基于TRMM卫星探测的夏季青藏高原降水和潜热分析

Summer Precipitation and Latent Heating over the Tibetan Plateau Based on TRMM Measurements

青藏高原对东亚大气环流、气候变化及灾害性天气的形成和发展都有重要的影响。本文利用热带测雨卫星(TRMM)探测结果、GPCP降水资料,研究了夏季青藏高原降水和潜热特点。GPCP资料分析结果表明,夏季青藏高原降水主要集中在它的东南部,7月和8月雅鲁藏布河谷及其以东的横断山脉地区降水显著,平均最大雨强达7 mm/h;而TRMM测雨雷达(PR)探测结果指出念青唐古拉山北侧存在一降水大值区,强度近3 mm/h;GPCP给出的地表降水率较TRMM测雨雷达探测结果高出一倍以上;夏季高原西部的平均降水率小于4 mm/h(GPCP)/2 mm/h(TRMM PR)。TRMM PR探测的统计结果分析表明,高原降水云"雨顶"(Storm Top)较周边地区高出2 km^4 km,如同"塔"状分布。研究结果还指出因地表海拔高,TRMM PR的降水类型分类方法不适用于青藏高原地区;根据降水廓线的特征,文中定义了青藏高原三种降水类型:深厚强对流、深厚降水和浅薄对流,并通过标准化廓线方法,指出了不同类型降水廓线之间的差异及其与周边地区降水廓线的差异。文中还给出了高原夏季总潜热分布及平均廓线,指出了高原潜热平均廓线与周边地区的差异;研究结果表明夏季高原降水具有强烈的日变化,降水峰值出现在午后地方时16点左右,这些降水多以零散块状水平分布,而在垂直剖面上呈"馒头"状分布。统计结果还发现青藏高原上对流活动较周边地区活跃,高耸的对流活动所形成的"云塔"如同"天梯",使得低层大气中的高水汽含量和低臭氧含量空气向高空输送,进而造成对流层上部和平流层低层水汽大值区和臭氧低值区。

The unique topography of Tibetan Plateau （TP） throws a great impact on ambient circulation, climate changing and the evolution of severe weather in East Asia. Jointly using measurements torm Tropical Rainfall Measuring Mission （TRMM） and Global Precipitation Climatology Project （ GPCP）, this study pays special attention to the aspects of summer precipitation and latent heat over the TP. A maximum of surface rainrate approaching 7mm/h in southeastern TP around Yarlung Zangbo Canyon is revealed by GPCP, while the maximum is only 3mm/h occurring at northern Nyaiqentanglha Mountains indicated by TRMM. The summer average of surface rainrate over the western TP, less than 4mm/h, derived from GPCP is also approximately two times that from TRMM. The storm top over TP presents itself as a tremendous tower that is 2 - 4kin higher than those in surrounding areas. Particularly, three categories of precipitation over TP are defined according to vertical profiles, named as deep strong convective, deep weak convective and shallow convective precipitation, since TRMM operating precipitation classification is proved to be improper for precipitation over TP. The differences of normalized precipitation profile between the three precipitation categories are clarified and a comparison is also conducted for geographical differences on latent heat profiles. The diurnal variation of TP precipitation is remarkable where the peak occurs at 4pm. It is also found that TP precipitation generally arises scatteredly associated with small horizontal scale and a vaulted vertical section. Furthermore, statistical results indicate stronger convective activities over TP than over adjacent areas. The high - level convection acts as a ladder to expediently transport upward parcels of air with much water vapor but little ozone, which results in high vapor content and low ozone content in the upper troposphere and lower stratosphere around TP.