【作者】 张守保；

【导师】 郭品文；

【作者基本信息】 南京信息工程大学 ， 气象学， 2009， 博士

【摘要】 本文利用历史天气图、常规和非常规加密观测资料、多普勒雷达资料、NCEP再分析资料、MM5模式模拟资料等,通过天气学分析、动力诊断分析、数值模拟等手段,对华北回流天气的形势特征、华北回流的性质、多普勒雷达特征、回流强降水过程中的中尺度系统结构等进行了比较全面的研究。主要结论有:使用NCEP再分析资料、GPS资料、天津铁塔资料对华北回流的性质进行了分析,在我们所分析的个例中发现自东北平原南下的冷空气,虽经过渤海,也是比较干燥的。使用数值模式针对水汽进行了敏感性试验,证明华北回流性质是干冷的,回流降水过程的水汽伴随中层的西南气流来自南方;同时使用数值模式对回流的作用进行了敏感性试验,结果证明偏东风的大小在降水中的作用不如中高层的西南风的作用大,因此在降水中主要起冷垫作用。太行山地形的存在使回流降水加大。通过对四次华北回流天气过程中多普勒雷达资料的分析,得到了华北回流天气的多普勒速度、反射率因子的特征。在强降水时段出现前常伴有区域性的冷平流层。在强降水回流过程中发现有逆风区存在,逆风区与强降水区配合。多普勒速度图上,低层冷平流、逆风区应该是降水加强一个判别指标。使用加密探测资料分析了2003年10月10～12日回流强降水过程中的中尺度雨团活动,应用中尺度滤波方法,诊断分析了华北回流暴雨过程中,回流冷空气与西南暖湿气流相遇产生的辐合带上的中尺度系统的结构特征。概括出华北回流天气尺度影响系统主要为:500hPa图上,位于40°N以北的高空低槽快速向东移动,经过我国东北时,引起中低层大量的冷空气南下,此冷空气经渤海侵入华北平原,表现在地面图上为一冷锋,锋后为东北或偏东风,此冷空气虽经渤海但性质是比较干冷的;位于河套的中层低槽东移,槽前西南暖湿气流在东北南下的冷楔上爬升产生降水天气。同时在回流强降水过程中还存在高低空急流。强降水区出现在高空急流出口处喇叭口状辐散流场中,低空急流左前方。在暖湿空气势力较强的前提下,在回流冷空气与暖湿气流相遇的辐合带中激发出中尺度系统。中尺度雨团与中尺度系统相伴,低空急流为中尺度系统提供水汽,同时中尺度系统带来强降水,降水释放凝结潜热有利于低空急流强和维持,天气尺度系统与中尺度系统相互作用的结果使得强降水维持时间较长。更多还原

【Abstract】 Using historical weather charts, conventional and non-conventional observational data, re-analysis data of NCEP, Meso-scale model output data ,etc, the return-flow events occurred over North China are documented. And many methods are uesd, such as, synoptic analysis, diagnosis, numerical simulation and dynamic theoretical research, to investigate the characteristics of the weather situation, the nature of return flow events occurring over North China and their Doppler radar characteristics. In the process of return flow events with heavy rain, the structure of Meso-scale weather system is also studied. Main conclusions are:In order to estimate the nature of return flow in North China , NCEP re-analysis data, the precipitable water vapor (PWV) data from GPS/MET, wind and moisture data observed by 255m meteorological tower located in Tianjin are analyzed. The results show that cold air coming from North-East Plain, though the Bohai Sea, is also relatively dry. The sensitive tests of numerical simulation for water vapor prove that return flow is dry and cold. The moisture comes from South part with south-west air flow. Contrast with easterly wind the speed of south-west air flow play an important role on the precipitation in return-flow events. And the lower level Northeast airflow acts as a cold wedge. Taihang mountain is in favor of rainfall.Based on 4 cases Doppler weather radar data of return-flow events, the radar echo characteristics are studied by base reflectivity, base velocity and VAD wind profile etc. After the cold advection appeared in low level at VAD wind profile, the heavy precipitation occurs. The Adverse Wind Region is found in rain storm. And the AWR nearly overlap on the center of heavy rain . Cold advection and AWR are valuable in nowcasting of rain storm.An analysis on the mesoscale feathers of a return flow events with rain storm over North China on October 10th—12th ,2003 is performed by using Automatic Weather Station data, NCEP re-analysis data and Doppler radar images. It shows that the new high time-space resolution observation data can well exhibit the signature of the event.the results show that the mesoscale rain clusters move with mesoccale low and shear.And these mesoscale systems are found on the convergence belt forming between warm wet southwesterly and cold dry return flow.Summing up a concept model for return flow events occurring over North China. The trough located in the north of 40°N on 500 hPa map moves eastward fastly, causes a large numbers of low-level cold air southward, the cold air enter to North China Plain through the Bohai Sea, and in the surface acts as a cold front. The warm and wet air before an eastward upper trough from Hexi creep up on the Wedge of cold air, and produce the heavy rainfall. And in the return flow events with rain-storm , the upper and low jet exits. Mesoscale systems are form in the convergence belt which warm and wet southwesterly meet the cold and dry return flow.更多还原