黄土高原β中尺度致洪暴雨特征及成因

Characteristics and Causes of Meso-β Scale Flood-Causing Rainstorm on Loess Plateau

利用MICAPS资料、多普勒气象雷达资料和NCEP资料等,对2012年7月26日20:00至27日20:00黄土高原发生的一次β中尺度致洪暴雨过程的特征及成因做了分析。结果表明:近地层能量比低值舌的活动是两次强降水产生的触发机制之一;暴雨过程两个强降水时段都对应邻近暴雨区的北方1 km以内的边界层大于20 m·s^(-1)偏东风相对风暴气流的建立,而邻近暴雨区的北方1 km以内的边界层大于15 m·s^(-1)偏东风相对风暴气流减弱消失、或范围大幅度缩小,则对应强降水的减弱或停止;涡度收支分析表明,第一次强降水前,由于水平平流项的作用在300 hPa附近形成很强的负涡度收支;第二次强降水前,主要是扭转项和垂直输送项的作用,同时在450~300 hPa形成很强的正涡度收支;视热源与视水汽汇分析表明:第一次强降水前,视热源在300 hPa附近出现比较强的冷却层;第二次强降水前,800~500 hPa视水汽汇远大于视热源,形成正的加热层;500~200 hPa视热源远大于视水汽汇,形成峰值接近11 K·(6 h)^(-1)的很强的加热层;而在200~130 hPa由于视热源的作用,形成冷却层。

MICAPS data,Doppler radar data,NCEP data,etc.are used to analyze the characteristics and causes of a meso-βscale flood-causing rainstorm on Loess Plateau from 20:00 BT 26 to 20:00 BT 27 July 2012.The results show that the activity of low energy ratio tongue in the surface layer is one of the trigger mechanisms for the two severe raifalls.The two periods of torrential rains both correspond to the estab-lishment of easterly winds relative to storm airflow faster than 20 m·s-1 that is adjacent to the north of the storm zone within 1 km of the boundary layer,while easterly winds relative to storm airflow within 1 km of the boundary layer close to the north of the storm zone get weakened and vanished,or the range drastically reduces,causing the severe precipitation to lesson or stop correspondingly.Analysis on <br> vorticity revenue and expenditure shows that before the first rainstorm the dominant factor is horizontal advection item in the formation of strong negative vorticity revenue and expenditure near 300 hPa.Before the second rainstorm,the dominant factors are twisting item and vertical transportation item in the forma-tion of strong positive vorticity revenue and expenditure in the 450-300 hPa at the same time.Analysis on apparent heat source and apparent moisture sink shows that before the first rainstorm,the appearance of apparent heat source near 300 hPa is quite strong cooling layer.Before the second rainstorm,positive heat-ing layer is formed for the apparent moisture sink is much larger than the apparent heat source in the 800-500 hPa.The formation of strong heating layer whose peak is close to 11 K·(6 h)-1 for the heat source is much larger than apparent moisture sink in the 500-200 hPa.Due to the role of the apparent heat source, cooling layer is formed in 200-130 hPa.