Numerical Simulation And Diagnostic Analysis About Evolution Mechanism Of An Explosive Cyclone

In this paper, we use PSU/NCAR MM5 model to make a research about an explosive cyclone that occurred in Western Pacific between December 19 and 21 in 1981, We have a good simulation about the evolution of the real weather process.We make a diagnostic analysis about the evolution and distribution of the wet potential vorticity of the integral result of the model simulation at each time. We find that the explosive of the cyclone has a closely relationship with the advection of the potential vorticity. It contributes to the development of the cyclone when the center of the potential vorticity is behind the cyclone at initial stages of the development of the cyclone and there is a manifest inverted conical subsidence zone under the 200hPa , which lies in the rear of cyclone . Generally under 300hPa the subsidence zone of the potential vorticity lies above cyclone at the violent stage of the development of the cyclone, however, the center of cyclone still lies near the potential vorticity of large value above 300hPa. In the last stages the center of cyclone lies in the zero line of the advection of the potential vorticity. The variation of the negative/positive value of the baroclinc potential vorticity under 850hPa has a very good correspondence with the development of the cyclone.One of factors which activize the explosive development of cyclone exists strong convective instability in lower layers from the analysis of the barotropic potential vorticity. In the violent stages of development of cyclone,the convective instability becomes weak greatly. The weakest convective instability is at the occluded stages of cyclone.Wet and dry numerical simulation tests for explosive cyclone over Western Pacific were performed. By contrast the results show that: Tropopause and constant temperature surface were raised by latent heat release in upper level and disturbance trough was produced because air flow ascended and became cold. Owing to this process adaption, inertial instability emergenced . Inertial instability always existed in strong inertial stability area, furthermore, acceleration field caused these two factors can give rise to air convergence and divergence in upper level, which made cyclone strengthened and precipitation enlarged. Reinforced precipitation caused latent heat enlarged again, which led to inertial instability augmented. The process of positive feedback had cyclone deepened.In a word , convective instability strong baxoclinicity barotropic advection of potential vorticity and latent heat release are factors which activize this explosive development of cyclone. Inertial instability barotropic advection of potentialvorticity the subsidence of the large value of potential vorticity above cyclone and geostrophic adjustment process is dynamical factors which make the cyclone developed violently.