Numerical Simulation And Mechanism Research Of Warm-sector Precipitation Over Jilin,Northeast China

This study simulated a warm-sector rainstorm event that occurred in Yongji,Jilin province on July 13 2017,which reproduced the development process that include the initiation of convective cells and linear system,organized development and the stages that form bow echo;based on these data,the cloud microphysical characteristics of the mesoscale convective systems were analyzed,and then discussed the possible cloud microphysical mechanisms causing the warm-sector precipitation.The conclusions are as follows:(1)This precipitation process in the Yongji occurred in a favorable multi-scale environmental configuration dominated by the northeast cold vortex;the mesoscale system convective cell in the warm-sector precipitation was triggered mainly at the coincidence zone between the ground convergence line formed by the narrow tube effect of the terrain and the shear line on the low layer;After the cell was triggered,it generated waves and propagated upstream and downstream,the superposition of the updraft,which belonged to the waves and the shear line on the lower atmosphere,can enhanced the vertical motion and the linear convection group was triggered.(2)The mesoscale systems was mainly the cold cloud systems,the large distribution of ice provided sufficient condensation nodules for this precipitation process.Diagnoses of the mass- and heat-hydrometeor budgets showed that the main source of rainwater was the accretion growth of cloud droplets,and the main sink was the collection of raindrop by ice during the triggering and organization of the precipitation system;while the main source of rain in the bow-shaped echo stage was the melting of radon,the main sink term were the evaporation of rainwater in the lower layer and the collection of rainwater by the graupel in the upper layer.The main heat source of warm-sector precipitation was the latent heat release from condensation of water vapor,and the main cooling term was the evaporation of rain and cloud water.In the bow-shaped echo stage,confluence of the inflow at the front and the backward inflow above the cold pad on the ground bring water vapor into the upper layer,the collection of raindrops by ice graupel made the content of graupel significantly increased.During the falling-off of graupel,because it passed through heating area with a long path and high temperature caused by water vapor evaporation,the melting speed of graupel was fast and caused the warm-sector rainstorm.(3)The horizontal component of the wet potential vortex had a good corresponding relationship with the accumulated precipitation three hours later,and it has certain significance for the prediction of precipitation in warm regions.