龙门山北段北川暴雨天气成因浅析

Analysis on the Cause of Rainstorm Weather in Beichuan

利用NECP FNL全球再分析资料和四川省区域自动站降水资料,选取北川羌族自治县2016~2019年8次典型暴雨天气过程,对暴雨过程的环流背景、水汽条件、动力条件、热力条件进行诊断分析,结果表明:(1)北川以地形暴雨为主,多夜雨,短时强降水特征显著。(2)暴雨环流形势以“东高西低”和“两高切变”型为主,低涡、短波槽和副热带高压相互作用,近地面川东及重庆南部常维持热低压,与西北路径经青藏高原入侵的冷空气交汇对峙。(3)对于全域性暴雨,850hPa低空急流多偏南,轴中心位于106°E,若以暖平流为主,则降雨量级大;对于区域性暴雨,850hPa低空急流不明显,700hPa急流位置偏北,强度偏弱,冷暖平流相当。(4)北川常处于水汽通量辐合中心,尤其是大暴雨和特大暴雨发生时北川地区垂直速度和垂直螺旋度均明显增大;同时,105°~110°E低空表现为高温高湿,而高空表现为干冷位势不稳定,雨区位于能量锋区边缘。

Based on the global reanalysis data of NECP FNL and the precipitation data of regional automatic stations in Sichuan Province,eight typical rainstorm weather processes in Beichuan Qiang Autonomous County from 2016 to 2019 were selected to diagnose and analyze the circulation background,water vapor condition,dynamic condition and thermal condition of the rainstorm process.The res-ults show that:(1)Beichuan is mainly characterized by topographic rainstorm,multi-night rain and short-term heavy rainfall.(2)The cir-culation pattern of rainstorm is mainly'high in the east and low in the west'and'two high shears'.Vortex,short wave trough and sub-tropical high interact with each other.Near the ground,the thermal low pressure in eastern Sichuan and southern Chongqing intersects with the cold air invaded by the northwest path through the Tibetan Plateau.(3)The 850 hPa low-level jet of the global rainstorm is mostly southward,and the axis center is located at 106°E.If the warm advection is dominant,the rainfall level is large.850hPa low level jet of the regional rainstorm is not obvious,700hPa jet position is north,the intensity is weak,cold and warm advection is similar.(4)Beichuan is often located in the convergence center of water vapor flux,especially when the heavy rain and extra-heavy rain occur,the upward vertic-al velocity and vertical helicity increase significantly in Beichuan.At the same time,the low altitude area of 105°~110°E is a high temper-ature and high humidity area,while the high altitude area is dry and cold potential and unstable.,the rain area is located at the edge of the energy front area.