地面气旋影响下两次华北暴雪（雨）过程分析

利用GRAPES模式、常规观测和NCEP再分析资料对2010年1月3日和2012年11月3日两次气旋影响华北地区的暴雪（雨）天气过程的形成机理进行对比分析。结果表明：两次暴雪（雨）过程中降水落区与地面气旋的相对位置有较大差别，“0103”过程发生在气旋的东部，“1103”过程发生在气旋的北部。通过检验，GRAPE模式能较好模拟两次降水的落区。通过数值模拟结果分析造成这种落区差异的原因。从热力方面来看，气旋的热力性质不同，“0103”过程一直保持暖心结构，“1103”过程冷空气不断被气旋卷入，使气旋逐渐变为冷心结构，造成冷暖空气相互作用方式不同。另一方面，“0103”过程冷暖空气的交汇发生在气旋与高压系统之间，且在气旋中心附近形成锢囚；而“1103”过程发生在气旋内部，过程的锋面系统由北向南倾斜。另外，“1103”过程水汽是被近地层气旋不断卷入；从风场垂直分布来看，两次过程发生前均有近地面层偏东风的建立，结束时均伴随着中低层系统过境，风向由南风转为北风，但降水过程中风场的演变明显不同。

Analysis of two heavy snow/rain processes influenced by surface cyclone in North China

Based on the GRAPES model data,conventional observation meteorological data,and NCEP reanalysis data,mechanisms of the two heavy snow/rain processes on January 3,2010（code 0103）,and November 3,2012 （code 1 103）in the North China were analyzed.The results indicate that the rain falling areas and relative locations of the surface cyclone are significantly different in these two processes.Precipitation mainly occurs in the east of cyclone for the ＆quot;0103＆quot;process,while it is in the north for the ＆quot;1 103＆quot;process.By test,the GRAPE model could simulate well the rain falling areas for the two processes.In terms of the analysis of numerical simulation results, the reasons for the characteristics of precipitation distribution can be explained as follow：From the thermodynamic features,thermodynamic characteristics of cyclone are different for the two processes.It is warm core structure for the ＆quot;0103＆quot;process,while it is cold core structure for the＆quot;1 103＆quot;process.The cold air is continually invaded into the cyclone in the ＆quot;1 103＆quot;process and results in its cold core structure.On the other hand,cold air and warm air converge between cyclone and anticyclone for the＆quot;0103＆quot;process and form the occlusion around the center of the cyclone,while they convege within the cyclone for the＆quot;1 103＆quot;process and front system leans from south to north. Furthermore,entrainment of water vapor by cyclone occurs at the low level for the＆quot;1 103＆quot;process.From the verti-cal distribution of the wind field,there is surface easternly wind before two processes occur,and the middle and low level flow transits when processes end up.Wind direction changes from south to north,while the evolution of wind field is obviously different during the process of precipitation.