The Characteristics Of Environmental Conditions Of Severe Short-range Precipitation And Case Studies

In order to analyze the spatial and temporal distribution of Chinese severe short-rangeprecipitation, a statistical study based on the rainfall data of more than2,000national weatherstations from2005to2009is conducted. The conclusions are: These areas, containing theEastern Tibetan Plateau, northeastern of Sichuan Basin, the coastal areas of Guangdong,Guangxi, Fujian, Jiangsu, Zhejiang province, the middle and lower reaches of the Yangtze River,Yellow River, are the most frequent regions for the short-term heavy precipitation; May toAugust, especially July in a year, and the15-22o'clock in a day are the times when theshort-term heavy precipitation appears frequently.In order to analyze the characteristics of environmental conditioins of severe short-rangeprecipitation, large hail, severe thunderstorm winds and the co-existence convective weather,understand their similarities and differences, and thus, identify the type of impending severeconvective weather based on the potential forecasting, a statistical study based on the relatedsounding data during2002-2011is conducted. The conclusions are:1) Differences of theenvironmental background are relatively significant between the pure short-term heavy rain(including type I, II) and large hail or severe thunderstorm winds. Compared with the latter, theformer has smaller temperature-difference between700hPa and500hPa, which is the same asthat between850hPa and500hPa, weak vertical wind shear, relatively high altitude of0℃,-20℃and balance layer, and larger dew point temperature at the ground and the height of1.5kmabove it. The type I (accounting for the majority of the short-term heavy rain), with its higherrelative humidity at the whole layer, is obviously different from the others.2) Co-existencesevere weather is similar to the large hail weather and the severe thunderstorm winds weather, inthe following aspects: the shape of stratification and dew curve, the value of CAPE and the0-6km vertical wind shear. That is: there is an obvious dry layer at the middle troposphere andlarger value of CAPE and vertical wind shear. However, the co-existence weather has relativelyhigh altitude of balance layer, larger dew point temperature at the ground and the height of1.5km above it and smaller temperature-difference between850hPa and500hPa. In theserespects, co-existence weather is closer to the pure short-term heavy rainfall.The detailed case studies are made, including Huaixi extraordinary storm of Anhuiprovince on July8,2007, the local heavy precipitation in Beijing on August6,2007and the short-range precipitation in Guangzhou on May7,2010, based on the routine upper-air andsurface observation, the Doppler weather radar data, FY-2C,2E Satellite imagery (infraredimages).The heavy precipitation in Anhui case had a relatively long duration, and zonaldistribution form west to east, across a large range. This case, occurring in the Meiyu period,was generated by low-level shear line with the Subtropical high retreating south and theSouthwest jet enhancing; Beijing local heavy precipitation occurred at the junction of Haidianand Chaoyang districts for one hour. It was generated by the dew point front in the mesoscaleconvergence field of the surface wind.The Guangzhou case, occurring in the first flood period ofSouth China, was affected by low-level shear line and triggered by the weak, shallow, cold air,with the forward-tilting trough passage.The Anhui case and Guangzhou case all occurred by the direct impact of the meso-andmicro-scale synoptic systems in the favorable conditions of large-scale weather situation. Inthese two cases, there is a shear line and southwest jet which transports water vapor and unstableenergy to the rainfall area in the low-level. The rainfall area is located in the wet and warmregion and has favorable humidity condition of the whole layer of atmosphere. And near theprecipitation area, there is a region of unstable atmospheric stratification, which is conductive tothe continual generation of the convective systems. Differently, there is a high-level jet and largevertical wind shear in the Guagnzhou case, which is in favor to the generation and maintenanceof the highly organized severe convective storm. In the Beijing case, the rainfall area lies in theedge of warm and moist tongue, which is a strongly unstable region in synoptic meteorology.In the Anhui case, the main feature of the radar echo is a banded echo from west to east,corresponding to the severe rainfall area, and during the maintenance of the heavy rain, thebanded echo stays without obviously moving. The main process of the echo formation is: thenew convective cells are produced constantly in the west and southwest of the rainfall area,move toward east or northeast, and then enhanced in the process of echo moving and merging.In the process of the echo band evolution, there is a formation of herringbone echo. The mainreason for the heavy precipitation is "train effect". In the echo evolution of Guangzhou case,there is also a banded echo caused by the convergence of direction and speed in the wind field.The strong echo band, corresponding to the convergence line in the wind field, is relatively long,narrow, and moves south. In the field of radar radial velocity, a number of small and meso-scalevortex can be found, the position of which corresponding to the supercell storm. Similar to theAnhui case, in the Guangzhou heavy rain process, the convective cells, moving from theunstable region in the west and northwest, constantly merge into the banded echo and form the"train effect", cause the short-term severe precipitation. Beijing local heavy precipitation is caused by the stagnation of supercell storm between Haidian and Chaoyang district. In the fieldof radar radial velocity, the mesocyclone is wrapped in the supercell storm. In the evolution ofradar echo, the three-body scattering 'spike' echo and side lobe echo have also been detected inthe middle and upper elevation.