The Numerical Simulation And Diagnosis Research Of Rainstorm And Severe Convection Weather In Northeast China

A rainstorm in northeast China affected by the North China cyclone during 5~ 6 August 2003, was successfully simulated by MM5 model in dais paper. Big scope south airflow and vapor transport and convergence brought by meso-scale jet, offer vapor condition which rainstorm occur and develop. Energy front has offered energy condition to produce severe convection. Severe convergence brought by Low-level jet pulsation, and severe divergence brought by upper-level jet is directly trigger mechanism of this intense rainstorm. The severe vertical velocity is severe convection trigger to offer dynamical condition for severe convection generation in lower-troposphere.Through analysis of potential vorticity in equity-entropy surface field, a relatively high potential vorticity center in cyclone top in low-troposphere have discovered, and make cyclone develop in a more deep cyclone circulation by this; And an anticyclone circulation zone with more severe low potential vorticity in high-troposphere. Low-level cyclone circulation with high-level anticyclone circulation, is helpful to form low-level convergence and high-level divergence, and make the rising airflow nearby cyclone keep and strengthen so that have offered necessity condition for convection precipitation. Through analysis of potential vorticity in isobaric surface field, in low-troposphere a positive potential vorticity disturbance exist and form incline disturbance column northward before rainstorm generation, at the same time have also reflected positive potential vorticity disturbance for severe convection weather trigger role in lower-troposphere; Soon positive potential vorticity disturbance in high-troposphere downward, form one vertical disturbance column, now corresponding precipitation develop stage; In the prosperous stage of rainstorm that maintains isolines of horizontal distribution and still have straight positive potential vorticity disturbance in 600 -700 hpa isobaric surface field; When near ground arises negative potential vorticity disturbance, precipitation also weaken.Q vector divergence field submit piece form district of convergence and divergence,have reflected meso-scale character. In the interface of convergence district and divergence district of Q vector divergence, accompany severe convection precipitation and convection precipitation strengthen following convergence center strength, weaken following divergence center weaken.The positive storm-relative helicity center is accompany with low-level jet in 850-hpa isobaric surface fields. Severe cumulus precipitation of 3h center appear in the left side of positive stonn-relative helicity center, i.e. positive storm-relative helicity center is not synchronization with cumulus precipitation center of 3h, the cumulus precipitation center of 3h falls behind the positive storm-relative helicity center. The change of the positive stonn-relative helicity value has reflected the severe weak tendency of rainstorm and its system approximately.