2016年夏末南疆地区中尺度对流系统(MCS)活动特征

摘要

2016年夏末南疆地区短时强降水天气频发,中尺度对流系统活动频繁.利用强降水频发时段2016年8月8日—9月16日逐时FY-2G红外亮温(TBB)资料对南疆地区中尺度对流系统(MCS)进行分析,共获得92个生命史≥3h的中-β尺度对流系统(MβCS),包括β中尺度对流复合体(MβCCS)和β中尺度持续拉长状对流系统(MβECS).根据南疆地区的极端干旱气候背景,文中中-β尺度对流系统的尺度判定标准为云顶亮温(TBB)≤-32℃的连续冷云区直径≥20 km.对MCS的分布和活动特征进行了分析,结果表明:圆状MCS和带状MCS发生的频次相当.天山南坡和昆仑山北坡是MCS活跃区,MCS移动方向主要以偏东或东北方向为主,南疆地区活动最频繁的MCS生命史为3～4 h.南疆地区MCS具有明显的日变化特征,午后和傍晚是MCS最活跃的时段.与MβCCS相比,MβECS具有更明显的夜发性特征.昆仑山北坡MCS的最活跃时段早于天山南坡MCS,而天山南坡MCS夜间和凌晨形成的特征更为显著.生命史为3～5 h的短生命史MCS主要在午后和傍晚形成发展,并在形成后2 h达到成熟,生命史超过6 h的长生命史MCS多发于午后和凌晨,并且其发展阶段更长.文中给出了1个引发短时强降水的MβCCS和1个MβECS的云团演变特征.%The short-time heavy rain occurred frequently during the late summer of 2016 over southern Xinjiang,where mesoscale convective systems occurred commonly. Based on the FY-2G TBB (equivalent temperature of black body)dataset from August 8th to September 16th,2017,the 92 MCSs(Mesoscale Convective Systems)including MβCCS(Meso-β Circular Convective System) and MβECS (Meso-β Elongated Convective System) with life-cycle greater than 3 hours were analyzed. According to the extreme drought climate background there,the scale of meso-β-scale was defined as that the diameter of cold cloud continuous area of TBB value≤-32℃ is greater than 20km in this paper. The temporal and spatial distributions and active features of the MCSs were analyzed. The results indicate that the frequency of MβCCS and MβECS is almost the same. The southern slopes of Tianshan Mountains and the northern slopes of Kunlun Mountains are the main MCS active areas. Eastward and northeast are their main moving directions while their duration is 3～4 hours. The diurnal variations of MCS over southern Xinjiang were obviously different. The peak time for MCS initiation is around afternoon and nightfall. MβECS had a nocturnal occurrence characteristic compared with MβCCS. The active periods of the MCSs over the northern slopes of Kunlun Mountains were earlier than that in the southern slopes of Tianshan Mountains. MCSs over the southern slopes of Tianshan Mountains had a nocturnal occurrence characteristic. Short life MCSs formed and developed in the afternoon and evening,and matured after 2 hours. Long life MCSs formed in the afternoon and morning with a longer development stage. Finally,one MβCCS causing rainfall and one MβECS were further presented.