大气热源对高原低涡不同发展阶段的影响——2013年7月个例分析

Effect of Atmospheric Heat Source on the Tibetan Plateau Vortex During Different Developmental Stages—A Case Study in July 2013

高原低涡是夏季青藏高原(简称高原)及其下游地区的主要降水系统。本文利用ERA5逐小时再分析资料、FY-2E卫星云顶亮温逐小时数据和TRMM 3 h降水资料,对2013年7月19~21日活动于高原的一次低涡过程进行了诊断分析。此低涡在高原期间的活动时间长达56 h,将其分为初生、发展及移出高原前三个阶段,着重分析了高原大气热源在低涡不同阶段的关键作用和机理。结果表明:此低涡在发展过程中表现为阶段性增强的特征,位势涡度倾向方程诊断发现非绝热加热的垂直梯度是造成低涡发展增强的主要因素,即非绝热加热极值所在高度的下方和上方分别有正的和负的位涡制造,从而加强了低层的气旋和高层的反气旋。进一步分析可知大气热源在低涡发展过程中也表现出阶段性增强的特征,最大值出现在正午时段,且在低涡移出高原前阶段最强。低涡的生成与地面暖中心有关,这归因于地表感热加热的作用;而低涡的后续发展则主要依赖于凝结潜热加热,加热高度位于对流层中层,这主要是由垂直运动将低层的水汽集中到中层,产生水汽凝结所致。

The Tibetan Plateau(TP)vortex(TPV)is the main precipitation system in summer over the TP and downstream regions.This study analyzes a TPV case from 19 to 21 July 2013,based on high-resolution ERA5 reanalysis,the temperature of black body(TBB)obtained from the Fengyun-2E(FY-2E)satellite,and precipitation amount from TRMM(Tropical Rainfall Measurement Mission).The TPV case keeps active on the TP for about 56 h,which can be divided into three stages:Initial,development,and moving-out.Further,the roles of atmospheric heat sources in TPV during different stages and the related mechanisms are investigated.The results show that the TPV intensity increases with fluctuations.Furthermore,by diagnosing the potential vorticity(PV)tendency equation,it was found that the vertical gradient of diabatic heating is the main factor causing TPV development,i.e.,a positive(negative)PV is produced below(above)the height where the maximum center of diabatic heating is situated,strengthening the low-level cyclonic and high-level anticyclonic circulations.Further analyses indicate that the atmospheric heat source increased with fluctuations,with the maximum value appearing at noon and the strongest in the moving-out stage.Notably,the formation of TPV is related to the surface warming center driven by surface sensible heat,while its enhancement is mainly dependent on the latent heat of condensation.Furthermore,the main contributor to the latent heat is analyzed as a vertical transport of water vapor that promotes TPV development.