杭州2015年前两场梅汛期暴雨的物理量与降水转化率对比分析

Comparative Analysis of Physical Quantities and Precipitation Conversion Rate on the First Two Meiyu Rainstorms in Hangzhou in 2015

利用NCEP FNL 1°×1°再分析资料及常规观测资料,对杭州2015年前两场梅汛期暴雨过程进行了对比分析。结果表明:(1)两次过程均受高层辐散、500 hPa南支槽、700 hPa和850 hPa切变以及高低空急流的影响,但第一次过程高低空急流更为强盛、环流形式持续时间较长。(2)首场暴雨是在垂直尺度较大的系统里包含不同高度的次级环流所造成的,即为对流层中低层和中层系统叠加作用的结果,而第二场暴雨的影响系统垂直尺度更大。分析发现水汽输送最强时段未必对应于雨强峰值时段,后者可能落后于前者一段时间,而只有当对流层中低层正涡度层厚度显著增大,且辐合、垂直上升运动以及水汽辐合强度均较大时,雨强方达最大,否则降水减弱。因此通过分析梅汛期暴雨过程中动力因子和水汽因子等物理量场的配置,可大致预测雨强最大时段及降雨持续的时间。(3)两次过程的暴雨都发生在850 hPa能量锋区南侧340 K附近及以上的高能区中。

Based on the NCEP FNL1°×1°reanalysis data and the conventional observed data,the first two Meiyu rainstorm weather processes in Hangzhou in2015are studied.The conclusions are as follows:(1)Divergence of higher layer,south branch trough at500hPa and shear lines at700hPa and850hPa as well as the upper and lower jets provide favorable conditions for each heavy rain.However,in the first Meiyurainstorm process,the upper and lower jets are stronger as well as the circulation pattern is longer.(2)The first rainstorm which is caused by secondary circulations from different levels is the result of the superposition of the middle and lower troposphere and the middle layer,while the system’s vertical scale of the second process is larger.It’s showed that the period of the strongest moisture transportation is notalways in tune with that of the maximum rainfall intensity,it's likely that the latter lags behind the former for a period of time,only when the thickness of positive vorticity in the middle and lower troposphere increases significantly as well as convergence,vertical ascending motion and water vapor convergence are all stronger will rainfall intensity peak,otherwise the precipitation decreases.Therefore,by analyzing the configuration of physical quantities such as dynamic factors and water vapor factors,the maximum rainfall intensity time and rainfall duration can be predicted roughly.(3)The two Meiyu rainstorms both occurred in the high energy zone of nearing and exceeding340K where is the south side of the energy front at850hPa.