一次大暴雨过程中两个强降水时段差异对比

Comparative Analysis of Two Strong Precipitation Periods During an Extended Heavy Rain Process

基于FY-2G卫星云图资料、ERA5再分析资料、自动站与CMORPH降水产品融合的小时分辨率降水资料,重点针对2015年6月26—29日川陕交界附近发生的一次强降水天气过程两个强降水时段[28日03:00—15:00(第1阶段)和28日20:00至29日08:00(第2阶段)]的云图特征、环流形势、假绝热过程和可逆绝热过程中的不稳定特征进行对比分析。结果表明:200 h Pa强辐散的维持,500 h Pa切变稳定少动和850 h Pa川陕交界气流辐合区维持,为第1阶段暴雨的发生发展提供了有利条件,中-α尺度对流系统(meso-αconvective system,简称MαCS)在中高层西南气流引导下北上影响川陕交界区形成强降水。500和700 h Pa切变、低层偏南气流维持是导致第2阶段暴雨的重要因素,切变附近对流云团发展合并影响川陕交界形成第2阶段强降水。与第2阶段暴雨中心相比,第1阶段暴雨中心低层水汽含量更高,暴雨区上空上升气流区伸展高度更高、强度更强,影响第1阶段暴雨区的云层更为深厚密实。两个时段强降水中心气块按可逆绝热过程抬升的不稳定度比按假绝热过程抬升更高;两个时段暴雨中心CAPE高值区均分布在低层800~700 h Pa附近,表明800~700 h Pa抬升的气块在绝热过程中受到的浮力均较大;低层有利的不稳定条件和水汽条件相配合,更有利于暴雨的发展。

Using FY-2G satellite data,ERA5 reanalysis data,and the integrated hourly resolution precipitation data from automatic weather stations,as well as CMORPH precipitation products,this paper focused on a comparative analysis of cloud-image characteristics,circulation features,and the parcel buoyancy instability of a pseudo adiabatic process and a reversible adiabatic process in two particularly strong precipitation periods from 03:00 BST to 15:00 BST 28(the period 1)and from 20:00 BST 28 to 08:00 BST 29(the period 2)during a heavy rain process occurring at the boundary between Sichuan and Shaanxi from June 26 to 29,2015.The results show that the maintenance of strong divergence on 200 hPa,a steady shear on 500 hPa,and maintenance of 850 hPa wind convergence at this boundary provided favorable conditions for the occurrence and development of heavy rain during the period 1.The heavy precipitation in the period 1 forming at the boundary between Sichuan and Shaanxi was affected by a MαCS(meso-αconvective system)moving northward steered by the southwest flow in middle to upper levels.The 500 and 700 hPa shear and the maintenance of a southerly airflow in the lower layers were important factors leading to heavy rain in the period 2.The development and merging of convective cloud clusters near the shear contributed to the formation of heavy rain in the period 2 at the boundary between Sichuan and Shaanxi.The low-level water vapor content over the rainstorm center in the period 1 was higher than that in the period 2.The updraft area over the rainstorm area extended higher,the updraft was stronger,and the cloud layer in the rainstorm area was deeper and denser in the period 1 than in the period 2.In both periods,the instability of the parcel’s vertical displacement according to a reversible adiabatic process was higher than that according to a pseudo-adiabatic process over the center of the heavy rain.The high-value areas of CAPE over the rainstorm centers of both periods all distributed between 800 and 700 hPa,which indicated that the parcel lifted between 800 and 700 hPa had large buoyancy during the adiabatic process.The favorable instability condition and the water vapor condition reinforced one another in the lower layer,which was conducive to development of heavy rain.