基于TRMM PR和VIRS探测的青藏高原夏季横切变线云降水个例分析

Analysis on Precipitation and Cloud of Transverse Shear Line Cases in Summer over Qinghai-Tibetan Plateau based on TRMM PR and VIRS Detection

利用热带测雨卫星(TRMM)搭载的测雨雷达(PR)和可见光/红外扫描仪(VIRS)探测结果的融合数据,结合ECMWF再分析资料,分析了1998年6月22日(轨道号:03257)和2011年7月3日(轨道号:77642)两个夏季青藏高原横切变线个例的云降水特征。结果表明,高原横切变线降水回波顶高度多分布于4~10 km,局部可达12 km,其降水强度85%以上为0. 5~2. 5 mm·h^-1,仅局部达20 mm·h^-1以上。云粒子尺度(云粒子有效半径)分布较为均匀,多数尺度分布在10~30μm之间,尺度峰值均为16μm,局部尺度可达30μm以上,液态水路径的峰值均在1. 50 kg·m^-2左右。降水回波顶高度最高可达17 km,近地面降水回波强度最大可达50 d BZ,降水回波主要出现在6~10 km高度,其强度大体在17~25 d BZ。横切变线降水中浅薄降水、深厚弱对流降水、深厚强对流降水的垂直结构差异明显,并相应产生不同的近地面降水强度。

The characteristics of precipitation and cloud of two transverse shear line cases in the Qinghai-Tibetan Plateau on June 22,1998( orbit number: 03257) and July 3,2011( orbit number: 77642) were investigated based on combining measurements of the tropical rainfall measuring mission( TRMM) precipitation radar( PR) and visible and infrared scanner( VIRS) together with European Centre for Medium-Range Weather Forecast( ECMWF) reanalysis data. Results indicate that storm top height in the region near the transverse shear line over the Qinghai-Tibetan Plateau varies from 4 km to 10 km and only in some region the storm top height reaches about 12 km. Approximately 85% rain rate near the transverse shear line region over Qinghai-Tibetan Plateau varies from 0.5 mm·h^-1 to 2. 5 mm·h^-1 and greater than 20 mm·h^-1 only in small scale area. It is apparent that the area is mostly sprinkle. The spectral distributions of effective particle radius( Re) and liquid water path( LWP) are different. The distribution of cloud particle dimension,namely the effective particle radius of cloud particle is evenly distributed,mostly varies in 10 ~ 30 μm and the maximum of effective particle radius is 16 μm. And the sizes of cloud particle is 5 μm smaller than that in oceanic cloud system in a general way. It is noticed that the effective particle radius of cloud particle may up to 30 μm in some region. For the LWP( liquid water path),the maximum is 1. 5 kg·m^-2. And according to the previous work,it is known that the LWP is 0. 3 kg·m^-2 less than that in frontal precipitation cloud system in eastern China. The storm top height can reaches about 17 km and the maximum echo of near surface rain rate is 50 dBZ,the precipitation echo mainly exist in 6 ~ 10 km and 17 ~ 25 dBZ. The differences in precipitation vertical structure between shallow precipitation,deep weak convective precipitation and deep strong convective precipitation are evident in the transverse shear line region over Qinghai-Tibetan Plateau and show different near surface rain rate. There also some differences exist in precipitation vertical structure of precipitation cloud with different phases near the cloud top,but the differences in near surface rain rate are not evident.