Mesoscale analyses of the Sichuan flood catastrophe, 11-15 July 1981.

Abstract

During the period 11-15 July 1981,heavy rainfall occurred over the Sichuan basin in China, resulting in severe floods that took a large toll in human life and property damage. Synoptic analyses indicate that early in this period the southerly monsoon flow was particularly strong near the basin because of a favorable positioning of the Pacific subtropical high and the Indian monsoon depression. Mesoscale analyses show that the flood was directly related to the extreme development of a long-lived mesoscale vortex (called southwest (SW) vortex by Chinese meteorologists) over the basin as it merged with another mesoscale vortex generated over the Tibetan Plateau. Mesoscale heat and moisture budgets suggest that the latent heat release associated with cumulus convection contributed substantially to the development of the SW vortex. It is found that heating due to convective eddy flux convergence of sensible and latent heat is about half the amount of latent heat release due to condensation. Moisture flux analyses and isentropic trajectories indicate that the major moisture source for the flood was from the Bay of Bengal. We hypothesize that the formation of the SW vortex was a consequence of the blocking of the southwesterly monsoon flow by the mesoscale mountain range (located at the southeastern corner of the Tibetan Plateau).-from Authors