The Statistic And Diagnostic Analysis Of MeiYu Storm Rainfall And The Fringe Study Of Subcritical Symmetric Instability

Statistical and diagnostic analysis were carried out in the MeiYu strom rainfall process from 00UT of 11th to 00UT of 23 th June, 1998 in this study. Results showed that the stability of South Asia high pressure ,subtropic high pressure and Bengal Gulf trough's location was the advantaged position to this rainfall process.The elements of vorticity , divergence,specific humidity, moisture flux divergence and K index etc. were benefited to the form and development of strom rainfall over the rainfall region.By the analysis of the relationship among subcritical symmetricinstability , symmetric instablity and rainfall,it showed that bothsubcritical symmetric instability and symmetric insatbility sprung theincrease of rainfall in some extent.then we verified the theory ofsubcritical symmetric instability the first time.By the use of MM5 ,we simulated the rainfall process from 12UT of 12th to 12UT of 13th June,1998 successfully .and the diagnostic analysis was carried out to study the relationship between low level jet and rainfall, the relationship between helicity and rainfall and the relationship between vertical velocity and rainfall. We found that the mesocale change of low level jet in time scale had a close relationship with the rainfall. Total helicity, average helicity and local helicity on 850hpa also had good relationship with the rainfall.The vertical veloctiy has the good homologous relationship with the rainfall.On the base of study above, we studied the relationship between the subcritical symmetric instability and rainfall in small time scale and found that the appearance of subcritical symmetric instability max value was before the appearance of rainfall max value.The result was coincided with the diagnostic analysis result in large time scale.we verified the theory of subcirtical symmetric instability the second time.After studying the relationship between subcritical symmetric instability and low level jet ,we found that the appearance of subcritical symmetric instability max value was before the appearance of low level jet max value.