浙江中部地区初夏两次暴雨天气过程对比分析

Comparison Analysis of Two Torrential Rain Systems in Early Summer in Central Zhejiang

文中利用NCEP再分析资料、FY-2E红外云图TBB资料和加密观测资料,对浙江中部地区2018年5月7—8日(简称“5.7”暴雨)、5月18—19日(简称“5.18”暴雨)两次暴雨天气过程进行对比分析,研究暴雨发生发展的环流特征与中尺度条件差异。结果表明:地面辐合线加强触发暖区暴雨发生,且地面辐合线的强度、移向与新生单体的发展密切相关,强回波在地面辐合线附近合并加强形成“列车效应”。金衢盆地内地形辐合与阻挡产生强迫上升运动对MCS的发展起到促进和加强作用。“5.7”暴雨对流发展高度较低,暖云层深厚,降水回波在暴雨区稳定维持,属于积状和层状云混合降水;“5.18”暴雨对流云发展旺盛、具有混合相层与暖云层剖面结构,属于积状云为主的混合降水。“5.7”暴雨属冷锋前部型暴雨,“5.18”暴雨为暖切变型暖区暴雨。暖区暴雨预报可着眼于浙中地区低空急流发展,中层的干侵入和地面辐合线的加强维持作用。

Two torrential rain processes in 7-8 May 2018(“5.7”)and 18-19 May 2018(“5.18”)in central Zhejiang were compared and analyzed based on the conventional observation data,the NCEP reanalysis data and the TBB of FY-2E,and the circulation characteristics of rainstorm occurrence and development and the difference of mesoscale conditions were discussed.The results indicated that the intensity and moving direction of surface convergence line were closely related to the development of new cells.The merging and development of strong echo near surface convergence line were favorable for“train effect”.An upward motion forced by the topographic convergence and barrier promoted and strengthened the development of MCS.In the“5.7”heavy rain case,the convective developed strongly with a deep warm cloud layer and low convective height.The echo lasted for a long time in the rainstorm area.In the“5.18”heavy rain case,the convective clouds developed severely,and exhibited warm cloud layer and mixing liquid phase layer.The“5.7”heavy rain case was the cold-front-type,while the“5.18”heavy rain case was the warm shear-line.The forecast of warm-sector heavy rain should be focused on the building and enhancement of the low-level jet in central Zhejiang as well as the enhanced frontogenesis of convergence line in the surface low pressure,the intrusion of middle-level dry air.