Diagnostic Analysis of Meso-scale Simulated Rainfall of a Continuous Heavy Rain in South China

摘要

According to the diagnostic precipitation calculation methods,a continuous heavy rain occurred in South China during June 2010 was diagnosed for its macro-scale precipitation situation,meanwhile,under the synoptic system of "upper trough-Southwest China vortex (SW vortex)-shear line-low level jet",a torrential rainfall taken place in Jiangxi,Fujian and Hunan from 06-19-20 to 06-20-14 was simulated with a three-nested WRF model,in which,the meso-scale rain belt and micro-scale rainfall were deteriorated into being by analysis of their distributed precipitation of high space and time resolution,with diagnosis of the precipitable water in air column,stratified unstable energy,pseudo-convection precipitable water in air column,moisture flux,moisture weighted mean wind,vertical velocity,condensation-function precipitation rate,air moisture,cloud water,cloud ice and rain water flux divergence,etc.The simulation and diagnostic analysis shows that,the heavy rains are characterized in South China by atmospheric macro-scale circulation of the "positive anomalous in the middle high latitudes-negative anomalous in the middle low latitudes-the subtropical ridge being positive anomaly towards west-anomalous activities of the Monsoon Trough" in East Asia,which makes macro-scale abundant mass of vapor over the Bay of Bengal and the South China Sea to cross into the Mainland of South China; many meso-scale rainstorms developed in high value of saturated water vapor,cloud water,cloud ice,etc.,i.e.the total mass of water,where is wind convergence and ascent motion area for there is warm-damp jet in its upstream; the precipitation rate of condensation-function and that of flux divergence of the total mass of water are both products of the wind or divergence field,that initiates vertical motions;.the precipitation rate of condensation-function gradually approaches reasonable approximations suitable for the explicit precipitation physical process in the model atmosphere with the model's spatial and temporal resolution improve,for it can form rainfalls from meso-α-scale to meso-β-scale to meso-γ-scale,and their precipitation rates in every time integration be close to that of real torrential rains and should react rainfall's intensity,consistency and continuity,that is to say,when the model grid is 4 km,a lot ofmeso-γ-scale rainfalls with the condensation-function precipitation rate be 30-150mm/h can be simulated taking place in the system of "SW Vortex-Shear-line"; and the precipitation rate of droplet collection growth of cloud water,cloud ice,etc.,in super-saturated clouds with them,just be their flux divergence respectively,but together or each other,which must be added to the rate of condensation-function.Thus,the synoptic dynamic factor of the meso-scale rainfalls come into being in the model atmosphere is only wind field or divergence field especially in the weather system,e.g.in the meso-scale convergence line,that is,the vertical movement field is completely determined by the divergence field (and terrain) of high space and time resolution in the model atmosphere,so does all of the precipitation rates above.