Classification Of Thunderstorm Processes With The Circumfluence Types In Summer In Beijing,Tianjin And Hebei

Based on the cloud-to-ground (CG) lightning data, hourly precipitation merged by surface precipitation in China and CMORPH (Climate Prediction Center Morphing Technique),45 thunderstorm processes in summer in Beijing, Tianjin and Hebei were selected out from June to August during 2008-2012. These 45 cases were divided into three types of "more CG and weaker precipitation (L+R-) thunderstorm" and "more CG and stronger precipitation (L+R+) thunderstorm" and "less CG and stronger precipitation (L-R+) thunderstorm" according to the magnitude of rain and the amount of CG, including 16 L+R- and 21 L+R- and 8 L+R- processes. Secondly, synoptic information and radiosonde data, and ECMWF 0.5°×0.5° reanalysis data were used to contrast the circumfluence patterns and environmental field characteristics of these processes. Then composite method served to synthesize and tested the characteristics of the general circulation field of three kinds of thunderstorms. Based on the statistics and composite results, the concepts of circulation model of various types of thunderstorm processes were summarized. Statistics derives that, the intensity of water vapor transporting determined precipitation while the instability of stratification influenced the amount of CG lightning. L+R-and L+R+processes with more CG lightning occurred in favorable environment of trough at middle level and trough or shear line at low level. The transmission of water vapor of the former was mainly in eastward path, while the latter was largely from strong southwesterly flow in the northwest side of western Pacific subtropical high (WPSTH). The intensity of trough at middle level and shear line at low level, and convective instability index of L-R+ processes were obviously weaker than those of the other two types. However the transport of water vapor was relatively sufficient, coming from southwesterly flow in the northwest side of WPSTH which lay northward of L+R+ processes. All of three kinds of processes were affected by front systems which nonetheless were more active in thunderstorms with stronger precipitation.From mesoscale atmospheric circulations to start, the causes of a sudden local heavy rainfall with lightning and hail occurred in Beijing on 7 August,2015 were delicately investigated by analyses of surface and conventional sounding data, Doppler weather radar data and wind profile radar data. Detailed analysis of local heavy rainfall taken place in Beijing demonstrates:The heavy rain occurred in a strong unstable stratification. The middle and lower troposphere trough and surface wind convergence line facilitated the development of convection in northwest of Hebei, which then moved southeast and caused heavy rain in the northwest of Beijing. The direct producer of heavy rainfall over central Beijing was locally thunderstorms triggered by convergence between the cold pool outflow of pre-existing thunderstorms and the warm, moist southeast airflow in the boundary layer. The terrain in the northwest of Beijing accelerated downhill cold pool outflow and lift the thunderstorm cold pool outflow. Then, the cold westerly outflow overlapped above the warm and moist easterly flow near surface that increased the convective instability of atmosphere and contributed to the initiation of thunderstorms at the east side of the mountain.