川西高原冰雹特征及天气形势分析

Characteristics of Hail and Weather Conditions in Eastern Tibetan Plateau,Western Sichuan

对2008～2017年阿坝州所有冰雹进行时空分布特征分析,对冰雹直径大于等于5mm的大冰雹个例进行天气形势、物理量分析。阿坝州的冰雹天气主要出现在3～10月,其中5月冰雹日数最多;日变化特征中降雹主要集中在14～19时;空间分布降雹主要集中在西北部海拔3000m以上地区。阿坝州大冰雹天气形势分为西藏高压型,西北气流型、高原切变型3种典型的类型,在大环境下,中低层切变辐合配合层结不稳定和地面冷空气影响,容易出现大冰雹等强对流天气。从环境参数看,有75. 8%个例达到上干下湿的不稳定状态;超过75%的大冰雹发生在400～600hPa垂直温度差17℃以上、500hPa为上升运动、BLI为负值的不稳定的大气层结中;所对应的400～600hPa垂直风切变大部超过8. 2m·s^(-1); CAPE值大部分都在325J·kg-1以上,CIN值大部分小于14. 4J·kg-1; SSI值大部分大于226. 4。

The temporal and spatial distribution characteristics of all hailstones, circulation patterns and physical quantities of large hailstones with hail diameters greater than or equal to 5ram were analyzed in the Aba prefecture from 2008 to 2017. The hail weather in Aba prefecture mainly occurred from March to October, with the most hail days in May. The dailychange characteristics of the hail is mainly concentrated at the 14：00μm. to19：00μm.. According to the spatial distribution, the hailstorms are mainly concentrated in the northwestern region above 3,000 m sea level. The hail weather conditions in Aba Prefecture can be divided into three typical types： high pressure type in Tibet, northwest airflow type, and high altitude shear type. Under large environments, the middle and low layer shear convergence and stratification are unstable and the cold air on the ground may affect the situation. Hail and other strong convection weather. From the environmental parameters,the 75.8% of the cases reached the unstable state of dry and wet. More than 75% of heavy hail occurs at 400 -600 hPa vertical temperature difference is above 17℃, 500hPa ascending motion, BLI is negative unstable atmosphere in the knot,and the corresponding vertical wind shear at 400 -600hPa exceeds 8.2m · s^-1 Most CAPE values in heavyhail days are above 325 J· kg^-1 , and CIN values are mostly below 14.4J · kg^-1. Most of the SSI values are greater than 226.4.