From January to June 2023, meteorological droughts of varying degrees occurred in southwestern China, eastern North China, northern East China, central southern China, southern South China, and central Northeast China, seriously affecting agricultural production and restricting local economic development. To improve the ability to respond to drought disasters, timely carry out disaster prevention and reduction work, and conduct real-time summaries of drought situations. This article uses K index, MCI index, T-N flux and CABLE land surface model, as well as meteorological observation data, reanalysis data, soil moisture data to comprehensively analyze the spatiotemporal distribution characteristics and causes of regional drought events. The results are as follows: (1) In the first half of 2023, severe regional drought occurred in southwestern China and eastern Inner Mongolia. The southwestern region experienced atransition from sustained to sudden drought, while Inner Mongolia continued to experience drought. (2) During the same period, the 500hPa geopotential height field showed a two trough and two ridge pattern at mid to high latitudes. The western Pacific subtropical high pressure abnormally extended westward and uplifted northward, and the Rossby waves at mid latitudes in Eurasia were abnormally weak, resulting in a weakening of the influence of flat westerly winds and cold air in mid to high latitudes, resulting in less precipitation in the southwest and eastern Inner Mongolia, leading to regional drought. (3) In the first half of 2023, the winter La Niña event shifted to the spring El Niño event, resulting in weak convective activity in the southwest region and triggering sustained hot and dry weather; The distribution of sea surface temperature sensitive areas in Inner Mongolia has led to the stability of its upstream high-pressure ridge, resulting in drought and limited rainfall in the eastern region of Inner Mongolia.

Drought is one of the natural disasters with the widest global impact. The anomalous drought and heatwave event that occurred in the Yangtze River Basin in summer of 2022 is not only of high intensity but also of long duration, it is a rare and significant drought event leading to very serious socioeconomic impacts in China. In view of the extreme nature of this event, this paper reveals the possible influence of atmospheric circulation and external forcing anomalies on this drought event based on an objective analysis of the evolutionary characteristics of this event. It is found that the meteorological drought index and soil moisture monitoring results consistently indicate that this drought event started to appear in June, developed rapidly in July, and further expanded and intensified in both extent and intensity in August. At the same time, the overall temperature in the basin was high, with the number of high temperature days exceeding 40 days in some areas. In addition, anomaly of evapotranspiration over the basin in summer was the second highest on record since 1960, second only to the high temperature drought event in 2013, which further exacerbated the degree of water deficit in the Yangtze River Basin. From the perspective of circulation characteristics, the abnormal intensifying and westward extension of the western Pacific subtropical high pressure, the small area and weak strength of the polar vortex and the intensifying and eastward shift of the South Asian high pressure in summer jointly led to weak water vapor transport conditions and prevailing sinking air currents in the Yangtze River Basin, making the overall conditions unfavorable for the occurrence of precipitation. The persistence of the La Niña event, the appearance of negative Indian Ocean Dipole (IOD) and the persistence of the negative snow cover anomaly in the northwestern Tibet Plateau in spring may be the main external forcing factors leading to the circulation anomaly in this summer.

Based on the intensified hourly rainfall observation data of regional automatic weather stations, the characteristics of extreme precipitation from May to September during 2008-2017 in southwestern Hubei was analyzed by using percentile method. Satellite cloud photograph TBB data and NCEP reanalysis data with 0.5°×0.5° spatial resolution were adopted to analyze the causes of typical cases. The results are as follows: (1) The degrees of extreme precipitation at different stations were not comparable because of large difference in threshold ranges between hourly heavy rainfall and daily extreme precipitation. The stations with high frequency of hourly heavy rainfall and heavy rainstorm mainly distributed around the mountains with topographic convergence and uplift. Hourly heavy rainfall mainly occurred during the period of 00:00-03:00 and 16:00-19: 00. (2) Most of the extreme precipitation in southwestern Hubei occurred near Hefeng with large altitude difference. Low-level jet flow and topographic effect caused the back propagation of mesoscale convection system during the eastward migration process, which led to long duration of precipitation and large accumulated rainfall. (3) The thermodynamics and vertical structures were different for the extreme precipitation processes in different periods. For warm sector extreme precipitation in June, thermal effect dominated and the upper layer systems developed before the lower. Dynamic effect was main for extreme precipitation in September, in which frontal zone was obvious, and the whole system strengthened.

This paper uses YHGSM 0．25°×0．25°high resolution numerical products data as the background and does experiments for a month(from July 1 to 31，2009)in Chinese region with the WRF mode and WRF data assimilation system．The experiments were divided into 3 groups:no data assimilating，assimilating conventional data and assimilating ATOVS satellite data，then made the situation field tests and gave the TS scores．The results showed that the average error of geopotential height field and temperature field at both high－level and middle－level improved over time in the group 2 and the group 3 compared with that of the group 1 experiment．The specific humidity of the group 3 experiment at middle－level got better results in the early forecast and the improvement at other levels was not obvious．Precipitation forecast comparison shows that the group 3 experiment improved the TS score in the early forecast．

This paper analyzed the continuous detecting data ofLanzhou CINRAD /CC Radar abouta hailprocess occurred in Dingxi on July 18, 2008, summarized themain characteristics of the radarproducts during this hailprocess such as reflectivity, radial velocity,RCS vertical section, vertical integrated liquid content and so on. Then it discussed the detection methods for monitoring hail by DopplerRadar, found out the typical echo characteristic of supercell storms such as hook echo, bounded weak echo region(BWER),echowal,l suspended echo, obvious influx nick, existingmesocyclone etc., and summed up some informationwhich are good fornowcasting ofhai,l such as severe change ofVIL, corresponding relationship ofET and hailprocess, obvious three-body scatter characteristic and so on, these information will be of great value for us to detect severeweather events by radar.

Firstly,the working p rincip le and measurement p recision of the Airda - 3000Q type atmospheric wind p rofiler (AWP) were introduced. Then, a contradistinctive analysis on the wind p rofile data acquired by both AWP and synchronous balloon sounding was conducted to estimate the reliability ofAWP for detectingwind field. The results show that under the stable weather condition, the p rofiler’s detection ofwind direction and wind speed had some deviation compared by the balloon’s detection from the ground to 200 m height due to the detecting blind spots of the AWP and the ground clutter, but above 200 m, both wind field p rofiles correlated well;Under the comp lex weather condition, theirwind p rofiles had obvious deviation because the wind information on the different height acquired by AWP is a temporal average of wind field in a time period, but the wind data measured by sounding balloon on a specific height is the instantaneous value while balloon passed by.