NONHYDROSTATIC NUMERICAL SIMULATION FOR THE“96.8”EXTRAORDINARY RAINSTORM AND THE DEVELOPING STRUCTURE OF MESOSCALE SYSTEM

During the period of 3—5 August 1996(for short “96.8”),an extraordinary rainstorm eventoccurred in Henan,Hebei and Shanxi Provinces in China,resulting in severe flood catastrophe.Synoptic analyses indicated that the stable gross col field and the interaction between a northwardmoving typhoon(down into low pressure)and its east lateral Pacific subtropical high were thelarge-and meso-scale circulation conditions of the “96.8” extraordinary rainstorm.The mesoscaletyphoon-low and its specific dynamical and thermodynamical structures were directly related to thisrainstorm event.The nonhydrostatic version of mesoscale numerical model MM5 was used toconduct investigation of numerical simulation for this case.The simulation with the full physicalprocesses of nonhydrostatic version MM5 was basically possessed of a capability to reproduce thegenesis,development and evolution of the large-scale and meso-α scale synoptic systems.Thesimulative results using a two-way interactive nesting procedure revealed that the typhoon-low waspossessed of an intensive coupled mechanism between the dynamical and thermodynamical fields,namely,the developing typhoon-low was possessed of a structure of the.cyclonic vorticity columnwith warm center and high humidity,the vorticity column on the lower levels was the moistconvective instability and negative moist potential vorticity structure:the intensive ascendingvertical motion and the intense divergence on upper levels and intensive convergence on the lowerlevels as well as the development of the convective cloud cluster were intercoupling:the intensesouthern wind jet companied by the typhoon-low was not only the interaccompanying andintercoupling condition of the development and maintenance of the typhoon-low and convectivecloud cluster,but also was the transportable belt of the moisture source and heat energy of the“96.8”extraordinary rainstorm.The analysis of simulative results of precipitation indicated thatthe distribution of the rainfall belt and rainfall rate was basically consistent with that of theobservation in spite of some rainfall centers less or larger than those of the observation for coarseor fine mesh domain,respectively.