On the evolution of a long‐lived mesoscale vortex over the Yangtze River Basin: Geometric features and interactions among systems of different scales

Abstract

AbstractA long‐lived mesoscale vortex that caused extremely heavy rainfall events over the Yangtze River Basin was reproduced reasonably by the advanced Weather Research and Forecasting model. Using simulations, the three‐dimensional geometric features of the vortex, as well as the interactions between the vortex and its background circulations (BCs), were investigated. Results indicated that the geometry features of the vortex were closely related to vortex evolution, vortex‐related convection processes and precipitation, and vortex‐BC interactions. Growth in the horizontal size of the vortex favored its sustainment. The vortex tended to produce stronger convection processes and precipitation as its orientation became closer to the west‐east direction. The circulation budget revealed that the convergence‐related shrinking, the BC transport, and the effects caused by vortex movement were the dominant factors for vortex development. Divergence‐related stretching dominated vortex dissipation, and the transport effects associated with the BC and the eddy flows also accelerated this attenuation. The energy budget indicated that the vortex intensely interacted with its BCs during its lifetime. The BCs affected the vortex through downscaled energy cascade and mean transport; the eddy flow reacted to its BCs via upscaled energy cascade and eddy transport. Generally, the vortex had more dynamic than thermodynamic interactions with its BCs. BC effects were vital to the vortex evolution, whereas the variation in the BCs was predominantly determined by their own effects, although the reaction of the vortex‐related eddy flow cannot be ignored in the variation of the BC dynamical fields.