A numerical study of convection initiation in Southwestern Xinjiang, Northwest China

Convection initiation (CI)  occurred near the oasis region surrounded by gobi desert in the Southwestern Xinjiang, Northwest China is investigated using a real-data, high-resolution Weather Research and Forecasting (WRF) simulation. Observations revealed that many CIs occurred successively near oasis region, some of which developed significantly in both size and intensity and eventually become a strong mesoscale convective system (MCS). The WRF simulation captured the general features of the CIs and MCS. Lagrangian vertical momentum budgets were conducted along the backward trajectories of air parcels within three convective cells. The total vertical acceleration was decomposed into dynamic and buoyant components. The results showed that the buoyant acceleration played a decisive role for about half of the air parcels during the CI, which was contributed by the dry air buoyancy. However, the dynamic acceleration mainly contributed during the CI for about one fourth of the air parcels. The dynamic acceleration can be further decomposed into five terms based on anelastic approximation. The positive dynamic acceleration was mainly caused by the vertical twisting term associated with the mid-level vertical shear, while the extension term contributed negatively to the dynamic acceleration. The other two terms related to horizontal curvature and height variation of density were negligibly small.