LAUSR

Based on regional model simulations of two distinct cases of the southwest vortex (SWV), this study compares their thermal and dynamic features and the differences in the evolution between a steady SWV and an eastwardly propagating SWV. The main results are as follows: (1) the rainfall period and area are determined by the location and movement of the SWV. The pathway of SWV movement is largely controlled by large-scale circulation, especially the subtropical high, which may have a blocking effect on the SWV. Generally, a stable subtropical high extending to the west has a blocking effect that leads to a steady SWV without much movement, while the eastward and southward retreat of the subtropical high favors the eastward propagation of the SWV; (2) both of the SWV types exhibit a vertical structure of convergence, positive vorticity, vertical motion maxima and a divergence center sequentially from the lower to the upper atmosphere. The localized thermal conditions are more important in steady SWV than in the eastwardly propagating SWV, while dynamic effects dominate in the eastwardly propagating SWV; (3) the strength of the convective activity of the eastwardly propagating SWV is significantly greater than that of the steady SWV due to the increased atmospheric instability. The vertical velocity, vorticity, divergence and surrounding wind speed are much greater for the eastwardly propagating SWV than the steady SWV, which favors the increased strength and high-level development of the eastwardly propagating SWV.