江西一次暴雨过程的诊断分析

Diagnostic Analysis of a Heavy Rainfall Process in Jiangxi

利用NCEP 1°×1°再分析资料、地面与探空资料、卫星资料等,对2012年5月12日发生在江西省中部的一次暴雨过程进行诊断分析。结果表明:本次暴雨过程发生在冷锋南侧地面倒槽区,由高层西风槽、低层低空急流及切变线、低涡共同影响所致。中低层西南气流的加强,一方面使暴雨区有充足的水汽输送,同时也使该区对流不稳定度加大,加强了暴雨区上空的对流上升运动。中尺度辐合线是强对流暴雨的触发机制,而冷锋影响使地面东风气流加强,冷空气入侵致中尺度辐合线演变为中尺度低压,中尺度低压是江西短时强降水长时间持续的机制;500 h Pa高空槽东移,槽前正涡度平流向江西上空输送,利于低层低涡生成和维持、上升运动加强,从而导致降水增强。冷空气影响初始阶段,>10 mm·h-1的中尺度雨团产生在中尺度辐合线及其所演变成低压的1、2象限即中尺度辐合线或中尺度低压偏北一侧,随着冷空气的进一步入侵,中尺度雨团产生于中尺度低压的偏南一侧。

Based on NCEP 1°×1° reanalysis data, ground and radiosounding data, satellite data, the heavy rainfall process occurred in the central part of Jiangxi province on May 12, 2012 is analyzed. The results show that this rainfall process occurs in the south of cold front over surface inverted trough, caused jointly by upper level westerly trough, low-level jet and shear line, and low vortex. Strengthening of southwest airflow over middle-low level, not only makes enough vapor transport and increase of convec- tive instability, but also enhances ascending motion over heavy rain area. Mesoscale convergence line is the trigger mechanism of strong convection rainstorm. Mesoscale low pressure from mesoscale convergence line owing to cold front making augmentation of surface easterlies and invasion of cold air is the long time continuous mechanism of short time strong precipitation in Jiangxi. Trough aloft over 500 hPa moving east and positive vorticity advection transporting over Jiangxi in favor of lower layer vortex generation and ma- intenance, and reinforce of ascending motion, lead to precipitation enhancement. The initial stage of cold air, mesoscale rain clusters over 10 mm ·h-1 generate from mesoscale convergence line and in 1 and 2 quadrant of area of its evolvement to low pressure, i.e. mesoscale convergence line, or north side of me- soscale low pressure. With the further invasion of cold air, mesoscale rain clusters generate from south side of mesoscale low pressure.