Mechanisms of Convection Initiation in the Southwestern Xinjiang, Northwest China: A Case Study

Abstract

The mechanism of convection initiation (CI) occurring in the Southwest Xinjiang, Northwest China is investigated using quantitative budget analysis of vertical momentum for the first time. The Weather Research and Forecasting (WRF) model is used to reproduce and analyze the CI events. The observations showed that many CIs occurred continuously, with an intense mesoscale convective system eventually forming. The overall features of the CIs were well captured by the simulation. Lagrangian vertical momentum budgets, in which the vertical acceleration was decomposed into dynamic and buoyant components, were performed along the backward trajectories of air parcels within two convective cells. The results showed that the buoyant acceleration is the major contributor in both the slow and rapid lifting period of the CI, while the dynamic acceleration also showed a considerably positive effect only during the rapid lifting period. The buoyant acceleration during the slow lifting period was due to the warm advection generated by the radiative heating near the mountainous area on the south side of Tarim Basin in the afternoon. The buoyant acceleration during the rapid lifting period was from the latent heat release within the convective cell. Further decomposition of the dynamic acceleration showed that the vertical twisting related to the vertical shear of horizontal wind almost completely dominated the dynamic acceleration, while the horizontal curvature and extension showed very weak contribution. These findings provide some new insights into the roles of buoyant and dynamic forcing in the mechanism of CI in Southwest Xinjiang.