Gaoyuan qixiang (Oct 2022)
Analysis of Multi-scale Characteristics of Three Different Types of Heavy Rainfall in Sichuan Basin
Abstract
By using ERA-5 reanalysis data， combined with intensive automatic stations， conventional soundings， and networked radar data， a comparative analysis of three different rainstorm processes in Sichuan Basin during the summer of 2013 is made and the influence that different scale weather systems on the movement， propagation and structural evolution of convective systems under different atmospheric stability conditions and topography is revealed.Results show that： the heavy rain process occurred in the western of Sichuan Basin from 19th to 20th June （hereinafter referred to the Western Basin Type case） was triggered by the 700 hPa southerly warm and wet airflow that strengthened at night along the steep slope of the Chuanxi Plateau.The convective system appeared as a slender linear pattern along the plateau slope at the initial stage， then it was affected by the interaction between the convective cold pool along the edge of the basin and the low-level warm and wet southeast airflow.The mature MCSs（Meso-scale Convective Systems） manifested as a rightward shifting storm with backward propagation characteristics， which developed toward the middle of the basin and gradually moved away from the plateau topography.As the warm and wet inflow on the front side of the convection system significantly weakened， the convection system weakened and dissipated.The heavy rain process occurred in the central of sichuan basin from 29th June to 1st July （hereinafter referred to the Central Basin Type case） was a long-life history convective precipitation process， which was related to the evolution of the southwest vortex system.The convective system was triggered on the baroclinic front area outside the low-level shallow warm vortex （below 850 hPa） along the 700 hPa warm and wet tongue， and it was organized into a linear convection system along the left side of the low-level jet axis in the middle troposphere.After convection was generated， through the interaction between the outflow of the shallow cold pool generated from the southern part of the convective system and ambient warm and humid air currents， new convective systems were triggered and developed towards the area with high value θse.The convection system gradually evolved from "linear" to "arc-shaped".Later， as the vortex airflow tilted toward the middle troposphere， new convetions were continously trigerred by cyclonic convergent airflow on the pseudo-equivalent temperature front area， then the convective systems gradually evolved into a spiral rain belt distribution in the middle of the basin.As the low vortex centers in the middle and low troposphere gradually overlap with the height， the spiral convective rainband gradually shrinked toward the center of the low vortex and eventually disappeared.The heavy rain process occurred around the Sichuan Basin from 4th to 5th July（hereinafter referred to the Peripheral Basin Type case） was directly related to the process of cold air crossing the Qinling-Daba Mountains and intruding into the basin from the northwest side of the basin.The convection system was first triggered by the cold air along the steep topography of the western edge of the basin.As the cold air advanced to the south， convection systems moved to the topographical edge of the southwestern part of the basin.As cold air in the basin accumulated in the western part of the basin and expanded eastward in the lower layer， the convection in the middle troposphere above the shallow cold pad is unstable and warm Under the uplift of wet shear， the eastern part of the basin triggered an elevated thunderstorm and developed and organized along the shear line.
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