ISSN 1000-0526
CN 11-2282/P
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    2021,47(9):1029-1046, DOI: 10.7519/j.issn.1000-0526.2021.09.001
    Abstract:
    The GRAPES regional operational model in the National Meteorological Centre significantly overestimated the snowfall amount over North China that occurred in 29-30 November 2019. In this paper, the simulated results from the operational WSM6 cloud microphysics scheme are compared with those from Liu-Ma scheme and the ERA5 reanalysis data to investigate the possible reasons. The results show that during this snowfall, the sedimentations of ice crystals and snow were the main contribution in WSM6 scheme, while the precipitation of Liu-Ma scheme was mainly through the sedimentations of snow and graupel, and ice crystals produced less precipitation. The WSM6 scheme evidently underestimated the liquid water content in the atmosphere and the ice crystal content was the largest composition of the ice-phase particles, followed by the snow content. These features were significantly different from the ERA5 data and the Liu-Ma scheme, and the latter two were in good agreement. Compared with the Liu-Ma scheme, the WSM6 scheme had a higher ice crystal content in the lower layer of the model and a larger average ice crystal falling speed, and their combination made ice crystal precipitation become an important contribution to the formation of this snowfall case. The average snow falling speed in the WSM6 scheme was greater than that of Liu-Ma scheme, which was the main reason why the column snow content was small and the precipitation of snow was more than that of the Liu-Ma scheme. In the WSM6 scheme, the deposition/sublimation process of ice crystals dominated the ice-phase microphysical processes so that the sublimation processes of snow and graupel and the condensation process of cloud water were obviously insufficient. This was the main reason for more ice crystals, less snow and cloud water in WSM6 scheme. The sensitivity test for the ice crystal deposition/sublimation process (SVI) revealed that the SVI conversion rate was positively correlated to surface precipitation, and took on a “seesaw” relationship with the column cloud water content. When the SVI conversion rate was reduced, the ground snowfall tended to be significantly reduced and the column cloud water content increased significantly.
    2021,47(9):1047-1061, DOI: 10.7519/j.issn.1000-0526.2021.09.002
    Abstract:
    Based on the GRAPES_3 km model developed independently by China and calculating the hourly maximum updraft helicity (UH), we have developed the probabilistic forecast technology which exceeds a certain threshold of UH in different forecast time periods. Since the value of UH can represent the ascending motion and rotation intensity of convective storm, the UH probabilistic forecast product can be used as the probabilistic forecast guidance which characterizes severe convective wind and hail. We verified the probabilistic forecast products of daily tests and typical cases in North China, Northeast China and South China from 14 June to 31 July 2019, the results show that it has a good forecast performance. Compared to the subjective forecast, the threat score (TS) of the objective product for severe convective wind and hail is greatly increased in North China, Northeast China and South China, respectively. Especially for the weak large-scale forcing process in South China, the product can significantly reduce the missing alarm rate (MAR) and significantly increase the TS. In addition, the product can predict the shape distribution and moving propagation characteristics of convective storm, and the region of probabilistic forecast is similar to the observation of severe convective wind and hail. We verified the probabilistic forecast products with different UH thresholds and spatial Gaussian smoothing parameters, the results show that the TS of the products calculated by lower UH threshold is higher than that of higher threshold due to lower MAR. The products with Gaussian smoothing parameter of 20 km have the best forecast performance.
    2021,47(9):1062-1072, DOI: 10.7519/j.issn.1000-0526.2021.09.003
    Abstract:
    Based on the data of microwave radiometer, automatic station and Zhangjiakou Radiosonde from 22 January to 30 March 2019 in the Genting Venue of Winter Olympic Games, the accuracy of retrieved temperature and humidity profile was analyzed, and the characteristics and causes of night heat and water vapor were discussed in combination with the 6 h reanalysis data of NCEP/NCAR. The results show that the temperature and water vapor density retrieved by microwave radiometer have a good correlation with the observations by radiosonde and automatic stations, but that of the relative humidity is slightly poor. The mean error (ME) of temperature retrieved by microwave radiometer is relatively small at all levels, and the availability is strong; the root mean squared error of water vapor density are relatively large near the ground, and decrease with the increase of height; the ME of relative humidity at all levels is large, and the maximum reaches 25%. In addition, cloud and precipitation cause the error of temperature and water vapor density to increase at most heights, but the error of relative humidity with precipitation, at most altitudes, is obviously smaller than that under conditons of clear sky and cloud. Further study on the characteristics of heat and water vapor at night shows that the inversion layer structure at night is very common in the Genting Venue, with a probability of 50%. The inversion layer top is generally near or below the mountain top. When combined with warm advection, the thickness and temperature difference of inversion layer will be greatly enhanced. The warm advection and the subsidence movement in the middle and lower layers behind the cold front may bring obvious night temperature increasing to the venue. In the process of temperature increasing dominated by subsidence movement, the profile of microwave radiometer shows that the temperature in the middle and lower layers increases as a whole, and the water vapor density in the lower layers decreases obviously under the effect of subsidence and divergence. In the warming process dominated by warm advection, the warming intensity decreases with height, and the warming process shows obvious humidification phenomenon.
    2021,47(9):1073-1085, DOI: 10.7519/j.issn.1000-0526.2021.09.004
    Abstract:
    Based on conventional weather data, FY-2F satellite data, Doppler radar products, densely-observed data from automatic surface weather observation system and ERA-Interim 0.125°×0.125° reanalysis data, the ambient condition and evolution of the short-time extreme precipitation event in Chongqing on 19 April 2019 is analyzed. The results show that under weak synoptic-scale vertical motion, this severe rain process was formed by a quasi-stationary meso-β scale convective system (MβCS) over Qijiang River Valley and its vicinity. Before the development of the severe convection, the local water vapor was sufficient, and stratification instability which was established and maintained by the wetter low-level and the drier mid-high-level was prominent. With the terrain inclining from southwest to northeast, Qijiang River Valley, located in the transition zone from Yungui Plateau to Sichuan Basin, was surrounded by mountains on three sides. Flowing from the south side of the valley, the increasing meso-γ scale convective cell brought about heavy rainfall and cold pool in the river valley. The strong mesoscale temperature gradient between the cold pool and the eastern slope of the valley promoted the intense convergence of the near-surface southwest wind to the eastern hillside, which was advantageous to the eastward convergence of the convective cell and strengthening, then the convection was organized into an isolated MβCS. With the coaction of continuous enhancement of the cold pool, topography blocking effect, merging of two MγCSs and weak ambient flow, the MβCS moved slowly, finally resulting in the localized extreme short-time rainfall over Qijiang and Wansheng.
    2021,47(9):1086-1098, DOI: 10.7519/j.issn.1000-0526.2021.09.005
    Abstract:
    The radar data of Haikou dual polarization Doppler during the tornado processes in Tunchang County and Danzhou City of Hainan on 29 August 2019 are analyzed. The tornadoes occurred in a convective storm in the typhoon rain belt about 370 km to the right of Typhoon Podul. Both tornado occurrences were related to the mergering of the storms. One occurred at 12 min before the mergering of the storm cells, and another occurred at 5 min after the storm cells merged. The merger of the cell led to enhancement of the storm reflectivity with the storm height increasing, and the cyclone in the storm strengthened rapidly. Tornadic vortex signature (TVS) was detected during two tornadoes, and the time of detection of TVS was 27 min and 5 min earlier than the time of the tornadoes. Corresponding to the position of the TVS before the tornado occurred, the correlation coefficient (CC) value did not change. When the tornado occurred, the CC value of the position of the TVS suddenly decreased to below 0.8, and the low-value of the CC continued for more than 20 min after the tornado occurred. Both tornadoes had the rear storm cells merged. The tornado occurred at the rear of the main storm cells at the junction where the two storm cells merged.
    2021,47(9):1099-1112, DOI: 10.7519/j.issn.1000-0526.2021.09.006
    Abstract:
    Compared with the situation on clear days, the vertical distribution of aerosol and meteorological conditions during haze and heavy haze events in central part of Shandong Province from 2007 to 2017 are analyzed by utilizing the data of CALIPSO (The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) and NCEP FNL (Final Operational Global Analysis) 1°×1° reanalysis data. The results show that aerosol particles in haze and heavy haze weather mainly concentrate below 2.7 km and 1.5 km in the lower troposphere. With 0.9, 1.66 and 1.34 km as the critical heights, the extinction coefficient (EC) of clear days, haze days and heavy haze days decreases exponentially above the critical height and logarithmically below the height. The average annual paraticulate deploarization ratio (PDR) and color ratio (CR) range of haze days and severe haze days are 0.1-0.3 and 0.5-0.9, respectively. In heavy haze days, aerosol particles below 2 km are relatively regular and small in size, and their irregularity and size increase sharply within 2-4 km. PDR increases gradually with height in and below 7 km but decreases gradually above 7 km. Different from clear days, CR basically increases with the height on haze days. The contribution of polluted dust aerosol to near-ground EC on heavy haze days and haze days is 0.58 km-1 and 0.36 km-1, respectively. The second is 〖JP2〗the polluted continental type, contributing 0.27 km-1 and 0.20 km-1〖JP〗 respectively. On the heavy haze days, the low average wind speed and high relative humidity in and below 1.5 km are conducive to the increase of EC. On haze days, low average wind speed and high relative humidity are maintained at a higher height, making the height of aerosol high concentration layer up to 2.7 km. During haze days, the sources of near-surface pollutants are long-distance transmission from Mongolia, Inner Mongolia and the neighboring provinces. In heavy haze days, the transport of pollutants in the direction of Mongolia and Henan accounts for more, reaching to 25.26% and 31.58% respectively. The proportion of multi-layer inversion corresponding to heavy haze is close to 50%, and the proportion of ground+low-suspended type and ground+high-suspended type are the largest. Since these two types of inversion correspond to smaller outflow below the inversion layer, the atmosphere is more stable,and aerosol particles are concentrated in the lower layer when it is heavy haze weather.
    2021,47(9):1113-1121, DOI: 10.7519/j.issn.1000-0526.2021.09.007
    Abstract:
    Using the methods of element consistency, internal consistency and spatial consistency, the data qualities of 81 national surface meteorological stations in Anhui Province from 1961 to 2018 are controlled. The Bayes discriminant model is trained based on the normal year data after quality control, and the icing data of abnormal year are corrected by the model. The results show that total 84 years’ annual icing days from 38 stations in Anhui Province are abnormal, mainly concentrated in 1961-1970, 1988-1999 and 2015-2017, and fail to pass the quality control. The main reasons for these phenomena are the simplification of historical observation tasks of some stations, the adjustment of meteorological station classification, the reform of ground meteorological observation operation and so on. Then, by using the Bayes discriminant method, several discrimination models of icing weather phenomena are constructed. After verification, it is found that Model 1 and Model 3 have higher recognition accuracy, hit rate and TS score but lower false alarm rate. Considering the simplicity of calculation, Model 1 is selected to correct the icing data of abnormal years day by day. In addition, through the comparison of the icing weather phenomena correction results of Lu’an, Taihe and Wuwei Stations in abnormal years, we find that the model based on Bayes discriminant method is more reasonable for the correction of the icing weather phenomena caused by different reasons in different time periods, and the variation trend of annual icing days after correction is more in line with the actual situation, which shows that the Bayes discrimination model is reasonable and feasible to correct the icing weather phenomena.
    2021,47(9):1122-1134, DOI: 10.7519/j.issn.1000-0526.2021.09.008
    Abstract:
    Based on the improved stratification analysis method, the freezing rain fall zones and the altitudes of five severe freezing rain processes that occurred in China during 2008-2019 are calculated, and the result is verified by using the glaze data observed at 2 〖KG-*5〗000 stations and the ice disaster data of power grid. The calculated freezing rain fall zones cover both the areas with glaze and the areas with severe freezing rain disaster. The calculated altitudes of freezing rain occurrence are also consistent with the altitudes of ice disasters. The calculated results can well explain the phenomenon that there is freezing rain disaster but no glaze records under complex terrain conditions. The five calculated freezing rain fall zones are superimposed, showing that there is a freezing rain belt from Guizhou, Hunan, Jiangxi to Zhejiang, with the day number of freezing rain from high to low. The freezing rain belt can develop northward to Sichuan, Chongqing, Hubei and southern Anhui, and southward to Yunnan, Guangxi, Guangdong and northern Fujian. There is a typical cold-warm-cold stratification above the freezing rain zone. However, there is a warm-cold-warm-cold stratification above the freezing rain zone in greatly undulate terrain, such as Zhejiang and the north of Guangxi, Guangdong and Fujian, that is, there is a shallow warm layer with temperature higher than 0℃ near the surface. Therefore, the freezing rain usually occurs in the mountainous areas with an altitude above 300-400 m in Zhejiang and northern Fujian. The northeast of Guangxi and the northwest of Guangdong are also affected by the deep warm layer, and the freezing rain mostly occurs in the hillside areas with an altitude of 300-1 〖KG-*5〗300 m.
    2021,47(9):1135-1145, DOI: 10.7519/j.issn.1000-0526.2021.09.009
    Abstract:
    In this paper, the GPS-PWV (GPS/PWV) of GPS inversion of 11 stations in the central and eastern Qilian Mountains from 2016 to 2018 is used to analyze the characteristics of the spatio-temporal distribution, zonality and vertical charge of precipitable water vapor. The results show that compared to the PWV calculated from sounding data from Zhangye and Minqin stations, the average root-mean-square error and deviation are 2.1 mm and 1.07 mm respectively. GPS/PWV is slightly larger than RS/PWV, and the correlation coefficient of the two results reaches 〖JP2〗0.97. The PWV in the central and eastern Qilian Mountains has characteristics of obvious daily, monthly and seasonal variations. The daily maximum of PWV appears between 11:00-16:00 BT and the minimum between 01:00-05:00 BT. The monthly maximum occurs in August, and the monthly minimum is in January-February. The PWV seasonal variation shows a decreasing order from summer to autumn, spring and winter. The areas with high PWV values are mainly located in the southern part of Qilian Mountains, with obvious low-value areas at Gangcha and Minhe stations in the middle section of Qilian Mountains. PWV has obvious characteristics of zonatity and vertical change. The correlation coefficient between PWV and altitude reaches -0.77. PWV increases gradually from west to east with longitude, showing a change of high-low-high trend from south to north. In addition, the spatial distribution and seasonal change of PWV are also related to the effect of monsoon.
    2021,47(9):1146-1155, DOI: 10.7519/j.issn.1000-0526.2021.09.010
    Abstract:
    The Hubei Meteorological Forecast Service Integration Platform is designed and developed based on the MICAPS4 Web Platform developed by National Meteorological Centre, which can effectively connect China Integrated Meteorological Information Sharing System (CIMISS) and the distributed database of Meteorology Information Comprehensive Analysis Process System version 4 (MICAPS4). The platform integrates guidance and warning of primary focus, sharing and enquiry of real-time monitoring, comparative analysis of climate characteristics, comprehensive analysis of weather forecast, associative retrieval of service products, product generation and one-click distribution, application of professional service and management of information data system. The platform adopts key technologies including intensive application of meteorological big data, rule matching of work guidance, customized synthesis of automatic product generation and collaborative linkage of service response feedback. The platform has helped to realize the stable application in the three-level meteorological departments of the cities and counties in Hubei Province. The application results show that the integrated platform has greatly improved the level of business intensification and service collaboration of meteorological forecast service in provinces, cities and counties, promoting the establishment of the specifications of various operational processes including information transmission, product manufacture, service distribution and linkage response. The successful practice of applying MICAPS4 web framework to the establishment of the integrated platform of meteorological forecast service in Hubei Province has provided an effective alternative for the domestic provincial meteorological departments to follow the state-level technological development in time and carry out the construction of meteorological operation system under the big data application scenario.
    2021,47(9):1156-1161, DOI: 10.7519/j.issn.1000-0526.2021.09.011
    Abstract:
    The vorticity and divergence are two basic and important diagnostic physical quantities for the evolution process of the synoptic systems and phenomena in the common meteorological coordinate systems. In this paper, the formula between the vorticity in the isobaric coordinates (“p” coordinate) and one in the local rectangular coordinates (“z” coordinate) is obtained via coordinate transformation method. So done for the divergence. The results show that the expression forms of the vorticity and the divergence are exactly same in both coordinates, but they have essential differences. The vorticity in the “p” coordinate not only indicates the rotation of the air parcel around the vertical axis, but also implies the atmospheric baroclinity. Similarly, the divergence in the “p” coordinate not only expresses the relative variable ratio of the horizontal area of the air parcel, but also indicates the atmospheric baroclinity. In the area of the front, the difference of the vorticity is very obvious in “p” coordinate and “z” coordinate, and the same difference is found for the divergence. If the atmosphere is barotropic, the vorticity in the “p” coordinate equals that in the “z” coordinate. The same is true for the divergence. The vorticity and divergence both have the dynamic and thermodynamic natures of the atmosphere in the “p” coordinate.
    2021,47(9):1162-1168, DOI: 10.7519/j.issn.1000-0526.2021.09.012
    Abstract:
    The main characteristics of the general atmospheric circulation in June 2021 are as follows. There was one polar vortex center with stronger strength than normal in the Northern Hemisphere. The 500 hPa geopotential height over Europe was stronger than normal. The western Pacific subtropical high moved northward during middle dekads of this month and then southward in the last dekad. In June, the monthly mean precipitation of China was 91.5 mm, which was less than the normal by 8%. The negative precipitation anomaly reached 20%-50% in most part of Jiangnan, north part of South China and Jianghuai Region. In some regions the negative anomaly exceeded 50%. However, the positive precipitation anomaly reached more than 50% in northern Inner Mongolia, western Heilongjiang Province and eastern Jilin Province as well as central and eastern Liaoning Province. The monthly mean temperature of China was 20.8℃, which was a little higher than the usual. However, it was even 2℃ warmer than the normal in northern Henan Province, central Jiangsu Province and southern Qinghai Province. In June, eight regional torrential rain processes which mostly occurred in South China, and the observed values at many stations reached the standard of extreme precipitation events. Two typhoons were generated and neither of them landed in China in June. There were 44 stations where extreme high temperature events occurred and these stations are mostly located in the regions of Huanghuai, Jianghuai and South China. In addition, the daily maximum temperature at four stations broke the historical record.
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    Available online:  October 12, 2021 , DOI:
    Abstract:
    The mesoscale characteristics of a local short-time severe convective rainstorm that occurred at the eastern foot of Helan Mountains in August Ningxia in 2019 were analyzed based on the data from H8 satellite, Doppler radar, ERA5 hourly reanalysis, automatic weather station and conventional observation data. The results showed that: (1) The southerly jet of 700 hPa that established 6 hours before the rainstorm and strengthened at night not only contributed to high temperature, high humidity, and the enhancement of atmospheric instability and dynamic and thermal uplift mechanisms in the lower layers of the rainstorm area, but also helped mesoscale ground convergence line to trigger the meso-β scale convective system in the eastern slope of Helan Mountains and strengthen it to meso-α scale convective system, leading to the generation and development of the severe convective rainstorm eventually. (2) The rainstorm occurred in the front-left of jet axis of 700 hPa, the high humidity area with water vapor flux ≥6 g?cm-1?s-1?hPa-1 of 700 hPa and specific humidity ≥12 g?kg-1 of 850 hPa, the high energy area with convective available potential energy ≥1500 J?kg-1, the high temperature area with θse ≥346 K of 850 hPa, the vertical upwarding area with centric intensity ≤-1.2 Pa?s-1 of 800 hPa, and the front of cold cloud where the large gradient (G) of cloud top brightness temperature (TBB) occurred. (3) During the strongest rainfall period, the jet axis was closest to the rainstorm area, the TBB ≤-66 ℃, the G ≥27 ℃?km-1, the radar composite reflectivity (Z) ≥65 dBZ, the echo tops (H ) ≥10 km, the vertical integrated liquid water (VIL) ≥11 kg?m-2, and the area of the cold cloud below -52 ℃ was about 1/5 of mesoscale convective complex. (4) The lower TBB was and the higher G and cooling rate (CR) were, the greater intensity of precipitation would be. The minimum TBB, the maximum G, the leap of Z and VIL, and the increase of echo height appeared 10~20 minutes earlier than the maximum rainfall, and the mesoscale ground convergence line appeared 30 minutes earlier than the rainfall.
    Available online:  September 28, 2021 , DOI:
    Abstract:
    In the early morning of 7 July , 2016, due to the influence of mesoscale convective system (MCS), a sudden local rainstorm occurred in Nanjing. Development of the MCS including convection triggering, quasi-stationary backward propagation, heavy rainfall supercell and cold pool driving lasted for nearly 8 hours and resulted in serious waterlogging. The weather background and MCS evolution characteristics of this heavy rainfall process were analyzed in detail by using multi-source datasets from Doppler radar, automatic stations, wind profile, China regional reanalysis (CNRR), Jiangsu merged assimilation analysis and so forth. The results showed that (1) The transit of a mesoscale forward-tilting trough induced low pressure at the surface, strengthening convergence, forming an uplifting movement and triggering linear convective storms; (2) The warm and humid southwesterly flow between 3km and 6km was significantly enhanced and uplifted in the meso-β-scale secondary circulation; the favorable configuration of the meso-γ-scale low-level low pressure and the southwesterly flow made the MCS over Nanjing exhibit a quasi-stationary feature of backward propagation, and eventually leading to a heavy precipitation supercell in 8 consecutive radar volume scans; (3) The drag effect of heavy precipitation formed a downdraft, which led to the outflow near the surface and stimulated a new convection on the south side, causing the MCS to move slowly to the south. As the downdraft strengthened in the MCS, a cold pool appeared on the ground. The strong divergence accelerated the movement of the MCS, and then the heavy precipitation process ended.
    Available online:  September 27, 2021 , DOI:
    Abstract:
    For the uncertainty of heavy rain belt forecast of the ECMWF model in the Yangtze-Huaihe river basin in China during the extremely long 2020 Meiyu period, 10 typical long and narrow heavy rain belts were collected to analyze the location forecast bias, forecast stability and continuity of forecast bias using the method for object-based diagnostic evaluation (MODE). Ensemble sensitivity analysis (ESA) was also used to analyze the key synoptic systems which cause the typical forecast bias of the heavy rain belts. Result showed that: Forecast uncertainty of the eastern part of rain belts is generally higher than that of the western part, especially during the medium range where forecast uncertainty further strengthens. During short range, both the western and eastern part of rain belts have obvious northward systematic forecast bias. The western part of rain belts has relatively lower missing rate, better stability and continuity than the eastern part. During medium range, the forecast error of the eastern part of rain belts grows obviously and the average latitude variation of the eastern part is also higher than that of the western part. The results of ESA indicate that the northward forecast bias of the eastern part of rain belts is caused by the joint effect of the 500 hPa high-level trough, the subtropical high, the 850 hPa low-level jet, the shear line and the unrealistic positive feedback between them and precipitation latent heat releasing, where the development and strengthen of high-level trough and low-level jet is one of the background characteristics of the northward forecast bias of the eastern part of rain belts.
    Available online:  September 26, 2021 , DOI:
    Abstract:
    The evaluation results of ECMWF and GFS on the track and intensity forecasts of typhoons affecting Zhejiang from 2016 to 2019 show that ECMWF is better than GFS for track forecasting, and GFS has more advantages for intensity forecasting. On this basis, the paper proposes a feasible typhoon initialization scheme to improve the performance of typhoon forecasting skill. Based on ECMWF and GFS analysis fields and oceanic typhoon observation data, using typhoon vortex separation, the vortex field is obtained by separating the GFS analysis field, and after vortex relocation and maximum wind speed adjustment procedure,it is superimposed with the large-scale environmental field separated from the ECMWF analysis field to realize the reconstruction of typhoon initial field. For 14 typhoons affecting Zhejiang in recent years, the hindcasting results of the mesoscale numerical weather forecast model which use the new reconstruction scheme demonstrate that the new scheme gives full play to the ECMWF’s advantages in track forecasts and GFS’s advantages in intensity forecasts and improves the forecast accuracy of typhoon track and intensity effectively. The absolute error of track forecast is reduced by 21 km and the standard deviation is reduced by 26.6 km compared with the prediction of the GFS-driven mesoscale model. Compared with the forecast result of the EC-driven mesoscale model, the absolute error of intensity forecast is reduced by 1.7 m·s-1 and the standard deviation is reduced by 2.3 m·s-1. The analysis of the typical case of Super Typhoon Lekima (2019) further indicates that the initial field reconstruction technology has a better forecasting ability for atmospheric circulation characteristics and typhoon's warm core structure.
    Available online:  September 26, 2021 , DOI:
    Abstract:
    This paper used controlling data, National Centers for Environmental Prediction(0.5°×0.5°) reanalysis data by 6 hours and X-band dual-polarization radar observing data to diagnose and analyze the hailstorm triggered by small trough. According to the features of occurrence and development and these predictive indexes with good indicative significance to the hailstorm triggered by small trough, a diagnosis method was constructed. By the method, three hailstorms with different intensity triggered by small trough were diagnosed and analyzed, and the prediction effects were verified. The results indicate that:The hailstone potential of individual cases can be diagnosed effectively by the corresponding relationship between the central region with a large value of the vertical helicity of humid heat force greater than 0.8×10-1?m3?K?kg-1?s-2 and the center region with a large value of the vertical helicity of water vapor greater than 0.8×10-5m?s-1 and the hailstone land.During strong wind shear and monomer amalgamation promote its occurrence and development. In view of this feature, the probability of hailstorm monomer developing into strong hailstorm can be diagnosed by using the correspondence between the center region of large value with the absolute value of thermo shear advection parameter greater than 3×10-8K?Pa-1?s-1 and the threshold value of the relation between 45dBz echo top height and 0℃ height. The difference in squall line strong hailstorm and hailstorm were diagnosed by using the dignosis of hailstorm triggered by small trough formed by the above prediction indexes combined with echo features.
    Available online:  September 26, 2021 , DOI:
    Abstract:
    Convective initiation (CI) means the beginning of strong convective weather activities. The study of CI mechanisms is a critical and difficult problem of mesoscale meteorology, and is critical to improve the scientific knowledge of the evolution of local sudden strong convection and the nowcasting of strong convective weather. The research results of surface-based CI mechanisms and elevated CI mechanisms at home and abroad are summarized. Surface-based CIs usually are triggered by boundary layer convergence lines. In addition, temperature and humidity disturbance, instability, misocyclone, vertical shear, topography and other factors also have a certain impact on the time and position of surface-based CIs. Atmospheric instability is sensitive to the change of local temperature, especially humidity, and has a great influence on CI. The interaction of ambient vertical wind shear and thermonamic field of boundary, the feedback between vertical velocity and vorticity of misocyclone, and the thermodynamic effects caused by topography will influence the surface-based CIs. Most elevated CIs are related to the bores, gravity waves and low-level jets. The low-level jets transport water vapor upward and northward, reducing the stability of the environment, and the shear associated with the low-level jets can also produce updraft, which is important for nocturnal elevated CI. Convectively generated gravity waves and bores are conducive to the elevated CI, which can lift the lower atmosphere and reduce the stability. Elevated convergence and weak but persistent mesoscale lifting are also helpful to increase the possibility of elevated CI. This article can be used for reference in the CI-releated research and the prediction and early warning of local sudden strong convection.
    Available online:  September 26, 2021 , DOI:
    Abstract:
    In order to further discuss the application effect of a new type of "up-drift-down" sounding data to data assimilation and numerical prediction, assimilation comparisons were carried out based on the WRF(Weather Research and Forecast) model and WRFDA(WRF Data Assimilation) system. In this paper, based on the quality evaluation and sparseness of the new radiosonde data, the descending data is combined with the conventional observation data and assimilated, and the influence and reasons of the data on the rainstorm forecast quality in the middle and lower reaches of the Yangtze River are discussed. The main test results include: the accuracy of the latest test data is verified by cross-comparison of the test data with the FNL data and the sounding data of the same station; the scheme of combining the characteristic layers with the specified layers can be used to sparse the ascending and descending segments of the new radiosonde, which can get better results; the rainstorm forecasting technique can be improved to some extent by adding the data in the descending section; the adjustment of wind field and humidity field is one of the important reasons for the improvement of rainstorm forecasting skills.
    Available online:  September 14, 2021 , DOI:
    Abstract:
    Based on the best-track data from Joint Typhoon Warning Center and ERA-interim 1°×1° reanalysis data from 1979-2018,a study is conducted to investigate the activity characteristics of super cyclonic storms formed in autumn over the North Indian Ocean. The results show that the number of super cyclonic storms formed in autumn over the North Indian Ocean increased significantly after 1998. The average maximum potential intensity (MPI) index of the North Indian Ocean in 1999-2018 is higher than that in 1979-1998. Compared with 1979-1998, the higher average sea surface temperature and ocean heat content in 1999-2018 provide favorable conditions for the formation and development of super cyclonic storms. Weaker vertical wind shear, stronger water vapor flux and lower level cyclonic vorticity transport promote the sustained growth of cyclonic storm intensity
    Available online:  September 14, 2021 , DOI:
    Abstract:
    Based on Emergency Events Database (EM-DAT) and Dartmouth Flood Observatory (DFO) disaster datasets, this study compares the variation characteristics of frequency, magnitude and fatalities of floods in South Asia and Southeast Asia during 1985-2019. The trends of Tropical Cyclone (TC)-associated floods are also discussed. The results show that frequency of floods in Southeast Asia is about 15% more than that in South Asia for recent 35 years. Among all floods, the frequency of TC-associated floods in Southeast Asia is around 4 times more than that in South Asia. The TC-associated floods account for approximately 20% of all floods in Southeast Asia. Monthly distribution shows that floods in South Asia concentrate in June – August which exhibiting a unimodal pattern while TC-associated floods in South Asia present a bimodal distribution. Floods in Southeast Asia are evenly distributed throughout the year. Trend test of averaged floods by two databases indicate that both floods in South Asia and Southeast Asia has significantly increased over recent 35 years while the flood-induced fatalities per flood event decreased significantly. On average, the magnitude of floods in Southeast Asia is smaller than that in South Asia, but there is a significant increasing trend in the magnitude of floods in Southeast Asia during recent 35 years. In addition, both economic losses of floods in South Asia and Southeast Asia based on EM-DAT data exhibit obvious increasing trend over the past 35 years.
    Available online:  September 14, 2021 , DOI:
    Abstract:
    Based on land use/cover change dataset at a resolution of 30m*30m, degree monitoring and index for chilling dew wind are extracted under underlying surface for double-season late rice, which are used to reveal characteristics for chilling dew wind. It is clear that the start date of for chilling dew wind in 2020 is earlier and the number of lasting days is longer than the average values during 2000-2020. Low to heavy chilling dew wind is occurred across rice area. There are 24.7% of rice exposed to chilling dew wind, which is the third largest since 2000. The percent of low, medium and heavy chilling dew wind is 9.7%, 12.8% and 4.9%, respectively. In terms of statistic in provinces, it is obvious that 99.9%, 99.4% and 91.8% rice is respectively affected by chilling dew wind in Hunan, Jiangxi and Zhejiang, which are higher than that in other provinces. The area percent subjected to chilling dew wind in Hunan, Hubei, Anhui and Jiangsu is largest since 2000, while that in Guangdong is small. The area percent subjected to heavy chilling dew wind in Jiangxi is largest, though the percent subjected to chilling dew wind is fifth largest. The major degree of chilling dew wind is low in Zhejiang, Fujian and Guangxi. The integrated index is 4.21, 7.16, 7.16 and 12.59 for double-season late rice, Hunan, Jiangxi and Hubei, which is second largest. Moreover, the index is the largest in Jiangxi and Zhejiang.
    Available online:  September 08, 2021 , DOI:
    Abstract:
    The observed yield of winter wheat from 123 agrometeorological observation stations and the announced yield of winter wheat at county level where the observation station was located were used to integrate the observed yield and announced yield at province and national level by the proportion of winter wheat planting area. And the observed yield and announced yield sequences of winter wheat were compared and analyzed at province and national level. The observed and announced yield of winter wheat at national level were predicted based on the climate suitability index forecast method. The forecast accuracy of different yield sequences were compared and analyzed. The results showed that:(1) the observed yield was large than the announced yield at province level in all provinces, and the difference between the two yields differed markedly. The correlation coefficient between observed and announced yield was good in each province and the correlation passed the significant test except Xinjiang province. The correlation coefficient between observed yield and announced yield at national level reached 0.97, and the observed yield could reflect the characteristic of announced yield. (2) The percent of consistency statistics of trend meteorological yield of observed and announced yield remained good at national level, so it was suitable to carry out yield prediction. While it was unsuitable to carry out yield prediction at province level due to the low percent.(3) The accuracy of different yield sequences in forecasting their own sequences was high and the accuracy of announced yield was higher than the observed yield. The accuracy of the forecast conversion of the announced yield by using the observed yield would be reduced. Conclusively, it is feasible to carry out yield forecast at national level based on the observed yield series because of the real-time, objectivity and representative of the observed yield. At the same time, the new yield series could provide new data support for yield forecast.
    Available online:  July 27, 2021 , DOI:
    Abstract:
    The urban hydrological model is introduced into the urban flash floods forecasts and warning issue. The land use and land cover (LULC) types data and gridded urban drainage network capacity being parameterized in the model, and forced by the radar rainfall estimates (QPEs and QPFs), the model simulated the urban surface hydrological response and hydraulic processes. The hydraulic model is based on the shallow water equation, which the Alternating-Direction-Implicit (ADI) is used to solve the differential equation by tow steps in the x direction and y direction, respectively. This solution comprises the back water effects in simulation and indirectly intimates the multiple flow direction methods, which recalls the surface water dispersion in turbulence or diffusional effects. The case study demonstrates the online and offline running of the urban hydrological model purposed for the flash floods warning, partially for the model validation. The online hydrological model took the case study on the “7.21” thunderstorm in the year of 2012 occurred in Beijing, in which the radar quantitative-rainfall estimates (QPEs) were forced on the model for reproducing the gridded inundation mappings. The model simulation results resembled the flash floods scenarios of the waterloggings and water inundations on the “7.21” thunderstorm day. The offline model simulation addressed the measuring the rainfall intensity threshold for the ranked risks of the storm producing flash floods, especially the rainfall intensity thresholds for floods-susceptible places (FSPs). Therefore, the hydrological model simulation deduced the 1h, 3h and 6h cumulative rainfalls thresholds inducing water inundation depths over 0.2m, 0.5m, 0.8m and 1.2m in more than 49 FSPs, which had been the rainfall intensity thresholds of the flash floods warning in the blue, yellow, orange and red signals, respectively. The rainfall intensity thresholds in risk warning ranks can be referred by the forecasters for flexible flash floods warning issuances in convenience. The research initiates a possible service mode for the effectiveness improvement on the urban flash floods warning and forecasts, efficiently combining the technologies of the Auto-nowcasting system and the hydrological model, especially forming the backbones for the convenient warning and forecasting services operations, easiness in data manipulation and rational computation resources allocation.
    Available online:  July 09, 2021 , DOI:
    Abstract:
    In this study, the key area of upstream southwest wind speed was established, which is closely associated with Spring Persistent Rains in Hunan (SPRH). The starting date, ending date, rainfall, rainy period and intensity index of SPRH were defined from 1980 to 2014. The temporal and spatial patterns of SPRH rainfall were analyzed. The anomaly of the atmospheric circulations during the strong/weak SPRH period and sea surface temperature (SST) during the early period were discussed. Results showed that: The climate average of SPRH occurred from the 13 pentads to the 27 pentads, whereas the starting date and ending date of SPRH varied in different years. The rainfall of SPRH was exceeded normal conditions during the periods of before the mid-1980s and after 2014, whereas it was lower than normal conditions during the periods of the mid-1980s to 2014. The strong years of SPRH in whole province were found in 1981, 1992, 2014 and 2016. By contrast, the weak years of SPRH in whole province occurred after 1990 including 1991, 1994, 2008 and 2011. In the strong SPRH years in whole province, the western pacific subtropical high (WPSH) remarkably became stronger and westward; the Indo-Burmese trough tended to become weaker; and an anomalous anticyclone existed in the southern Yangtze River regions in low-level wind field. Hunan was located in the center of anomalous anticyclone, which led to strong SPRH. However, in the weak SPRH years, WPSH evidently became weaker; the Indo-Burmese trough tended to become stronger; and an anomalous cyclone was found in southern China. Additionally, Hunan was located in the center of anomalous water vapor divergence, resulting in weaker SPRH in whole province. In the following year of the occurrence of El Nino events, SPRH started earlier, longer rainy period, more intensive rainfall amount compared with the normal years. On the contrary, during the following year of the occurrence of La Nina, SPRH started later, shorted rainy periods, lower rainfall amount and weaker rainfall intensity compared with the normal years.
    Available online:  June 28, 2021 , DOI:
    Abstract:
    Based on the datasets of Meiyu monitoring and observation of precipitation and NCEP atmosphere reanalysis and sea surface temperature, the abnormal characteristics of Meiyu over the Yangtze–Huai River Basin (YHRB) in 2019 and its causes of large-scale circulation are analyzed. The results are as follows: (1) The abnormal characteristics obviously showed that the Meiyu onset date was later than normal compared with a shorter duration, the Meiyu precipitation presented a distribution pattern of the more in the south and the less in the north of the Yangtze River over YHRB which was less than normal in overall in the Meiyu season of 2019. Among the three subareas, the Meiyu period of the subarea of the middle and lower reaches of Yangtze River was almost simultaneous with that of Jiangnan subarea, and the Meiyu of the Jianghuai subarea was not obviously. (2) Due to the periodical enhancement of the cold air between June 8 to 15 it was impeded and delayed that the seasonal northward of East Asian summer monsoon, which lead to the conversion later from winter to early summer of the circulation pattern in East Asian and Meiyu onset date also later over YHRB. It can be regarded as the precursory signals of Meiyu onset date later over YHRB in 2019 that the sea surface temperature in Indian Ocean was warmer than normal in May-June and the reverse date of MTGMUT was later over 60o~80oE of South Asia. (3) Compared with climate mean state, the eastern ridge of South Asian high and East Asia westerly jet were southward at upper-level, the circulation meridionality in the middle-high latitude in Eurasia was stronger and the western ridge of Northwest Pacific subtropical high was southward and the geopotential height east of Australia was higher at middle-level, the intensity was weaker and the northernmost was southward of the East Asia summer monsoon at low-level. Due to the combined influence of the above-mentioned abnormal characteristic , it was under the control of the strong divergence at upper-level and the strong meridional gradient convergence of vapor flux at low-level in the south of the Yangtze River over YHRB. That is greatly conducive to the development of vertical upward movement and the occurrence of heavy rainfall and cause the distribution pattern of the Meiyu precipitation in 2019 with the more in the south and the less in the north of the Yangtze River over YHRB.
    Available online:  June 17, 2021 , DOI:
    Abstract:
    Using conventional observation data, doppler radar data of Xi’an station, ground weather station observation data and ERA5 reanalysis data (0.25*0.25), the environmental conditions and triggering mechanism of four severe convection weathers in Guanzhong area under the influence of subtropical high from 2015 to 2018 were comparative analyzed. These four cases resulting in local geological disasters and urban flooding, however, the global model failed to forecast a short-term rainstorm. Results show that the severe convection in Guanzhong area under the control of subtropical high often coexists with the hot weather. When severe convection occurs, low-level atmospheric water vapor content is large, the atmospheric precipitable water can be more than 50 mm, relative to the systemic rainstorm occurred in the peripheral of the subtropical high, the water vapor transmission is relatively weak, the strength of the water vapor transmission determines the total rainfall in the severe convection process. Convergence center is located on the ground to 800 hPa, compared with the systemic rainstorm, the convergence center position is lower, and the main role of low-level convergence is to overcome convection suppression, release unstable energy. Favorable environmental conditions for the occurrence of severe convection including strong potential unstable layer, low LFC, medium intensity convective available potential energy and thick warm clouds. The trigger mechanism is mainly cold front and low-level wind convergence line, when there is a cold front in the upstream, the cooling effect of precipitation behind the cold front will increase the temperature gradient to enhance the cold front, cold air in the lower layer invades the atmosphere with high temperature and high humidity controlled by subtropical high, triggering severe convection occurs; The convection in warm regions is usually triggered by ground convergence line, convection induced cold pools can form gust front and trigger new convection. Qinling terrain has a significant impact on the movement and spread of the severe convection. The convective that triggers in north of Guanzhong area and move southward can easily cause heavy rain storm because of the rain belt blocked by Qinling. The new convective occurred along the terrain convergence line in the northern Qinling triggers new convective development in Guanzhong area, as the potential energy is converted to kinetic energy during the descending process, the convection system moves faster and the duration of heavy precipitation is shorter, it is easier to produce large-scale thunderstorm and gale weather.
    Available online:  May 10, 2021 , DOI:
    Abstract:
    Based on hourly and 5-minute observation data of automatic weather station, swan mosaic product of radar combined reflectivity factor in the middle reaches of the Yangtze River and NCEP FNL reanalysis data, the characteristics of four convective storms with low-echo-centroid type of short-term heavy precipitation in Wuhan were analyzed. The results showed that: (1) the characteristics of convective system induced by different weather background were different. Under the background of warm forcing, the environmental conditions were high energy and high humidity, and the accumulation of thunderstorm cold pool was conducted to triggering linear convection in the stable precipitation front; under the baroclinic frontogenesis background, the convergence of cold and warm was intense, and the baroclinic was strengthened; there were more mesoscale cyclone waves on the ground, and the stable precipitation in the front area was often accompanied by a short-term strong drop Under the quasi barotropic background, the baroclinic atmosphere was weak, but the high-energy and high humidity environment as well as the near surface layer flow field forcing and local thermal difference were easy to trigger severe thermal convection activities. (2) According to the radar echo characteristics and precipitation characteristics of convective storms, TS type moved faster, resulting in a small range of short-term heavy rainfall; quasi-stationary type showed that the echo of large-scale stratiform cloud with zonal trend was stable, and there were multiple cumulus convective echoes in the middle. The precipitation enhancement in each stage corresponds to the new convective cell passing through Wuhan station; the consolidation type was in the circulation When the wave merges, it was often accompanied by the occurrence of heavy rainfall, and the echo shape and direction after merging affect the intensity and duration of precipitation. (3) Under different environmental background, trigger inducement and organizational form, the surface meteorological elements before and after the occurrence of short-term heavy rainfall showed different change characteristics; the different front characteristics and convection trigger positions leaded to different temperature changes. (4) Ground mesoscale system played an important role in triggering and organizing the development of MCS. Its generation, elimination and transformation usually heaved a certain advance in time for MCS. Paying attention to the development and evolution of ground mesoscale systems such as ground convergence line and temperature front area was of great significance for predicting the triggering and organizational evolution of MCS.
    Available online:  April 23, 2021 , DOI:
    Abstract:
    Several intense tornadoes (≥EF3) in China in recent years resulted in heavy casualties and serious economic losses. The tornado has a very small scale, and its occurrence frequency in China is extremely low. At present, tornadoes cannot still be forecast in operation in China. However, with the development of observation networks of new-generation weather radar and surface automatic weather stations, damage survey and numerical weather prediction model, remarkable progress in tornado research in China has been made. The climatology, synoptic backgrounds and favorable environmental conditions for tornado in China have been understood, and it has also been found that the favorable environmental conditions for tornado in different synoptic backgrounds are somewhat different. The damage survey process and analysis technology of tornado disaster have been developed and completed. The damage surveys and analyses of several intense tornadoes, such as the 2016 Funing, Jiangsu Province EF4 tornado, have been made in detail. More understandings of meso- and micro-scale characteristics of tornadic convective storms have been got, including the findings of the storm cold pool with appropriate intensity, the bottom of the mesocyclone generally lower than the height of 1 km, the positive intensity correlation between tornado and its parent mesocyclone, slantwise mesocyclone, tornadic debris signature, descending reflectivity core, and multi-vortex structure of some tornadoes. Two tornadoes have successfully been ideally simulated using a fine-resolution cloud model, and the tornado-scale vortices in the convective eyewall of 2005 typhoon Matsa and the multiple vortices of the 2016 Funing tornado have been successfully simulated by using the WRF (Advanced Weather Research and Forecast) model. Future, we still need to further develop tornado detection technology, and to study fine surface meteorological element distribution and structure features, tornado vortex and lightning activity of tornadic convective storms, and close studies on the development mechanisms of tornado are surely needed using finer-resolution observation data and higher-resolution numerical weather simulation, in order to provide more scientific foundations to promote the tornado forecasting and warning ability in China.
    Available online:  January 14, 2021 , DOI:
    Abstract:
    By virtue of the daily temperature observations of 2400 stations in China from 1960 to 2019, the climatological characteristics of the cold event in China are systematically analyzed, and the relationship between cold wave, cold air process and the Arctic Oscillation (AO) is discussed. The results show that the cold wave and cold air process in China mainly occur in autumn, winter and spring, and the frequency and intensity have obvious monthly and seasonal differences. Regional cold wave has the highest frequency in autumn, and national cold wave and all types of cold air have the highest frequency in winter. The average intensity of regional cold event is the largest in February, and the average intensity of national cold event is the largest in November. Based on the analysis of winter temperature in China, the past 60 years can be divided into two stages, that is, the cold period from 1960 to 1986 and the warm period from 1987 to 2019. In the winter of cold period, the frequency of the national cold wave shows a significant decrease trend (-0.57 times/10 years), and the frequency of regional cold air and all-type (the sum of national type and regional type) cold air processes in winter shows a significant upward trend of 1.37 times/10 years and 1.28 times/10 years, respectively. In the warm period, there is a significantly decreasing trend of national cold wave frequency (-0.17 times/10 years) and a significantly increasing trend of regional cold air frequency (0.53 times/10 years) in January. The frequency and intensity of cold wave and cold air over China are closely related to the Arctic Oscillation (AO). On the interannual scale, the frequency (intensity) of various cold wave in various seasons is negatively correlated with the AO index, but the frequency (intensity) of various cold air in winter is positively correlated with AO index. On the interdecadal scale, the frequency of winter regional cold wave, the frequency of national cold wave, and the intensity of national cold wave are significantly positively correlated with the AO index.
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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.
      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.
      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.
      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.
      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.
      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.
      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.
      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.
      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.
      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.
      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.
      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(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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