ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 48,Issue 9,2022 Table of Contents
2022, 48(9):1077-1089.
DOI: 10.7519/j.issn.1000-0526.2022.051201
Abstract:
The horizontal diffusion term is often used in the model to suppress nonlinear calculation instability or dampen of false short waves, but this will cause excessive dissipation of small-scale kinetic energy in the numerical model near the truncation scale. To compensate the excessively dissipated small-scale kinetic energy back to the model, a stochastic kinetic energy backscatter (SKEB) method is introduced into the CMA-REPS regional ensemble prediction system. First, based on the random field obtained in the first-order autoregressive random process in the horizontal direction expanding the spherical harmonic function we calculate the local kinetic energy dissipation rate caused by numerical diffusion scheme. Then, we construct the random flow function forcing, transform it into horizontal wind speed disturbance, and make random compensation for the dissipated kinetic energy. We carried out a 10 d ensemble prediction test and a randomized time and space scale sensitivity test in September and October 2018 (choose 1st, 7th, 13th, 19th, and 25th), and evaluated the test results here. The main conclusions of the research work are as follows. By comparing the ensemble prediction results of the test using the SKEB scheme and the test without the SKEB scheme, we see that the use of the SKEB scheme can increase the kinetic energy spectrum of the CMA-REPS regional model in the small scale region, improving the CMA-REPS ensemble prediction system to the actual atmosphere to some extent. The introduction of SKEB scheme in regional ensemble prediction can significantly improve the spread of U and V in horizontal wind field of regional model. The SKEB program has improved the forecasting skills to a certain extent, such as reducing the CRPS scores of the horizontal wind fields U and V, and also reducing the outlier scores of the horizontal wind field, temperature and 10 m wind speed. The sensitivity tests based on the SKEB method for six time scales of random pattern (1, 3, 6, 9,12, 15 h of the time series τ) and five spatial correlation scales (the maximum cutoff wave number Lmax is selected as 80, 100, 120, 160, 200, 240) show that the ensemble prediction is sensitive to the six time scales of the stochastic model of the SKEB method. And the experiment whose time scale is set to 12 h and the maximum truncation wave number is set to 240 show the best performance. Therefore, we can draw the conclusion that the SKEB scheme can compensate for the small-scale kinetic energy dissipated at the truncated scale, and effectively improve forecasting skills.
The horizontal diffusion term is often used in the model to suppress nonlinear calculation instability or dampen of false short waves, but this will cause excessive dissipation of small-scale kinetic energy in the numerical model near the truncation scale. To compensate the excessively dissipated small-scale kinetic energy back to the model, a stochastic kinetic energy backscatter (SKEB) method is introduced into the CMA-REPS regional ensemble prediction system. First, based on the random field obtained in the first-order autoregressive random process in the horizontal direction expanding the spherical harmonic function we calculate the local kinetic energy dissipation rate caused by numerical diffusion scheme. Then, we construct the random flow function forcing, transform it into horizontal wind speed disturbance, and make random compensation for the dissipated kinetic energy. We carried out a 10 d ensemble prediction test and a randomized time and space scale sensitivity test in September and October 2018 (choose 1st, 7th, 13th, 19th, and 25th), and evaluated the test results here. The main conclusions of the research work are as follows. By comparing the ensemble prediction results of the test using the SKEB scheme and the test without the SKEB scheme, we see that the use of the SKEB scheme can increase the kinetic energy spectrum of the CMA-REPS regional model in the small scale region, improving the CMA-REPS ensemble prediction system to the actual atmosphere to some extent. The introduction of SKEB scheme in regional ensemble prediction can significantly improve the spread of U and V in horizontal wind field of regional model. The SKEB program has improved the forecasting skills to a certain extent, such as reducing the CRPS scores of the horizontal wind fields U and V, and also reducing the outlier scores of the horizontal wind field, temperature and 10 m wind speed. The sensitivity tests based on the SKEB method for six time scales of random pattern (1, 3, 6, 9,12, 15 h of the time series τ) and five spatial correlation scales (the maximum cutoff wave number Lmax is selected as 80, 100, 120, 160, 200, 240) show that the ensemble prediction is sensitive to the six time scales of the stochastic model of the SKEB method. And the experiment whose time scale is set to 12 h and the maximum truncation wave number is set to 240 show the best performance. Therefore, we can draw the conclusion that the SKEB scheme can compensate for the small-scale kinetic energy dissipated at the truncated scale, and effectively improve forecasting skills.
2022, 48(9):1090-1100.
DOI: 10.7519/j.issn.1000-0526.2022.040601
Abstract:
Based on the reanalysis data, the causes of persistent precipitation over southern China during February-March 2019 and the relationship with Madden-Julian Oscillation (MJO) are studied. This persistent precipitation can be divided into two episodes. During the first episode, the precipitation covered the whole southern China, during the second episode it mainly occurred in South China, with intensity stronger than the first. The large-scale circulation analyses show that during this precipitation event, the abnormal geopotential height over southern China and western Pacific was low in the west and high in the east, which was conducive to the occurrence of abnormal southerlies and moisture transport. During the first episode, moisture convergence and upward movement appeared obviously over the whole southern China; during the second episode, stronger moisture convergence and upward movement occurred only in South China. The diagnostic analyses of moisture budget show that the anomalous moisture flux divergence during the two episodes was primarily caused by the meridional moisture convergence, which contributed more than 70% to moisture flux divergence. By comparing the evolution of precipitation and MJO activity, we find that the variation of precipitation was closely related to the phase and amplitude of MJO. When the amplitude of MJO enhanced (weakened) obviously, the anomalous precipitation over southern China increased (decreased). The scale analyses of meridional moisture convergence suggest that the interaction between moisture and circulation at the low-frequency scale (longer than 90 days) and the intraseasonal scale (30-90 days) plays a decisive role in the meridional moisture convergence, especially low-frequency moisture convergence by intraseasonal meridional wind. Therefore, the MJO activity over the tropical region can play a significant role in the persistent precipitation over southern China through regulating the low-frequency moisture transport by the intraseasonal meridional wind.
Based on the reanalysis data, the causes of persistent precipitation over southern China during February-March 2019 and the relationship with Madden-Julian Oscillation (MJO) are studied. This persistent precipitation can be divided into two episodes. During the first episode, the precipitation covered the whole southern China, during the second episode it mainly occurred in South China, with intensity stronger than the first. The large-scale circulation analyses show that during this precipitation event, the abnormal geopotential height over southern China and western Pacific was low in the west and high in the east, which was conducive to the occurrence of abnormal southerlies and moisture transport. During the first episode, moisture convergence and upward movement appeared obviously over the whole southern China; during the second episode, stronger moisture convergence and upward movement occurred only in South China. The diagnostic analyses of moisture budget show that the anomalous moisture flux divergence during the two episodes was primarily caused by the meridional moisture convergence, which contributed more than 70% to moisture flux divergence. By comparing the evolution of precipitation and MJO activity, we find that the variation of precipitation was closely related to the phase and amplitude of MJO. When the amplitude of MJO enhanced (weakened) obviously, the anomalous precipitation over southern China increased (decreased). The scale analyses of meridional moisture convergence suggest that the interaction between moisture and circulation at the low-frequency scale (longer than 90 days) and the intraseasonal scale (30-90 days) plays a decisive role in the meridional moisture convergence, especially low-frequency moisture convergence by intraseasonal meridional wind. Therefore, the MJO activity over the tropical region can play a significant role in the persistent precipitation over southern China through regulating the low-frequency moisture transport by the intraseasonal meridional wind.
2022, 48(9):1101-1115.
DOI: 10.7519/j.issn.1000-0526.2022.040602
Abstract:
Based on the observational and NCEP reanalysis data, the frontogenesis and instabilities in two continuous autumn torrential rain days in Henan Province in September 2011 are diagnosed. The results show that there existed a northeastsouthwest frontal zone in north central Henan Province in the two torrential rain days. The frontal zone showed the quasistationary feature. The similarities between the frontogenetical functions of two torrential rain days are that, before the heavy rain, frontogenesis was demonstrated in most parts of the frontal zone; in the occurrence of heavy rain, frontogenesis got strengthened in high and low levels but weakened in middle level of 600-500 hPa and frontolysis even appeared at about 400 hPa, which was caused by the strengthening of vertical motion. When the heavy rain got weak, frontogenesis in high level and frontolysis area both descended in height, corresponding to the weakening of vertical motion. The differences are that the middle tropospheric frontal zone was stiff during the night of the second torrential rain day, frontogenesis centers were getting near warm zone, which was the result of strengthening of convective rainfall and enhancement of precipitation efficiency and condensation latent heat release. The roles of terms of frontogenetical function were different. The contribution of deformation process to forntogenesis was the greatest; the role of tilting term was mainly frontolysis. The strong frontolysis center at 400 hPa during heavy rain is the distinct manifestation of contribution of tilting term. The two torrential rain days are both of inertial stability. The first torrential rain day was convective stable but symmetric instable, so the heavy rain band was the result of symmetric instability. On the second torrential rain day, convective instability and symmetric instability coexisted at about 700 hPa in frontal zone, so the heavy rain band was caused by convectivesymmetric instabilities and thunderstorms during the night were of the characteristics of elevated thunderstorms. Furthermore, on the first torrential rain day, there was consistent slanted updraft in the warm side of frontal zone; frontogenesis center, symmetric instability center and upward motion center appeared together, showing that frontogenesis provided a favorable condition for the release of symmetric instability. On the second torrential rain day, there was an obvious mixture of slanted convection and vertical convection; the starting point of vertical updraft was just the convectivesymmetric instabilities area. Vertical updraft was much stronger than the slanted upward flow on the first torrential rain day, indicating that gravitational convection is dominant.
Based on the observational and NCEP reanalysis data, the frontogenesis and instabilities in two continuous autumn torrential rain days in Henan Province in September 2011 are diagnosed. The results show that there existed a northeastsouthwest frontal zone in north central Henan Province in the two torrential rain days. The frontal zone showed the quasistationary feature. The similarities between the frontogenetical functions of two torrential rain days are that, before the heavy rain, frontogenesis was demonstrated in most parts of the frontal zone; in the occurrence of heavy rain, frontogenesis got strengthened in high and low levels but weakened in middle level of 600-500 hPa and frontolysis even appeared at about 400 hPa, which was caused by the strengthening of vertical motion. When the heavy rain got weak, frontogenesis in high level and frontolysis area both descended in height, corresponding to the weakening of vertical motion. The differences are that the middle tropospheric frontal zone was stiff during the night of the second torrential rain day, frontogenesis centers were getting near warm zone, which was the result of strengthening of convective rainfall and enhancement of precipitation efficiency and condensation latent heat release. The roles of terms of frontogenetical function were different. The contribution of deformation process to forntogenesis was the greatest; the role of tilting term was mainly frontolysis. The strong frontolysis center at 400 hPa during heavy rain is the distinct manifestation of contribution of tilting term. The two torrential rain days are both of inertial stability. The first torrential rain day was convective stable but symmetric instable, so the heavy rain band was the result of symmetric instability. On the second torrential rain day, convective instability and symmetric instability coexisted at about 700 hPa in frontal zone, so the heavy rain band was caused by convectivesymmetric instabilities and thunderstorms during the night were of the characteristics of elevated thunderstorms. Furthermore, on the first torrential rain day, there was consistent slanted updraft in the warm side of frontal zone; frontogenesis center, symmetric instability center and upward motion center appeared together, showing that frontogenesis provided a favorable condition for the release of symmetric instability. On the second torrential rain day, there was an obvious mixture of slanted convection and vertical convection; the starting point of vertical updraft was just the convectivesymmetric instabilities area. Vertical updraft was much stronger than the slanted upward flow on the first torrential rain day, indicating that gravitational convection is dominant.
2022, 48(9):1116-1129.
DOI: 10.7519/j.issn.1000-0526.2022.042101
Abstract:
In the summer of 2020, Chongqing experienced the third most precipitation amount in the same period since 1961 and the maximum in the same period in June-July, so it was extremely anomalous. In this paper, we investigate the main causes for the abnormal summer precipitation in Chongqing in 2020 by using daily precipitation from 34 meteorological stations in Chongqing and daily geopotential height, wind, relative humidity and other reanalysis data from NCEP/NCAR as well as monthly sea surface temperature (SST) from NOAA during the summer of 1961-2020. We adopt the modern statistical diagnostic methods such as correlation and synthesis for the analysis. The results show that in summer 2020, especially in June-July, the atmospheric circulation in the high and low latitudes over the Eurasian region showed the “+ - +” circulation type distribution, and the longitude of the circulation was obvious. The first type of circulation configuration with typical rainy summer in Chongqing appeared, thus causing the abnormally more precipitation in summer 2020. The analysis of the external forcing signal indicates that the positive ENSO event from autumn-winter 2019 to spring 2020 made the certainty probability of Chongqing’s summer precipitation increase. At the same time， the positive equatorial Indian Ocean dipole anomaly in autumn 2019 contributed to the anomalous increase of Chongqing’s summer precipitation in 2020. The effects of the two events were superimposed on each other when they occurred simultaneously, causing the extreme anomalous increase of Chongqing’s summer precipitation. ENSO and Indian Ocean dipole were the important precursor signals affecting Chongqing summer precipitation anomaly, so paying attention to these two signals in advance could provide meaningful references for Chongqing summer precipitation prediction.
In the summer of 2020, Chongqing experienced the third most precipitation amount in the same period since 1961 and the maximum in the same period in June-July, so it was extremely anomalous. In this paper, we investigate the main causes for the abnormal summer precipitation in Chongqing in 2020 by using daily precipitation from 34 meteorological stations in Chongqing and daily geopotential height, wind, relative humidity and other reanalysis data from NCEP/NCAR as well as monthly sea surface temperature (SST) from NOAA during the summer of 1961-2020. We adopt the modern statistical diagnostic methods such as correlation and synthesis for the analysis. The results show that in summer 2020, especially in June-July, the atmospheric circulation in the high and low latitudes over the Eurasian region showed the “+ - +” circulation type distribution, and the longitude of the circulation was obvious. The first type of circulation configuration with typical rainy summer in Chongqing appeared, thus causing the abnormally more precipitation in summer 2020. The analysis of the external forcing signal indicates that the positive ENSO event from autumn-winter 2019 to spring 2020 made the certainty probability of Chongqing’s summer precipitation increase. At the same time， the positive equatorial Indian Ocean dipole anomaly in autumn 2019 contributed to the anomalous increase of Chongqing’s summer precipitation in 2020. The effects of the two events were superimposed on each other when they occurred simultaneously, causing the extreme anomalous increase of Chongqing’s summer precipitation. ENSO and Indian Ocean dipole were the important precursor signals affecting Chongqing summer precipitation anomaly, so paying attention to these two signals in advance could provide meaningful references for Chongqing summer precipitation prediction.
2022, 48(9):1130-1139.
DOI: 10.7519/j.issn.1000-0526.2022.041802
Abstract:
Based on the rainfall data of the middle and lower reaches of the Yangtze River (MLRYR) during Meiyu season (MYS), NCEP/NCAR daily reanalysis data, NOAA monthly average sea surface temperature (SST) and Arctic sea ice (ASI) indices data, the circulation characteristics and precursory signals of the abnormal rainfall in MLRYR after 2000 are studied by correlation analysis, regression analysis and other methods. A prediction model is established and a prediction experiment is carried out. The results show that when there is more precipitation in MLRYR, the low-value systems near Balkhash Lake and Bohai Bay in the Eurasian mid-latitudes are more active, the upper-level westerly jet stream is southward and eastward, the low-level wind field is distributed in meridional wave train, the East Asian summer monsoon is weaker, and the Meiyu front is strong in the area from the Sea of Japan to MLRYR, which results in strong ascending motion and convergence of water vapor flux over MLRYR, thus increasing the rainfall therein. The anomalous SST over tropical eastern Pacific (TEP) and ASI in previous winter are the main precursors of abnormal Meiyu rainfall over MLRYR. The anomalous anticyclone over South China Sea during MYS induced by the positive phase of SST over TEP and ASI are beneficial to the convergence of cold air and warm moist air over MLRYR. So that the rainfall over MLRYR increases. Therefore, the rainfall multiple regression prediction model constructed by the use of SST and ASI factors for MLRYR during MYS can produce better results of fitting and prediction.
Based on the rainfall data of the middle and lower reaches of the Yangtze River (MLRYR) during Meiyu season (MYS), NCEP/NCAR daily reanalysis data, NOAA monthly average sea surface temperature (SST) and Arctic sea ice (ASI) indices data, the circulation characteristics and precursory signals of the abnormal rainfall in MLRYR after 2000 are studied by correlation analysis, regression analysis and other methods. A prediction model is established and a prediction experiment is carried out. The results show that when there is more precipitation in MLRYR, the low-value systems near Balkhash Lake and Bohai Bay in the Eurasian mid-latitudes are more active, the upper-level westerly jet stream is southward and eastward, the low-level wind field is distributed in meridional wave train, the East Asian summer monsoon is weaker, and the Meiyu front is strong in the area from the Sea of Japan to MLRYR, which results in strong ascending motion and convergence of water vapor flux over MLRYR, thus increasing the rainfall therein. The anomalous SST over tropical eastern Pacific (TEP) and ASI in previous winter are the main precursors of abnormal Meiyu rainfall over MLRYR. The anomalous anticyclone over South China Sea during MYS induced by the positive phase of SST over TEP and ASI are beneficial to the convergence of cold air and warm moist air over MLRYR. So that the rainfall over MLRYR increases. Therefore, the rainfall multiple regression prediction model constructed by the use of SST and ASI factors for MLRYR during MYS can produce better results of fitting and prediction.
2022, 48(9):1140-1152.
DOI: 10.7519/j.issn.1000-0526.2022.051602
Abstract:
Based on GPM/DPR dual-frequency precipitation radar, FY-2E satellite and surface precipitation data, the infrared brightness temperature, horizontal distribution and vertical structure characteristics of the four snowfall processes during mature period in northern Xinjiang are analyzed. The results show that the cloud top brightness temperature of the snowfall is concentrated at 210-245 K, and the snowfall clouds are mainly stratiform clouds. The middle clouds contribute the most to the precipitation intensity, and the near-surface precipitation rate is mostly distributed between 0.5-2.0 mm·h-1. The echo top height in areas with high precipitation rate is mainly concentrated in the range of 3.0-4.5 km, and there is a positive correlation between the echo top height and the variation of near-surface precipitation rate. The range of radar reflectivity factor (Z) is between 22-35 dBz, and the height of the strong echo center is mainly distributed in 1.25-4.50 km. The configuration with mass weighted average diameter (Dm) of 1.01-1.25 mm and particle number concentration (dBNw) of 32-36 contributes the most precipitation, and the corresponding heights are 2.19-2.50 km and 2.13-2.67 km. Near the surface, there are more large particles produced by the collision-convergence process, and the Dm reaches 2.33-3.00 mm near surface. Toward the surface, Z and Dm are almost constant or slightly increase, and the values of Z and Dm are positively correlated to the variation of surface rainfall.
Based on GPM/DPR dual-frequency precipitation radar, FY-2E satellite and surface precipitation data, the infrared brightness temperature, horizontal distribution and vertical structure characteristics of the four snowfall processes during mature period in northern Xinjiang are analyzed. The results show that the cloud top brightness temperature of the snowfall is concentrated at 210-245 K, and the snowfall clouds are mainly stratiform clouds. The middle clouds contribute the most to the precipitation intensity, and the near-surface precipitation rate is mostly distributed between 0.5-2.0 mm·h-1. The echo top height in areas with high precipitation rate is mainly concentrated in the range of 3.0-4.5 km, and there is a positive correlation between the echo top height and the variation of near-surface precipitation rate. The range of radar reflectivity factor (Z) is between 22-35 dBz, and the height of the strong echo center is mainly distributed in 1.25-4.50 km. The configuration with mass weighted average diameter (Dm) of 1.01-1.25 mm and particle number concentration (dBNw) of 32-36 contributes the most precipitation, and the corresponding heights are 2.19-2.50 km and 2.13-2.67 km. Near the surface, there are more large particles produced by the collision-convergence process, and the Dm reaches 2.33-3.00 mm near surface. Toward the surface, Z and Dm are almost constant or slightly increase, and the values of Z and Dm are positively correlated to the variation of surface rainfall.
2022, 48(9):1153-1161.
DOI: 10.7519/j.issn.1000-0526.2022.041301
Abstract:
Based on the surface observation and ERA5 hourly reanalysis data from 2000 to 2014, 43 factors were selected to characterize the temperature, humidity and microphysical characteristics of four types of precipitation phases (rain, snow, sleet, freezing rain). The objective forecast method of precipitation type in the middle reaches of Yangtze River is studied by using CatBoost algorithm and the fine terrain height preprocessing. The results show that this method has good classification and forecast effect for rain, snow and freezing rain. The accuracy and spatial fineness of precipitation type discrimination can be improved by using the fine terrain height preprocessing. Compared with the ECMWF prediction, the prediction accuracy of rain, snow and freezing rain has increased by 9.9%, 39.1% and 11.1% respectively, but the improvement of sleet was not obvious.
Based on the surface observation and ERA5 hourly reanalysis data from 2000 to 2014, 43 factors were selected to characterize the temperature, humidity and microphysical characteristics of four types of precipitation phases (rain, snow, sleet, freezing rain). The objective forecast method of precipitation type in the middle reaches of Yangtze River is studied by using CatBoost algorithm and the fine terrain height preprocessing. The results show that this method has good classification and forecast effect for rain, snow and freezing rain. The accuracy and spatial fineness of precipitation type discrimination can be improved by using the fine terrain height preprocessing. Compared with the ECMWF prediction, the prediction accuracy of rain, snow and freezing rain has increased by 9.9%, 39.1% and 11.1% respectively, but the improvement of sleet was not obvious.
YAO Wen
,
ZHANG Jing
,
YU Qingbo
,
ZENG Yajie
,
CHENG Lei
,
ZHANG Guoping
,
LI Li
,
CUI Futao
,
ZHAO Yue
2022, 48(9):1162-1170.
DOI: 10.7519/j.issn.1000-0526.2022.041401
Abstract:
Based on the CINRAD/SA and dualpolarization weather radar data of Yingkou in Liaoning Province during 2018-2020, the early morning departure activities of birds from their habitats in the Liaohe River Delta Wetland and the surrounding areas are analyzed. The results show that there are obvious seasonal and daily changes in the activities of birds in the Liaohe River Delta and the nearby wetland.The echo of birds detected by weather radar is concentrated from late July to mid October, especially from August to September. There is a positive correlation between the time of bird echo and the time of daybreak. The echo of birds shows obvious ring-shape characteristics on the reflectivity products, and the strongest can reach more than 40 dBz. In terms of Doppler velocity products, they are divergent. In the case of high wind speed, the echo of the birds deviates significantly to the downwind direction. The distribution of difference reflection (ZDR) of the bird echo is not uniform, and the maximum reflectivity is 3-7 dB. The correlation coefficient (CC) of the bird echo is small and uniform, which is different from the ground echo, and is related to the intensity of the reflection factor of the echo. When the reflection intensity is greater than 30 dBz, CC is between 0.7-0.8. When the reflection intensity is less than 30 dBz, CC is mostly less than 0.6. Dual polarization radar products have obvious advantages in the recognition of bird echo, which can effectively eliminate the bird echo in precipitation and improve the accuracy of short-term and nowcasting forecast. However, the differential phase shift rate (KDP) and HCL do not reflect the echo of birds.
Based on the CINRAD/SA and dualpolarization weather radar data of Yingkou in Liaoning Province during 2018-2020, the early morning departure activities of birds from their habitats in the Liaohe River Delta Wetland and the surrounding areas are analyzed. The results show that there are obvious seasonal and daily changes in the activities of birds in the Liaohe River Delta and the nearby wetland.The echo of birds detected by weather radar is concentrated from late July to mid October, especially from August to September. There is a positive correlation between the time of bird echo and the time of daybreak. The echo of birds shows obvious ring-shape characteristics on the reflectivity products, and the strongest can reach more than 40 dBz. In terms of Doppler velocity products, they are divergent. In the case of high wind speed, the echo of the birds deviates significantly to the downwind direction. The distribution of difference reflection (ZDR) of the bird echo is not uniform, and the maximum reflectivity is 3-7 dB. The correlation coefficient (CC) of the bird echo is small and uniform, which is different from the ground echo, and is related to the intensity of the reflection factor of the echo. When the reflection intensity is greater than 30 dBz, CC is between 0.7-0.8. When the reflection intensity is less than 30 dBz, CC is mostly less than 0.6. Dual polarization radar products have obvious advantages in the recognition of bird echo, which can effectively eliminate the bird echo in precipitation and improve the accuracy of short-term and nowcasting forecast. However, the differential phase shift rate (KDP) and HCL do not reflect the echo of birds.
2022, 48(9):1171-1185.
DOI: 10.7519/j.issn.1000-0526.2021.080501
Abstract:
Sandstorm is one of the most serious disaster weather in the spring of Hexi Corridor. Understanding the atmospheric boundary layer characteristics of sandstorms is an important means to improve the prediction and early warning level and reduce the impact of sandstorm. Using daily high-resolution sounding data at 08:00 BT and 20:00 BT and the ground wind-sand observation data from Dunhuang, Jiuquan, Zhangye and Minqin stations over Hexi Corridor in the spring of 2006-2016, this article investigates the variation characteristics of vertical structure of atmospheric boundary layer in terms of dust intensity at different stations, daily change and duration of duststorm as well as duststorms under different circulation situations from surface up to 5 km height. The results show that the intensity of temperature inversion in the presence of sandstorm at 08:00 BT was above 1.6℃·（100 m）-1, the dry layer thickness of less than 40% relative humidity was more than 3 km, the dry layer thickness of less than 30% relative humidity was more than 1.5 km and the maximum wind speed at 20:00 BT was more than 13 m·s-1. Due to the influence of altitude, topography and underlying soil properties, the lower wind field has obvious diurnal variation and valley wind effect. It was high temperature, dry air, big wind speed and more dust in Dunhuang and Minqin. Zhangye had heigher wind speed affected by the narrow tube effect in the corridor. The lower layer of Dunhuang was mainly southeast to southwest wind, but its upper level and other stations were mainly west to northwest wind. For daily variation of meteorological conditions in the boundary layer at the time of sandstorm, it was dry and warm in morning, but wet, cold and strong wind in the afternoon. The maximum wind speed was 17.6 m·s-1， occurring at height of 0.9 km, south wind occurred near ground from night to morning, west wind occurred in afternoon, dry and light wind occurred over night. When the sandstorm lasted for a long time, the temperature was low in the morning and evening, and the dry layer of the atmosphere with relative humidity ≤ 30% was 2.85 km thick at 08:00 BT in less than 5 hours, while the dry layer being 1.05 km thick lasted for more than 5 hours at 20:00 BT and it was thicker in the morning and night, shallow in the afternoon. The minimum threshold of depression of the dew point was 16-17℃ with maximum height of 2.85-3.00 km. Under different sandstorm circulation conditions, the ridge type was dry and cold in the morning, the maximum wind speed was 14.6 m·s-1 at 0.75 km height， the trough type was wet with cold and strong wind in the afternoon, and the maximum wind speed was 15.7 m·s-1 at 0.9 km height; and the westerly type was dry with cold and light wind blowing near the ground, but wind speed was stronger at the height between 1.2-3.5 km in the morning and higher than 2.4 km in the evening.
Sandstorm is one of the most serious disaster weather in the spring of Hexi Corridor. Understanding the atmospheric boundary layer characteristics of sandstorms is an important means to improve the prediction and early warning level and reduce the impact of sandstorm. Using daily high-resolution sounding data at 08:00 BT and 20:00 BT and the ground wind-sand observation data from Dunhuang, Jiuquan, Zhangye and Minqin stations over Hexi Corridor in the spring of 2006-2016, this article investigates the variation characteristics of vertical structure of atmospheric boundary layer in terms of dust intensity at different stations, daily change and duration of duststorm as well as duststorms under different circulation situations from surface up to 5 km height. The results show that the intensity of temperature inversion in the presence of sandstorm at 08:00 BT was above 1.6℃·（100 m）-1, the dry layer thickness of less than 40% relative humidity was more than 3 km, the dry layer thickness of less than 30% relative humidity was more than 1.5 km and the maximum wind speed at 20:00 BT was more than 13 m·s-1. Due to the influence of altitude, topography and underlying soil properties, the lower wind field has obvious diurnal variation and valley wind effect. It was high temperature, dry air, big wind speed and more dust in Dunhuang and Minqin. Zhangye had heigher wind speed affected by the narrow tube effect in the corridor. The lower layer of Dunhuang was mainly southeast to southwest wind, but its upper level and other stations were mainly west to northwest wind. For daily variation of meteorological conditions in the boundary layer at the time of sandstorm, it was dry and warm in morning, but wet, cold and strong wind in the afternoon. The maximum wind speed was 17.6 m·s-1， occurring at height of 0.9 km, south wind occurred near ground from night to morning, west wind occurred in afternoon, dry and light wind occurred over night. When the sandstorm lasted for a long time, the temperature was low in the morning and evening, and the dry layer of the atmosphere with relative humidity ≤ 30% was 2.85 km thick at 08:00 BT in less than 5 hours, while the dry layer being 1.05 km thick lasted for more than 5 hours at 20:00 BT and it was thicker in the morning and night, shallow in the afternoon. The minimum threshold of depression of the dew point was 16-17℃ with maximum height of 2.85-3.00 km. Under different sandstorm circulation conditions, the ridge type was dry and cold in the morning, the maximum wind speed was 14.6 m·s-1 at 0.75 km height， the trough type was wet with cold and strong wind in the afternoon, and the maximum wind speed was 15.7 m·s-1 at 0.9 km height; and the westerly type was dry with cold and light wind blowing near the ground, but wind speed was stronger at the height between 1.2-3.5 km in the morning and higher than 2.4 km in the evening.
2022, 48(9):1186-1194.
DOI: 10.7519/j.issn.1000-0526.2022.042201
Abstract:
Scientific and reasonable disaster indexes are the basis and key to the effective disaster early warning and accurate disaster impact assessment. In this study, based on the principle of wind damage to agricultural facilities, the wind disaster indexes of protected agricultureare divided into two levels. Level Ⅰ is for the damage to the main structure of the facility, Level Ⅱ is for the damage to the shed film. Based on the local climate characteristics and design service lifetime of solar greenhouses and plastic tunnels, the extreme value probability distribution model is used to analyze the maximum wind speed observation data of 2467 weather stations from 1989 to 2018, and the maximum wind speed of 20-year and 10-year return period are calculated. On this basis, the wind resistance of different types of agricultural facilities and the disaster-causing factors are considered comprehensively, and the wind disaster indexes for solar greenhouses and plastic tunnels of different levels based on extreme wind speed are established. According to the main distribution areas of solar greenhouses and plastic tunnels in China, the wind disaster indexes distribution maps are drawn. Based on the 2009-2018 wind disaster data of protected agriculture and the wind disaster cases of representative provinces in each region in 2020, the wind disaster indexes determined in this study are in good agreement with the disaster-bearing body’s degree of damage and the observed wind speed. And the method for determining the wind disaster index is feasible.
Scientific and reasonable disaster indexes are the basis and key to the effective disaster early warning and accurate disaster impact assessment. In this study, based on the principle of wind damage to agricultural facilities, the wind disaster indexes of protected agricultureare divided into two levels. Level Ⅰ is for the damage to the main structure of the facility, Level Ⅱ is for the damage to the shed film. Based on the local climate characteristics and design service lifetime of solar greenhouses and plastic tunnels, the extreme value probability distribution model is used to analyze the maximum wind speed observation data of 2467 weather stations from 1989 to 2018, and the maximum wind speed of 20-year and 10-year return period are calculated. On this basis, the wind resistance of different types of agricultural facilities and the disaster-causing factors are considered comprehensively, and the wind disaster indexes for solar greenhouses and plastic tunnels of different levels based on extreme wind speed are established. According to the main distribution areas of solar greenhouses and plastic tunnels in China, the wind disaster indexes distribution maps are drawn. Based on the 2009-2018 wind disaster data of protected agriculture and the wind disaster cases of representative provinces in each region in 2020, the wind disaster indexes determined in this study are in good agreement with the disaster-bearing body’s degree of damage and the observed wind speed. And the method for determining the wind disaster index is feasible.
2022, 48(9):1195-1208.
DOI: 10.7519/j.issn.1000-0526.2022.053001
Abstract:
Based on the operational real-time typhoon data of National Meteorological Centre and other sources of observations including automatic station and satellite images, the main characteristics of typhoon activities in Western North Pacific and the South China Sea in 2021, including influential tracks, strength, wind and rainfall, are analyzed and reviewed. It is found that in 2021, the genesis region was obviously westward, with five typhoons generated in the South China Sea. The overall strengths of the typhoons were weaker than normal, and six typhoons experienced rapid strengthening activities, among which Typhoon Chanthu increased to 40 m·s-1 within 24 hours, which was rare in the past 30 year. Six typhoons made landfall in China and the other two affected coastal areas. The forecast error analysis shows that the main strength forecast error was due to the rapid strengthening cases, while the track forecast error was mainly caused by the sharp turning of typhoons. Under the weak steering flow, the northward movement of Typhoon In-Fa after slowing down was related to the influence of upper-tropospheric cold low. The increase of offshore deep convection caused by land-sea thermal difference and local convergence could be the main reason for the offshore rapid strengthening of Typhoon Cempaka. Under the background of the obvious adjustment of the subtropical high, Typhoon Chanthu dwelled over the northern part of the East China Sea for three days bringing obvious rainfall and gale winds to the East China.
Based on the operational real-time typhoon data of National Meteorological Centre and other sources of observations including automatic station and satellite images, the main characteristics of typhoon activities in Western North Pacific and the South China Sea in 2021, including influential tracks, strength, wind and rainfall, are analyzed and reviewed. It is found that in 2021, the genesis region was obviously westward, with five typhoons generated in the South China Sea. The overall strengths of the typhoons were weaker than normal, and six typhoons experienced rapid strengthening activities, among which Typhoon Chanthu increased to 40 m·s-1 within 24 hours, which was rare in the past 30 year. Six typhoons made landfall in China and the other two affected coastal areas. The forecast error analysis shows that the main strength forecast error was due to the rapid strengthening cases, while the track forecast error was mainly caused by the sharp turning of typhoons. Under the weak steering flow, the northward movement of Typhoon In-Fa after slowing down was related to the influence of upper-tropospheric cold low. The increase of offshore deep convection caused by land-sea thermal difference and local convergence could be the main reason for the offshore rapid strengthening of Typhoon Cempaka. Under the background of the obvious adjustment of the subtropical high, Typhoon Chanthu dwelled over the northern part of the East China Sea for three days bringing obvious rainfall and gale winds to the East China.
2022, 48(9):1209-1216.
DOI: 10.7519/j.issn.1000-0526.2022.080201
Abstract:
The main characteristics of the atmospheric circulation in June 2022 are as follows. The polar vortex with multi centers in the Northern Hemisphere was weaker than normal, the 500 hPa geopotential height field over the Ural Mountains was significantly weaker than normal, and the position of the Western Pacific subtropical high was close to normal moving northward in the last ten days of June. The average precipitation across China in June was 112.0 mm, 9.1% more than the climatology. Shandong, Jilin and Liaoning provinces recorded the most precipitation in the same period since 1961 and Fujian Province also recorded its second most precipitation. The national average temperature in China was 21.3℃, which was 0.9℃ higher than the climatology and also highest record since 1961. There were six regional torrential rain events in this month, mainly concentrated in South China in the first and second dekads, and then moved northward orderly to Sichuan Basin, Huang-Huai Region and Northeast China in the last dekad. There was one typhoon generated in June, which was weaker than normal. In the middle and late June, thunderstorms, gales, hail and short-time severe precipitation occurred in several provinces in northern China, causing heavy damages to local areas. In the early and middle of June, persistent high temperature caught the eastern part of Northwest China, Huang-Huai Region, and southern North China, with high temperature days in some regions exceeding 10 days. The daily maximum temperature at 33 stations broke its highest temperature record.
The main characteristics of the atmospheric circulation in June 2022 are as follows. The polar vortex with multi centers in the Northern Hemisphere was weaker than normal, the 500 hPa geopotential height field over the Ural Mountains was significantly weaker than normal, and the position of the Western Pacific subtropical high was close to normal moving northward in the last ten days of June. The average precipitation across China in June was 112.0 mm, 9.1% more than the climatology. Shandong, Jilin and Liaoning provinces recorded the most precipitation in the same period since 1961 and Fujian Province also recorded its second most precipitation. The national average temperature in China was 21.3℃, which was 0.9℃ higher than the climatology and also highest record since 1961. There were six regional torrential rain events in this month, mainly concentrated in South China in the first and second dekads, and then moved northward orderly to Sichuan Basin, Huang-Huai Region and Northeast China in the last dekad. There was one typhoon generated in June, which was weaker than normal. In the middle and late June, thunderstorms, gales, hail and short-time severe precipitation occurred in several provinces in northern China, causing heavy damages to local areas. In the early and middle of June, persistent high temperature caught the eastern part of Northwest China, Huang-Huai Region, and southern North China, with high temperature days in some regions exceeding 10 days. The daily maximum temperature at 33 stations broke its highest temperature record.
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ISSN:1000-0526 CN:11-2282/P