四川盆地暖区暴雨特征分析

给出四川盆地暖区暴雨的定义,并根据天气形势和影响系统将其分为西南涡型、副热带高压边缘型、西南急流型和东南风型四类。然后利用2008—2018年5—9月常规和自动站逐时降水资料统计分析四类暖区暴雨的时空分布特征和降水性质,并选取典型个例,对暴雨中尺度特征和成因进行了分析。主要结论包括:四类暖区暴雨易发于山脉迎风坡、喇叭口地形、平原和丘陵山地不均匀下垫面附近。西南涡型和西南急流型暴雨范围广且成片,西南涡型暴雨主要位于盆地中部和南部,西南急流型暴雨主要出现在盆地中部到龙门山脉北段和大巴山脉;副热带高压边缘型和东南风型暴雨分散,主要出现在盆地西部;降水都具有明显的日变化,呈现为单峰型,夜间加强,白天减弱;暖区暴雨由对流性和稳定性降水组成,降水量级越大,对流性越明显,其中,副热带高压边缘型和东南风型对流性降水明显,西南涡型和西南急流型稳定性降水明显;暖区暴雨直接由β中尺度云团发展造成,西南涡型和西南急流型中尺度对流系统持续时间≥6 h,副热带高压边缘型和东南风型中尺度对流系统持续时间≤6 h,但四类暖区暴雨单站对流性降水(20~50 mm·h^-1)的持续时间一般不超过3 h,≥50 mm·h^-1的短时强降水维持时间不超过1 h,若超过1 h易造成极端降水事件,西南涡型和西南急流型容易出现极端强降水;四类暖区暴雨发生在高能高湿不稳定环境条件下,平均CAPE值超过1000 J·kg^-1,K指数在40℃左右,850 hPa平均假相当位温在85℃左右,平均比湿可达16 g·kg^-1。

Analysis of Warm-Sector Rainstorm Characteristics over Sichuan Basin

The warm-sector rainstorms over the Sichuan Basin were defined and classified into four types based on the synoptic situation,including the southwest vortex(SWV),the edge of subtropical high(ESH),the southwest jet(SWJ),and the southeast wind(SEW)types.By using the conventional and the hourly precipitation data of automatic weather station from May to September during 2008-2018,we statistically analyzed the spatio-temporal distribution of warm-sector rainstorms and the nature of precipitation as well as the mesoscale characteristics and causes for their formation.The major characteristics obtained from the research are that the four types of warm-secfor rainstorms usually occur in windward slope of mountain,bellmouth topography and near the uneven surface which is transitional zones between plain,hills and uplands,etc.The SWV and SWJ types have a large area,and the former mainly occurs in the middle and south of the basin and the latter from the middle of the basin to the north of Longmen Mountains and Daba Mountains.The ESH and SEW types are decentralized precipitation,and the precipitations usually occur in the west of the basin.All the four types of precipitation have substantial diurnal variation,showing a single peak type,which is strengthened at night but weakened during the day.The warm-sector rainstorms consist of stable and convective precipitations.The heavier the daily rainfall is,the more obvious convective nature the precipitation has,of which,the convective precipitation of ESH and SEW types is obvious,and the stable precipitation of SWV and SWJ types is obvious.The warm-sector rainstorms are directly caused by the development of MβCSs,the lifetimes of SWV and SWJ types are≥6 h,and those of ESH and SEW types are≤6 h.All the four types of convective precipitation(20-50 mm·h-1)last for no more than 3 h,and the flash heavy rain(≥50 mm·h-1)lasts for no more than 1 h,otherwise,it is very easy to cause extreme precipitation events.SWV and SWJ types are prone to extreme heavy rainfall.The four types of rainstorms occur in the unstable environment with high energy and high humidity.The average CAPE value is more than 1000 J·kg-1,K index is about 40℃,θse of 850 hPa is about 85℃,and the average specific humidity can reach 16 g·kg-1。