ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
The Role of Parallel Ridges and Valleys on the Southern Slope of the Daba Mountain in Mesoscale Convective Systems and Heavy Rainfall
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Abstract:
Using encrypted automatic station data, ERA5 reanalysis data, and radar detection data, this study analyzed the circulation pattern, mesoscale convective system organization and propagation characteristics, as well as the combined effects of Parallel ridges and valleys in Eastern Sichuan and Daba Mountain terrain on a heavy rainstorm process in the northern part of Parallel ridges and valleys in Eastern Sichuan and the southern foothills of the Daba Mountain from June 17-18, 2021. The result showed that the heavy rainstorm in the southern foothills of the Daba Mountain occurred under the background of a southwest low vortex, in the high temperature and humidity area before the cold front, and went through three evolutions of mesoscale convective systems. The new convection repeatedly formed at the southern end of the Parallel ridges and valleys in Eastern Sichuan, moved northward along the southwest airflow, intensified and organized, forming multiple northeast-southwest oriented convective bands parallel to the ridge-valley mountain range, and the precipitation was intensified by the train effect of convective cells and the superposition effect of rain bands. The terrain had an important impact on the boundary layer wind field, with a deflection phenomenon at the southern end of Parallel ridges and valleys in Eastern Sichuan, forming a ground convergence line distributed along the mountain, and a ground convergence center was maintained in the southern foothills of the Daba Mountain, with mesoscale convective systems organizing, developing, and moving along the ground convergence line. Namely, the new convection formed at the southern end and developed vigorously at the convergence center at the northern end. The windward slope terrain of the Daba Mountain had a blocking and converging effect on the transport of water vapor and energy, with a quasi-stationary east-west water vapor convergence belt and a high pseudo-equivalent potential temperature value area maintained at the southern foothills of the Daba Mountain. The boundary layer frontogenesis area, positive vorticity area, low-level convergence area, and strong upward motion area developed along the Daba Mountain, making the mesoscale convective systems in Parallel ridges and valleys in Eastern Sichuan move northward to the southern foothills of the Daba Mountain. The mesoscale convective systems stagnated there and develop vigorously, triggering this heavy rainstorm event in mountainous area.
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