ISSN 1000-0526
CN 11-2282/P
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    2022,48(11):1361-1372, DOI: 10.7519/j.issn.1000-0526.2022.011502
    Abstract:
    Deep learning has been developed at an unprecedend speed in radar extrapolation of forecasting, so objective assessment of its applicability is an important prerequisites for operational applications. By utilizing the radar echo open data set of Guangdong-Hong Kong-Macao Greater Bay Area, the performances of 120 min radar echo extrapolation 〖JP2〗by convolutional gated recurrent unit neural network (ConvGRU) and fast dense optical flow (OF) methods based on semi-lagrangian advection scheme have been compared and evaluated based on the echo morphology, probability of detection (POD), false alarm rate (FAR) and threat score (TS). The results show that although the two methods both have effective extrapolation performance, they are not applicable to extrapolate the echo generation, enhancement and locally dispersed.
    2022,48(11):1373-1383, DOI: 10.7519/j.issn.1000-0526.2022.070101
    Abstract:
    By using ECMWF-IFS model data and observation data, this study established a fully connected neural network model (DL), tried to make more accurate temperature forecast based on deep learning method for the future 84 hours. The comparative evaluation of ECMWF-IFS and DL was made in 2020. The results show that DL correction can improve the ECMWF-IFS forecasts. The root mean square error (RMSE) of DL in most areas of Hunan is 1.5-2.0℃. There is a significant correction effect for ECMWF-IFS, and the improvement rate increases with the altitude of stations. The diurnal variation is also obvious for the RMSE of ECMWF-IFS/DL model. The RMSE is higher in the afternoon (with higher improvement rate), but lower before sunrise. The improvement rate has different diurnal variation characteristics at different altitudes. DL model shows higher accuracy in the whole year, of which the higher improvement rate appears in October and November (lower in December). In addition, the forecast results in a cold wave process was evaluated. In the accuracy for daily maximum/minimum temperature and the RMSE for 3 h temperature, DL model shows obvious correction ability for the systematic deviation from ECMWF-IFS. The DL temperature curve for single station is much closer to observation than the ECMWF-IFS forecast. Thus, the model can significantly reduce numerical weather prediction error, and its products could basically meet the demands of daily forecast service.
    2022,48(11):1384-1401, DOI: 10.7519/j.issn.1000-0526.2022.042001
    Abstract:
    In order to reveal the evolution characteristics and effects of low-level jet (LLJ) during the formation of summer rainstorms, comprehensive observational data and reanalysis data are used to compare and analyze the two summer rainstorm cases with different synoptic types and rainstorm intensities in Beijing. The data include the wind profiler radar (WPR), NCEP/GFS reanalysis data (0.5°×0.5°), and hourly precipitation data from automatic weather stations. The results show that the 16 July rainstorm process in 2018 (shortened as “7·16” rainstorm) was formed under the influence of southwest low-level jet (LLJ) at the edge of the subtropical high. The eastward movement of the vortex and trough, the continuously strengthening of the LLJ, and the influence of terrain convergence line provided extremely favorable conditions including low-level water vapor transport, convergence and uplift conditions for the occurrence of extreme rainstorm. The 22 July rainstorm process in 2019 (shortened as “7·22” rainstorm) was formed under the influence of the LLJ in front of the upper-level trough, which was caused by downward propagation of the upper-level jet during its eastward movement. This kind of LLJ has relatively smaller impacts on water vapor transport and convergence in the lower layers. Within 3 hours before the two rainstorms, similar characteristics appeared as follows: the low-level wind speed increased, the minimum height of LLJ decreased, the LLJ index sharply increased, obvious vertical wind shear occurred below 1500 m, and the vertical wind shear gradually〖JP2〗 increased with the approach of rainstorm. During the “7·16”〖JP〗 rainstorm, the occurrence of the convective cells was triggered by the boundary layer jet (BLJ), and the developing convective system was well organized by the joint action of the LLJ and the terrain convergence line. So, these are the key reasons for the formation of extreme heavy rainfall along the mountains. The characteristic parameters of the LLJ (maximum wind speed of LLJ, minimum height of LLJ, LLJ index) and the magnitude of the vertical wind shear below 1500 m are important indicators for the occurrence of rainstorm.
    2022,48(11):1402-1417, DOI: 10.7519/j.issn.1000-0526.2022.071502
    Abstract:
    The temporal and spatial distributions of thunderstorm gales in Yunnan are analyzed based on conventional observation data, observed lightning data and significant weather reports from 2011 to 2020. The results are as follows. Thunderstorm gales tend to occur from February to August, characterized by a bimodal pattern, and seen mostly in April. It is easier to see thunderstorm gales in spring than in summer and the daily peaks often appear from 16:00 BT to 17:00 BT. The durations of most thunderstorm gales are 1-4 hours. The high frequency areas are mainly distributed near mountains, including the east of Jade Dragon Snow Mountain, the east of Cangshan Mountain, the Ailao Mountain and the Wuliang Mountain. According to different types of large scale circulation background, three basic synoptic situation configurations of regional thunderstorm gales in Yunnan are proposed, that is, the southern branch trough type, low pressure trough type and quasi-barotropic type. The thunderstorm gale of the southern branch trough type occurs most. The physical parameters are calculated based on NCEP reanalysis data, representing the environmental characteristics such as thermal, dynamical and water vapor conditions, and then the characteristics of physical parameters are analyzed, considering the influence of monthly variation and different backgrounds of atmospheric circulation. The index thresholds of thunderstorm gales are worked out. The results show that the dynamic condition for thunderstorm gale in spring is much better than in summer, and the thermal condition is more significant in summer. The dynamic condition of southern branch trough type or vapor conditions of quasi-barotropic type is better than other weather types. Most meteorological physical parameters tend to increase 6 hours before most thunderstorm gales occur, which indicates that they develop to be more favorable for thunderstorm gale. This finding could provide useful information to the nowcasting and warning of thunderstorm gales.
    2022,48(11):1418-1427, DOI: 10.7519/j.issn.1000-0526.2022.041002
    Abstract:
    In order to study the echo characteristics of short-term heavy rainfall in the process of severe rainstorm in Changjiang River Basin, by using the data of weather, radar echo and meteorological, hydrological and rainfall in Changjiang River Basin, as well as the methods of meteorology, statistics, radar meteorology and image processing, this paper studies 10 severe rainstorm processes in Changjiang River Basin from 2000 to 2020. The results show that the severe rainstorm process mainly depends on the short-term heavy rainfall caused by convective activities, including the short-term heavy rainfall and the range of heavy rainfall. When the accumulated rainfall of 3 h is ≥ 100 mm, the red warning of severe rainstorm can be issued in advance. The monitored short-term heavy rainfall accumulated for 3 h at a single monitoring station can be issued earlier to improve the effect of severe rainstorm prediction service. Ultra low-level jet, low-level vortex, high-altitude trough, low-level convergence and high-level divergence play an important role in the process of severe rainstorm in Jingdezhen City. Heavy precipitation is caused by strong echo cell, strong echo short band or other echoes in a wide range of mixed precipitation, and the echo intensity is 45-55 dBz. STI product information can not only reflect the movement information of strong echo, but also analyze the convergence of echo, which has a good reference value for short-term and imminent prediction. On the echo band covering Jiangxi east-west direction, there are many short band echoes in south-north direction, which move from west to east to form “train effect”. The vertical velocity of wind profile radar product can roughly reflect the echo movement. The CR intensity 〖JP2〗causing the torrential rain is mostly〖JP〗 45-50 dBz, the average height of echo top is 12-13 km, the VIL is 5-10 kg·m-2, and the average extension height of strong echo of 45 dBz is 6 km. When the CR intensity is above 45 dBz: the strong echo area reaches Grade 3, and there is a great possibility of short-term heavy precipitation. The strong echo area is in Grade 2, mostly between 20-30 mm·h-1. When the strong echo area is at Grade 1, the precipitation intensity is basically below 20 mm·h-1. These research results could provide a reference basis for understanding, monitoring and early warning the echo characteristics and prediction of short-term heavy rainfall in severe rainstorm in Changjiang River Basin.
    2022,48(11):1428-1438, DOI: 10.7519/j.issn.1000-0526.2022.11.091601
    Abstract:
    Based on the gauges data of 2423 meteorological stations in China, continuous statistical metrics (correlation coefficient: R, root mean squared error: RMSE, mean absolute error: MAE, relative error: RE) and classified statistical metrics (probability of detection: POD, false alarm ratio: FAR, bias score: Bias, equitable threat score: ETS) are used to analyze the accuracy of Global Prediction Measurement (GPM) precipitation products from three dimensions including different spatial scales, different time scales and different precipitation intensity so as to explore the applicability of GPM satellite precipitation products over mainland China. The main results show that from different spatial scales, GPM precipitation has high observation accuracy in all regions, and the correlation coefficient (R) values of 72% stations exceede 0.7, with the best in East China and relatively poor in Northwest China. RE is concentrated in 0-20%. The accuracy of different altitude-zone elevations show that the overestimation of GPM is more obvious in low altitude (< 2000 m) and high altitude (> 4000 m) regions, and the applicability of GPM data is relatively good in mid-altitude regions (2000-4000 m). In terms of different temporal scales, the total annual precipitation of GPM is consistent with that of rain gauges, and the R is 0.75, but there is a certain deviation in the amount of precipitation, with RMSE being 6.15 mm·d-1. The consistency between GPM precipitation products and rain gauges is better from January to October, with the R above 0.7, slightly lower in November and December. The error value in summer is higher than that in winter, and the RE is positive mostly. In addition, the accuracy results of different precipitation intensity suggests that POD decreases with the increase〖JP2〗 of precipitation intensity. GPM precipitation products have a better detection ability for “moderate rain” intensity, while the detection ability for “light rain” and “heavy rain” is slightly weaker. 〖JP〗
    2022,48(11):1439-1448, DOI: 10.7519/j.issn.1000-0526.2022.052001
    Abstract:
    Since the meridional positions of the east and west part of western Pacific subtropical high (WPSH) affect the climate over China differently, we redefined the meridional index of WPSH in this study. The mean latitude of the location of 500 hPa geopotential height maximum along several meridian in 10°-60°N, 110°-130°E and 10°-60°N, 130°-150°E is defined as new west index (Index_NEW_west) and new east index (Index_NEW_east), respectively. Their average value is defined as new meridional index of WPSH (Index_NEW). The correlation between these indices and summer precipitation over eastern China is more significant than the ridge index defined by National Climate Centre (Index_NCC), 〖JP2〗specifically for the positive correlation between Index_NEW_west and precipitation over North China Plain. The negative correlation between Index_NEW_east and precipitation over Yangtze River Basin is similar to that of Index_NCC. Regression of the 500 hPa horizontal wind with respect to Index_NEW_west (Index_NEW_east) presents anticyclonic circulation over western North Pacific and the anticyclone center locates near 38°N, 130°E (40°N, 145°E). The various collocations between north/south anomalies of Index_NEW_west/Index_NEW_east correspond to four types of rainfall patterns. The good relationship between the interannual variation of new indices and summer precipitation over eastern China could provide more valuable references for the study of precipitation prediction and interseasonal movement of rainfall band.
    2022,48(11):1449-1459, DOI: 10.7519/j.issn.1000-0526.2022.050901
    Abstract:
    Based on the observation of Parsivel disdrometer at Shangqiu Station in Henan Province, Feicheng and Shouguang stations in Shandong Province, Lushun and Changhai stations in Liaoning Province, the raindrop size distributions of Typhoon Rumbia after landfall in 2018 are analyzed. The results show that Shangqiu, Feicheng and Shouguang stations have the similar characteristics of the average raindrop size distribution at different rain intensities with high concentration of small raindrops and low concentration of large raindrops, and part of the average drop size distributions have the characteristics of balanced raindrop size distributions. On the contrary, the average raindrop size distributions at Lushun and Changhai stations have low concentration of small raindrops and high concentration of large raindrops, and the average raindrop size distribution is controlled by ice phase. The Z-R relation of Shangqiu, Feicheng and Shouguang stations are similar, and the Z-R relation between Lushun and Changhai is similar. There is a great difference in indexes between the two types, indicating that the microphysical characteristics of precipitation are obviously different.The parameter of normalized Gamma distribution of raindrop size distribution shows that the convective precipitations in Shangqiu, Feicheng and Shouguang have the characteristics of maritime raindrop size distribution, and the microphysical processes are mainly of warm rain process, which is dominated by the coalescence growth, and the mixing of warm rain and ice phase. By contrast, the convective precipitations at Lushun and Changhai stations have the characteristics of continental raindrop size distribution, and the microphysical processes are predominated by the ice phase and the mixing of warm rain and ice phase.The above analyses indicate that although the Typhoon Rumbia in Henan and Shandong provinces were affected by cold air continuously, there was no obvious change in the microphysical characteristics, the cloud microphysical process changed significantly after it weakened into an extratropical cyclone.
    2022,48(11):1460-1474, DOI: 10.7519/j.issn.1000-0526.2022.042102
    Abstract:
    Using the 0.05°×0.05° temperature grid forecast guidance products issued by China Meteorological Administration and the hourly temperature data of land surface data assimilation system (CLDAS), this paper designs three intelligent grid temperature forecast correction algorithms based on the average filtering and corrects the 3 h temperature forecasts with 240 h lead time starting from 20:00 BT every day in the northern Xinjiang Plain from April to May 2019. Then the forecast effect of three kinds of revised products and guidance forecast products are compared and tested. The results show that the accuracy and stability of air temperature and frost forecast were obviously improved after the three filtering corrections. In the results of time-division test, compared with the original guide forecast product, the root mean square error (RMSE) of the three corrected products decreased by 0.79, 0.85 and 0.88℃ on average, the accuracy of temperature forecast increased by 6.11%, 6.38% and 6.46% on average, the accuracy of frost forecast increased by 3.00%, 5.81% and 7.31% on average, respectively. Moreover, the RMSE of 24 h frost forecast decreased by 4.21, 4.41 and 4.35 h, respectively. In the regional test results, the RMSE of the temperature of the three revised products decreased by 0.66, 0.71 and 0.90℃, and the accuracy of the temperature forecast increased by 5.7%, 6.1% and 6.1%, respectively. The accuracy of frost forecast increased significantly in the area of 600-1200 m above sea level in the southeast of Junggar Basin, increasing by 2.5%, 4.8% and 5.4% respectively, but not obvious in other frost areas. The RMSE of 24 h frost duration forecast was reduced by 0.81, 0.63 and 0.56 h. In comparison, the effect of the revised forecasts by the optimal ensemble algorithm is the best.
    2022,48(11):1475-1486, DOI: 10.7519/j.issn.1000-0526.2022.052601
    Abstract:
    Affected by the westerly trough, subtropical high pressure and Typhoon Lichma, a localized heavy rainstorm occurred in Gaotang County on the West Shandong Plain from 20:00 BT 9 to 08:00 BT 10 August 2019. Based on FY-4A satellite cloud images, ECMWF numerical forecasts, dual-polarization Doppler radar data, ADTD lightning system positioning data, regional station minute rainfall, raindrop size distribution as well as the Beijing 3 km regional model products, this paper analyzes the causes for the localized heavy rainstorm in Gaotang and the microphysical characteristics of the severe precipitation. The conclusions are as follows. Before the localized heavy rainstorm, obvious cracks appeared in the westerly trough cloud belt at the bottom of which cold airs diffused to the front of the trough, forming a meso-α scale low-altitude shear line with the warm and humid airflow in front of the trough. In the early stage of the localized heavy rainstorm, due to the superposition of the downdraft outflow of strong shear line convection and the cold air diffusing from the bottom layer, the outflow boundary echo zone quickly moved away from the parent body so that the strong shear line echo zone was placed on the bottom cold air cushion and weakened quickly. The convection triggered by the outflow boundary and the quasi-linear pair of echoes formed by the warm and humid air advancing to the northwest were all dominated by convective precipitation. The precipitation intensity was high, the duration was short and the accumulated rainfall was small, but due to the different properties of the bottom layer, there were obvious differences in their raindrop size distribution. The low-altitude shear line was maintained for a long time, causing warm and humid air to accumulate continuously and forming a large value area of θse on the warm side of the shear line. At the beginning of the severe precipitation, the vertical upward movement on the shear line was significantly enhanced, and the maximum upward speed at 925 hPa was higher than 1.5 Pa·s-1, and two meso-β scale cyclone disturbances were formed, triggering the release of environmental instability energy and the deep moist convection. Cloud images and echoes show that the severe precipitation cloud clusters moved through the rainstorm area successively along the shear line, producing the “train effect” and thus resulting in the severe precipitation near Gaotang. After the westerly trough and shear line echoes combined, relatively abundant supercooled water kept maintaining at 6-10 km above Gaotang, promoting the growths of ice crystals and precipitation particles and making the precipitation intensity stronger, the peak of heavy precipitation widened, and the ground precipitation increased significantly. During the localized heavy rainstorm, there was an obvious double-peak structure in the scale spectrum of ground raindrops. The peak position with raindrop diameter at 1.2 mm was stable relatively while the other peak was at the end of the small raindrops with diameters at 0.3-0.5 mm. Statistical analysis suggests that the time series of large raindrops is synchronized with the time series of minute precipitation, and the correlation coefficient reaches 0.9867. The time series of small raindrops lags behind the time series of minute precipitation by 2 minutes.
    2022,48(11):1487-1496, DOI: 10.7519/j.issn.1000-0526.2022.102101
    Abstract:
    The main characteristics of the general atmospheric circulation in August 2022 are as follows. There were two polar vortex centers in the Northern Hemisphere and they were stronger than normal. The circulation at middle-high latitudes of the Eurasia showed a latitudinal type, and the ridge to the north of Caspian Sea was unusually strong. The western Pacific subtropical high was stronger than that of the climatological normal, and its location was more westerly compared to that in normal years. The monthly mean temperature across China was 22.4℃, higher than normal (21.1℃) by 1.3℃, and the monthly mean precipitation was 82.4 mm, 23.1% lower than normal (107.1 mm). During this month, the high temperature days in China were abnormally more as the result of the persistent influence of the regional high temperature events. The meteorological drought condition in the Yangtze River Basin and other places continued to develop. Five tropical cyclones were active over the South China Sea and the western North Pacific, among which Typhoon Mulan (No.2207) and Typhoon Ma-on (No.2209) made landfall in China, but generally the number of landfall typhoon was less than usual. Convection events occurred frequently and there were eight torrential rain processes in this month, causing localized serious damages.
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    Available online:  December 02, 2022 , 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, the downburst cluster can extend over several hundred Kilometers which enhanced over many noncontinuous small areas, the enhancing mechanism may not be the strong downdraft divergent outflow. The definition of downburst is reviewed. Downbursts under two different situations are discussed, 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.
    Available online:  November 30, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.111801
    Abstract:
    By using weather radar, upper level and ground observations and 1×1°NCEP reanalysis field data, the characteristics of mixed-type convective weather were analyzed during the formation and development of Jianghuai cyclone in spring, and the reasons why different types of convective weather occurred and intensified have been explained preliminarily. The results show that there are differences in temporal and spatial distribution and convective characteristics of different types of severe convective weather. local hail is mainly produced by discrete convective line in the formation stage of cyclone, and banded short-time heavy precipitation is produced by TL\AS MCS where is located on herringbone convective line in the formation stage of cyclone and behind S-shaped convective line in the development stage of cyclone, large region gale is produced by TS MCS on the S-shaped convective line in the development stage of Jianghuai cyclone. Jianghuai cyclone is the result of the baroclinic development of the large-scale weather systems, convective activities enhance the convergence of the low-level front and strengthen the formation and development of cyclone. The generation of strong convective weather is closely related to the dynamic and thermal field of Jianghuai cyclone. In the cyclone formation stage, the southwest vortex combined with the mountainous terrain provides the environmental field conducive to the formation of hail in Southwest Hubei. The warm shear line in the cyclone formation stage and the cold shear line affected by the South Branch trough in the cyclone development stage provide the environmental field conducive to the formation of storm train effect which produces short-time heavy precipitation. In the cyclone development stage, the cold shear line provides the environmental field conducive to the formation of the rear inflow jet which is the main factor of gale formation.
    Available online:  November 30, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.061801
    Abstract:
    To reduce the deviation between radar rainfall field and surface rainfall observations, it is proposed to calibrate the radar rainfall field with surface microwave links using the variational calibration method, the Kalman filter calibration method, the mean calibration method and the Kriging calibration method. Joint rainfall measurement experiments were conducted. The rainfall rates retrieved by two microwave links were used to calibrate the S-band radar rainfall field in two precipitation cases of different types. The calibration results were then compared with the measurements of rain gauges. The application processes and effectiveness of the schemes were also analyzed. The conclusions are as followed. 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和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.
    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.
    Available online:  October 26, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.090601
    Abstract:
    On June 22, 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, convective initiation and maintenance mechanisms and evolution of the precipitation characteristics by using reanalysis data, observations from weather stations, radiosonde station, wind profile radar and S-band dual-polarization radar measurements. The establishment of the nighttime boundary layer jet stream provides favorable unstable energy and water vapor conditions for precipitation to occur in this area. The main dynamic mechanism of convective initiation is the upward movement of airflow generated by assistance from dual low-level jets. At night, the initial convective cells were strengthened by the orographic lifting of Mt. Tianlu. The enhancement of southerly oceanic flows further promoted the convective activity in Jinjiang. Additionally, the continuous triggering and merging of new convection caused by offshore mountains and lifting southerly flows over outflow boundary that are enhanced by convectively generated cold pool lead to the second convective center in Gangmei. The rainfall convection shows a low centroid. The characteristics of quasi-stationary and slow-moving backward propagation convection result in extreme of cumulative precipitation.
    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.
    Available online:  October 26, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.040201
    Abstract:
    All-sky observations of space-based microwave imager contains information of strong meteorological sensitivity related to cloud and precipitation, But the observation error in all-sky data assimilation is apparently non-Gaussian behavior which cannot meet the basic assumption that the observation error is Gaussian in the data assimilation. A ‘symmetric cloud’ dependent all-sky observation error model developed by European Centre for Medium-Range Weather Forecasts (ECMWF)was used for FY-3C MWRI in this article, observations during super typhoon ‘Maria’ and ‘Lekima’ were selected, the all-sky observation error was analyzed after quality control and normalization. The results show: (1) The FG departures and ‘symmetric cloud’ both agree in map, the standard deviation of FG departures binned as a function of “symmetric cloud” shows larger observation error in cloudy situations than in clear sky. (2) the all-sky FG departure normalized by the symmetric error model become far more Gaussian than in clear sky. (3)All-sky assimilation is expected to bring 43.9~54.63% more data than clear sky assimilation in the future with the biggest increases in the area of the outer spiral cloud band and cloud wall of typhoon. This result preliminarily demonstrated the assimilation potential of FY-3C MWRI all-sky observation data, and the utilization of observation data of the current domestically made Fengyun series microwave imagers is expected to improve in numerical weather prediction.
    Available online:  October 17, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.101001
    Abstract:
    Based on surface conventional meteorological data, hourly observation data from regional meteorological stations and ERA5 reanalysis data, the evolution characteristics and formation mechanism of mesoscale low-level jet and mesoscale vortex during a heavy rainfall in Henan Province from July 19 to 20, 2021 were analyzed. The results show that the process of the heavy rain was directly related to the formation and development of the low level jet and mesoscale vortex. The establishment and development of low level jet was synchronized with the occurrence and enhancement of precipitation, while the mesoscale vortex appeared about 10 hours after the establishment of low level jet, and the low level jet developed strongly with the enhancement of low level vortex development. The strengthening and westward extension of the western Pacific subtropical high and eastward movement of the low pressure on the southeast of the Hetao Area increased the geostrophic wind, which was the main reason for the formation of the low level jet. The existence of allobaric wind was the main reason for the easterly jet. The horizontal convergence and torsion in the lower troposphere caused by low level jet were the main reasons for the development of mesoscale vortex in the middle and lower troposphere. The vertical vorticity advection caused by the vertical motion were the main reasons for the enhancement of the voriticy in the middle troposphere. The condensation latent heat in the middle troposphere was another important reason for the vortex development.
    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.
    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.
    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.
    Available online:  September 29, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.081501
    Abstract:
    In order to improve the precipitation forecasting skill of CMA-MESO (China Meteorological Administration Mesoscale model) at 3 km resolution, three different horizontal correlation characteristic scale of background error covariance are obtained with 2 dimension discrete cosine transform filter from 3 months (2 June to 31 August, 2018) background errors samples, and three horizontal co-correlation scale are fitted and implemented in CMA_MESO operational testing system with recursive filter of three different scale, thus to replace the single-scaled recursive filtering. Results show that the profiles of three horizontal co-correlation scale with height is similar, with tens to 100 kilometers apart. The analysis qualities and verification of precipitation forecasting between the control experiments (single-scaled recursive filtering) and sensitivity experiments (three different scaled recursive filtering) with CMA_MESO system at 3 km resolution are compared. The numerical results indicate that the wind and relative humidity analysis is more close to observation in sensitivity experiments. The increments difference of temperature analysis is very small. In addition, the precipitation forecast skill is improved in sensitivity experiments. The first 6 h precipitation forecast TS (Threat Score) value of 1-31 July, 2018 with cold start is higher and the Bias value is more close to 1 in sensitivity experiments. Meanwhile, the TS value of every 6 h precipitation in 24 h forecasting term with warm start is improved too.
    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.
    Available online:  September 15, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.071501
    Abstract:
    Data from the second generation laser raindrop spectrum of PARSIVEL at Xuzhou and Xinyi in Jiangsu were used to analyze the precipitation in different stages caused by "Rumbia" and "Lekima" from 2018 to 2019. The results are as follows. (1)Mainly small raindrops are in small rain intensity, while the intensity increases the diameter of raindrops increase. There are more big raindrops in heavy rain.(2)With much more small and medium raindrops,"Lekima" precipitation event has the characteristic of that caused by tropical typhoon. Contrarily, with much more big raindrops,"Rumbia" precipitation event has the characteristic of that caused by extratropical typhoon.(3)During both of the heavy rain event, larger average spectrum width and diameter of raindrops, a higher raindrop concerntration, a multi-peak at the large raindrops, with Gamma distribution, which are characteristics of convective precipitation. Large spectrum width and maximum diameter of raindrops in weak rain event by "Rumbia", while a small average diameter, basically the Gamma distribution, which are characterized by mixed cloud precipitation. On the contrary, in weak rain event by "Lekima", there are smaller average spectrum width, raindrop diameter and more small raindrops, a smooth spectral pattern, in Marshall-Palmer (MARSHALL-PALMER) distribution, which are characterized by stratiform cloud precipitation.(4)Heavy rain is mainly caused by convective cloud containing more large raindrops, and also mixed cloud. Small and medium raindrops in mixed cloud precipitation contribute most both in number and precipitation. Although there are more small and medium raindrops in convective cloud precipitation, the raindrops with larger diameter contribute mainly.(5) Compared with the empirical relations, the typhoon precipitation derived from the actual index of Z-R relations might be underestimated or overestimated. The empirical relations are not applicable to different type of precipitation. It is necessary to summarize the Z-R relations applicable to different precipitation types in different places and seasons.
    Available online:  September 15, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.082202
    Abstract:
    The multi-model integration test of the Bayesian Model Average (BMA) method is carried out for the forecast after correcting the errors of 2m temperature, 10m wind speed, and 2m relative humidity from December 1,2020 to March 15,2021 in the Beijing-Tianjin-Hebei region, based on four models of CMA-GFS, CMA-REPS, CMA-MESO3km, and CMA-MESO1km. The results show that the root-mean-square error of each model’s element is significantly reduced after error calibration. The prediction effect of the BMA multi-model blending is much better than that of calibrated output of every participant model. Compared with the original errors of several models, the improvement of the 2 m temperature integration forecast is between 0.5~1.4℃, and the improvement rate of the root mean square error is about 20~40%. In the meantime, the root-mean-square error of 10 mwind speed and 2 m relative humidity improved by 12~45% and 25~35%, respectively. The horizontal root mean square error distribution of .each element is significantly different in different terrain heights, and the error distribution of different elements has been significantly reduced throughout the region, In addition, BMA can obtain the full probability density function, which can quantitatively predict the uncertainty of each parameters.
    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.
    Available online:  September 05, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.071001
    Abstract:
    In order to explore the impacts of urban agglomeration in Guangdong-Hong Kong-Macao Greater Bay Area on local extreme heavy rainfall, this paper conducts 3DVar assimilation of doppler radar data to simulate an extreme heavy rainfall event that occurred in the Greater Bay Area on May 22, 2020, based on the WRF-ARW mesoscale numerical model, GSI-3DVAR assimilation system and ERA5 reanalysis data provided by ECMWF. The influence process and mechanism of urban on local extreme rainfall are studied. The results show that, compared with no assimilation of any observational data, adding the assimilation of radar reflectivity and radial wind data can improve the simulation ability of precipitation, especially for the heavy rainstorm magnitude of more than 250 mm. Observation and control experiment jointly show that the urban agglomerations in the Greater Bay Area acts as a local "heat source", increasing the temperature of the boundary layer through sensible and latent heat, resulting in significant heat island effect, which then strengthen the convective instability within lower atmosphere. On the other hand, strong friction dissipation reduce the wind speed in boundary layer so that it catches more warm and moist air within the urban area, forming stronger thermal instability and moisture convergence, and then leading to the rainfall center inner the urban area. The sensitivity experiment (i.e., removal of urban land use) further shows that friction dissipation caused by urban underlying surface affect dynamic thermodynamic environments in boundary layer below 800 hPa, resulting in stronger southwesterly and unstable atmospheric condition over downstream of the urban area in urban removal experiment. Also, the convection is lifted by the local topography, enhancing vertical upward movement, which finally result in stronger rainfall intensity than the control experiment and the location of the rainfall area more inclined to the downstream of the urban.
    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.
    Available online:  August 29, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.072301
    Abstract:
    The Western Pacific - South China Sea - East Indian Ocean (two oceans and one sea) region has an important impact on the weather and climate, national security, as well as social economy of China. However, due to the limitation of data conditions, the existing research on high sea winds are mainly focused on the offshore, resulting in insufficient understanding of the temporal and spatial distribution, the characteristics of changes and their mechanisms of high sea winds in the Western Pacific - South China Sea - East Indian Ocean region. There is an urgent need to use new high-resolution data for in-depth research, but at present, there are relatively few comparative studies between ERA5 reanalysis surface winds and the observation data. Therefore, this paper compares the ICOADS moored buoy observation data with the ERA5 reanalysis data in the two oceans and one sea area, and the results show that the ERA5 reanalysis surface winds can well show the distribution and variation characteristics of sea surface wind field. In addition, the ERA5 reanalysis data has high temporal and spatial resolution, long time series and complete data records. It is feasible and has certain advantages to use it for climate analysis of high sea winds. However, it should be noted that the ERA5 reanalysis surface wind speed generally has a systematic bias of underestimating the observed wind speed. In particular, the greater the observed wind speed, the greater the deviation of ERA5 from the observed wind speed.
    Available online:  August 18, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.080101
    Abstract:
    Studying the characteristics of the temporal and spatial changes of PM2.5 and its influence is of great significance to the understanding of air pollution prevention and control. Based on the measured data of PM2.5 , daily and annual data sets of CHAP, precipitation, the re-analyze data set of ERA5, monthly data sets of MCD19A2, fire spots data from SNPP/VIIRS satellite monitoring,some analysis methods such as least squares were used to explore the temporal and spatial distribution patterns and causes of the annual and seasonal PM2.5 in southwest Yunnan. The results show that: The concentration of PM2.5 is low at the north and east, and high at the south and west in the region of southwest Yunnan; the concentration of PM2.5 is the lowest in July and the highest in March, showing an inverted S-shaped distribution; the concentration of PM2.5 is the highest in spring and the lowest in summer; except for spring, the concentration of PM2.5 in other three seasons have a certain degree of volatility, and the reduction degree of PM2.5 concentration often fluctuates within -30% to -20% in the recent 20 years. In the past 8 years, the percentage change is often less than -30% in summer, autumn and winter, which shows a significantly weakening trend; the pollutants from seasonal fires in surrounding oversea regions provided a stable source of pollution under the westerly airflow, which causing small fluctuations in the concentration of PM2.5 but the obvious spatial difference in the percentage of change in the spring. From February to April, the fires in the eastern Part of Myanmar were concentrated, and the pollutants produced by the fires were guided by the westerly air flow, and caused subsidence under the dynamic structure configuration of dispersion in the middle and lower layers and convergence in the upper layers, which resulted in the seasonal strengthening of PM2.5 in the study area. A larger range of favorable meteorological conditions for the diffusion of pollutants and more precipitation cleaning can somewhat reduce the contribution of pollutant transport in the atmosphere outside of southwest Yunnan to PM2.5 pollution.There was a significant positive correlation between the number of fire points and the concentration of PM2.5, but the impact on PM2.5 lags behind the change of fire points by 2 days, which gradually weakens from south to north in the region. From January to May each year, the spring plowing and burning activities from eastern Myanmar have dominant and continuous impacts on the concentration of PM2.5 in the study area.
    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.
    Available online:  August 12, 2022 , 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 January 1, 2016 to December 31, 2020. By Using the time proportion algorithm to calculate the cloud fraction, the distributions of cloud layers, cloud-base height and cloud fraction were studied through data analysis. The results show that, the cloud structure on 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 are mainly occupied by low and medium clouds. Compared with 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 6:00 PM and 6:00AM, especially in summer, showing obvious diurnal variation.
    Available online:  August 12, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.081001
    Abstract:
    In this paper, radar extrapolation and high-resolution numerical weather prediction are blended to get a 6 h quantitative precipitation forecast over the Yangtze River delta region of China. The method used here is based on a mainstream blending framework, while modifications and calibrations were 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 applied by using Weibull function fitting and object recognition. A weighted blending of extrapolation and NWP is then applied based on scale and forecast time. Finally, real-time Z-R relation conversion is used. Results show that blending method can extend forecast time of the extrapolation forecast, calibrate the intensity and position bias of NWP, therefore makes a better result than the two.
    Available online:  August 11, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.072701
    Abstract:
    Targeting for the extreme precipitation process of the Henan “7.20” rainstorm, this paper focused on revealing the feature of the water vapor transportation, the budget of the water vapor flux and the transformation of water vapor and the associated impact on the variation of the local precipitation based on the FNL reanalysis data, the gauge precipitation data and the high-resolution simulation results. The results show that the water vapor over the ocean can be continuously transported to the extreme precipitation area by the water vapor channel built by the synergistic effect between the powerful and quasi-stationary ‘Yanhua’ Typhoon over the East Sea and the stable atmospheric circulation pattern in the middle and high latitude zone. Then the local water vapor constrained within the extreme precipitation area can be further transported from the low level of troposphere to the middle and high level of troposphere depending on the dynamical convergence mechanism in the low level of troposphere, which is dominated by the mesoscale synoptic system and the blocking effect of the windward slope, and the vertical transportation of the water vapor is indeed favorable for the reinforcement of the convection in the extreme precipitation area. Finally, under the synergistic effect of the convective ascending motion and the orographic lifting mechanism of the windward slope, the precipitation intensity is remarkably reinforced by strengthening the deposition process of the local water vapor. The remarkable increase of the precipitation efficiency within the windward slope region is directly responsible for the occurrence of the extreme precipitation in the perspective of microphysical processes. This paper not only comprehensively reveals the main source and the consumption process of the local water vapor dominated by the muti-scale synoptic system in the extreme precipitation event, but also advance the understanding of the occurrence mechanism of the extreme precipitation.
    Available online:  August 09, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.062901
    Abstract:
    Beijing Daxing International Airport, as a super large international hub with huge throughput, has a large amount of aircraft exhaust emissions during its operation. The impact on the atmospheric environment around the airport should not be ignored.. In order to study the impact of aircraft exhaust emissions on the atmospheric environment under adverse meteorological conditions, the adverse meteorological conditions period is selected in 2020 based on the Beijing air quality data. According to the relevant basic data of the 2025 planning of Daxing International Airport, the Emissions and Dispersion Modeling System (EDMS) is used to establish the list of exhaust emission sources of the airport and simulate and predict the diffusion of air pollution. The results of pollution meteorological analysis show that there are meteorological characteristics such as small calm wind, high humidity, thin thickness and strong grounding temperature inversion during adverse meteorological conditions. Beijing experienced the heavy pollution process, accompanied by the low visibility weather situation. Under the influence of adverse meteorological conditions, the parameters such as friction velocity and mixing layer height are at a small level, indicating that the diffusion conditions of air pollution are poor. The model prediction results show that aircraft exhaust has a great impact on the surrounding environment, and the ground concentration of pollutants has the time distribution law of low in the daytime and high at night. The characteristics of pollution meteorology and aircraft emission concentration distribution under adverse meteorological conditions have reference value for the research on airport air pollution control measures.
    Available online:  August 01, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.071401
    Abstract:
    The particle size distributiondistribution of the particle number concentration (PNC) is not only affected by the average field of meteorological factors such as temperature, air humidity and wind, but also closely regulated by the boundary layer mixing such as turbulence. Based on the simultaneously observed meteorological factors and particle size distributionsize distribution of PNC in the range of 14.6~660 nm in November 2018, impact of different meteorological factors, especially turbulence, on the particle size distributionPNC in different modes were explored, which helps to further understand the roles of meteorological factors in haze development. The results showed that increased relative humidity can reduce the particle number concentration (PNC)the PNC in nuclear mode and Aitken mode, but increases the PNC in accumulation mode. Elevated temperature increases the PNC in the nuclear mode. Elevated wind speed, turbulent kinetic energy, frictional velocity and turbulence intensity can dilute and then remove the particles in the Aiken and accumulation mode, but can increase the PNC in the nuclear mode. In contrast to the diurnal variation of turbulence, total PNC in Aitken mode and accumulation mode was low in the day and higher in the nighttime. On clean days, total PNC in the nuclear modal continued to climb in the afternoon and reached a peak at the nightfall. A time lag was found in the nuclear mode PNC increase in contrast to the turbulence development. After the turbulence developed for 3 to 5 hours, the PNC in nuclear mode begins to increase significantly. Enhanced turbulence could enlarge the distance between the newly formed particles and dilute pre-existing particle concentration, which are regarded as the sink of newly formed particles.
    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.
    Available online:  July 07, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.042901
    Abstract:
    Historical similar typhoons are important references for typhoon prediction and decision-making besides conventional methods. However, it is time-consuming and laborious to retrieve similar information from a large number of historical typhoons. In this paper, a similarity retrieval method of subtropical high based on improved visual geometry group model (VGG16) is proposed to query historical similar typhoons based on subtropical high similarity. Through the image extraction, data enhancement, model learning and optimization of 19736 subtropical high corresponding times in the typhoon season from 1979 to 2020, and taking the learned perceptual image patch similarity (LPIPS) as the measurement index of subtropical high similarity, an improved VGG16 model is finally established. The test results show that greatly similar historical typhoons can be found by using this model. The similarity between the historical similar typhoon ranked first retrieved by this model and the target typhoon is 92.55%, which provides a very meaningful reference for Typhoon forecasters. At the same time, compared with the traditional manual recognition, the model has shorter recognition time and higher retrieval efficiency, and can be applied in typhoon forecast and research.
    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.
    Available online:  June 01, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.032601
    Abstract:
    The return sounding observation is a new high-altitude observation technique developed in China. In addition to the observation of vertical profile in the ascending stage, at the same time, the atmospheric sounding in the period of floating and falling is added, and the space-time densification of the sounding profile is realized automatically. In this paper, the ERA5 reanalysis data is used as the "true value" , and the return sounding simulation system is used to construct the return sounding simulation observation, an observation System Simulation experiment (OSSEs) was conducted based on GRAPES-MESO and 3D-var assimilation System. The results of numerical experiments show that compared with the traditional single-rise sounding observation, the simulated sounding observation of the descending section of the return sounding can effectively improve the precipitation forecasting skills of GRAPES under the condition of national network formation, at the same time, the forecast of factor field (temperature, humidity and wind field) is improved, the improvement rate is about 2% ~ 5% . In addition, the analysis results of typical weather cases show that the increase of round-trip drift sounding observations can improve the initial model deviation, thus more accurate simulation of precipitation distribution. The research results of this paper provide theoretical support for the future scientific layout and application of the return sounding..
    Available online:  June 01, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.050601
    Abstract:
    This article uses 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 2021 to August 2021 , according to different The detection advantages of the equipment and the diurnal variation of the boundary layer are combined with the observation data of laser aerosol radar, microwave radiometer, and wind profiler radar to obtain the all-weather atmospheric boundary layer height. Comparing the height of the boundary layer obtained from the inversion with the height of the all-weather atmospheric boundary layer provided by the sounding data calculation and the ERA5 reanalysis data, it is found that: (1) The joint inversion boundary layer height is in good agreement with the atmospheric boundary layer height provided by the ERA5 data. (2) Laser aerosol radar is suitable for the observation of the convective boundary layer during the day, 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; (3) 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; (4) The joint inversion of boundary layer height obtained in this article is compared with the height difference of the atmospheric boundary layer obtained from the sounding data. The standard deviation is 51m. Compared with the average value of the atmospheric boundary layer height in a certain range provided by the ERA5 data, joint inversion of the boundary layer height can more accurately reflect the atmospheric boundary layer height in a smaller range.
    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.
    Available online:  May 16, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.020901
    Abstract:
    The Dongtan site, located in a national natural reserve on Chongmin island of Shanghai, has been developed to carry out atmospheric composition measurements since 2006. Based on the particulate matter and meteorological measurements from 2008 to 2015 at Dongtan, the arriving air mass is classified, the PM2.5 background level and its annual variation are examined, the potential source of higher level of PM2.5 is also identified in this article. The annual variation of PM2.5 concentration presents in-significant trend from 2008 to 2015, but stable fluctuation from 26.8 to 32.7 μg?m^(-3). However, the ratio of PM2.5/PM10 increases from 0.84 to 0.92, indicating more and more formation of secondary aerosols observed at Dongtan. The air mass arriving at Dongtan could be aggregated into 3 types of back trajectories, named as land, ocean, and land/ocean mixing, accounting for 32%, 37.8% and 29.3% respectively. In which, the PM2.5 background concentration ranges stably from 11~15μg·m-3 in ocean air mass, but 29~56 μg?m^(-3) in land air mass, showing largely seasonal variability. The potential source of relatively higher PM2.5 observed at Dongtan presents clear seasonal transition from areas north to Shanghai including Jingjinji, Huanghuai and Jiangsu, Anhui provinces in autumn and winter to southern YRD region including Zhejiang province and its seaboard extending to Fujian province in summer by PSCF analysis. In general, higher PM2.5 loading at Dongtan is mostly contributed by air mass from Shanghai and its neighboring city clusters including Suzhou, Wuxi, Changzhou, Hangzhou, Jiaxing and Huzhou etc. It is noting that air mass recycled from Yellow sea and Bo sea is also the important source area for the elevated PM2.5 observed at Dongtan in spring, autumn and winter.
    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.
    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.
    Available online:  April 02, 2022 , DOI: 10.7519/j.issn.1000-0526.2021.083101
    Abstract:
    A comparison of two rainstorms ocurred in June 2001 and July 1986 (hereafter “01.6” and “86.7”) related to distant typhoons affecting Jiangsu Province during Mei-yu period shows that: (1) For “01.6”, the precipitation duration is shorter, the precipitation area is motionless, the rainfall intensity is stronger. For “86.7”, the precipitation duration is longer, the precipitation area moves from north to south, the rainfall intensity is weaker. (2) In terms of atmospheric circulations, during “01.6” process, the subtropical high extends significantly to the north. The northward extended inverted trough of typhoon and low level jet form the low-level convergence and transport warm and moist air together. The low-pressure troughs at middle- and upper-level are stable. The influence of upper-level cold air is weaker. During “86.7” process, the northward extension and impact of typhoon’s inverted trough are weaker. The convergence of low-level wind and the transportation of warm and humid air flow rely?more?on low-level jet than on typhoon’s inverted trough. The low-pressure troughs at middle- and upper- level both move eastward and southward quickly. The influence of upper-level cold air is strong. (3) In terms of dynamical analysis, the high-level divergence and low-level convergence of “01.6” process are more intense, the coupling of positive vorticity at lower level and negative vorticity at upper level is more stable and deep, the non-geostrophic wet Q vector convergence is stronger, and all these dynamic processes stay over the southeastern part of Jiangsu. For “86.7”, the dynamic processes are weaker. The coupling of divergence and vertical vorticity move from north-central Jiangsu to the southeastern part of Jiangsu. The non-geostrophic Q vector convergence zone covers eastern part of Jiangsu. (4) Compared with “86.7”, the low level water vapor flux convergence of “01.6” is stronger. The air over the rainstorm area of “01.6” is more saturated. The deep saturated layer “01.6” is formed earlier, and maintain longer. (5) In terms of thermodynamical analysis, the convective instability of middle- and lower-level atmosphere is stronger, but the E index and E index increment of “01.6” are greater, which demonstrates that the middle- and low-level atmosphere contains more energy and water vapor.
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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.
      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.
      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.
      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.
      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.
      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.
      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.
      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.
      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.
      2012,38(1):1-16, DOI: 10.7519/j.issn.1000-0526.2012.1.001
      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 21 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.
      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.
      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.
      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.
      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.
      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.
      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.
      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.

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