A Theory On General Nonlinear Subcritical Moist Symmetrical Instability And Numerical Simulation

Firstly,the Analysis-Method has been used on General Nonlinear Subcritical Moist Symmetrical Instability(GNSMSI).Several criterions of GNSMSI have been derived.Secondly,the critical values of original disturbance amplitude are calculated respectively when Meso-scale atmosphere stratification is stable and unstable.It is found that it is easier for GNSMSI to happen in saturated moist atmosphere than in dry air when the stratification is unstable.Even if the stratification is stable,it is still easy for GNSMSI to happen.Based on this theory,one precipitation process is simulated and analyzed.Some conclusion are derived as follow:(1)The thermal,dynamic and vapor conditions are beneficial to the occurrence of rainfall.We can find a counter-circulation which can lead to the instability of stratification.The southern warm and moist flow provides the storm a lot of energy through the convergence in low level.There is intense convective instability favor of the occurrence of GNSMSI around the rainfall area.(2)High and low level jets have close relations with the precipitation.The relations are the indicative function of high level jet and the northward move of precipitation lead by the northward move of low level jet and the southward move of high level jet.(3)Subcritical symmetric moist instability may be the most important mechanism after the analysis of relations of the maximum value of disturbance wind with the maximum value of one hour precipitation and the minimum value of the index of linear symmetric stability.The maximum value of disturbance wind has 1-7 hours indicative function.The tendency of the occurrence and development in vertical direction of GNSMSI is in close relation with the vertical distribution of condensation heating.