Analysis on Formation Reason of "0902" Blizzard in Northeast China

[Objective]The research aimed to analyze formation reason of ＂ 0902＂ blizzard in northeast China. [Method]By using timely observation data,NCEP reanalysis data and Doppler radar data at Baishan station,blizzard process in southeast part of northeast China during 12-13 February,2009 was analyzed. [Result]Snowfall zone of the blizzard process was wide,snowfall was more,snowfall gradient was big,and snowfall time relatively concentrated. These characteristics reflected that the blizzard process had significant convection characteristics. Baroclinic disturbance at high-altitude straight frontal zone and ground warm frontogenesis caused by eastward movement and northward advancement of North China low vortex at low altitude were the circulation characteristics in the process. Water vapor from the sea went northward as southwest airflow,and strongly converged in blizzard zone,which provided sufficient water vapor condition for the blizzard. Before heavy snowfall occurred,there was accumulation process of heat and energy. Conditional symmetric instability was main unstable mechanism of the blizzard. During heavy snowfall period,ascending branch of secondary vertical circulation at exit zone of high-altitude jet coupled with ascending branch of secondary vertical circulation of warm frontegenesis at low layer,inducing strong development of the vertical motion. Doppler radar intensity echo revealed that it was easy to generate blizzard in the area where echo intensity was consistently above 20 dBz. Strong wind velocity convergence zone at radical velocity field especially adverse wind zone was favorable for the generation of blizzard. [Conclusion]The research could provide reference for blizzard forecast in northeast China.

Analysis on the Disastrous Weather of Serious Drought in Northwest Hunan in Summer and Autumn of 2009

[Objective] The research aimed to analyze the disastrous weather of serious drought in Northwest Hunan in summer and autumn of 2009.[Method] According to the meteorological data in Zhangjiajie of Northwest Hunan during the drought period from June to September,2009,the disaster characteristics of continuous drought in summer and autumn were analyzed.Based on NCEP/NCAR 2.5°×2.5° reanalysis data,by using the climatic diagnostic method,the formation reason of serious drought was initially analyzed from the circulation characteristics in the middle and high latitudes,Western Pacific subtropical high,the abnormal characteristics of sea surface temperature in the equatorial Middle Eastern Pacific Ocean and the tropical system activity.[Result] The characteristics of serious drought in Northwest Hunan in summer and autumn of 2009 were the quick developed speed,wide influence range,long duration,big disaster loss and long high temperature time.The influence range,duration and harm degree were rare to see in the history.During the arid period(June-September),the atmospheric circulation was abnormal.The polar vortex in the northern hemisphere was weak,and the center was by north.It was two-trough-one-ridge type in the middle and high latitudes of Eurasia.The long-wave trough existed respectively near Balkhash Lake and from Sea of Okhotsk to the east coast in China.The long-wave ridge maintained from Lake Baikal to Central Asia and stabilized in 90°-110° E of Central Asia.From the middle dekad of June to the middle dekad of September,the westerly index increased.The zonal circulation was the main one in the middle and high latitudes of Eurasia.The cold air in the high-latitude frontal zone spread eastward with the small-amplitude fluctuation form along the latitude circle direction,and was difficult to pass the westerly barrier near 45° N to reach the low latitude.Meanwhile,Western Pacific subtropical high jumped northward to control Jiangnan and South China for a long time.The down airflow was prevalent.It was hot and rainless.The drought developed quickly.The sea surface temperature in the equatorial Middle Eastern Pacific Ocean started to rise in June,and it entered into El Nino state.When El Nino event of obvious temperature increasing started to appear in spring and summer,the plum rain amount was less in the middle and low reaches of Yangtze River in the year or next year.The probability was 80%.In El Nino year,the typhoon was less.In addition,for the influence of strong Western Pacific subtropical high,the landing pathway of typhoon was by east or south.The kind of typhoon had the small role for easing the drought in Northwest Hunan.[Conclusion] The research provided the theory basis for improving the prediction level of short-term climate and the understanding of extreme climate event.