The Variation Characteristics of Mesoscale Convection System in a Severe Convective Torrential Rain over the Northeast Slope of the Qinghai-Xizang Plateau

Abstract

A rare torrential rain occurred in the northern Linxia and western Lanzhou on the northeast side of the Qinghai-Xizang Plateau from 20:00 （Beijing Time， the same as after） on 22 to 08:00 on 23 July， 2018， with the maximum total rainfall of 176.8 mm and the maximum hourly rainfall of 61.6 mm.Based on the data of satellite， CINRAD， automatic weather stations and reanalysis data， the occurrence and development characteristics of the mesoscale convective system （MCS） causing severe convective rainstorm and its trigger mechanisms were analyzed.The results show that： （1） Severe convective rainstorms occurred under the favorable configuration of a warm and humid air flow of the periphery of Western Pacific subtropical high combined with multiple zonal fluctuations driving cold air eastward.The environment of high temperature and humidity created favorable conditions for the occurrence of severe convective rainstorm.（2） Two MCS developed successively caused severe convective rainstorms in the northern Linxia and western Lanzhou.The isolated convective cloud clusters strengthened and merged into the first stage of MCS.The MCS spreading to the southwest and the clouds moving from the Gannan plateau to the northeast gradually merged into the MCS of the second stage in the heavy rain area.Heavy rainfall over 10 mm·（10min）-1 occurred at the edge of cloud cluster in the upwind direction， and the heavy rainfall is closely related to the development of convective cloud clusters.（3） During the severe convective rainstorm， the strong echo in the first stage had obvious backward propagation characteristics.The strong convective cell had a high frequency of impact on the heavy rainstorm area， and the significant "Train Effect" moving from south to north caused intermittent heavy rainfall lasting more than 6 hours.（4） Mesoscale wind speed pulsations in the boundary layer， surface convergence line and special terrain are the main factors that triggered the occurrence and development of mesoscale convective systems.The formation， maintenance and movement of the surface mesoscale convergence line had a good correspondence with the location of heavy rainfall.

Keywords

• the northeast slope of the qinghai-xizang plateau
• severe convective torrential rain
• mcs
• train effect