大气探测资料在中尺度暴雨中的分析和应用

Analysis and Application of New Atmospheric Detection Data in a Mesoscale Heavy Rainfall Event

使用近几年强化气象业务观测网建设所获得的大气探测资料,包括每小时1次的自动雨量站资料、逐时的GOES-9卫星红外云图TBB资料、多普勒雷达反射率因子、径向速度及回波顶高资料,并结合NCEP/NCAR再分析资料,对2003年6月29—30日淮河流域大暴雨过程进行了中尺度观测研究。分析表明:高时空分辨率的大气探测资料能较好地描述暴雨过程的中尺度特征;同时,停滞在淮河一带的梅雨锋和切变线为此次大暴雨发生提供了有利的背景条件;暴雨过程期间,淮河流域梅雨锋云系上共有11个β-中尺度对流云团发生,它们是暴雨的直接制造者;此次大暴雨过程主要由2次中尺度强降雨时段组成,中尺度雨团的源地集中在安徽西北部,雨团的发生与β-中尺度对流云团活动有密切关系;雷达回波的分析显示,此次暴雨是混合云降水所致,在层状云降水区中有许多对流云回波,对流回波区和径向速度场所反映的中尺度辐合线与中尺度对流系统的演变有密切的关系。

An analysis on the mesoscale features of a heavy rainfall event over Huaihe River valleys on 29--30 June, 2003 is performed by using the new atmospheric detection data, including automatic weather station data, radar images（reflectivity echoes, velocity field and echo top height）, satellite TBB images, and NCEP/NCAR reanal-ysis data. It shows that the new high time-space resolution observation data can well exhibit the signatures of the event. The results show that： ① the effective and reasonable assembly of various synoptic systems in the middle and low troposphere level provide good background conditions for the event, such as the two-blocking high circulation pattern in the middle and high latitudes, the steady maintenance of the sub-tropical high pressure, the propagation of westerly trough from the northwest region, the occurrence and development of low vortex in the Meiyu front and low level shear-line sustained in Huaihe River region, low level jet and so on; ② the heavy rainfall is directly associated with 11 meso-β convective cluster produced in Meiyu front cloud system, the statistics results show that these meso-β convective cluster are produced in the cold and warm shear-line in the low troposphere level or in the convergence area of mesoscale low pressure, which shows the feature of daily variation which mainly appears in the afternoon;③ this heavy rainfall process is consisted of two intense rainfall periods, in which mesoscale rain area is generated by meso-β convective systems with its source located in the northwest Anhui Province; ④ radar echo demonstrates that the heavy rainfall is caused by merging cloud echoes, there are many convective clouds echoes in the stratus rainfall region, the convective clouds reflectivity echoes areas and mesoscale convergence line exhibited in the radar velocity fields are often related to the occurrence and development of the meso-β convective systems; ⑤ mesoscale low level vortex has a perpendicular structure of slantwise updraft current, and a weak subsiding cold flow in its northwest which may reflect the impact of baroclinic system in the middle latitude area. The entrainment of the dry and the cold air in the middlelevel of troposphere leads to the non-homogeneity distribution of Meiyu front cloud system, so that it is favorable to the occurrence of mesoscale convective system. Also, some real observation phenomena of a heavy rainfall event over Huaihe River valleys during the target period are studied. The physics mechanics of mesoscale rain band, such as the low level flow fields structure and topographic uplift influence on this event is needed to be further analyzed in the near future.