两次北上相似路径台风导致的暴雨湿位涡诊断分析

Diagnostic analyses of heavy rainfalls caused by two similar northward-moving typhoons using moist potential vorticity

利用2012年8月28—29日和2019年9月7—8日水平分辨率为0.25°×0.25°的ERA5再分析资料、地面观测资料和中国气象局热带气旋最佳移动路径数据,对两次北上相似移动路径的台风“布拉万”和“玲玲”导致东北地区暴雨天气过程的湿位涡进行诊断分析。结果表明:台风导致的强降水与假相当位温的密集带对应较好,降水主要位于假相当位温密集带偏暖一侧,锋区越强,降水量越大。两个台风过程均在降水前期存在对流不稳定层结,为台风降水提供初始能量积累。初始时刻出现湿对称不稳定,是台风中心西北侧暴雨出现的主要因素。降水增强时刻,大气对流不稳定再次参与,说明低层对流不稳定提供了降水快速增强的主要能量。低层湿正压项(MPV1)和湿斜压项(MPV2)的绝对值均出现先增大后减小再增大的趋势,强降水主要分布在两个极值中间过渡时段。两次北上台风引起的吉林省中部暴雨带均与低层850 hPa的MPV2负值区和MPV1的正值区有较好的对应关系。

Using the ERA5 reanalysis data of August 28-29 in 2012 and September 7-8 in 2019 with a horizontal resolution of 0.25°×0.25°,ground observation data,and the China Meteorological Administration tropical cyclone optimal moving path data,the diagnosis and analysis of wet potential vorticity of two typhoons"Bolaven"and"Lingling"with similar moving path northward causing heavy rainfalls in Northeast China were carried out.The results show that the heavy rainfalls caused by typhoons correspond well with the dense zone of pseudo-equivalent potential temperature(θse),and the rainfall is mainly located on the warm side of the dense zone ofθse.The stronger the front zone is,the greater the rainfall is.Both typhoon processes have convectively unstable stratification in the early rainfall period,which provides initial energy accumulation for typhoon rainfall.The wet symmetry instability at the initial moment is the main factor for the occurrence of heavy rainfall on the northwest side of the typhoon center.During the time of rainfall enhancement,the instability of atmospheric convection is involved again,indicating that the instability of low-level convection provides the main energy for the rapid enhancement of rainfall.The absolute values of the wet barotropic term(MPV1)and the wet baroclinic term(MPV2)in the lower layer experienced an increase first,followed by decrease,and then changing to increase again,and the heavy rainfall mainly distributes in the intermediate period of the two extreme values.The rainstorm belts in central Jilin province caused by the two northward typhoons have a good correspondence with the negative MPV2 and positive MPV1 areas at the lower level of 850 hPa.