Causal Analysis of a ShortTime Strong Rainfall Based on RMAPS and Observation Data
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Abstract:
An exceptional shorttime strong rainfall happened in the Beichen district of Tianjin at the midnight of 8 Aug 2017 and its intensity surpassed 70 mm·h-1. Using the methods of multidata superposition analysis, quantitative analysis of radar echo parameters, and lowlevel wind field retrieval, etc., RMAPS (Rapidrefresh Multiscale Analysis and Prediction System) products and various observation data are used to analyze this rainfall. The results indicate: (1) The multicell storms in the southern extremity of MβCS (Mesoβscale Convective System) during the backpropagation caused this rainfall. The merging process had an important impact on the structure and enhancement of the storm system. After merging, echo volume parameter 〖WTBX〗V〖WTBZ〗40 〖KG*3〗(the volume of the reflectivity above 40 dBz) increased by 23.3%. Before the rise of 〖WTBX〗V〖WTBZ〗40, variable parameter 〖WTBX〗F〖WTBZ〗V40-up6 (the change of strong echo volume of above 40 dBz above 6 km height in 6 min) suddenly dropped, indicating that the echo was about to develop explosively. (2) The ground convergence line formed by the cold pool outflow and surface southeast winds was the key to maintain the convective system; the low level wind shear also influenced the trigger and development of convection; accompanied by heavy rainfall, CAPE suddenly dropped from the peak and the low level vertical wind shear index α increased, indicating the relationship among unstable energy, vertical wind shear, and convection process. (3) The large value area of the instability parameter SWEAT had an early indication of the heavy rainfall area; the lead time was about 3 hours; and the location where the surface warmwet area from the Bohai Sea and pseudo equivalent temperature dense zone met was the focus of falling area nowcast.
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Supported by:Beijing E-Tiller Technology Development Co., Ltd.
Supported by:Beijing E-Tiller Technology Development Co., Ltd.