Analysis on Mesoscale Characteristics of a Rainstorm Process in Southeastern Gansu

  • WANG Baojian ,
  • KONG Xiangwei ,
  • FU Zhao ,
  • HUANG Yuxia
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  • Center of Lanzhou Meteorological Observatory, Lanzhou 730020, China

Received date: 2014-12-10

  Online published: 2016-12-28

Abstract

A rare torrential rainfall process which show the long lasting, strong concentrating and obvious mesoscale characteristics attacked southeastern Gansu province on 19-20 June 2013. This rainfall process consisted of 76.8% warm-area precipitation and low-level shear line precipitation. The causes of torrential rainfall and characteristics of mesoscale system are studied in detail by using conventional and unconventional observation data, NCEP reanalysis data, satellite data and Tianshui radar data. During the period of warm-area precipitation, it shows that the related circulation patternare similar to the typical circulation patternin this area. However, thelow-level wind shear shifts westward and the rainfall area isaffected by the warm air. High temperature and high humidity in the low level reduce the LCL and LFC height and weaken the lifting condition, corresponding withthecold trough in the middle level and then forming theunstable stratification. Besides, the low-level temperature inversion in the early stage isalso conducive to the accumulation of unstable energy. On the other hand, the low-level vertical wind shear, jet stream, and the effect of terrain elevation arelikely to play an important role in triggering and maintaining the convection there. The Strong convectioncorrespondsto the low-level jet stream. The convective cells mainly generateoverthe Huixian-Chengxian basin. The mesoscale convective system showthe characteristics of warm cloud precipitation, low-mass center, high efficiency, backward propagation and train effects. During the period of low-level shear line precipitation, the Wudu vortex located overthe northeast Qinghai-Xizang Plateau developsand strengthensdue to the warm advection, positive vorticity advection in the middle level, and low-level cold air intrusion. Besides, the thickness of wet layer increasesin the troposphere, and the thermal instability condition diminishessignificantly. As a result, the low-level shear line, vortex, and the ground convergence line formthe synoptic-scale upward movement, causing a wide range of stability precipitation. For both the warm-area precipitation and low-level shear line precipitation, there showthree obvious water vapor transportation channel in the lower troposphere:around the east of the Qinghai-Xizang Plateau from the bay of Bengal, through Central China from the South China Sea, and through East China from the east coast. Warm and moist air areconstantly transported to the torrential rainfall area from the tropical and subtropical and result thewater vapor convergence.

Cite this article

WANG Baojian , KONG Xiangwei , FU Zhao , HUANG Yuxia . Analysis on Mesoscale Characteristics of a Rainstorm Process in Southeastern Gansu[J]. Plateau Meteorology, 2016 , 35(6) : 1551 -1564 . DOI: 10.7522/j.issn.1000-0534.2015.00114

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