青藏高原、中国东部及北美副热带地区夏季降水系统发生频次的TRMM资料分析

Analysis of Occurrence Frequency of Precipitation Feature over Tibetan Plateau,East China and Subtropical North America in Boreal Summer Using TRMM Data

利用1998—2011年夏季(6-8月)TRMM卫星资料分忻青藏高原(TP)、中国东部(EC)及北美副热带西部(WNA)和东部(ENA)降水系统的发生频次,定义降水系统为TRMM测雨雷达观测到近地面有降水的相邻像元组成的个体,即RPF(Radar Precipitation Feature),将RPF分为全体RPF、大面积RPF(面积>1000 km^2)和小面积RPF(面积不<400)km^2)3组,对比分析四个区域内各组的RPF个数发生频次和RPF像元个数发生频次,主要结果如下:(1)全体RPF的个数发生频次在青藏高原地区最高,北美东部地区最低;全体RPF的降水像元个数发生频次在中国东部最高,青藏高原最低。(2)四个区域内RPF发生频次的日变化主要为单峰结构,峰值出现在当地午后至傍晚,且大面积RPF的峰值时间晚于小面积RPF的;中国东部地区RPF降水像元个数发生频次则具有双峰结构。(3)RPF降水像元个数发生频次的分析结果与以往基于地面观测降水量的分析结果相似。

Using TRMM data from 1998 to 2011.occurrence frequency of radar precipitation feature(RPF)over Tibetan Plateau(TP).eastern China(EC),west subtropical North America(WNA) and east subtropical North America(ENA) in boreal summer(June—August) are comparatively analyzed.A RPF is defined as a three-dimensional object consisting of pixels with precipitation near the ground observed by the TRMM precipitation radar.For each region.RPFs are divided into three groups:all RPF.large RPF(area larger than 1000 knr).and small RPF(area less than or equal to 400 km^2).Occurrence frequency of RPF number and occurrence frequency of RPF pixel number in each group over each region are analyzed.The results are as follows:(1) The maximum and minimum occurrence frequencies of RPF number are over TP and ENA,respectively.In contrast,the maximum and minimum occurrence frequencies of RPF pixel number are over EC and TP,respectively.(2) Diurnal variations of occurrence frequency of RPF over the four regions mainly present a single peak in afternoon to late-afternoon,with the peak of the large RPF appearing later than that of the small RPF.In contrast,diurnal variation of occurrence frequency of RPF pixel number over EC presents double peaks.(3) Diurnal variations of occurrence frequency of RPF pixel number are consistent with those of rainfall based on rain gauge observations in previous literature.