2018年拉萨汛期两次强降水成因综合对比分析

A Comprehensive Analysis on the Causes of Two Heavy Rainfall during the Flood Season of year 2018 in Lhasa

文章利用常规气象资料、地面自动站资料、NCEP FNL1°×1°再分析资料和卫星云图对2018年7月和9月发生在西藏自治区拉萨市的两次暴雨的环流场背景场、物理量场和卫星云图进行分析。分析结果表明:两次暴雨过程均为高原切变线影响,南部印度半岛至孟加拉湾一带低值系统活跃,西南风为水汽输送提供了有利条件;两次暴雨过程中水汽通量散度最大值区域主要集中于550至700hPa;TBB梯度大的地方易产生强降水,存在对应的关系, TBB梯度最大的区域基本与降水出现的区域相对应,TBB绝对值最大处并不是TBB梯度最大处,当TBB绝对值最大,对流发展最旺盛时,上升运动强盛,地面降水不一定强,而当TBB值由最低值快速上升或者下降时,其对应站点的降水很强;都有明显的上升运动;低层都出现了中心值;上升运动高度较低非常利于暴雨发生。

The background field,physical quantity field of circulation and satellite cloud maps of two rainstorms in July and September 2018 in Lhasa of Tibet Autonomous Region were analyzed with using conventional meteorological data,ground automatic station data,NCEP FNL1 o×1 oreanalyzed data and satellite cloud maps.Two rainstorms processes in July and September 2018 was affected by the plateau shear line with active low value system in the belt of southern Indian Peninsula to Bengal Bay and a favorable conditions for water vapor transportation provided by the southwest wind.The maximum water vapor flux divergence during the period of two rainstorms was mainly concentrated from 550 to 700 hPa where large TBB gradient was prone to strong precipitation,and there was a corresponding relationship between them.The region with the largest gradient of TBB basically corresponded to the region where precipitation occurs.The maximum absolute value of TBB was not to be the largest value of TBB gradient.When the absolute value of TBB is the largest with the strongest convection,the ascending motion is strong so that ground precipitation is not necessarily strong.When the TBB value rises or falls rapidly from the lowest value,the precipitation is strong at the corresponding site.Both two rainstorms processes have obvious upward movements with central values occurred at lower layers and with a lower height of ascending movement that was very conducive to heavy rains.