Diagnosis And Numerical Simulation Of Nonlinear Subcritical Symmetric Instability Function In A Rainstorm Process

Diagnostic analyses are carried out for the rainstorm from 2000BT 5th July 2005 to 0800BT 12th July 2005 and WRF model is applied to simulate precipitation process from 0800BT 6th July 2005 to 2000BT 7th July 2005. Results show that: (1) The intensity of precipitation from 2000BT 5th July 2005 to 0800BT 12th July 2005 and the convective cloud cluster's activeness(determined by the lowest temperature of TBB and the surface area of the lowest temperature) are generally consistent; the intenser precipitation processes in whole process relate closely to upper and lower jets. (2)The rainstorm process can be divided into two periods, nonlinear subcritical symmetric instability is the main mechanism. (3)Zonal disturbance wind component u and meridional v enhanced are respectively in advance of precipitation's enhancement, the peaks of u and v disturbances indicate precipitation peak which emerges after 12 or 24 hours as well as peaks of ageostrophic intensity and cold or warm air's peak. (4)It is shown that space-time allocation among peaks of upper jet, lower jet, upper disturbance wind, lower disturbance wind and precipitation. (5)The vertical upward current at meso and upper levels that strong south cold current at upper level stimulates migrates southerly as well as downwards and strengthen rapidly along with time to around 500Hpa, and future rainstorm will be stimulated. (6)At earlier stage of rainfall, rapid intensification of upper level vorticity is in advance of divergence's at similar place, but reversely at lower level. The intensification of upper level divergence to half the peak and intensification of lower level divergence to the peak respectively indicate the rainfall that will occur after about 4 hours.The remarkable variety of divergence and vorticity occurs to the north of rainfall position, and at lower level, it is to the south of rainfall position or bordering on coincideing. Upper level divergence and vorticity fields and the lower level's migrate bordering on coinciding along with time. The new physical mechanism that nonlinear subcritical symmetric instability stimulates rainstorm is shown. (7) At about 2 hours before rainfall, the instability energy is the most near precipitation zone; when the precipitation is the intensest, the most of instability energy is released; the releasing of latent heat is major heating factor in rainfall; the convective instability, symmetry instability and conditional symmetry instability exist near the rainfall zone.