TRMM卫星对青藏高原东坡一次大暴雨强降水结构的研究

Structure analysis of heavy precipitation over the eastern slope of the Tibetan Plateau based on TRMM data

中文关键词:  暴雨  青藏高原  β中尺度  TRMM卫星  多普勒雷达

英文关键词:Heavy rain  Tibetan Plateau  TRMM  Doppler radar  Meso-β scale

中文摘要:

      利用热带测雨卫星（TRMM）探测资料，NCEP、ERA-Interim再分析资料，结合C波段多普勒雷达和其他地面观测资料，研究了2013年7月21日发生在青藏高原东坡的一次大暴雨强降水结构。结果表明，高能、高湿的不稳定大气在700 hPa切变线及地面辐合线的触发下产生了此次大暴雨，降水具有明显的强对流性质。从水平结构来看，降水系统由成片的层云雨团中分散分布的多个对流性雨团组成，对流样本数远少于层云，但平均雨强是层云的4.7倍，对总降水的贡献达到25.6%；以超过10 mm/h雨强为强度标准，3个20-50 km、回波强度在45-50 dBz的β中尺度对流雨团零散地分布在主雨带中，对应<210 K的微波辐射亮温区和 ≥ 32 mm/h的地面强降水；对流降水的雨强谱集中在1-50 mm/h，其中20-30 mm/h的雨强对总雨强的贡献最大，这与中国东部降水有着显著区别，而90%的层云降水的雨强均小于10 mm/h。从垂直结构来看，对流降水云呈柱状自地面伸展，平均雨顶高度随地面雨强的增强而不断升高（5-12 km），强降水中心区域的质心在2-6 km；降水廓线反映出强降水系统中降水主要集中在6 km以下高度范围，且降水强度在垂直方向分布不均匀，对流降水和层云降水的强度随高度升高的总趋势是趋于减弱，但在一定高度范围内，对流降水强度随高度升高而增大，并且在多个地表雨强廓线中都有体现。此外，地基雷达的探测结果也表明了强降水的低质心特点及显著的逆风区演变特征，这是对TRMM PR探测的验证和补充。

英文摘要:

      The horizontal and vertical structure of a heavy rainfall system occurred over the eastern slope of the Tibetan Plateau on 21 July 2013 has been studied by using TRMM data, NCEP-FNL operational global analysis data and ERA-Interim analysis data in combination with Doppler radar and other surface observational data.The result indicates that the heavy rainfall system, which was triggered by unstable stratification combined with 700 hPa shear line and surface convergence line, consisted of a main stratiform precipitation cloud cluster and several scattered convective precipitation clouds characterized by high precipitation intensity. Although the total amount of convective rainfall was less than that of the stratiform rainfall, averaged convective rainfall rate was 4.7 times larger than the stratiform rainfall rate and convective rainfall accounted for 25.6% of the total rainfall. The horizontal scale was about 20-50 km for a reference precipitation rate of 10 mm/h. The spectral distribution of convective rainfall intensity indicated that the rainfall intensity was largely concentrated within the range of 1-50 mm/h, and the rainfall with intensity of 20-30 mm/h made the greatest contribution to total rainfall. Meanwhile, almost 90% of the stratiform rainfall was below 10 mm/h. Vertically, the top of the heavy precipitation system could reach up to 12 km above the ground with a low core structure (below 6 km). Most precipitation occurred in the levels from ground to near 7 km and the distribution of precipitation rate in vertical was inhomogeneous. In general, precipitation decreased with increasing height, but within a certain range of height, convective precipitation increased with height. As a verification dataset and supplement for TRMM PR, Doppler radar observations also showed the characteristics of low precipitation center in this rainfall event.