Studying the evolution characteristics of a gust front and the physical mechanisms of extreme winds behind it using multiple types of radar products is of great reference significance for improving the forecasting and early warning capabilities of catastrophic gale weather. Using conventional upper-air and surface observational data, ERA5 reanalysis data of the European Center for Medium-Range Weather Forecasts, S-band dual-polarization radar data and X-band phased-array radar data, the characteristics of radar products of a gust front and the extreme wind process behind the gust front in Shaoxing of Zhejiang Province on July 10, 2023 were analyzed. The results show that this process occurred under the background of southwest airflow at both high and low altitudes. The upper air was at the edge of the subtropical high, and at 925 hPa, it was in the convergence area of southwest wind speeds. The atmospheric thermal instability and uplift conditions were better. After multiple convective cells merged into a multi-cell storm, the gust front was formed at the outflow boundary of it. The gust front underwent three stages: development, rupture, and weakening. At the weakening stage, a new mesoscale convective zone was triggered behind it, and the backward propagation characteristics were obvious. The maximum wind speed induced by the gust front occurred during its weakening stage, while the extreme wind of the process occurred during the eastward movement and northward lifting of the mesoscale convective band triggered by the gust front. The internal vortex structure of the convective cells which generated the extreme winds only existed at an altitude of 800 m, and the convergence of wind direction and speed was mainly at the middle and upper levels. The gusts of 6-7 levels were generated when the vortex circulation weakened and disappeared, and the core of the reflectivity factor decreased, and the lower levels of the storm turned into downdraft. The extreme wind was generated later when the inflow behind the storm turned back into updraft and converged with the downdraft at middle levels. It was also accompanied by radial convergence in the middle layer horizontally, which indicated an increase in sinking airflow. Due to the relatively small contribution of downward momentum transfer, the extreme wind was mainly caused by strong sinking airflow.

Heavy rainfalls and floods, waterlogging triggered by rainstorms are one of the most serious natural disasters in Ningxia. This paper constructs an integrated rainstorm hazard risk warning model in Ningxia to effectively predict the risk of heavy rainfall and issue risk warnings in advance, by using the Analytic Hierarchy Process (AHP) and Delphi method, and considering four factors including hazard, exposure, vulnerability, and disaster mitigation capacity, the model incorporates 14 evaluation indicators such as population, economy, elevation, and vegetation etc. in Ningxia. Combined with GIS technology, a rainstorm event simulation was conducted. The results show that the model comprehensively and objectively reflected integrated risk distribution during rainstorms. The analysis of the rainstorm on July 10, 2022 indicated that the regions with the highest hazard were Jinfeng District and Xixia District of Yinchuan, Litong District of Wuzhong, Qingtongxia County, eastern Yanchi County, and Yuanzhou District of Guyuan; the highest exposure was in Yinchuan; the highest vulnerability was in western Qingtongxia, Tongxin County, Haiyuan County, Xiji County, and Pengyang County; the weakest disaster mitigation capacity was in Haiyuan County, and the highest integrated risk areas were Jinfeng District of Yinchuan, Litong District of Wuzhong, Haiyuan and Xiji County. Integrating the model with smart grid forecasting, the integrated rainstorm hazard risk can be calculated, which provides scientific basis for precise prevention in practical operations.

Based on daily MCI and identification method of persistent regional drought events, the persistent regional drought events in summer and autumn were identified in Hunan Province from 1961 to 2017. And on this basis, the spatio-temporal characteristics of evaluation indexes including frequency, duration, intensity and start date, end date of persistent regional drought evens were analyzed. The results show that the persistent regional drought events occurred 1.4 times per year on average in Hunan Province in summer and autumn from 1961 to 2017, and the annual variation trend of drought events wasn’t obvious. The decadal variation characteristic was obvious, the drought frequency was the least in the 2000s, but the accumulative intensity of drought was the strongest and lasting days of drought were the longest. The drought events were fewer and weaker in the 1990s. The continuous droughts from summer to autumn dominated in Hunan Province, and occurred more frequently from July 28 to October 14. The drought events persisted mainly from 15 d to 30 d, and the longest lasted 183 d. The duration of general drought events was less than 40 days, while for severe drought events and above it was more than 110 days. The spatial distributions of persistent regional drought events mainly appeared three patterns including the whole province pattern, northwestern pattern and southern pattern in Hunan Province. The drought events with the whole province pattern were the most, and drought grades reached mostly heavy level and above. The persistent regional drought events were less in the north and more in the south of Hunan Province, and the accumulative intensity of drought increased gradually from northwest to southeast. The drought degree in northwestern Hunan was lighter, while in Dongting Lake, central and southern Hunan it was heavier.

Based on daily precipitation, mean air temperature, maximum and minimum air temperature, wind speed and direction (four times a day) data during 1961-2018, and hourly precipitation data during 1978-2018 from 6 national meteorological stations around the Poyang Lake as well as the reanalysis data of European Center during 1979-2018, the climate difference between the east and the west side of the Poyang Lake caused by the cold-heat source effect on different time scales was analyzed. The results are as follows: (1) There was an obvious cold-heat source effect in the Poyang Lake. The diurnal temperature range in the Poyang Lake area was 2-4 ℃ smaller than that in mountainous areas, and the high temperature days was half of that in other areas of the same latitude in Jiangxi Province. (2) The precipitation in the Poyang Lake was also less than other areas of Jiangxi. The precipitation in the east and the west side of the lake presented the cyclical fluctuation in a year, there were more precipitation from August to October in the west side of the lake, while there were more rainfall in other months in the east side of the lake, the difference was obvious especially in middle of winter and summer. (3) There were differences of precipitation between the east and the west of the lake at day and night. The precipitation in the east of the lake was more obvious at night in January, while in September it was more obvious in the west of the lake at day. (4) Lake-land wind existed in the Poyang Lake. The average wind speed at 02:00 BST in January at Yongxiu station in the west side of the lake was higher than that of Duchang station in the east side of the lake, and the west wind component occurred more. In August, the average wind speed at Duchang station was higher than that of Yongxiu station at 14:00 BST, and the south wind occurred more frequently. (5) Compared with 14:00 BST, the atmospheric ascending motion was more obvious at 02:00 BST in the main area of the Poyang Lake in January, the near-surface wind field converged. While compared with 02:00 BST in August, subsidence movement was more obvious at 14:00 BST, and near-surface wind field diverged.

Based on the conventional observation data, Doppler radar products at Kashi station, FY-2D satellite cloud images and NCEP/NCAR reanalysis data, the formation mechanism and mesoscale weather system of four rainstorm processes under the anomalous circulation background in the west of Southern Xinjiang in August 2016 were analyzed comparatively. The results show that the more rainstorms in the western part of Southern Xinjiang in August 2016 occurred under the circulation background of the strong Ural Mountains high ridge on 500 hPa and Polar lows, anomalous water vapor convergence zone on 700 hPa over Tibetan Plateau and longitudinal oscillation of South Asia high. And the establishment, development and decline of the Ural Mountain high ridge on 500 hPa were closely related with rainstorms in the western part of Southern Xinjiang in August 2016. The intensity of rainstorm was closely related with 850 hPa warm ridge and temperature difference above 28 ℃ between 500 hPa and 850 hPa, while the differences of humidity layer thickness below 500 hPa, easterly airflow below 700 hPa, surface shear line and dry line resulted in different intensity, falling area and duration of rainstorm. The water vapor transport at the southern boundary was important source of rainstorm in the western part of Southern Xinjiang, while at the eastern boundary it was important supply of short-term heavy rainfall in the area. The humidity gradient on satellite images was conductive to the occurrence of convective weather, while the structures of the strong echo, low centroid and high cloud top of radar were beneficial to the occurrence of short-term heavy rainfall.

Abstract:Results from the data of meteorological disasters in 2008 in Langfang show that the torrential rain and flood disasters are the
most damageable．From 1949 to 2007，the direct economic losses caused by the torrential rain and flood disasters are 198．673 billion，
which are 82．2%of those caused by all the meteorological disasters．The sustainable development of national and local economic is
significantly affected by the torrential rain and flood disasters．Based on the system theories and principles of natural disasters evaluation，8 indexes are calculated，including topographic index(H)，intensity(C)and frequency(R)index of the torrential rain and lood disasters，onomical disaster bearing capacity index(E)，economic loss index(E')，life vulnerability index(L)，life damage ndex(L')and disaster relief index(K)，respectively．Combined disaster index were obtained for each county after systematically assessed the regional differences in risks of the torrential rain and flood disasters in Langfang，and 4 grades(extremely high，high，medium and low)were used to divide the torrential rain and flood disasters．Studies on the division of the torrential rain and flood disasters an provide us scientific basis for the precaution of the torrential rain and flood disasters and reduction of their economic losses and taking effective measures to these disasters．