather station, dual-polarization radar, millimeter-wave cloud radar, temperature profiler and ERA5 hourly reanalysis data, the characteristics of the multi-source observation data of the precipitation phase change during the extreme heavy snowstorm in the western area of Shandong on 7 November 2021 are analyzed. The results show: This process is combined influenced by the westerly trough, low vortex shear line and cold front. The system has strong baroclinicity, with low-level jet. Though the snowfall duration is not long, the hourly intensity of snow precipitation is high. Therefore, Extreme heavy snowfall appears in the western area of Shandong. The multi-source observational data captures the precipitation phase and change information well in this process. Wind and vertical velocity of wind profiler radar, correlation coefficient and zero-degree bright band of dual-polarization radar, reflectivity, vertical liquid water content, velocity and spectral width of millimeter-wave cloud radar, boundary layer temperature of temperature profiler and the two-dimensional images and information of particles from the 2D video raindrop spectrometer can be used as indicators for judging the phase of the precipitation, so these provide a reference for 0—1 hour short-term nowcasting. During this process, air temperature above the ground cooled very rapidly, the rain quickly turned to snow and the sleet only lasted for a short time. The cooling of air temperature above the ground is caused by the combination of strong negative temperature advection, vertical motion and non-adiabatic effect. In the three, the effect of negative temperature advection is the largest, the precipitation diabatic effect is the second, and the vertical motion effect is the smallest. The strong negative temperature advection and the negative temperature advection intensity increasing with the decrease of height, results in the rapid cooling of air temperature above the ground.
Based on automatic weather station, dual-polarization radar, millimeter-wave cloud radar, temperature profiler and ERA5 hourly reanalysis data, the characteristics of the multi-source observation data of the precipitation phase change during the extreme heavy snowstorm in the western area of Shandong on 7 November 2021 are analyzed. The results show: This process is combined influenced by the westerly trough, low vortex shear line and cold front. The system has strong baroclinicity, with low-level jet. Though the snowfall duration is not long, the hourly intensity of snow precipitation is high. Therefore, Extreme heavy snowfall appears in the western area of Shandong. The multi-source observational data captures the precipitation phase and change information well in this process. Wind and vertical velocity of wind profiler radar, correlation coefficient and zero-degree bright band of dual-polarization radar, reflectivity, vertical liquid water content, velocity and spectral width of millimeter-wave cloud radar, boundary layer temperature of temperature profiler and the two-dimensional images and information of particles from the 2D video raindrop spectrometer can be used as indicators for judging the phase of the precipitation, so these provide a reference for 0—1 hour short-term nowcasting. During this process, air temperature above the ground cooled very rapidly, the rain quickly turned to snow and the sleet only lasted for a short time. The cooling of air temperature above the ground is caused by the combination of strong negative temperature advection, vertical motion and non-adiabatic effect. In the three, the effect of negative temperature advection is the largest, the precipitation diabatic effect is the second, and the vertical motion effect is the smallest. The strong negative temperature advection and the negative temperature advection intensity increasing with the decrease of height, results in the rapid cooling of air temperature above the ground.
Available online: March 03, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.021001
Abstract:
Due to the small spatiotemporal scale and large change rate of turbulence, and the lack of large-scale field observation, there is little research on the characteristics of atmospheric turbulence in China. Since 2011, China has begun to store second level high-resolution soundings data, which makes it possible to deeply study the characteristics of turbulence in various parts of China. When using radiosonde data to diagnose and analyze the characteristics of turbulence, it is necessary to consider the impact of instrument noise on the analysis results. Firstly, this paper analyzes the impact of instrument noise on the analysis results in China, proves that noise will reduce the average turbulent dissipation rate in the troposphere, and proves the necessity of removing noise. On this basis, Thorpe analysis method is used to analyze the relationship between the intensity of turbulence (turbulence dissipation rate) and the type of underlying surface in detail. Results in the troposphere, the annual average grassland turbulence was the strongest, followed by dryland crops, paddy crops, shrubs and wasteland. In the lower stratosphere, it is still affected by the underlying surface, and the annual average turbulence of grassland is still the strongest, followed by dry land crops. The turbulence shows obvious seasonality on different underlying surfaces, and the intensity and frequency of the upper troposphere are the highest in summer. The results of this paper will help to understand the characteristics of turbulence and provide reference information for aircraft flight safety and the improvement of turbulence parameterization scheme.
Due to the small spatiotemporal scale and large change rate of turbulence, and the lack of large-scale field observation, there is little research on the characteristics of atmospheric turbulence in China. Since 2011, China has begun to store second level high-resolution soundings data, which makes it possible to deeply study the characteristics of turbulence in various parts of China. When using radiosonde data to diagnose and analyze the characteristics of turbulence, it is necessary to consider the impact of instrument noise on the analysis results. Firstly, this paper analyzes the impact of instrument noise on the analysis results in China, proves that noise will reduce the average turbulent dissipation rate in the troposphere, and proves the necessity of removing noise. On this basis, Thorpe analysis method is used to analyze the relationship between the intensity of turbulence (turbulence dissipation rate) and the type of underlying surface in detail. Results in the troposphere, the annual average grassland turbulence was the strongest, followed by dryland crops, paddy crops, shrubs and wasteland. In the lower stratosphere, it is still affected by the underlying surface, and the annual average turbulence of grassland is still the strongest, followed by dry land crops. The turbulence shows obvious seasonality on different underlying surfaces, and the intensity and frequency of the upper troposphere are the highest in summer. The results of this paper will help to understand the characteristics of turbulence and provide reference information for aircraft flight safety and the improvement of turbulence parameterization scheme.
Available online: March 03, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.030301
Abstract:
Supersaturation in the cloud is the one of key factors affecting cloud macro- and micro-properties. The Explicit Mixing Parcel Model (EMPM) is used to study the evolution of supersaturation of cloud droplets during the entrainment-mixing process. The results show that in this process, the supersaturation decreases firstly due to entrained dry air, and then increases due to evaporation of droplets until the parcel restores new saturation. Secondly, the effects of different thermal, dynamic and microphysical factors on the reduction of supersaturation and saturation recovery time are as follows: (1) Factors of small reduction and quick recovery are the high relative humidity of the entrained dry air and initial cloud droplet concentration. The higher humidity means less effect of entrainment. The higher droplet number concentration corresponds to the smaller droplet size and the faster evaporation, and thus the supplement to the humidity of dry air is strong. (2) The factor of large reduction and slow recovery is the large fraction of entrained dry air. The more dry air is entrained, the more evaporation of droplets. (3) The factor of large reduction and quick recovery is the high turbulent kinetic energy dissipation rate. The faster the mixing process, the faster cloud droplets evaporate. The results will help to improve the understanding of the entrainment mixing process and warm cloud precipitation theory.
Supersaturation in the cloud is the one of key factors affecting cloud macro- and micro-properties. The Explicit Mixing Parcel Model (EMPM) is used to study the evolution of supersaturation of cloud droplets during the entrainment-mixing process. The results show that in this process, the supersaturation decreases firstly due to entrained dry air, and then increases due to evaporation of droplets until the parcel restores new saturation. Secondly, the effects of different thermal, dynamic and microphysical factors on the reduction of supersaturation and saturation recovery time are as follows: (1) Factors of small reduction and quick recovery are the high relative humidity of the entrained dry air and initial cloud droplet concentration. The higher humidity means less effect of entrainment. The higher droplet number concentration corresponds to the smaller droplet size and the faster evaporation, and thus the supplement to the humidity of dry air is strong. (2) The factor of large reduction and slow recovery is the large fraction of entrained dry air. The more dry air is entrained, the more evaporation of droplets. (3) The factor of large reduction and quick recovery is the high turbulent kinetic energy dissipation rate. The faster the mixing process, the faster cloud droplets evaporate. The results will help to improve the understanding of the entrainment mixing process and warm cloud precipitation theory.
Available online: March 03, 2023 , DOI: 10.7519/j.issn.1000-0526.2022.113001
Abstract:
In order to study the extrapolation predictability of cloud images or cloud clusters with different scales, two things were done. First, a cloud detection method suitable for FY-4 satellite infrared cloud images (10.8 μm) was designed, and the cloud clusters with different scales were separated by the regional recognition algorithm. Second, the optical flow method of HS global constraint scheme was used to carry out extrapolation test. The results show that: 1) In the extrapolation forecasting of brightness temperature, the available optical flow information is close to 6 hours. the RMSE of bright temperatures in 0.5, 1 and 6 hours are about 5, 9 and 17K respectively. The accuracy of extrapolation prediction decreases with the increasing of time length in forecasting. 2) Because of diurnal variations in brightness temperature, the cloud detection results are used in the following extrapolation tests. 2-1) In the short extrapolation time, the main error is caused by the deviations from cloud location; During the first to sixth hours, the main error is caused by the prediction errors from cloud location and cloud area. 2-2)The accuracy of extrapolation forecasting decreases as the spatial scale of the cloud cluster decreasing. The useable time lengths of extrapolating cloud clusters in scales >2000km, 200-2000km, 20-200km, and <20km are shorter than 6 hours, 2 hours, 1 hour and 10 minutes, respectively. The extrapolated results in all scales are similar with that in the scale >2000km. 2-3)The useable time length is closely related to the evolutions of physical properties and the life length of clouds in different scales. The research results can give a significant guide in extrapolation forecasting of infrared cloud image in operational applications.
In order to study the extrapolation predictability of cloud images or cloud clusters with different scales, two things were done. First, a cloud detection method suitable for FY-4 satellite infrared cloud images (10.8 μm) was designed, and the cloud clusters with different scales were separated by the regional recognition algorithm. Second, the optical flow method of HS global constraint scheme was used to carry out extrapolation test. The results show that: 1) In the extrapolation forecasting of brightness temperature, the available optical flow information is close to 6 hours. the RMSE of bright temperatures in 0.5, 1 and 6 hours are about 5, 9 and 17K respectively. The accuracy of extrapolation prediction decreases with the increasing of time length in forecasting. 2) Because of diurnal variations in brightness temperature, the cloud detection results are used in the following extrapolation tests. 2-1) In the short extrapolation time, the main error is caused by the deviations from cloud location; During the first to sixth hours, the main error is caused by the prediction errors from cloud location and cloud area. 2-2)The accuracy of extrapolation forecasting decreases as the spatial scale of the cloud cluster decreasing. The useable time lengths of extrapolating cloud clusters in scales >2000km, 200-2000km, 20-200km, and <20km are shorter than 6 hours, 2 hours, 1 hour and 10 minutes, respectively. The extrapolated results in all scales are similar with that in the scale >2000km. 2-3)The useable time length is closely related to the evolutions of physical properties and the life length of clouds in different scales. The research results can give a significant guide in extrapolation forecasting of infrared cloud image in operational applications.
Available online: March 01, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.022301
Abstract:
Climate change induced by human activities is already affecting many weather, climate and water extremes in every region across the globe. Every additional increment of global warming will lead to larger changes in extremes. If there is no action on global carbon neutralization, further increases in the intensity and frequency of hot extremes, and decreases in the intensity and frequency of cold extremes, will occur throughout the 21st century and around the world. And the intensity and frequency of heavy precipitation as well as agricultural and ecological drought in some regions will also undergo a significant increase. Today’s children and future generations are more vulnerable to the risk of future climate change and extremes. They are projected to experience nearly four-fold increase in extreme weather, climate and water events by the end of this century. In view of the increasingly severe risk of climate change and extreme events, it is urgent to actively pursue the carbon peaking and carbon neutrality goals and strong reductions in the emissions of methane and other greenhouse gases. At the same time, it is urgent to formulate policies and measures related to disaster prevention and mitigation, and promote the construction of extreme event monitoring and early warning system and resilience. Additionally, it cannot be ignored to enhance the prevention of compound extreme events and small probability-high impact event to ensure the well-being and sustainable development of future generations.
Climate change induced by human activities is already affecting many weather, climate and water extremes in every region across the globe. Every additional increment of global warming will lead to larger changes in extremes. If there is no action on global carbon neutralization, further increases in the intensity and frequency of hot extremes, and decreases in the intensity and frequency of cold extremes, will occur throughout the 21st century and around the world. And the intensity and frequency of heavy precipitation as well as agricultural and ecological drought in some regions will also undergo a significant increase. Today’s children and future generations are more vulnerable to the risk of future climate change and extremes. They are projected to experience nearly four-fold increase in extreme weather, climate and water events by the end of this century. In view of the increasingly severe risk of climate change and extreme events, it is urgent to actively pursue the carbon peaking and carbon neutrality goals and strong reductions in the emissions of methane and other greenhouse gases. At the same time, it is urgent to formulate policies and measures related to disaster prevention and mitigation, and promote the construction of extreme event monitoring and early warning system and resilience. Additionally, it cannot be ignored to enhance the prevention of compound extreme events and small probability-high impact event to ensure the well-being and sustainable development of future generations.
Available online: February 13, 2023 , DOI: 10.7519/j.issn.1000-0526.2022.121201
Abstract:
A relatively large number of the convective storms which affect Beijing and Hebei province can often be traced to the Taihang Mountains. The study analyzes warm season convective storms between 2011 and 2020 developing in the eastern foothills of the Taihang Mountains. The statistical analysis is based on the national composite radar reflectivity factor data mosaics to increase the understanding of the evolution of these convective storms, including the changing of intensity, lifespan and so on. The results show that 1) there are four high-frequency centers of strong echoes≥45 dBz which located in northern Shijiazhuang, southern Beijing, south-central Baoding and western Cangzhou. The storms often strengthen significantly in the foothills of northern Shijiazhuang and western Cangzhou. 2) For strengthened convective storms, they are most active in mountainous areas around 1700 BT and mainly affect plain areas between 1800BT and 0200 BT. 3) The more westerly the path, the more cases of mountain-to-plain convective storms, the higher the percentage of convective intensification, and the greater the moving speed. 4) During the downhill process, most convective storms become stronger and more organized. For the convective storms whose echo strength ≥45 dBz at the initial moment of going downhill, more than 85% of them can successfully reach the plains, and more than 90% of them with horizontal scale exceeding 100 km and solidly connected structures can successfully reach the plains. 5) The strong echo areas of the strengthened convective storms expand dramatically as they go downhill. Strong echo areas expand to about 2 times larger than their initial echo areas when they reach the foothill, and the average areas in the plains can reach 4.6 times as big as their initial echo areas. 6) Most of the strengthened convective storms take only 1-2 hours to go downhill and last 4-8 hours on the plains. The storm types of the convective storms which last 4-8 hours on the plains are dominated by linear MCS (47%) and nonlinear MCS (30%).
A relatively large number of the convective storms which affect Beijing and Hebei province can often be traced to the Taihang Mountains. The study analyzes warm season convective storms between 2011 and 2020 developing in the eastern foothills of the Taihang Mountains. The statistical analysis is based on the national composite radar reflectivity factor data mosaics to increase the understanding of the evolution of these convective storms, including the changing of intensity, lifespan and so on. The results show that 1) there are four high-frequency centers of strong echoes≥45 dBz which located in northern Shijiazhuang, southern Beijing, south-central Baoding and western Cangzhou. The storms often strengthen significantly in the foothills of northern Shijiazhuang and western Cangzhou. 2) For strengthened convective storms, they are most active in mountainous areas around 1700 BT and mainly affect plain areas between 1800BT and 0200 BT. 3) The more westerly the path, the more cases of mountain-to-plain convective storms, the higher the percentage of convective intensification, and the greater the moving speed. 4) During the downhill process, most convective storms become stronger and more organized. For the convective storms whose echo strength ≥45 dBz at the initial moment of going downhill, more than 85% of them can successfully reach the plains, and more than 90% of them with horizontal scale exceeding 100 km and solidly connected structures can successfully reach the plains. 5) The strong echo areas of the strengthened convective storms expand dramatically as they go downhill. Strong echo areas expand to about 2 times larger than their initial echo areas when they reach the foothill, and the average areas in the plains can reach 4.6 times as big as their initial echo areas. 6) Most of the strengthened convective storms take only 1-2 hours to go downhill and last 4-8 hours on the plains. The storm types of the convective storms which last 4-8 hours on the plains are dominated by linear MCS (47%) and nonlinear MCS (30%).
Available online: February 13, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.012901
Abstract:
The main characteristics of climate in summer 2022 were accurately predicted by National Climate Center (NCC), including “the overall climate condition is unfavorable, with regional and phased floods and droughts, significantly uneven spatial distribution of rainfall, and the main anomalous-rainfall belt locates in the northern China”. The position of main anomalous-rainfall belt and spatial distribution of floods and drought in China was well predicted in advance in the end of March 2022. The prediction of seasonal progress of East Asian summer monsoon and rainy season was also consistent with observations. For example, the onset date of South China Sea summer monsoon was in the 3rd pentad of May, earlier and deficit Meiyu occurred over the middle and lower reaches of Yangtze River, the rainy season of North China started earlier than the climatology with above-normal precipitation, etc. The predicted less tropical cyclone genesis over western North Pacific and high probability of northward typhoon was basically consistent with the observations. The hot summer in 2022 and the spatial pattern of temperature anomalies in China were well captured. The prediction of “the temperature in most part of central and eastern China and Xinjiang is above normal, with more high temperature days and heat waves” was in good agreement with the observations. The main deficiency of the prediction was the underestimation of the spatial coverage and extremity of the record-breaking heat wave and drought in the whole basin of Yangtze River. The prediction of flood season in 2022 focused on the impact of multiyear La Nina event and the tropical Indian Ocean dipole mode on the summer monsoon circulation over East Asia. The intensity of western North Pacific subtropical high was abnormally strong with northward displacement and westward extension of the ridge line. With the intensified East Asian summer monsoon, and active northeast cold vortex in early summer, the above factors synergistically contributed to the formation of main anomalous-rainfall belt in Northeast China, North China, and eastern part of Northwest China.
The main characteristics of climate in summer 2022 were accurately predicted by National Climate Center (NCC), including “the overall climate condition is unfavorable, with regional and phased floods and droughts, significantly uneven spatial distribution of rainfall, and the main anomalous-rainfall belt locates in the northern China”. The position of main anomalous-rainfall belt and spatial distribution of floods and drought in China was well predicted in advance in the end of March 2022. The prediction of seasonal progress of East Asian summer monsoon and rainy season was also consistent with observations. For example, the onset date of South China Sea summer monsoon was in the 3rd pentad of May, earlier and deficit Meiyu occurred over the middle and lower reaches of Yangtze River, the rainy season of North China started earlier than the climatology with above-normal precipitation, etc. The predicted less tropical cyclone genesis over western North Pacific and high probability of northward typhoon was basically consistent with the observations. The hot summer in 2022 and the spatial pattern of temperature anomalies in China were well captured. The prediction of “the temperature in most part of central and eastern China and Xinjiang is above normal, with more high temperature days and heat waves” was in good agreement with the observations. The main deficiency of the prediction was the underestimation of the spatial coverage and extremity of the record-breaking heat wave and drought in the whole basin of Yangtze River. The prediction of flood season in 2022 focused on the impact of multiyear La Nina event and the tropical Indian Ocean dipole mode on the summer monsoon circulation over East Asia. The intensity of western North Pacific subtropical high was abnormally strong with northward displacement and westward extension of the ridge line. With the intensified East Asian summer monsoon, and active northeast cold vortex in early summer, the above factors synergistically contributed to the formation of main anomalous-rainfall belt in Northeast China, North China, and eastern part of Northwest China.
Available online: February 10, 2023 , DOI: 10.7519/j.issn.1000-0526.2022.122201
Abstract:
Based on the ECMWF ensemble prediction system (EC-EPS) and the potential vorticity tendency (PVT) diagnosis, this work examines the contributions of physical factors to track forecast of typhoon Chanthu (2114) by comparing two distinct ensemble members. It is found that the typhoon center of two ensembles both move towards the area with the largest wave number one component (WN1) of PVT. The contribution of the horizontal advection term is dominant most of the time, followed by the diabatic heating term, and the contribution of the vertical advection term is relatively small. The PVT discrepancy of the two members at bifurcation time is mainly attributed to the diabatic heating term, while that after the bifurcation time is still dominated by the horizontal advection term (i.e., steering flow). The asymmetric convective activities of two ensemble members also show different distribution at bifurcation time, which is consistent with the direction of diabatic heating, that is, the asymmetric convective structure and the vertical gradient of diabatic heating may play a key role in the movement of typhoon when the steering flow is weak, which is largely affected by the environmental factors such as water vapor, potential instability, and low-level jet. This work emphasized the impact of diabatic heating processes (including development and asymmetric structure of convective activities) in typhoon track forecast for more accurate prediction when steering flow is weak.
Based on the ECMWF ensemble prediction system (EC-EPS) and the potential vorticity tendency (PVT) diagnosis, this work examines the contributions of physical factors to track forecast of typhoon Chanthu (2114) by comparing two distinct ensemble members. It is found that the typhoon center of two ensembles both move towards the area with the largest wave number one component (WN1) of PVT. The contribution of the horizontal advection term is dominant most of the time, followed by the diabatic heating term, and the contribution of the vertical advection term is relatively small. The PVT discrepancy of the two members at bifurcation time is mainly attributed to the diabatic heating term, while that after the bifurcation time is still dominated by the horizontal advection term (i.e., steering flow). The asymmetric convective activities of two ensemble members also show different distribution at bifurcation time, which is consistent with the direction of diabatic heating, that is, the asymmetric convective structure and the vertical gradient of diabatic heating may play a key role in the movement of typhoon when the steering flow is weak, which is largely affected by the environmental factors such as water vapor, potential instability, and low-level jet. This work emphasized the impact of diabatic heating processes (including development and asymmetric structure of convective activities) in typhoon track forecast for more accurate prediction when steering flow is weak.
Available online: February 08, 2023 , DOI: 10.7519/j.issn.1000-0526.2022.121801
Abstract:
Based on the airborne microwave radiometer(G-band water Vapor Radiometer, named GVR),a retrieval algorithm of liquid water path based on BP neural network and Decker model is established by using the Beijing sounding data as the training data, and the airborne microwave radiation transfer equation as the forward algorithm. The observation height is added as an input variable, a new cloud model considering the influence of temperature on the cloud water phase, and the historical sounding data is completed to increase the integral height to 30km are applied in the new algorithm. Error analysis shows that the new algorithm is effective for improving the retrieval accuracy of local liquid water path. The comparative analysis of the liquid water path retrieval value and the sounding data calculation value shows that the correlation coefficient between the retrieval value and sounding data calculation value reaches 0.998, the absolute error and relative error of non-zero liquid water path are 0.0018- 0.0524mm and 1.37%-16.9%, the absolute error of 0-value liquid water path is 0.0005-0.023mm, which is significantly smaller than the retrieval result of the GVR own algorithm. Compared with similar liquid water path retrieval algorithms, the retrieval accuracy of this algorithm is also slightly better. The retrieval accuracy of this new algorithm was verified by the aircraft field observation test, and the detection data of the Tianjin precipitation enhancement aircraft King Air-B300 on June 30, 2021 was selected. The cloudless period upward of the GVR was selected based on the observation by on-board personnel and the number of particles measured by the airborne CIP probe. The retrieval results of the GVR own algorithm and this new algorithm were compared with the value of 0. The liquid water path retrieval error obtained by this new algorithm is 0 during the period, the retrieval error range obtained by the own algorithm is 0.0006-0.0056mm and the average error value is about 0.001mm.
Based on the airborne microwave radiometer(G-band water Vapor Radiometer, named GVR),a retrieval algorithm of liquid water path based on BP neural network and Decker model is established by using the Beijing sounding data as the training data, and the airborne microwave radiation transfer equation as the forward algorithm. The observation height is added as an input variable, a new cloud model considering the influence of temperature on the cloud water phase, and the historical sounding data is completed to increase the integral height to 30km are applied in the new algorithm. Error analysis shows that the new algorithm is effective for improving the retrieval accuracy of local liquid water path. The comparative analysis of the liquid water path retrieval value and the sounding data calculation value shows that the correlation coefficient between the retrieval value and sounding data calculation value reaches 0.998, the absolute error and relative error of non-zero liquid water path are 0.0018- 0.0524mm and 1.37%-16.9%, the absolute error of 0-value liquid water path is 0.0005-0.023mm, which is significantly smaller than the retrieval result of the GVR own algorithm. Compared with similar liquid water path retrieval algorithms, the retrieval accuracy of this algorithm is also slightly better. The retrieval accuracy of this new algorithm was verified by the aircraft field observation test, and the detection data of the Tianjin precipitation enhancement aircraft King Air-B300 on June 30, 2021 was selected. The cloudless period upward of the GVR was selected based on the observation by on-board personnel and the number of particles measured by the airborne CIP probe. The retrieval results of the GVR own algorithm and this new algorithm were compared with the value of 0. The liquid water path retrieval error obtained by this new algorithm is 0 during the period, the retrieval error range obtained by the own algorithm is 0.0006-0.0056mm and the average error value is about 0.001mm.
Available online: February 08, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.0206001
Abstract:
According to the requirements of weather, climate and ecological environment monitoring for land surface temperature (LST) at high spatial resolution and all-weather, this paper develops the spatial downscaling algorithm of LST from geostationary meteorological satellite observation and the reconstruction algorithm of LST under cloud from polar orbiting meteorological satellite observation respectively. The LST spatial downscaling model of geostationary meteorological satellite makes full use of the advantages of geostationary meteorological satellite observation in both high time-frequency and multi-spectrum. A nonlinear statistical regression model is established based on the daily variation characteristics of LST and brightness temperature of relevant channels of the same remote sensor of FY-4A.And theunderlying surface types are also taken into consideration. The method is applied to the LST downscaling of FY-4A AGRI. The results show that the developed downscaling model can not only downscale the LST of FY-4A AGRI from 4 km to 2 km, but also maintain the accuracy of LST before downscaling, and the maximum RMSE of LST before and after downscaling is 1.35K. For the LST reconstruction under cloud of Polar Orbiting Meteorological Satellite , the DINEOF model is developed, and the secondary correction of the results is carried out based on land-Use data, so as to realize the all-weather acquisition of Polar Orbiting Meteorological Satellite LST. The method is applied to polar orbiting meteorological satellite FY-3D MERSI LST, and the results are as expected.
According to the requirements of weather, climate and ecological environment monitoring for land surface temperature (LST) at high spatial resolution and all-weather, this paper develops the spatial downscaling algorithm of LST from geostationary meteorological satellite observation and the reconstruction algorithm of LST under cloud from polar orbiting meteorological satellite observation respectively. The LST spatial downscaling model of geostationary meteorological satellite makes full use of the advantages of geostationary meteorological satellite observation in both high time-frequency and multi-spectrum. A nonlinear statistical regression model is established based on the daily variation characteristics of LST and brightness temperature of relevant channels of the same remote sensor of FY-4A.And theunderlying surface types are also taken into consideration. The method is applied to the LST downscaling of FY-4A AGRI. The results show that the developed downscaling model can not only downscale the LST of FY-4A AGRI from 4 km to 2 km, but also maintain the accuracy of LST before downscaling, and the maximum RMSE of LST before and after downscaling is 1.35K. For the LST reconstruction under cloud of Polar Orbiting Meteorological Satellite , the DINEOF model is developed, and the secondary correction of the results is carried out based on land-Use data, so as to realize the all-weather acquisition of Polar Orbiting Meteorological Satellite LST. The method is applied to polar orbiting meteorological satellite FY-3D MERSI LST, and the results are as expected.
Available online: February 08, 2023 , DOI: 10.7519/j.issn.1000-0526.2023.013002
Abstract:
Based on hourly observation from 74 meteorological stations in Zhejiang Province, the models of ordinary linear regression and those considering spatial heterogeneity are adopted to explore the spatial estimation and impact factors of summer afternoon precipitation in Zhejiang Province in this study. It is found that: (1) A main rain band decreasing from the southwest to northeast with two precipitation centers in the south and north, respectively, forms in the summer afternoon in Zhejiang Province. (2) Geographical, topographic and meteorological factors jointly affect the spatial distribution of summer afternoon precipitation in Zhejiang Province. (3) The model of geographically neural network weighted regression (GNNWR) based on neural network and considering the spatial heterogeneity works significantly better than the models of ordinary linear regression and the geographically weighted regression, in terms of model performance and spatial distribution pattern of estimated precipitation, suggesting that the GNNWR model has the value of further application in the field of meteorology.
Based on hourly observation from 74 meteorological stations in Zhejiang Province, the models of ordinary linear regression and those considering spatial heterogeneity are adopted to explore the spatial estimation and impact factors of summer afternoon precipitation in Zhejiang Province in this study. It is found that: (1) A main rain band decreasing from the southwest to northeast with two precipitation centers in the south and north, respectively, forms in the summer afternoon in Zhejiang Province. (2) Geographical, topographic and meteorological factors jointly affect the spatial distribution of summer afternoon precipitation in Zhejiang Province. (3) The model of geographically neural network weighted regression (GNNWR) based on neural network and considering the spatial heterogeneity works significantly better than the models of ordinary linear regression and the geographically weighted regression, in terms of model performance and spatial distribution pattern of estimated precipitation, suggesting that the GNNWR model has the value of further application in the field of meteorology.
Available online: January 16, 2023 , DOI: 10.7519/j.issn.1000-0526.2022.112101
Abstract:
In order to evaluate consensus and correction model base on objective numerical forecast，which was applied on public service, this paper focused on big error days and temperature-drop days, to make objective verification on OCF consensus model and main collection members’ daily maximum and minimum temperature forecast. Result showed: OCF consensus model performed better than collection members overall, the accuracy was higher in summer and lower in winter. And OCF enlarged daily temperature range and effectively reduced error. OCF has less big error days than collection members, but showed larger errors in 2-3d forecasting periods, and winter half year. The big error days were related to collection members and obvious temperature-drop. It was found that the forecast performance of OCF, ECMWF and NCEP declined in temperature-drop days, especially the error of OCF daily maximum temperature forecast increases rapidly. In temperature-drop days, OCF has effectively corrected daily minimum temperature and daily maximum temperature in non-drop areas, but the daily maximum temperature error was obvious in temperature-drop area. Finally, process verification was conducive to discover the defects of objective forecasts and consensus, correction methods, therefore comes to the improve directions.
In order to evaluate consensus and correction model base on objective numerical forecast，which was applied on public service, this paper focused on big error days and temperature-drop days, to make objective verification on OCF consensus model and main collection members’ daily maximum and minimum temperature forecast. Result showed: OCF consensus model performed better than collection members overall, the accuracy was higher in summer and lower in winter. And OCF enlarged daily temperature range and effectively reduced error. OCF has less big error days than collection members, but showed larger errors in 2-3d forecasting periods, and winter half year. The big error days were related to collection members and obvious temperature-drop. It was found that the forecast performance of OCF, ECMWF and NCEP declined in temperature-drop days, especially the error of OCF daily maximum temperature forecast increases rapidly. In temperature-drop days, OCF has effectively corrected daily minimum temperature and daily maximum temperature in non-drop areas, but the daily maximum temperature error was obvious in temperature-drop area. Finally, process verification was conducive to discover the defects of objective forecasts and consensus, correction methods, therefore comes to the improve directions.
Available online: January 05, 2023 , DOI: 10.7519/j.issn.1000-0526.2022.112001
Abstract:
Rainfall attenuation to X-band weather radar measurement is significant, and leads to radar reflectivity factor weakening and inadequate in quantitative applications. By using the Z-Kdp correction method, data collected by an X-band dual-polariaztion Doppler weather radar at Pudong Shanghai were tested. The specific scheme is as follows: when KDP ≥0.3 deg/km, the value of KDP is used to correct; when KDP < 0.3 deg/km, the empirical formula between A and Z is used to correct the attenuation. The convective precipitation case (September 17, 2020) and the stable precipitation case (February 26, 2021) were selected for test. After attenuation correction and system bias correction, the results show that not only the value but also the spatial distribution of the X-band’s radar reflectivity factor is close to that of a S-band weather radar. Such Z-Kdp method is valid to correct the attenuation from both convective rainfall and stable rainfall.
Rainfall attenuation to X-band weather radar measurement is significant, and leads to radar reflectivity factor weakening and inadequate in quantitative applications. By using the Z-Kdp correction method, data collected by an X-band dual-polariaztion Doppler weather radar at Pudong Shanghai were tested. The specific scheme is as follows: when KDP ≥0.3 deg/km, the value of KDP is used to correct; when KDP < 0.3 deg/km, the empirical formula between A and Z is used to correct the attenuation. The convective precipitation case (September 17, 2020) and the stable precipitation case (February 26, 2021) were selected for test. After attenuation correction and system bias correction, the results show that not only the value but also the spatial distribution of the X-band’s radar reflectivity factor is close to that of a S-band weather radar. Such Z-Kdp method is valid to correct the attenuation from both convective rainfall and stable rainfall.
Available online: January 04, 2023 , DOI: 10.7519/j.issn.1000-0526.2022.080601
Abstract:
The greater Khingan Mountains area is an important ecological resource protection area in China due to its complex terrain and various biological species. Understanding and recognizing the microphysical properties of clouds is of great significance for studying the climate change and precipitation characteristics in the region. Based on CloudSat -CALIPSO (CloudSat-Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observations) data, the macroscopic and microscopic physical characteristics of the clouds in the Greater Khingan Mountains are analyzed. The results show that the annual average cloud occurrence frequency over the greater Khingan Mountains is 59.5%, mainly composed of altostratus, cirrus and stratocumulus, and the cloud occurrence frequency in spring and summer is higher than that in autumn and winter. The clouds are mainly thin clouds, and 61.41% of the clouds are less than 2km thick. The cloud top height and cloud bottom height show the distribution form of double peak and single peak respectively. The occurrence frequency of single-layer cloud is the highest, accounting for 69.19% of the total cloud. With the increase of cloud layer, the occurrence frequency of clouds decreases gradually. The cloud liquid water content in the Greater Khingan Mountains is abundant, with an annual average value of 244.41mg/m3, which is about 4 times the annual average ice water content. 83.2% of cloud water resources are concentrated in low-altitude areas below 5km from the ground. The annual mean values of effective particle size and number concentration of water droplets are 15.86μm and 34.47 /cm3, respectively, which are lower than the average values of ice crystals. The water content and effective particle size in the cloud show a single-peak distribution with height, while the particle number concentration of cloud droplet shows a double-peak distribution at low altitude.
The greater Khingan Mountains area is an important ecological resource protection area in China due to its complex terrain and various biological species. Understanding and recognizing the microphysical properties of clouds is of great significance for studying the climate change and precipitation characteristics in the region. Based on CloudSat -CALIPSO (CloudSat-Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observations) data, the macroscopic and microscopic physical characteristics of the clouds in the Greater Khingan Mountains are analyzed. The results show that the annual average cloud occurrence frequency over the greater Khingan Mountains is 59.5%, mainly composed of altostratus, cirrus and stratocumulus, and the cloud occurrence frequency in spring and summer is higher than that in autumn and winter. The clouds are mainly thin clouds, and 61.41% of the clouds are less than 2km thick. The cloud top height and cloud bottom height show the distribution form of double peak and single peak respectively. The occurrence frequency of single-layer cloud is the highest, accounting for 69.19% of the total cloud. With the increase of cloud layer, the occurrence frequency of clouds decreases gradually. The cloud liquid water content in the Greater Khingan Mountains is abundant, with an annual average value of 244.41mg/m3, which is about 4 times the annual average ice water content. 83.2% of cloud water resources are concentrated in low-altitude areas below 5km from the ground. The annual mean values of effective particle size and number concentration of water droplets are 15.86μm and 34.47 /cm3, respectively, which are lower than the average values of ice crystals. The water content and effective particle size in the cloud show a single-peak distribution with height, while the particle number concentration of cloud droplet shows a double-peak distribution at low altitude.
Available online: January 04, 2023 , DOI: 10.7519/j.issn.1000-0526.2022.081601
Abstract:
The research proposed a method to calculate the radar detection coverage with a specific altitude corresponding to one point on the surface，and used the terrain elevation data to analyze the detection capabilities of 23 new-generation weather radars in Shaanxi and surrounding provinces. Additionally，executed the numerical simulation of the negative elevation angle observation mode and obtained the optimal minimum observation elevation angle of the three mountaintop radars. The results show that the primary and secondary coverage rates of the new-generation weather radar for different altitudes over Shaanxi were：48.6% and 2.3% at 0.5km，80.0% and 18.9% at 1km，and 98.7% and 74.5% at 2km，99.9% and 97.1% at 3km and 100% at 4km. Considered the 3 X-band weather radars of Shaanxi，the primary and secondary coverage rates were increased to 82.7% and 32.1% at 1km，respectively. On this basis，a method used the average annual rainfall，GDP and population data to calculate the priority of radar coverage in blind areas and counties in Shaanxi were suggested. The findings of this study provide a theoretical and technical support for the construction of weather radar in the blind area of radar coverage in the future.
The research proposed a method to calculate the radar detection coverage with a specific altitude corresponding to one point on the surface，and used the terrain elevation data to analyze the detection capabilities of 23 new-generation weather radars in Shaanxi and surrounding provinces. Additionally，executed the numerical simulation of the negative elevation angle observation mode and obtained the optimal minimum observation elevation angle of the three mountaintop radars. The results show that the primary and secondary coverage rates of the new-generation weather radar for different altitudes over Shaanxi were：48.6% and 2.3% at 0.5km，80.0% and 18.9% at 1km，and 98.7% and 74.5% at 2km，99.9% and 97.1% at 3km and 100% at 4km. Considered the 3 X-band weather radars of Shaanxi，the primary and secondary coverage rates were increased to 82.7% and 32.1% at 1km，respectively. On this basis，a method used the average annual rainfall，GDP and population data to calculate the priority of radar coverage in blind areas and counties in Shaanxi were suggested. The findings of this study provide a theoretical and technical support for the construction of weather radar in the blind area of radar coverage in the future.
Available online: December 05, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.101201
Abstract:
The sub-grid terrain of model is not analyzed, resulting in the difference between the height of the ground observation station and the corresponding point of the model. However, the 10m wind speed predicted by the model is a diagnostic quantity based on the model terrain height. Due to the influence of the terrain difference, the model wind speed prediction deviates from the actual observation. Monin-Obukhov similarity theory shows that the vertical change of wind speed near the ground conforms to the logarithmic rate characteristics. Based on similarity theory, the deviation revision scheme is constructed to revise the wind speed forecast from the mode terrain to the actual terrain, and the atmospheric stability determination factor is introduced to the scheme. Analyze of more than 760 stations in North China in summer and winter, it is found that the average deviation of wind speed forecast within 12 hours can be reduced by more than 20%, the 24-hour decline can also reach more than 10%, and the root mean square error of wind speed within different forecast periods can also be reduced by 5%-8%, The revised scheme has a very obvious positive effect on the wind speed prediction of the model.
The sub-grid terrain of model is not analyzed, resulting in the difference between the height of the ground observation station and the corresponding point of the model. However, the 10m wind speed predicted by the model is a diagnostic quantity based on the model terrain height. Due to the influence of the terrain difference, the model wind speed prediction deviates from the actual observation. Monin-Obukhov similarity theory shows that the vertical change of wind speed near the ground conforms to the logarithmic rate characteristics. Based on similarity theory, the deviation revision scheme is constructed to revise the wind speed forecast from the mode terrain to the actual terrain, and the atmospheric stability determination factor is introduced to the scheme. Analyze of more than 760 stations in North China in summer and winter, it is found that the average deviation of wind speed forecast within 12 hours can be reduced by more than 20%, the 24-hour decline can also reach more than 10%, and the root mean square error of wind speed within different forecast periods can also be reduced by 5%-8%, The revised scheme has a very obvious positive effect on the wind speed prediction of the model.
Available online: November 29, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.112201
Abstract:
Based on the observational data and the mesoscale numerical model WRF, a typical low-vortex low-trough snowfall system occurred in Beijing on February 14, 2019 was analyzed and numerically simulated. The snowfall’s microphysical mechanism, snow formation process were discussed, and the numerical simulation analysis of cloud seeding were carried out. The results show that the water vapor caused by warm and humid advection near the low vortex front and the strong upward movement near the low vortex shear line caused the regional snow. . The sublimation growth of snow, the cloud water rimming on falling snow, the automatic conversion of cloud ice into snow, the ice crystals and snow collisions and aggregation are the main microphysical processes. Seeding simulation shows that , after seeding silver iodide (AgI), a large number of ice crystals are generated in the cloud, and the increased ice crystals are converted into snow through sublimation growth, collision, aggregation, and attachment, etc., which in turn leads to an increase in ground snowfall.
Based on the observational data and the mesoscale numerical model WRF, a typical low-vortex low-trough snowfall system occurred in Beijing on February 14, 2019 was analyzed and numerically simulated. The snowfall’s microphysical mechanism, snow formation process were discussed, and the numerical simulation analysis of cloud seeding were carried out. The results show that the water vapor caused by warm and humid advection near the low vortex front and the strong upward movement near the low vortex shear line caused the regional snow. . The sublimation growth of snow, the cloud water rimming on falling snow, the automatic conversion of cloud ice into snow, the ice crystals and snow collisions and aggregation are the main microphysical processes. Seeding simulation shows that , after seeding silver iodide (AgI), a large number of ice crystals are generated in the cloud, and the increased ice crystals are converted into snow through sublimation growth, collision, aggregation, and attachment, etc., which in turn leads to an increase in ground snowfall.
Available online: October 26, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.041501
Abstract:
It is important to diagnose and analysis 2m temperature prediction by GRAPES_RAFS system with 3km resolution in winter for the Winter Olympics meteorological service and GRAPES model system development. The 2m temperature prediction data of every 3h for 8 times a day from December 2020 to February 2021 are selected and diagnosed. The results show that different starting times the 8 forecast members can better characterize the diurnal variation characteristics of 2m temperature with a certain deviation from observation. The daily low temperature prediction is better, while the high temperature prediction is poor, and the prediction effect of the model on the heating process at 00-06 UTC is better than that of the cooling process at 06-21 UTC. The correction results show that the 2m temperature prediction deviation is mainly systematic deviation. When the 2m temperature prediction is corrected by the moving-biweight average method, the bias and the RMSE are reduced, especially in areas with large deviations before correction. The 2m temperature prediction deviation of different members is closer to each other after correction. The standard deviation diagnosis is found that 2m temperature prediction by RAFS system is better in Central and South China, while 2m temperature prediction is relatively poor in the Heihe-Tengchong area, the vicinity of the Tianshan Mountains, Yunnan-Guizhou and eastern Qinghai-Tibet Plateau. For the case of three regions with obvious difference in 2m temperature prediction (North China, East China and southwest) and the continuous test spectrum analysis in North China, i According to the large difference of standard deviation before and after temperature correction, three regions of North China, East China and southwest are selected to analyze the individual cases of three regions with obvious difference in 2m temperature prediction (North China, East China and southwest) and the continuous test in North China. It is found that the power spectrum energy gradually increases with the scale. When value of power spectrum energy is very small or abnormally large in the mesoscale range, the difference between 2m temperature prediction and observation is significant. The accurate capture of various scale information by the model is the key to 2m temperature prediction.
It is important to diagnose and analysis 2m temperature prediction by GRAPES_RAFS system with 3km resolution in winter for the Winter Olympics meteorological service and GRAPES model system development. The 2m temperature prediction data of every 3h for 8 times a day from December 2020 to February 2021 are selected and diagnosed. The results show that different starting times the 8 forecast members can better characterize the diurnal variation characteristics of 2m temperature with a certain deviation from observation. The daily low temperature prediction is better, while the high temperature prediction is poor, and the prediction effect of the model on the heating process at 00-06 UTC is better than that of the cooling process at 06-21 UTC. The correction results show that the 2m temperature prediction deviation is mainly systematic deviation. When the 2m temperature prediction is corrected by the moving-biweight average method, the bias and the RMSE are reduced, especially in areas with large deviations before correction. The 2m temperature prediction deviation of different members is closer to each other after correction. The standard deviation diagnosis is found that 2m temperature prediction by RAFS system is better in Central and South China, while 2m temperature prediction is relatively poor in the Heihe-Tengchong area, the vicinity of the Tianshan Mountains, Yunnan-Guizhou and eastern Qinghai-Tibet Plateau. For the case of three regions with obvious difference in 2m temperature prediction (North China, East China and southwest) and the continuous test spectrum analysis in North China, i According to the large difference of standard deviation before and after temperature correction, three regions of North China, East China and southwest are selected to analyze the individual cases of three regions with obvious difference in 2m temperature prediction (North China, East China and southwest) and the continuous test in North China. It is found that the power spectrum energy gradually increases with the scale. When value of power spectrum energy is very small or abnormally large in the mesoscale range, the difference between 2m temperature prediction and observation is significant. The accurate capture of various scale information by the model is the key to 2m temperature prediction.
Available online: October 16, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.092601
Abstract:
Alpine skiing is extremely sensitive to wind, and especially extreme wind speed is often one of the key factors that determine the smooth progress of the Winter Olympic Games. The numerical model data from the European Center for Medium-Range Weather Forecasts (ECMWF) and corresponding extreme wind observations of eight key stations in Yanqing competition zone of the Winter Olympic Games from January to March during 2018—2021 are used. The objective forecasting models of extreme wind speed are constructed based on three types of machine learning algorithms: decision tree (DT), random forest (RF) and gradient boosting decision tree (GBDT). The comparative evaluation results show that: the best predictors of extreme wind speed mainly focus on the wind speed and direction at different levels, and additionally include the vertical velocity for the individual station. Removing the wind direction leads to the decrease of accuracy and increase of mean absolute error (MAE) in most of models. On the whole, the GBDT and RF models based on the decision tree ensemble learning are superior to the single decision tree model (DT). The GBDT model has the least MAE ranging from 1.56 m/s to 3.57 m/s, and the maximum improvement rate is up to 8.7% compared with the DT model. Besides, the GBDT model is also skillful in the forecasts of super threshold extreme wind speed. All models have the increasing trend in the MAE and decreasing trend in the accuracy with the rising elevation of stations. As the forecasting lead time extends, the MAE of each model shows a periodic diurnal variation. Based on the stacking ensemble learning method, the RGL model is established using the two outstanding models, GBDT and RF, as the primary learner and the support vector machine as the secondary learner. The results indicate that: compared with the single model, the RGL model has a certain ability to improve the prediction of extreme wind speed, especially for the high altitude stations with relatively high winds.The MAE can be reduced by a maximum of 0.13 m/s, and the accuracy can be increased by a maximum of 0.022. The relevant research results have been well applied to the 2022 Beijing Winter Olympic and Paralympic Games.
Alpine skiing is extremely sensitive to wind, and especially extreme wind speed is often one of the key factors that determine the smooth progress of the Winter Olympic Games. The numerical model data from the European Center for Medium-Range Weather Forecasts (ECMWF) and corresponding extreme wind observations of eight key stations in Yanqing competition zone of the Winter Olympic Games from January to March during 2018—2021 are used. The objective forecasting models of extreme wind speed are constructed based on three types of machine learning algorithms: decision tree (DT), random forest (RF) and gradient boosting decision tree (GBDT). The comparative evaluation results show that: the best predictors of extreme wind speed mainly focus on the wind speed and direction at different levels, and additionally include the vertical velocity for the individual station. Removing the wind direction leads to the decrease of accuracy and increase of mean absolute error (MAE) in most of models. On the whole, the GBDT and RF models based on the decision tree ensemble learning are superior to the single decision tree model (DT). The GBDT model has the least MAE ranging from 1.56 m/s to 3.57 m/s, and the maximum improvement rate is up to 8.7% compared with the DT model. Besides, the GBDT model is also skillful in the forecasts of super threshold extreme wind speed. All models have the increasing trend in the MAE and decreasing trend in the accuracy with the rising elevation of stations. As the forecasting lead time extends, the MAE of each model shows a periodic diurnal variation. Based on the stacking ensemble learning method, the RGL model is established using the two outstanding models, GBDT and RF, as the primary learner and the support vector machine as the secondary learner. The results indicate that: compared with the single model, the RGL model has a certain ability to improve the prediction of extreme wind speed, especially for the high altitude stations with relatively high winds.The MAE can be reduced by a maximum of 0.13 m/s, and the accuracy can be increased by a maximum of 0.022. The relevant research results have been well applied to the 2022 Beijing Winter Olympic and Paralympic Games.
Available online: October 12, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.080102
Abstract:
A rare regional severe convection process of Guangxi occurred in 24-25 January 2020, which accompanied by the maximal range hail process from 2000. The abnormal development and eastward of the southern branch trough (SBT) are the disturbance backgrounds that provide necessary thermal, dynamic and water vapor conditions. Using conventional observation data, FY-2G satellite data, NCEP/NCAR and ERA5 reanalysis data, the SBT inducing the regional severe convection process is analyzed from the perspective of energy conversion. The results show that: The mid-latitude and subtropical westerly jets are stronger than climatological during the whole process, which is conducive to the upstream disturbance spreading. There are two active Rossby wave trains over the northern and southern Eurasia respectively. The southern subtropical westerly jet Rossby wave originated from the Mediterranean Sea plays a major role in regulating the SBT. The Rossby energy disperses along the jet stream and converges in SBT region, promoting the development and eastward of SBT. The northern one originated from the North Atlantic blocking plays a synergistic role, which promoting the development of the Urals cold trough and its merger with the Middle East trough, thereby enhancing the propagation of the southern one and further enhancing the SBT. The conversion from synoptic-scale available potential energy and the transport of kinetic energy from background field to synoptic-scale are the main contributions of synoptic-scale disturbance of SBT. The advection transport of kinetic energy redistributes the obtained synoptic-scale kinetic energy in space and thus maintains the SBT develop and moved eastward stably. Under above background, the downscaled kinetic energy cascade from synoptic-scale to convective scale is the main energy source of regional severe convective, and the stable conversion of convective scale available potential energy to kinetic energy promoting the occurrence and development of the convective disturbances in the middle and low troposphere.
A rare regional severe convection process of Guangxi occurred in 24-25 January 2020, which accompanied by the maximal range hail process from 2000. The abnormal development and eastward of the southern branch trough (SBT) are the disturbance backgrounds that provide necessary thermal, dynamic and water vapor conditions. Using conventional observation data, FY-2G satellite data, NCEP/NCAR and ERA5 reanalysis data, the SBT inducing the regional severe convection process is analyzed from the perspective of energy conversion. The results show that: The mid-latitude and subtropical westerly jets are stronger than climatological during the whole process, which is conducive to the upstream disturbance spreading. There are two active Rossby wave trains over the northern and southern Eurasia respectively. The southern subtropical westerly jet Rossby wave originated from the Mediterranean Sea plays a major role in regulating the SBT. The Rossby energy disperses along the jet stream and converges in SBT region, promoting the development and eastward of SBT. The northern one originated from the North Atlantic blocking plays a synergistic role, which promoting the development of the Urals cold trough and its merger with the Middle East trough, thereby enhancing the propagation of the southern one and further enhancing the SBT. The conversion from synoptic-scale available potential energy and the transport of kinetic energy from background field to synoptic-scale are the main contributions of synoptic-scale disturbance of SBT. The advection transport of kinetic energy redistributes the obtained synoptic-scale kinetic energy in space and thus maintains the SBT develop and moved eastward stably. Under above background, the downscaled kinetic energy cascade from synoptic-scale to convective scale is the main energy source of regional severe convective, and the stable conversion of convective scale available potential energy to kinetic energy promoting the occurrence and development of the convective disturbances in the middle and low troposphere.
Available online: October 10, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.081901
Abstract:
Clouds play an important role in weather forecasting. Accurate identification and segmentation of ground-based cloud images can effectively guide weather forecasting. Now most of the existing datasets are only suitable for single task learning, and ground-based cloud image recognition and segmentation technologies are mostly implemented by single task, thus identification and detection efficiency are low and the robustness of the algorithm is poor. Considering these problems, the ground-based cloud image datasets GBCD and GBCD-GT with labels and suitable for multi-task learning are constructed, based on which a ground-based cloud image recognition and segmentation joint network model GCRSegNet based on multi-task learning is designed. The model firstly extracts shared features through convolutional neural network, then a special network is designed for each task to extract more recognizable features. The segmentation network learns shared features to achieve ground-based cloud image segmentation, and the recognition network combines sharing features and segmentation features to achieve ground-based cloud image recognition. Through multiple groups of comparative experiments, it is shown that the network in this paper can accurately represent the features of ground-based cloud image. Meanwhile the accuracy of the recognition task can reach 94.28%, the pixel accuracy of segmentation task can reach 93.85%, and mean intersection over union reach 71.58%, which provides a possibility for practical application.
Clouds play an important role in weather forecasting. Accurate identification and segmentation of ground-based cloud images can effectively guide weather forecasting. Now most of the existing datasets are only suitable for single task learning, and ground-based cloud image recognition and segmentation technologies are mostly implemented by single task, thus identification and detection efficiency are low and the robustness of the algorithm is poor. Considering these problems, the ground-based cloud image datasets GBCD and GBCD-GT with labels and suitable for multi-task learning are constructed, based on which a ground-based cloud image recognition and segmentation joint network model GCRSegNet based on multi-task learning is designed. The model firstly extracts shared features through convolutional neural network, then a special network is designed for each task to extract more recognizable features. The segmentation network learns shared features to achieve ground-based cloud image segmentation, and the recognition network combines sharing features and segmentation features to achieve ground-based cloud image recognition. Through multiple groups of comparative experiments, it is shown that the network in this paper can accurately represent the features of ground-based cloud image. Meanwhile the accuracy of the recognition task can reach 94.28%, the pixel accuracy of segmentation task can reach 93.85%, and mean intersection over union reach 71.58%, which provides a possibility for practical application.
Available online: September 28, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.080302
Abstract:
To explore the effects of daily mean temperature on bronchitis outpatient visit in Lanzhou. The data on bronchitis outpatient visit, meteorology and atmospheric pollutants during 2013-2019 from three general hospitals in Lanzhou were collected. A distribution lag non-linear model was constructed to analyze the relationship between the temperature and the daily risk of bronchitis outpatient visit, and stratified analysis by sex and age group was performed. The effect of daily mean temperature on bronchitis outpatient visit was non-linear and lagging. The hazard effects of low temperature (-5.0 ℃), and high temperature (25.4 ℃) were the largest on the current day, and weakened gradually with the lag days, hazard effects of low temperature lasted for 13 days (lag1 ~ 13), and that of high temperature effect lasted 19 days. The cold effect had a greater harmful effect and duration than the heat effect. When the temperature was set to -5.0 ℃ and 25.4 ℃, the maximal cumulative lag effect appeared on lag0~14 d, and lag0~21 d respectively, the RR values were 2.832(95%CI: 2.411~3.326) and 1.070(95%CI: 1.054~1.086). The risk of bronchial outpatient visit caused by low temperature, and high temperature is greater for men than women, with a maximum cumulative relative risk of 3.089(95%CI: 2.601~3.669) and 1.085(95%CI: 1.067~1.104). The risk of outpatient visits for children aged 0-14 is significantly higher than that of other age groups at low temperature, the peak RR appeared on lag 0~14 d, with the value of 3.191(95%CI: 2.654~3.837), and when the temperature was at 25.4 ℃, the maximum value occurs on lag0~21 d, the RR values were 1.089(95%CI: 1.070~1.109).Both high temperature and low temperature increased the bronchitis outpatient visit risk, the harmful effect and duration of low temperature were greater than that of high temperature, children aged 0-14 were more sensitive to low temperature.
To explore the effects of daily mean temperature on bronchitis outpatient visit in Lanzhou. The data on bronchitis outpatient visit, meteorology and atmospheric pollutants during 2013-2019 from three general hospitals in Lanzhou were collected. A distribution lag non-linear model was constructed to analyze the relationship between the temperature and the daily risk of bronchitis outpatient visit, and stratified analysis by sex and age group was performed. The effect of daily mean temperature on bronchitis outpatient visit was non-linear and lagging. The hazard effects of low temperature (-5.0 ℃), and high temperature (25.4 ℃) were the largest on the current day, and weakened gradually with the lag days, hazard effects of low temperature lasted for 13 days (lag1 ~ 13), and that of high temperature effect lasted 19 days. The cold effect had a greater harmful effect and duration than the heat effect. When the temperature was set to -5.0 ℃ and 25.4 ℃, the maximal cumulative lag effect appeared on lag0~14 d, and lag0~21 d respectively, the RR values were 2.832(95%CI: 2.411~3.326) and 1.070(95%CI: 1.054~1.086). The risk of bronchial outpatient visit caused by low temperature, and high temperature is greater for men than women, with a maximum cumulative relative risk of 3.089(95%CI: 2.601~3.669) and 1.085(95%CI: 1.067~1.104). The risk of outpatient visits for children aged 0-14 is significantly higher than that of other age groups at low temperature, the peak RR appeared on lag 0~14 d, with the value of 3.191(95%CI: 2.654~3.837), and when the temperature was at 25.4 ℃, the maximum value occurs on lag0~21 d, the RR values were 1.089(95%CI: 1.070~1.109).Both high temperature and low temperature increased the bronchitis outpatient visit risk, the harmful effect and duration of low temperature were greater than that of high temperature, children aged 0-14 were more sensitive to low temperature.
Available online: September 14, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.082201
Abstract:
In recent years, the forecasting of tropical cyclone (TC) intensity has been improved. However, the intensity forecasting value is weaker in the years when TCs were frequently intensified over offshore waters. Focused on the factors affecting the intensified coastal TCs, the paper reviews the related research from two perspectives: environmental conditions and dynamic mechanism. It provides a detailed analysis of the effects of environmental atmospheric, ocean forcing mechanisms, structural changes in the inner core and water phase change in spiral bands on the intensifying process of coastal TCs. Such factors are good indicators for the forecasting of coastal TCs, which act together the intensifying process. Through comparing and summarizing relevant research results, a schematic model of impact factors is established in order to provide valuable reference for the operational forecast of the intensifying process of TCs over offshore waters.
In recent years, the forecasting of tropical cyclone (TC) intensity has been improved. However, the intensity forecasting value is weaker in the years when TCs were frequently intensified over offshore waters. Focused on the factors affecting the intensified coastal TCs, the paper reviews the related research from two perspectives: environmental conditions and dynamic mechanism. It provides a detailed analysis of the effects of environmental atmospheric, ocean forcing mechanisms, structural changes in the inner core and water phase change in spiral bands on the intensifying process of coastal TCs. Such factors are good indicators for the forecasting of coastal TCs, which act together the intensifying process. Through comparing and summarizing relevant research results, a schematic model of impact factors is established in order to provide valuable reference for the operational forecast of the intensifying process of TCs over offshore waters.
Available online: August 30, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.071201
Abstract:
The convective characteristics of rainstorms in China are considerable, but the statistical relationship between rainstorms and short-duration heavy rainfall, which is one of the severe convective weather, remains unclear. The characteristics of the contribution of two types of short-duration heavy rainfall (hourly rainfall ≥20 mm and hourly rainfall ≥50 mm, referred to as HR20 and HR50, respectively) to different intensities of rainstorms are obtained by analyzing the hourly rainfall data during 1951 and 2019. The results show that the area of rainstorm with high frequency of short-duration heavy rainfall is not consistent with the area of high frequency rainstorms. Short-duration heavy rainfall has the most significant impact on rainstorms over the southern part of North China, the Huanghuai River Basin and the Southwest to South China, where HR20 account for more than 50% of the rainstorm days. The southern part of North China and the central part of South China accounting for more than 70% is the highest. Furthermore, the proportion of short-duration heavy rainfall gradually increases as the rainstorm intensity enhances, especially the HR50 has increased significantly. More than 60% of the extreme torrential rain days are accompanied by HR50, indicating that the stronger the rainstorm, the more significant the convection. The total precipitation amount produced by short-duration heavy rainfall contribute the most to the rainstorm over regions such as the southern part of North China, Huanghuai area, the eastern part of Southwest China and southern China. The contribution of the short-duration heavy rainfall also increases significantly as the rainstorm intensity enhances, especially that of HR50 increased by more than 100%. In areas such as Jianghuai and South China, the contribution of the short-duration heavy rainfall is smaller, and its increase is relatively insignificant with the increase of the intensity of the rainstorm. In addition, when there is a short-duration heavy rainfall (HR20), the amounts of rainstorm and heavy rainstorm increase by an average of 20% and 40% respectively compared to where no short-duration heavy rainfall accompanied. It further demonstrates the convective characteristics of rainstorms in China.
The convective characteristics of rainstorms in China are considerable, but the statistical relationship between rainstorms and short-duration heavy rainfall, which is one of the severe convective weather, remains unclear. The characteristics of the contribution of two types of short-duration heavy rainfall (hourly rainfall ≥20 mm and hourly rainfall ≥50 mm, referred to as HR20 and HR50, respectively) to different intensities of rainstorms are obtained by analyzing the hourly rainfall data during 1951 and 2019. The results show that the area of rainstorm with high frequency of short-duration heavy rainfall is not consistent with the area of high frequency rainstorms. Short-duration heavy rainfall has the most significant impact on rainstorms over the southern part of North China, the Huanghuai River Basin and the Southwest to South China, where HR20 account for more than 50% of the rainstorm days. The southern part of North China and the central part of South China accounting for more than 70% is the highest. Furthermore, the proportion of short-duration heavy rainfall gradually increases as the rainstorm intensity enhances, especially the HR50 has increased significantly. More than 60% of the extreme torrential rain days are accompanied by HR50, indicating that the stronger the rainstorm, the more significant the convection. The total precipitation amount produced by short-duration heavy rainfall contribute the most to the rainstorm over regions such as the southern part of North China, Huanghuai area, the eastern part of Southwest China and southern China. The contribution of the short-duration heavy rainfall also increases significantly as the rainstorm intensity enhances, especially that of HR50 increased by more than 100%. In areas such as Jianghuai and South China, the contribution of the short-duration heavy rainfall is smaller, and its increase is relatively insignificant with the increase of the intensity of the rainstorm. In addition, when there is a short-duration heavy rainfall (HR20), the amounts of rainstorm and heavy rainstorm increase by an average of 20% and 40% respectively compared to where no short-duration heavy rainfall accompanied. It further demonstrates the convective characteristics of rainstorms in China.
Available online: August 12, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.071801
Abstract:
Abstract: Based on intensive surface automatic observation data, Doppler Radar data, Himawari-8 satellite data and ERA-5 high resolution reanalysis data, the synoptic background, environmental conditions and the evolution characteristics of mesoscale systems and convective storms of the EF2 tornado event that occurred in Gaoyou County, Jiangsu Province on 12 June 2020 was analyzed. The monitoring and early warning experience and forecasting thoughts were summarized as well. The results are shown as followed: (1) The Gaoyou tornado appeared during the first rainstorm at the beginning of Meiyu in Jiangsu Province. The synoptic environment was partly similar to Funing EF4 tornado on 23 June 2016, which both present the typical circulation during Meiyu period. The convective system producing tornado appeared in front of 500hPa westerly trough, in the southwest quadrant of 850hPa vortex and left side of low-level jet, with strong convective instability energy and low lifting condensation level. But CAPE and vertical wind shear were weaker than Funing tornado process. (2) The tornado occurred at the top of a moving β-mesoscale depression, which was located in the convergence area of surface divergence and the surface temperature warm tongue. The surface divergence near the center of storm had a sharp decline which might indicate the tornado. (3) The storm generating the tornado has a long life history. Continuous tornado vortex signature (TVS) has been recognized 60 minutes ahead. The storm intensified passing through Gaoyou Lake. Mesocyclones (M) appeared and coexisted with TVS within 8 radar volume scans. Before the tornado reached the ground, the bottom height of TVS decreased and shear increased significantly, the diameter of the mesocyclone decreased vertically in an inverted trapezoidal structure. The rotation speed shear increased and reached to the minimum height. All these features give good indications for the early warning of tornadoes. Based on synoptic-scale systems model, medium and small-scale environmental physical indexes, convective scale storm characteristic evolutions, Jiangsu meteorological departments had a progressive early warning as a successful practice.
Abstract: Based on intensive surface automatic observation data, Doppler Radar data, Himawari-8 satellite data and ERA-5 high resolution reanalysis data, the synoptic background, environmental conditions and the evolution characteristics of mesoscale systems and convective storms of the EF2 tornado event that occurred in Gaoyou County, Jiangsu Province on 12 June 2020 was analyzed. The monitoring and early warning experience and forecasting thoughts were summarized as well. The results are shown as followed: (1) The Gaoyou tornado appeared during the first rainstorm at the beginning of Meiyu in Jiangsu Province. The synoptic environment was partly similar to Funing EF4 tornado on 23 June 2016, which both present the typical circulation during Meiyu period. The convective system producing tornado appeared in front of 500hPa westerly trough, in the southwest quadrant of 850hPa vortex and left side of low-level jet, with strong convective instability energy and low lifting condensation level. But CAPE and vertical wind shear were weaker than Funing tornado process. (2) The tornado occurred at the top of a moving β-mesoscale depression, which was located in the convergence area of surface divergence and the surface temperature warm tongue. The surface divergence near the center of storm had a sharp decline which might indicate the tornado. (3) The storm generating the tornado has a long life history. Continuous tornado vortex signature (TVS) has been recognized 60 minutes ahead. The storm intensified passing through Gaoyou Lake. Mesocyclones (M) appeared and coexisted with TVS within 8 radar volume scans. Before the tornado reached the ground, the bottom height of TVS decreased and shear increased significantly, the diameter of the mesocyclone decreased vertically in an inverted trapezoidal structure. The rotation speed shear increased and reached to the minimum height. All these features give good indications for the early warning of tornadoes. Based on synoptic-scale systems model, medium and small-scale environmental physical indexes, convective scale storm characteristic evolutions, Jiangsu meteorological departments had a progressive early warning as a successful practice.
Available online: July 15, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.061001
Abstract:
The Chinese new generation of Doppler weather radar (CINRAD) has the advantages of high temporal and spatial resolution, and is capable of monitoring of precipitation intensity changes and real-time movement of precipitation regimes with detail information, and can effectively monitor disastrous weather events. The temporal and spatial distribution characteristics of summer precipitation in southern China are investigated based on measurements by Doppler multiradar mosaic data in South China from 2017 to 2020. Results show that: 1) the frequency of summer precipitation in South China is dominated by stratiform precipitation. In most parts of South China, the frequency of stratiform precipitation is more than 85%, while the frequency of convective precipitation only accounts for about 14%. The peak reflectivity and the frequency of convective precipitation in Guangdong are higher than those in Guangxi and Hainan. 2) both the peak reflectivity and precipitation frequency show strong diurnal variation with local solar time, and also exhibits discernible regional differences. The reflectivity peak is roughly similar to the spatial distribution of convective precipitation, and the frequencies along the coast are more higher than those in the inland region. Stratiform precipitation occur most frequently in the inland region than along the coast. 3) The frequency of stratiform precipitation is mostly concentrated at night and peaks in the morning; The peak reflectivity and convective precipitation are mostly concentrated in the daytime, the high-value region moves and expands from the western coast to the inland and eastern coast with time changes, reaches the peak between afternoon and night. 4) The diurnal variation of convective precipitation exhibits different bimodal patterns in coastal and inland region. A major peak in the morning and a secondary peak in the late afternoon, the morning peak in central Guangdong is significantly lower than the afternoon peak.
The Chinese new generation of Doppler weather radar (CINRAD) has the advantages of high temporal and spatial resolution, and is capable of monitoring of precipitation intensity changes and real-time movement of precipitation regimes with detail information, and can effectively monitor disastrous weather events. The temporal and spatial distribution characteristics of summer precipitation in southern China are investigated based on measurements by Doppler multiradar mosaic data in South China from 2017 to 2020. Results show that: 1) the frequency of summer precipitation in South China is dominated by stratiform precipitation. In most parts of South China, the frequency of stratiform precipitation is more than 85%, while the frequency of convective precipitation only accounts for about 14%. The peak reflectivity and the frequency of convective precipitation in Guangdong are higher than those in Guangxi and Hainan. 2) both the peak reflectivity and precipitation frequency show strong diurnal variation with local solar time, and also exhibits discernible regional differences. The reflectivity peak is roughly similar to the spatial distribution of convective precipitation, and the frequencies along the coast are more higher than those in the inland region. Stratiform precipitation occur most frequently in the inland region than along the coast. 3) The frequency of stratiform precipitation is mostly concentrated at night and peaks in the morning; The peak reflectivity and convective precipitation are mostly concentrated in the daytime, the high-value region moves and expands from the western coast to the inland and eastern coast with time changes, reaches the peak between afternoon and night. 4) The diurnal variation of convective precipitation exhibits different bimodal patterns in coastal and inland region. A major peak in the morning and a secondary peak in the late afternoon, the morning peak in central Guangdong is significantly lower than the afternoon peak.
Available online: June 24, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.051102
Abstract:
In view of the comprehensive evaluation on the forecast performance of disastrous heavy precipitation concerned by power grid industry, and by referring to the test of the effect of professional meteorological service of heavy precipitation in the main flood season (June-September, 2019) in Beijing-Tianjin-Hebei region, the paper has carried out in-depth analysis on using MODE (Method for Object-based Diagnostic Evaluation) in the inspection of short-term and impending forecast from two aspects, namely, target recognition of precipitation and target matching of precipitation. The results have shown that the heavy precipitations in the main flood season of Beijing-Tianjin-Hebei region were mainly concentrated from afternoon to the first half of the night, which were characterized by heavy in amount, small in range, easy false-alarms, and difficulty in predicting their spatial characteristics; The correlation coefficient of diurnal variation of the heavy precipitation frequency of short-term and impending forecast ranged from 0.78 to 0.94, while that of the diurnal variation of range was from 0.6 to 0.82. The forecast effect of moving path and rainfall intensity was slightly better than that of the falling area. The shorter the forecast time, the better the forecast effect of heavy precipitations and their spatial characteristics; The comprehensive forecast evaluation method put forward in the paper can make up for the shortcomings of traditional inspection methods, which can explore the potential and limitations of forecast, and provide reference for accurate and specialized meteorological services.
In view of the comprehensive evaluation on the forecast performance of disastrous heavy precipitation concerned by power grid industry, and by referring to the test of the effect of professional meteorological service of heavy precipitation in the main flood season (June-September, 2019) in Beijing-Tianjin-Hebei region, the paper has carried out in-depth analysis on using MODE (Method for Object-based Diagnostic Evaluation) in the inspection of short-term and impending forecast from two aspects, namely, target recognition of precipitation and target matching of precipitation. The results have shown that the heavy precipitations in the main flood season of Beijing-Tianjin-Hebei region were mainly concentrated from afternoon to the first half of the night, which were characterized by heavy in amount, small in range, easy false-alarms, and difficulty in predicting their spatial characteristics; The correlation coefficient of diurnal variation of the heavy precipitation frequency of short-term and impending forecast ranged from 0.78 to 0.94, while that of the diurnal variation of range was from 0.6 to 0.82. The forecast effect of moving path and rainfall intensity was slightly better than that of the falling area. The shorter the forecast time, the better the forecast effect of heavy precipitations and their spatial characteristics; The comprehensive forecast evaluation method put forward in the paper can make up for the shortcomings of traditional inspection methods, which can explore the potential and limitations of forecast, and provide reference for accurate and specialized meteorological services.
Liu Couhua, Dai Kan, Lin Jian, Wei Qing, Li Nina, Wang Baoli, Tang Buxing, Guo Yunqian, Zhu Wenjian, Tang Jian, Zeng Xiaoqing
Available online: June 01, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.050902
Abstract:
In order to evaluate the contribution of each process from numerical forecast, objective method to subjective forecast products to the accuracy of weather forecast, the Meteorological Evaluation Program Library (MetEva) is developed. Aiming at the whole process coverage of the verification algorithm and the comparability of the evaluation results, MetEva adopts a hierarchical architecture including basic layer and functional layer, and designs a modular inspection and calculation process based on a unified data structure. The program library provides over 400 functions around the steps of data reading, data merging and matching, sample selection, sample grouping, inspection calculation and result output for verification. MetEva provides 54 evaluation methods in five categories, which covers most of methods recommended by the World Meteorological Organization and algorithms in domestic specifications. By using matrix calculation in each module and providing parallel scheme for verification algorithms, the operation efficiency is improved. Taking the evaluation of temperature and precipitation forecast as an example, this paper briefly explains the application MetEva, and shows the value of it in verification. The program library has been released as open source, which can effectively support meteorological departments at all levels to carry out the evaluation of the whole process of weather forecast, so as to promote the development of weather forecast.
In order to evaluate the contribution of each process from numerical forecast, objective method to subjective forecast products to the accuracy of weather forecast, the Meteorological Evaluation Program Library (MetEva) is developed. Aiming at the whole process coverage of the verification algorithm and the comparability of the evaluation results, MetEva adopts a hierarchical architecture including basic layer and functional layer, and designs a modular inspection and calculation process based on a unified data structure. The program library provides over 400 functions around the steps of data reading, data merging and matching, sample selection, sample grouping, inspection calculation and result output for verification. MetEva provides 54 evaluation methods in five categories, which covers most of methods recommended by the World Meteorological Organization and algorithms in domestic specifications. By using matrix calculation in each module and providing parallel scheme for verification algorithms, the operation efficiency is improved. Taking the evaluation of temperature and precipitation forecast as an example, this paper briefly explains the application MetEva, and shows the value of it in verification. The program library has been released as open source, which can effectively support meteorological departments at all levels to carry out the evaluation of the whole process of weather forecast, so as to promote the development of weather forecast.
ZHU Shizhen, ZHANG Zhaoyi, WU Shixiao, YANG Jun, WANG Zhaoyu, SHI Chune, HU Hanfeng, ZHANG Hao, NI Ting, QIU Yujun, LU Chunsong
Available online: May 13, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.021001
Abstract:
Using the fog droplet spectrum and visibility data of two dense fog processes on January 12-13, 2019 in Shou County, Anhui Province, the microphysical characteristics (such as the spectral distribution, droplet number concentration, liquid water content, average diameter, spectral width, etc. )and the correlations among microphysical properties(number concentration, liquid water content, average diameter) in the different stages of fog are analyzed. The result shows that: both fog processes are radiation fog. If the strong inversion structure close to the ground maintains, the water vapor will be restrained in the inversion layer. It is conducive to the long-term maintenance of dense fog. The formation time of the fog at 20 m is later than that of the ground. In the early stage of formation, development and maturity, the microphysical characteristics of the ground fog are all larger than that at 20 m. At the late stage of maturity, the release of latent heat by condensation and ground heating may increase the intensity of turbulent mixing in the fog, making the fog uniform in the vertical direction. The fog processes at two heights are dominated by nucleation and condensation growth, but the collision-coalescence process also plays an important role in the fog on the ground. From the stage of formation, development to maturity, the collision-coalescence processes of the ground fog gradually strengthens. The correlation between the number concentration, water content, and average diameter generally ranges from a strong positive correlation to a weak positive or negative correlation. From the early stage to the late stage of the mature stage, the average diameter and number concentration of the fog at 20 m height change from a positive correlation to a negative correlation, which may be related to the factors such as turbulent, entrainment mixing, etc.
Using the fog droplet spectrum and visibility data of two dense fog processes on January 12-13, 2019 in Shou County, Anhui Province, the microphysical characteristics (such as the spectral distribution, droplet number concentration, liquid water content, average diameter, spectral width, etc. )and the correlations among microphysical properties(number concentration, liquid water content, average diameter) in the different stages of fog are analyzed. The result shows that: both fog processes are radiation fog. If the strong inversion structure close to the ground maintains, the water vapor will be restrained in the inversion layer. It is conducive to the long-term maintenance of dense fog. The formation time of the fog at 20 m is later than that of the ground. In the early stage of formation, development and maturity, the microphysical characteristics of the ground fog are all larger than that at 20 m. At the late stage of maturity, the release of latent heat by condensation and ground heating may increase the intensity of turbulent mixing in the fog, making the fog uniform in the vertical direction. The fog processes at two heights are dominated by nucleation and condensation growth, but the collision-coalescence process also plays an important role in the fog on the ground. From the stage of formation, development to maturity, the collision-coalescence processes of the ground fog gradually strengthens. The correlation between the number concentration, water content, and average diameter generally ranges from a strong positive correlation to a weak positive or negative correlation. From the early stage to the late stage of the mature stage, the average diameter and number concentration of the fog at 20 m height change from a positive correlation to a negative correlation, which may be related to the factors such as turbulent, entrainment mixing, etc.
Available online: May 12, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.050501
Abstract:
In view of the outstanding problems in the precipitation and model forecasts of the landfalling typhoons in South China, this paper analyzes the current research of the asymmetry of the precipitation distribution of the landfalling typhoon and the mechanism of the continuous rainstorm in the later period of landfalling. Relevant scientific issues that need in-depth study and measures of improving numerical predictions are put forward, in order to provide reference for the improvement of the forecast of heavy rainfall associated with tropical cyclone (TC) landfalling in South China. The analysis pointed out that the vertical shear of the environmental wind field, the boundary of the low-level air mass (such as the boundary of the cold pool), the intrusion of dry and cold air, mesoscale convective systems (MCSs) and the local topography are important factors that cause the asymmetric distribution of precipitation of the landfalling TC in South China. The occurrence of continuous rainstorms in South China during the late period of landfall is often related to the increase in monsoon activity. The active southwest monsoon provides favorable conditions for the development of MCSs in rainstorm. MCSs feed back to the large-scale circulation through latent heat heating, which lead to the maintenance of TC vortex circulation and the southwest monsoon, and cause iterative development of MCSs, resulting in continued heavy rains. To further improve the forecast of the model, it is essential to investigate and evaluate the performance of the current model, carry out in-depth research on the related scientific issues, and then propose effective improvement plans.
In view of the outstanding problems in the precipitation and model forecasts of the landfalling typhoons in South China, this paper analyzes the current research of the asymmetry of the precipitation distribution of the landfalling typhoon and the mechanism of the continuous rainstorm in the later period of landfalling. Relevant scientific issues that need in-depth study and measures of improving numerical predictions are put forward, in order to provide reference for the improvement of the forecast of heavy rainfall associated with tropical cyclone (TC) landfalling in South China. The analysis pointed out that the vertical shear of the environmental wind field, the boundary of the low-level air mass (such as the boundary of the cold pool), the intrusion of dry and cold air, mesoscale convective systems (MCSs) and the local topography are important factors that cause the asymmetric distribution of precipitation of the landfalling TC in South China. The occurrence of continuous rainstorms in South China during the late period of landfall is often related to the increase in monsoon activity. The active southwest monsoon provides favorable conditions for the development of MCSs in rainstorm. MCSs feed back to the large-scale circulation through latent heat heating, which lead to the maintenance of TC vortex circulation and the southwest monsoon, and cause iterative development of MCSs, resulting in continued heavy rains. To further improve the forecast of the model, it is essential to investigate and evaluate the performance of the current model, carry out in-depth research on the related scientific issues, and then propose effective improvement plans.
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2012,38(12):1482-1491, DOI: 10.7519/j.issn.1000-0526.2012.12.005
Abstract:
By using the conventional meteorological data, Doppler radar data and NCEP/NCAR reanalysis data, the characteristics of Doppler radar’s reflectivity, environmental condition and trigger mechanism of the heavy rain are analyzed and compared between two abrupt heavy rain processes occurring in Sichuan Basin on 3 July (7.3) and 23 July (7.23) 2011. The results show that: the “7.3” heavy rain happened under a typical circulation background, and moisture transporting to the heavy rain area from the South China Sea was smoothly, thus the heavy rainfall maintained so long, but the “7.23” heavy rain occurred behind the upper cold vortex, and convective unstable energy was abundant and vertical wind shear was strong, thus this heavy rain process happened with hail and thunderstorm weather accompanied, its radar reflectivity was 5 dBz stronger than “7.3” case and had the characteristics of severe storms such as the low level weak reflectivity and the upper echo overhang. As a whole, the non equilibrium force is contributed to the occurrence of heavy rain and it is the excited mechanism of the two heavy rainfalls, and the change of the divergence evolvement is consistent with the strength and the position of the heavy rain which would happen 6 hours later．
By using the conventional meteorological data, Doppler radar data and NCEP/NCAR reanalysis data, the characteristics of Doppler radar’s reflectivity, environmental condition and trigger mechanism of the heavy rain are analyzed and compared between two abrupt heavy rain processes occurring in Sichuan Basin on 3 July (7.3) and 23 July (7.23) 2011. The results show that: the “7.3” heavy rain happened under a typical circulation background, and moisture transporting to the heavy rain area from the South China Sea was smoothly, thus the heavy rainfall maintained so long, but the “7.23” heavy rain occurred behind the upper cold vortex, and convective unstable energy was abundant and vertical wind shear was strong, thus this heavy rain process happened with hail and thunderstorm weather accompanied, its radar reflectivity was 5 dBz stronger than “7.3” case and had the characteristics of severe storms such as the low level weak reflectivity and the upper echo overhang. As a whole, the non equilibrium force is contributed to the occurrence of heavy rain and it is the excited mechanism of the two heavy rainfalls, and the change of the divergence evolvement is consistent with the strength and the position of the heavy rain which would happen 6 hours later．
2006,32(10):64-69, DOI: 10.7519/j.issn.1000-0526.2006.10.010
Abstract:
Based on the data of CINRAD Doppler Radar which located at Xinle of Hebei Province,the hail,strong wind and heavy rainfall weather events in mid-south Hebei in 2004 are statistically analyzed.The routine radar products,such as echo reflectivity,radial velocity,Vertically Integrated Liquid(VIL)Water,hail index,mesocyclone,velocity azimuth display wind profile,etc.are used in this statistics.The results show that hail's VIL value is larger than generic thunder storm's.At the same time,greater VIL value and longer sustaining will bring about greater diameter hail and larger effect area.It is the very useful index to indicate strong wind in mesocyclone products and the wind direction sudden change in radial velocity products.A reference based on analyzing this type synoptic forecast with radar system in future is proposed.
Based on the data of CINRAD Doppler Radar which located at Xinle of Hebei Province,the hail,strong wind and heavy rainfall weather events in mid-south Hebei in 2004 are statistically analyzed.The routine radar products,such as echo reflectivity,radial velocity,Vertically Integrated Liquid(VIL)Water,hail index,mesocyclone,velocity azimuth display wind profile,etc.are used in this statistics.The results show that hail's VIL value is larger than generic thunder storm's.At the same time,greater VIL value and longer sustaining will bring about greater diameter hail and larger effect area.It is the very useful index to indicate strong wind in mesocyclone products and the wind direction sudden change in radial velocity products.A reference based on analyzing this type synoptic forecast with radar system in future is proposed.
Zhou Yuquan, Chen Yingying, Li Juan, Huang Yimei, He Xiaodong, Zhou Feifei, Wu Menxin, Hu Bo, Mao Jietai
2008,34(12):27-35, DOI: 10.7519/j.issn.1000-0526.2008.12.004
Abstract:
Cloud macro and micro physical characteristic parameters play an important role not only in the field of the analysis and forecast of the weather and climate, but also in the field of weather modification to identify the seeding c ondition. Based on the data from FY-2C/D stationary satellite and SBDART radiati on transfer model, associated with the sounding data and surface information, a method retrieving cloud macro and micro physical parameters is established in th is research. These parameters include cloud top height, cloud top temperature, d epth of super-cooled layer, depth of warm layer, cloud bottom height, depth of c loud, cloud optical thickness, cloud effective particle radius and cloud liquid water content. It has been run operationally. In this paper, the correlated info rmation such as physical meaning, retrieving method and technology, retrieving p rocess and data format are simply introduced. Furthermore, comparing with the ob servation of Cloudsat up to the minute, the retrieving results of main cloud par ameters are proved to be reasonable and usable. By contrast with same kind produ cts of MODIS, it also shows good corresponding relationship.
Cloud macro and micro physical characteristic parameters play an important role not only in the field of the analysis and forecast of the weather and climate, but also in the field of weather modification to identify the seeding c ondition. Based on the data from FY-2C/D stationary satellite and SBDART radiati on transfer model, associated with the sounding data and surface information, a method retrieving cloud macro and micro physical parameters is established in th is research. These parameters include cloud top height, cloud top temperature, d epth of super-cooled layer, depth of warm layer, cloud bottom height, depth of c loud, cloud optical thickness, cloud effective particle radius and cloud liquid water content. It has been run operationally. In this paper, the correlated info rmation such as physical meaning, retrieving method and technology, retrieving p rocess and data format are simply introduced. Furthermore, comparing with the ob servation of Cloudsat up to the minute, the retrieving results of main cloud par ameters are proved to be reasonable and usable. By contrast with same kind produ cts of MODIS, it also shows good corresponding relationship.
2017,43(7):769-780, DOI: 10.7519/j.issn.1000-0526.2017.07.001
Abstract:
The spatial distributions of severe convective wind (SCW) and nonsevere thunderstorms (NT) over South China, occurring between 08:00 BT and 20:00 BT during spring and summer in 2010-2014, were analyzed by using the observational data from China Meteorological Administration. And then, their environmental characteristics were compared between SCW and NT in spring and summer. It was found that SCW in summer is more frequently than that in spring and that NT in summer is about 3.6 times the counts of NT in spring. SCW events mainly concentrate in the western Guangdong to the Pearl River Delta Region. Compared to NT, SCW is generally associated with stronger baroclinity, instability and stronger dynamic forcing. The precipitable water and averaged relative humidity between 700-500 hPa of SCW tend to be higher than those of NT in spring, while the opposite is the case for the pattern in summer. In conclusion, it is obvious that the dynamic forcing for SCW in spring is much better than these in summer, while the thermal condition is more significant in summer.
The spatial distributions of severe convective wind (SCW) and nonsevere thunderstorms (NT) over South China, occurring between 08:00 BT and 20:00 BT during spring and summer in 2010-2014, were analyzed by using the observational data from China Meteorological Administration. And then, their environmental characteristics were compared between SCW and NT in spring and summer. It was found that SCW in summer is more frequently than that in spring and that NT in summer is about 3.6 times the counts of NT in spring. SCW events mainly concentrate in the western Guangdong to the Pearl River Delta Region. Compared to NT, SCW is generally associated with stronger baroclinity, instability and stronger dynamic forcing. The precipitable water and averaged relative humidity between 700-500 hPa of SCW tend to be higher than those of NT in spring, while the opposite is the case for the pattern in summer. In conclusion, it is obvious that the dynamic forcing for SCW in spring is much better than these in summer, while the thermal condition is more significant in summer.
2013,39(10):1284-1292, DOI: 10.7519/j.issn.1000-0526.2013.10.006
Abstract:
Based on the fog observation data during 24-27 December 2006 (advection radiation fog), NCEP NC reanalysis data (2.5°×2.5°) and GDAS global meteorological data (1°×1°), detailed trajectory analysis of the boundary layer characteristics and water vapor transport of the fog is investigated, combined with the weather condition, meteorological elements and physical quantity field. The results show that: (1) there is thick inversion layer, even multi layer inversion throughout the dense fog event. Temperatures of different inversion tops in the middle and high levels are 2-5℃ higher than the surface temperature. The thickness of inversion layer is more than 200 m, and it gets to 500 m at 08:00 BT 26 December, indicating the atmosphere is very stable and conducive to the convergence of water vapor before the fog forms. However, it is not favorable for the divergence of water vapor after the formation of fog, which helps the development and maintenance of the fog, causing the fog to last about 64 hours with dense fog (visibility <50 m) about 37 hours; (2) The divergence of water vapor flux in low level is negative in the advection fog event. The upper air has persistent moisture convergence and the strongest moisture convergence appears at 02:00 BT 25 December, being -30×10-7 g·s-1·cm-2·hPa-1. The accumulation of low level water vapor makes fog form and develop while the divergence of water vapor flux speeds up its dissipation. 〖JP2〗The long lasting advection radiation fog is mainly caused by the continuous water vapor convergence; (3) The water vapor path is from the coastal area in easten China to Nanjing. The water vapor is continuously supplied from sea during the fog event, with the water vapor flux maximum getting to 2 g·s-1·hPa-1·cm-1. The sufficient supply and supplementary of water vapor determines the duration of the fog.
Based on the fog observation data during 24-27 December 2006 (advection radiation fog), NCEP NC reanalysis data (2.5°×2.5°) and GDAS global meteorological data (1°×1°), detailed trajectory analysis of the boundary layer characteristics and water vapor transport of the fog is investigated, combined with the weather condition, meteorological elements and physical quantity field. The results show that: (1) there is thick inversion layer, even multi layer inversion throughout the dense fog event. Temperatures of different inversion tops in the middle and high levels are 2-5℃ higher than the surface temperature. The thickness of inversion layer is more than 200 m, and it gets to 500 m at 08:00 BT 26 December, indicating the atmosphere is very stable and conducive to the convergence of water vapor before the fog forms. However, it is not favorable for the divergence of water vapor after the formation of fog, which helps the development and maintenance of the fog, causing the fog to last about 64 hours with dense fog (visibility <50 m) about 37 hours; (2) The divergence of water vapor flux in low level is negative in the advection fog event. The upper air has persistent moisture convergence and the strongest moisture convergence appears at 02:00 BT 25 December, being -30×10-7 g·s-1·cm-2·hPa-1. The accumulation of low level water vapor makes fog form and develop while the divergence of water vapor flux speeds up its dissipation. 〖JP2〗The long lasting advection radiation fog is mainly caused by the continuous water vapor convergence; (3) The water vapor path is from the coastal area in easten China to Nanjing. The water vapor is continuously supplied from sea during the fog event, with the water vapor flux maximum getting to 2 g·s-1·hPa-1·cm-1. The sufficient supply and supplementary of water vapor determines the duration of the fog.
2009,35(1):55-64, DOI: 10.7519/j.issn.1000-0526.2009.1.007
Abstract:
A strong rainstorm is analysis which occurred in Xinghua located the north of Ji angsu province on 25 July 2007. Results show that wind disaster originated from two kinds of rainstorm. One kind was the gust front which occurred at the front of the storm. Strong wind of grade 7-9 was attained when it happened. Another ki nd was the downburst arose in the multi cell storm. The original height of refl ectivity core was higher than -20℃ isotherm. It had the characteristics of conv ergence on the mid level and descending of reflectivity core. The strong wind ab ove grade 10 was attained, when the descending airflow diverged strongly on the ground. A new cell was combined with the former storm above the gust front, thus the storm enhanced. When the downburst happened, the storm weakened, and another new cell was combin ed with the former storm. The downburst happened continuously, and the impact of gust front persisted.
A strong rainstorm is analysis which occurred in Xinghua located the north of Ji angsu province on 25 July 2007. Results show that wind disaster originated from two kinds of rainstorm. One kind was the gust front which occurred at the front of the storm. Strong wind of grade 7-9 was attained when it happened. Another ki nd was the downburst arose in the multi cell storm. The original height of refl ectivity core was higher than -20℃ isotherm. It had the characteristics of conv ergence on the mid level and descending of reflectivity core. The strong wind ab ove grade 10 was attained, when the descending airflow diverged strongly on the ground. A new cell was combined with the former storm above the gust front, thus the storm enhanced. When the downburst happened, the storm weakened, and another new cell was combin ed with the former storm. The downburst happened continuously, and the impact of gust front persisted.
FU Jiaolan, MA Xuekuan, CHEN Tao, ZHANG Fang, ZHANG Xidi, SUN Jun, QUAN Wanqing, YANG Shunan, SHEN Xiaolin
2017,43(5):528-539, DOI: 10.7519/j.issn.1000-0526.2017.05.002
Abstract:
An extremely severe precipitation event took place in North China in 19-20 July 2016. It was characterized by large rainfall, persistent rainfall, warm cloud rainfall, strong local rainfall intensity and orographic precipitation. Its rainfall was larger than that of the extreme rainfall in 3-5 August 1996, and only next to the amount of the 2-7 August 1963 extreme rainfall event. It occurred under the circulation background of the South Asia high moving eastward, the West Pacific subtropical high moving northwestward and the low vortex in the westerlies developing in mid high latitude. The abnormal development of Huanghuai cyclone, southwest and southeast low level jets, and the abnormally abundant moisture indicates that the dynamic lifting and moisture conditions favored this severe rainfall process significantly. The whole rainfall event presented clearly the phase characteristics, and could be divided into two stages. The first stage was the orographic rainfall caused by the easterly winds ahead of the trough from the early morning to the daytime of 19 July, while the second part was produced by spiral rain bands in the north side of Huanghuai cyclone from the night of 19 to the daytime of 20 July. In the first stage, the easterly low level jet was lifted by the Taihang Mountains, which continuously triggered the convective cells along the east edge of the mountains. The weak dry and cold advection at mid level and the strong warm and wet advection at low level jointly maintained the convective instability. The cold pool generated by heavy rainfall and the mesoscale frontogenesis process created by local orographic effect provided favorable conditions for severe convections to occur continuously. The second stage rainfall was mainly related to the development of cut off vortex and Huanghuai cyclone. The blocking of the high pressure system slowed the steps of Huanghuai cyclone in North China, thus leading to the long lasting rainfall process.
An extremely severe precipitation event took place in North China in 19-20 July 2016. It was characterized by large rainfall, persistent rainfall, warm cloud rainfall, strong local rainfall intensity and orographic precipitation. Its rainfall was larger than that of the extreme rainfall in 3-5 August 1996, and only next to the amount of the 2-7 August 1963 extreme rainfall event. It occurred under the circulation background of the South Asia high moving eastward, the West Pacific subtropical high moving northwestward and the low vortex in the westerlies developing in mid high latitude. The abnormal development of Huanghuai cyclone, southwest and southeast low level jets, and the abnormally abundant moisture indicates that the dynamic lifting and moisture conditions favored this severe rainfall process significantly. The whole rainfall event presented clearly the phase characteristics, and could be divided into two stages. The first stage was the orographic rainfall caused by the easterly winds ahead of the trough from the early morning to the daytime of 19 July, while the second part was produced by spiral rain bands in the north side of Huanghuai cyclone from the night of 19 to the daytime of 20 July. In the first stage, the easterly low level jet was lifted by the Taihang Mountains, which continuously triggered the convective cells along the east edge of the mountains. The weak dry and cold advection at mid level and the strong warm and wet advection at low level jointly maintained the convective instability. The cold pool generated by heavy rainfall and the mesoscale frontogenesis process created by local orographic effect provided favorable conditions for severe convections to occur continuously. The second stage rainfall was mainly related to the development of cut off vortex and Huanghuai cyclone. The blocking of the high pressure system slowed the steps of Huanghuai cyclone in North China, thus leading to the long lasting rainfall process.
2010,36(3):9-18, DOI: 10.7519/j.issn.1000-0526.2010.3.002
Abstract:
Potential vorticity (PV) is one of the important concepts in advanced synoptic and dynamic meteorology. This paper is a brief introduction to the theory of potential vorticity, including the concept of PV, the conservation and invertibility of PV, PV thinking, moist PV (MPV), and the application of PV theory.
Potential vorticity (PV) is one of the important concepts in advanced synoptic and dynamic meteorology. This paper is a brief introduction to the theory of potential vorticity, including the concept of PV, the conservation and invertibility of PV, PV thinking, moist PV (MPV), and the application of PV theory.
2014,40(2):133-145, DOI: 10.7519/j.issn.1000-0526.2014.02.001
Abstract:
By using the NCEP reanalysis data, the vapor budget of the area covered by the severe torrential rain over the northeast of North China on 21 July, 2012 is calculated according to the vapor budget equation. The results show that meridional water vapor transportation is dominant while the extremely heavy rain hits Beijing Region, where most moist vapor comes from the southern boundary below 500 hPa. The low level regional moisture convergence is consistent with the time and space when the torrential rain breaks out and develops. Above the middle level the vertical vapor transport is more prominent. Then the variation features of the vapor transport corridors and their moisture contributions are got through the HYSPLIT mode. The backward trajectory analyses illustrate two major vapor transport corridors. The moistest vapor derived from Yellow Sea and East China Sea along the low level make the main moisture contribution during the heavy precipitation. Moisture from the South China Sea and the Bay of Bengal strengthens the water vapor in the region when the heavy rain starts and develops. Also the drier vapor corridor along the high level from the northwest of China plays an important role in this case.
By using the NCEP reanalysis data, the vapor budget of the area covered by the severe torrential rain over the northeast of North China on 21 July, 2012 is calculated according to the vapor budget equation. The results show that meridional water vapor transportation is dominant while the extremely heavy rain hits Beijing Region, where most moist vapor comes from the southern boundary below 500 hPa. The low level regional moisture convergence is consistent with the time and space when the torrential rain breaks out and develops. Above the middle level the vertical vapor transport is more prominent. Then the variation features of the vapor transport corridors and their moisture contributions are got through the HYSPLIT mode. The backward trajectory analyses illustrate two major vapor transport corridors. The moistest vapor derived from Yellow Sea and East China Sea along the low level make the main moisture contribution during the heavy precipitation. Moisture from the South China Sea and the Bay of Bengal strengthens the water vapor in the region when the heavy rain starts and develops. Also the drier vapor corridor along the high level from the northwest of China plays an important role in this case.
2012,38(1):1-16, DOI: 10.7519/j.issn.1000-0526.2012.01.001
Abstract:
In this paper, the modulation of atmospheric MJO on typhoon generation over the northwestern Pacific and its mechanism are first studied by using the MJO index. The results show that the MJO plays an important modulation role in typhoon generation over the northwestern Pacific: The proportion of typhoon number is 21 between active period and inactive period; During the MJO active period, the proportion of typhoon number is also 2:1 between phases 5-6 and phases 2-3 of MJO. The composite analyses of atmospheric circulation show that there are different circulation patterns over the northwestern Pacific in different phases of the MJO, which will affect the typhoon generation. In phases 5-6 (2-3), the dynamic factor and convective heating patterns over western Pacific are favorable (unfavorable) for typhoon generation. Then， the comparing analyses of the 30-60 day low frequency kinetic energy in lower and higher levels of the troposphere show that the atmospheric intraseasonal oscillation over the northwestern Pacific has a clear impact on the typhoon generation. There is an evident positive (negative) anomaly area of 30-60 day low frequency kinetic energy in the more (less) typhoon years over the northwestern Pacific east of the Philippines, which means that strong (weak) atmospheric intraseasonal oscillation (ISO) over the northwestern Pacific is favorable (unfavorable) for typhoon generation. The analyses of 200 hPa velocity potential show that there is a clear divergence (convergence) pattern over the northwestern Pacific in the more (less) typhoon years, which is favorable (unfavorable) for typhoon generation. The modulation of the intraseasonal oscillation on the typhoon tracks over the northwestern Pacific is studied by observational data analyses. We classified the main classes of typhoon tracks into 5 types as straight west moving typhoons (I), northwest moving typhoons (II), recurving to Korea/west of Japan typhoons (III), landing on Japan typhoons (IV) and recurving to the east of Japan typhoons (V). Then the composite analyses of atmospheric low-frequency wind fields at 850, 500 and 200 hPa, corresponding to the typhoon forming date, for every typhoon track are completed. The analysis results of relationships between the low-frequency (ISO) wind fields and typhoon tracks have indicated that the typhoon tracks will be affected by wind pattern of the ISO. The low frequency positive vorticity belt (the maximum value line of cyclonic vorticity) associated with low-frequency cyclone (LFC) at 850 hPa is so closely related to the typhoon track, that the maximum value line (belt) of low frequency cyclonic vorticity can be an important factor to predicate the typhoon tracks over the northwestern Pacific. And the typhoon tracks will be also affected by the ISO circulation pattern at 200 hPa, particularly the strong low frequency wind associated with low frequency anticyclone (LFAC).
In this paper, the modulation of atmospheric MJO on typhoon generation over the northwestern Pacific and its mechanism are first studied by using the MJO index. The results show that the MJO plays an important modulation role in typhoon generation over the northwestern Pacific: The proportion of typhoon number is 21 between active period and inactive period; During the MJO active period, the proportion of typhoon number is also 2:1 between phases 5-6 and phases 2-3 of MJO. The composite analyses of atmospheric circulation show that there are different circulation patterns over the northwestern Pacific in different phases of the MJO, which will affect the typhoon generation. In phases 5-6 (2-3), the dynamic factor and convective heating patterns over western Pacific are favorable (unfavorable) for typhoon generation. Then， the comparing analyses of the 30-60 day low frequency kinetic energy in lower and higher levels of the troposphere show that the atmospheric intraseasonal oscillation over the northwestern Pacific has a clear impact on the typhoon generation. There is an evident positive (negative) anomaly area of 30-60 day low frequency kinetic energy in the more (less) typhoon years over the northwestern Pacific east of the Philippines, which means that strong (weak) atmospheric intraseasonal oscillation (ISO) over the northwestern Pacific is favorable (unfavorable) for typhoon generation. The analyses of 200 hPa velocity potential show that there is a clear divergence (convergence) pattern over the northwestern Pacific in the more (less) typhoon years, which is favorable (unfavorable) for typhoon generation. The modulation of the intraseasonal oscillation on the typhoon tracks over the northwestern Pacific is studied by observational data analyses. We classified the main classes of typhoon tracks into 5 types as straight west moving typhoons (I), northwest moving typhoons (II), recurving to Korea/west of Japan typhoons (III), landing on Japan typhoons (IV) and recurving to the east of Japan typhoons (V). Then the composite analyses of atmospheric low-frequency wind fields at 850, 500 and 200 hPa, corresponding to the typhoon forming date, for every typhoon track are completed. The analysis results of relationships between the low-frequency (ISO) wind fields and typhoon tracks have indicated that the typhoon tracks will be affected by wind pattern of the ISO. The low frequency positive vorticity belt (the maximum value line of cyclonic vorticity) associated with low-frequency cyclone (LFC) at 850 hPa is so closely related to the typhoon track, that the maximum value line (belt) of low frequency cyclonic vorticity can be an important factor to predicate the typhoon tracks over the northwestern Pacific. And the typhoon tracks will be also affected by the ISO circulation pattern at 200 hPa, particularly the strong low frequency wind associated with low frequency anticyclone (LFAC).
2011,37(10):1262-1269, DOI: 10.7519/j.issn.1000-0526.2011.10.009
Abstract:
Based on the daily precipitation data at 110 observational stations during 1961-2008 in South China， the climatic characteristics and variation of torrential rain days， rainstorm intensity and contribution which is in annual， the first and second flood seasons in South China were studied by using statistical and diagnostic methods， such as linear regression analysis， Mann Kendall test， wavelet analysis and the computation of trend coefficients. The results have shown that the annual mean torrential rain days have a decreasing trend from coastal regions to inland in South China in recent 48 years， the highest center is in Dongxing of Guangxi （14.9 d）， and the lowest center is in Longlin of Guangxi （3.2 d）. About 72% of the total torrential rain days occurred in the flood seasons with about 45% in the first season and 27% in the second season. The mean torrential rain days have increased faintly in annual， the first and second flood seasons in South China， but it is not obvious. There are the characteristics of interannual and interdecadal changes. The mean rainstorm intensity has increased faintly in annual and in the first flood season in South China. However, since 2005 it has become obviously. The mean rainstorm intensity has declined in the second flood season， but it is not obvious. The annual mean rainstorm contribution to the total rainfall has increased obviously， but the mean contribution is not obvious in the first and second flood seasons. The wavelet analysis has shown that the changes of torrential rain days， intensity and contribution which is in annual， the first and second flood seasons in South China have two significant periods of 2-3 a and 3-4 a.
Based on the daily precipitation data at 110 observational stations during 1961-2008 in South China， the climatic characteristics and variation of torrential rain days， rainstorm intensity and contribution which is in annual， the first and second flood seasons in South China were studied by using statistical and diagnostic methods， such as linear regression analysis， Mann Kendall test， wavelet analysis and the computation of trend coefficients. The results have shown that the annual mean torrential rain days have a decreasing trend from coastal regions to inland in South China in recent 48 years， the highest center is in Dongxing of Guangxi （14.9 d）， and the lowest center is in Longlin of Guangxi （3.2 d）. About 72% of the total torrential rain days occurred in the flood seasons with about 45% in the first season and 27% in the second season. The mean torrential rain days have increased faintly in annual， the first and second flood seasons in South China， but it is not obvious. There are the characteristics of interannual and interdecadal changes. The mean rainstorm intensity has increased faintly in annual and in the first flood season in South China. However, since 2005 it has become obviously. The mean rainstorm intensity has declined in the second flood season， but it is not obvious. The annual mean rainstorm contribution to the total rainfall has increased obviously， but the mean contribution is not obvious in the first and second flood seasons. The wavelet analysis has shown that the changes of torrential rain days， intensity and contribution which is in annual， the first and second flood seasons in South China have two significant periods of 2-3 a and 3-4 a.
2014,40(7):816-826, DOI: 10.7519/j.issn.1000-0526.2014.07.005
Abstract:
In term of precipitation data of 2400 stations from 1981 to 2010, annual, seasonal and monthly distribution and evolution characteristics of rainstorm were analyzed. The results show that the processes of rainstorm have been increased evidently since 21 century especially in the south of China, but the duration is relatively short. Rainstorm days have been increased, but the amount of precipitation is not as much as in 1990s. Variation trend of the annual (monthly) precipitation amount is in accordance with that of rainstorm days, but rainfall is averagely more while the rainstorm days are less during spring rainfall phase over the south of Yangtze River. Distribution of the maximum annual rainstorm days is very similar with that of the annual mean rainstorm days, revealing the feature of more in south and east but less in north and west. Maximum annual rainstorm days are more than double of annual average rainstorm days with multi centers due to the effect of topography. The months of maximum monthly rainstorm days over different regions of the same province are incompletely same as the result of the impact of different weather systems. Generally, rainstorm days have been increased since 2000, rainstorm begins earlier, ends latter and lasts longer than before. Nowadays, as the extreme rainfall events and secondary disasters happen frequently, it is conducive for the forecast of quantitative precipitation forecast (QPF) to learn the spatio temporal distribution and evolution features of rainstorm.
In term of precipitation data of 2400 stations from 1981 to 2010, annual, seasonal and monthly distribution and evolution characteristics of rainstorm were analyzed. The results show that the processes of rainstorm have been increased evidently since 21 century especially in the south of China, but the duration is relatively short. Rainstorm days have been increased, but the amount of precipitation is not as much as in 1990s. Variation trend of the annual (monthly) precipitation amount is in accordance with that of rainstorm days, but rainfall is averagely more while the rainstorm days are less during spring rainfall phase over the south of Yangtze River. Distribution of the maximum annual rainstorm days is very similar with that of the annual mean rainstorm days, revealing the feature of more in south and east but less in north and west. Maximum annual rainstorm days are more than double of annual average rainstorm days with multi centers due to the effect of topography. The months of maximum monthly rainstorm days over different regions of the same province are incompletely same as the result of the impact of different weather systems. Generally, rainstorm days have been increased since 2000, rainstorm begins earlier, ends latter and lasts longer than before. Nowadays, as the extreme rainfall events and secondary disasters happen frequently, it is conducive for the forecast of quantitative precipitation forecast (QPF) to learn the spatio temporal distribution and evolution features of rainstorm.
2011,37(5):599-606, DOI: 10.7519/j.issn.1000-0526.2011.5.012
Abstract:
Using the diurnal snow data of 120 meteorological stations in Yunnan Province during 1961-2008, the temporal and spatial distribution characteristics and the trend of climatic change of the annual and monthly snow fall are analyzed. It is pointed out that the total trend of snow frequency and covering stations has been decreasing in Yunnan in the recent 50 years. And the annual snow frequency has declined at a mean rate of 4.5 times per year. The temporal trends of monthly snow frequency and covering stations are all negative. Moreover the reduction of snow frequency in December is the largest in magnitude, therefore, it is the most remarkable. And the reduction of snow stations in April is the largest. As far as the spatial change of the secular trend variation of annual snow frequency is concerned, the reduction of annual snow frequency is larger in Northwest Yunnan than in its northeast and east, where the reduction rate is 0.44 times per year. And the temporal changes of annual snowfall and depth of snow cover are studied, the results show that the secular trends of annual snowfall and the maximum depth of snow cover are all positive. This means that in the nearly 50 years the heavy snow frequency has increased over Yunnan Province.
Using the diurnal snow data of 120 meteorological stations in Yunnan Province during 1961-2008, the temporal and spatial distribution characteristics and the trend of climatic change of the annual and monthly snow fall are analyzed. It is pointed out that the total trend of snow frequency and covering stations has been decreasing in Yunnan in the recent 50 years. And the annual snow frequency has declined at a mean rate of 4.5 times per year. The temporal trends of monthly snow frequency and covering stations are all negative. Moreover the reduction of snow frequency in December is the largest in magnitude, therefore, it is the most remarkable. And the reduction of snow stations in April is the largest. As far as the spatial change of the secular trend variation of annual snow frequency is concerned, the reduction of annual snow frequency is larger in Northwest Yunnan than in its northeast and east, where the reduction rate is 0.44 times per year. And the temporal changes of annual snowfall and depth of snow cover are studied, the results show that the secular trends of annual snowfall and the maximum depth of snow cover are all positive. This means that in the nearly 50 years the heavy snow frequency has increased over Yunnan Province.
2007,33(12):116-120, DOI: 10.7519/j.issn.1000-0526.2007.12.018
Abstract:
A comprehensive analysis and process system based on ArcGIS, and its chief targ et, its software frame, standardized data, database system, basic functions and its key technique, etc. are are described. The system is professional especially to weather modification, and it mainly applies to comprehensive analysis and pr ocess for weather modification, decision-making of operation schemes, appraisal of operation effectiveness, and services for enhancement precipitation or suppre ssion hail by ways of cannons or rocks, etc. In this system, information collect ion, analysis, management and comprehensive application of the weather modificat ion are realized. It also can be used in other fields in meteorology.
A comprehensive analysis and process system based on ArcGIS, and its chief targ et, its software frame, standardized data, database system, basic functions and its key technique, etc. are are described. The system is professional especially to weather modification, and it mainly applies to comprehensive analysis and pr ocess for weather modification, decision-making of operation schemes, appraisal of operation effectiveness, and services for enhancement precipitation or suppre ssion hail by ways of cannons or rocks, etc. In this system, information collect ion, analysis, management and comprehensive application of the weather modificat ion are realized. It also can be used in other fields in meteorology.
2011,37(1):122-128, DOI: 10.7519/j.issn.1000-0526.2011.1.017
Abstract:
The following are the main characteristics of the general atmospheric circulation in October 2010. There were two polar vortex centers in the Northern Hemisphere. The circulation presents a four wave pattern in middle high latitudes, in which the strong Ural ridge corresponds to a large 40 gpm positive anomaly area. Strength of the Western Pacific subtropical high is weaker than normal years. The monthly mean temperature (10.1 ℃) is 0.5 ℃ higher than the same period of normal years, and the mean precipitation (42.6 mm) is 15.1% above normal. The major weather events include: 8 precipitation processes occuring, in which a rare heavy rain has struck on Hainan in the first and middle dekad of October; two tropical cyclones generated, with one super typhoon (Chaba, numbered 1013) landed in Fujian; in the last dekad of October, strong cold air outbreak across most areas of China; heavy fog aroused in the central and eastern China.
The following are the main characteristics of the general atmospheric circulation in October 2010. There were two polar vortex centers in the Northern Hemisphere. The circulation presents a four wave pattern in middle high latitudes, in which the strong Ural ridge corresponds to a large 40 gpm positive anomaly area. Strength of the Western Pacific subtropical high is weaker than normal years. The monthly mean temperature (10.1 ℃) is 0.5 ℃ higher than the same period of normal years, and the mean precipitation (42.6 mm) is 15.1% above normal. The major weather events include: 8 precipitation processes occuring, in which a rare heavy rain has struck on Hainan in the first and middle dekad of October; two tropical cyclones generated, with one super typhoon (Chaba, numbered 1013) landed in Fujian; in the last dekad of October, strong cold air outbreak across most areas of China; heavy fog aroused in the central and eastern China.
2013,39(9):1163-1170, DOI: 10.7519/j.issn.1000-0526.2013.09.011
Abstract:
Drought and flood have significant impacts on catchment water use and ecological balance. To develop practical drought/flood monitoring indicators that only need a few climate variables, it is fundamentally necessary to explore the relationship between hydrology variables and climate variables for the specific catchment. This study investigates the correlations between lake water level and various time scale climatological indices according to the standardized precipitation index (SPI) and the standardized precipitation evapotranspiration index (SPEI), based on the monthly water level records from Honghu Lake representative gauging stations and the monthly observations of 8 meteorological stations in the Four Lake Basin. The results showed that extreme droughts and floods are primarily controlled by precipitation variability over the Four Lake Basin, and both SPEI and SPI are well related with lake water level of Honghu Lake while the degree of the correlation varies between different seasons and SPEI/SPI time scales, with the highest correlations for rainy summer and autumn months. Generally, the 4-6 month scale SPEI/SPI drought index is most closely correlated with lake water level of Honghu Lake, showing an apparent response of lake water level to the current and former months’ water surplus and deficiency. When compared with the historical time series of monthly average lake water level of Honghu Lake, the 5 month scale SPEI/SPI agrees well with the variability of the lake water level. The response relationship found during the study can not only aid the monitoring and forecasting of flood and drought conditions in the Four Lake Basin based on conventional weather data, but also provides some references for other places of China.
Drought and flood have significant impacts on catchment water use and ecological balance. To develop practical drought/flood monitoring indicators that only need a few climate variables, it is fundamentally necessary to explore the relationship between hydrology variables and climate variables for the specific catchment. This study investigates the correlations between lake water level and various time scale climatological indices according to the standardized precipitation index (SPI) and the standardized precipitation evapotranspiration index (SPEI), based on the monthly water level records from Honghu Lake representative gauging stations and the monthly observations of 8 meteorological stations in the Four Lake Basin. The results showed that extreme droughts and floods are primarily controlled by precipitation variability over the Four Lake Basin, and both SPEI and SPI are well related with lake water level of Honghu Lake while the degree of the correlation varies between different seasons and SPEI/SPI time scales, with the highest correlations for rainy summer and autumn months. Generally, the 4-6 month scale SPEI/SPI drought index is most closely correlated with lake water level of Honghu Lake, showing an apparent response of lake water level to the current and former months’ water surplus and deficiency. When compared with the historical time series of monthly average lake water level of Honghu Lake, the 5 month scale SPEI/SPI agrees well with the variability of the lake water level. The response relationship found during the study can not only aid the monitoring and forecasting of flood and drought conditions in the Four Lake Basin based on conventional weather data, but also provides some references for other places of China.
2013,39(3):281-290, DOI: 10.7519/j.issn.1000-0526.2013.03.002
Abstract:
By using conventional observation data and NCEP reanalysis data, diagnostic analysis is performed on a rainstorm process, which occurred on 22-25 July 2010 in the western part of Sichuan Basin. The result shows that the rainstorm was generated under the circulation background that low level southerly airflows had remained over the region from the South China Sea to Sichuan Basin, so this rainstorm was closely related to the evolution of the southerly wind speeds. The rainfall intensity increased as the south winds grew stronger. Speed convergence formed by the enhanced south winds and positive vorticity advections became main dynamic trigger factors for the rainstorm. Therefore, the rainstorm is pretty consistent with the low level convergence and the positive vorticity advection. In addition, the result of WRF numerical simulation further indicates that: the evolution of 3 h wind speed at 850 hPa has good indication for the development of mesoscale convective systems. On the leeward side of the 3 h wind speed increasing area, convective cloud clusters are to develop rapidly in the next 3 hours. Moreover, the topographic influence simulation tests suggest that the airflow convergence generated in the west of the Basin is closely related to the topography of plateau.
By using conventional observation data and NCEP reanalysis data, diagnostic analysis is performed on a rainstorm process, which occurred on 22-25 July 2010 in the western part of Sichuan Basin. The result shows that the rainstorm was generated under the circulation background that low level southerly airflows had remained over the region from the South China Sea to Sichuan Basin, so this rainstorm was closely related to the evolution of the southerly wind speeds. The rainfall intensity increased as the south winds grew stronger. Speed convergence formed by the enhanced south winds and positive vorticity advections became main dynamic trigger factors for the rainstorm. Therefore, the rainstorm is pretty consistent with the low level convergence and the positive vorticity advection. In addition, the result of WRF numerical simulation further indicates that: the evolution of 3 h wind speed at 850 hPa has good indication for the development of mesoscale convective systems. On the leeward side of the 3 h wind speed increasing area, convective cloud clusters are to develop rapidly in the next 3 hours. Moreover, the topographic influence simulation tests suggest that the airflow convergence generated in the west of the Basin is closely related to the topography of plateau.
2011,37(2):142-155, DOI: 10.7519/j.issn.1000-0526.2011.2.003
Abstract:
Using the Variational Doppler Radar Analysis System (VDRAS) combined with local unconventional observation data, a more in depth contrastive analysis is carried on the initiation mechanism of two storm cases in Beijing, one is 814 (August 14, 2008) case with strong rainfall that we call it as moist storm and the other is 824 (August 24, 2008) case with little rainfall that we call it as dry storm. The results show: (1) The synoptic scale systems of 814 storm were stable Northeast cold vortex low trough at 500 hPa and shear line at 850 hPa, the specific humidity that more than 12 g·kg-1 below 850 hPa and the relative humidity that more than 90% in the surface indicated that the atmosphere was very moist. It had convective instability caused by humidity advection in lower levels. The 824 storm had a prevailing straight west wind in high levels, an anticyclone in lower levels, and a surface cold front moving fast.The specific humidity that less than 6 g·kg-1, and the relative humidity that less than 30% below 850 hPa indicated that the atmosphere was very dry. It had convective instability caused by temperature advection. (2) There was much strong vertical wind shear in the whole vertical layer for 814 storm case, the clockwise wind direction with height within 500-1500 m intensified the warm and humidity inflow of lower layer advantageous to storm initiation and development. While there was weak vertical wind shear and unobvious warm and humidity inflow of lower layer for 824 case, which was not conducive to storm initiation and development. In addition, composited wind of the whole troposphere and storm movement speed were very low for 814 case, but they were very high for 824 case. (3) The 814 storm was formed by the collision and mergence of multi cell storms, a convergence line was formed by the cold pool outflow produced by the precipitation of the upstream of thunderstorm cell and the east wind in low levels which forced the low level warm and moist air to uplift, additionally the strong convective instability and vertical wind shear supported the formation and development of new storm. The interactions (collisions) of gust fronts in the leading edge of cold pool of multi cell thunderstorm group, further exacerbating the low level instability, leading to the regeneration and mergence of new convective thunderstorms. The 824 storm was a line convective system accompanied with cold front that rapid moved eastward and lasted for short time, there was no east wind with warm and moisture air accompanying the cold pool outflow produced by the downdrafts of thunderstorm. The absence of mesoscale lifting mechanism and moisture inflow couldn’t support the formation and development of new storm.
Using the Variational Doppler Radar Analysis System (VDRAS) combined with local unconventional observation data, a more in depth contrastive analysis is carried on the initiation mechanism of two storm cases in Beijing, one is 814 (August 14, 2008) case with strong rainfall that we call it as moist storm and the other is 824 (August 24, 2008) case with little rainfall that we call it as dry storm. The results show: (1) The synoptic scale systems of 814 storm were stable Northeast cold vortex low trough at 500 hPa and shear line at 850 hPa, the specific humidity that more than 12 g·kg-1 below 850 hPa and the relative humidity that more than 90% in the surface indicated that the atmosphere was very moist. It had convective instability caused by humidity advection in lower levels. The 824 storm had a prevailing straight west wind in high levels, an anticyclone in lower levels, and a surface cold front moving fast.The specific humidity that less than 6 g·kg-1, and the relative humidity that less than 30% below 850 hPa indicated that the atmosphere was very dry. It had convective instability caused by temperature advection. (2) There was much strong vertical wind shear in the whole vertical layer for 814 storm case, the clockwise wind direction with height within 500-1500 m intensified the warm and humidity inflow of lower layer advantageous to storm initiation and development. While there was weak vertical wind shear and unobvious warm and humidity inflow of lower layer for 824 case, which was not conducive to storm initiation and development. In addition, composited wind of the whole troposphere and storm movement speed were very low for 814 case, but they were very high for 824 case. (3) The 814 storm was formed by the collision and mergence of multi cell storms, a convergence line was formed by the cold pool outflow produced by the precipitation of the upstream of thunderstorm cell and the east wind in low levels which forced the low level warm and moist air to uplift, additionally the strong convective instability and vertical wind shear supported the formation and development of new storm. The interactions (collisions) of gust fronts in the leading edge of cold pool of multi cell thunderstorm group, further exacerbating the low level instability, leading to the regeneration and mergence of new convective thunderstorms. The 824 storm was a line convective system accompanied with cold front that rapid moved eastward and lasted for short time, there was no east wind with warm and moisture air accompanying the cold pool outflow produced by the downdrafts of thunderstorm. The absence of mesoscale lifting mechanism and moisture inflow couldn’t support the formation and development of new storm.
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