Effects of Terrain and Landmass Near Fujian Province of China on the Structure and Propagation of a Long-Lived Rainband in Typhoon Longwang (2005): A Numerical Study

摘要

A ~14-hr long-lived spiral rainband in Typhoon Longwang (2005) produced catastrophic rainfall in Fujian Province of China on 2 October 2005. In this study, the effects of terrain and landmass near Fujian on the structure and propagation of this rainband are investigated through high-resolution numerical simulations. Results show that although the terrain and landmass near Fujian played a marginal role in the formation of the rainband, both greatly affected the structure and propagation of the rainband. Namely, convection in the upwind sector of the rainband tended to be maintained and locked up near the coastline in the control experiment with both the terrain and landmass near Fujian retained,but shrank more inland with the terrain near Fujian flattened, and further inland with the landmass near Fujian replaced by the virtual ocean. It is found that due to the land-sea surface roughness contrast, the upstream tangential winds from ocean would be substantially decelerated over land and thus induced a local subgradient force onshore near the coastline. The radially inward agradient force and the subsequent surface friction helped maintain the moisture convergence, and thus convection and the cold pool in the upwind sector of the rainband near the coastline. Although the orographic lifting and blocking effects were found to be marginal to the moisture convergence in the rainband, the terrains near Fujian enhanced the deceleration of surface winds, enhancing the effect of land-sea surface roughness contrast on low-level moisture convergence and thus the lockup of the upwind sector of the rainband.