秦岭及周边地区暖季降水日变化及其成因分析

Diurnal Variations and Causes ofWarm Season Precipitation in Qinling and Surrounding Areas

利用三源降水融合资料和欧洲中期数值预报中心ERA5逐小时再分析数据,分析暖季秦岭及周边地区的降水日变化特征及可能的成因。研究表明:暖季秦岭南北降水日变化存在显著差异,秦岭南部降水日峰值主要是盆地地形影响下的夜雨,秦岭北部降水日峰值则是午后黄土高原上的昼雨。青藏高原东部延伸区、黄土高原等大地形对研究区域长、短时降水的空间分布贡献显著;秦岭南部短时降水频率高,但L3级降水强度相对较低,北部L3级降水频率低、强度大。盆地地形作用下夜间的山风与青藏高原南侧地形槽前定常西南暖湿上升气流叠加,800 hPa以上上升运动异常加强,形成多个铅直次级环流,是秦岭南部夜雨特别显著的重要原因;而白天受谷风的作用,使得地形槽前上升气流减弱,昼雨相对较少。午后热力作用加强,南风上升气流与中上层西北风下沉气流在700 hPa附近交汇,使得秦岭北部黄土高原午后强降水异常多发。

Based on three sources(automatic weather station observation,retrieve precipitation of satellite and weather radar)precipitation fusion data,the ERA5 reanalysis data from European Centre for Medium-range Weather Forecasts(ECMWF),the diurnal variation of warm season precipitation and its probable cause over Qinling and surrounding areashas been revealed.Results show that diurnal variations of precipitation on both sides of Qinling in the warm season were significantly different,affected by the topography,diurnal peaks of precipitation amount and precipitation frequency in the southern Qinling occurs at night and the north occurs at afternoon.The spatial distribution of long and short duration precipitation is significantly affected by the large terrain,the frequency of short-term precipitation in the southern Qinling is very high,but the precipitation intensity is relatively small,while the frequency of short-term precipitation in the northern Qinling is low but the intensity is very large.Mountain winds and the southwest warm and humid updraft air of terrain trough affected by the Tibetan Plateau over played is an important reason for the frequent occurrence of night rains in the southern Qinling.Affected by the valley wind circulations during the day,the updraft airweakened in the front of the terrain trough,itmakes the daytime precipitation less.The local heating of Loess Plateau,updraft and downdraft air intersection around 700 hPa,which causes the heavy rainfall more frequent in the northern Qinling in the afternoon.