北京“7.21”特大暴雨过程暖区降水和锋面降水的时空分布特征

The spatial and temporal distributions of warm sector rainfall and frontal rainfall for the torrential rain event in Beijing on 21 July 2012

利用常规观测资料、地面加密自动站资料、FY-2E红外卫星云图、多普勒天气雷达产品以及NCEP/NCAR逐6 h再分析资料,对2012年7月21日北京特大暴雨过程暖区降水与锋面降水阶段进行了细致划分,并对其不同阶段降水的时空分布特征作了比较分析。结果表明:以锋面相对于该过程总降水量中心的锋面移动情况作为降水阶段划分的主要依据,降水可划分为三个阶段,第一阶段(21日08—16时)主要为锋前暖区降水,降水中心位于河北省拒马河流域,北京西南部为次大值降水中心;第二阶段(21日16—20时)主要为锋面过境降水,降水中心位于北京西南部的房山区;第三阶段(21日20时—22日03时),北京西南部有显著锋后降水,降水中心与过境锋面相对应,位于北京东南部与河北交界处。该过程暴雨中心降水由暖区降水、锋面过境降水和锋后降水构成,其分别约占总降水量的40%、46%、14%。北京西北部、东北部和东南部降水主要由锋面降水构成,暖区降水所占比例在15%以下。河北省拒马河流域洪涝灾害主要由暖区暴雨引起,北京西南部洪涝灾害既有暖区降水的作用,又有锋面过境降水的作用。

Using the conventional observation data,the data from intensive automatic weather stations,FY-2E infrared images,Dopplerweather radar products and NCEP/NCAR6-hourly reanalysis data,we have conducted detailed analysis and division to warm sector rainfalland frontal rainfall for the torrential rain event in Beijing on21July2012,and carried out comparative analysis of the spatial and temporaldistribution of the different stages of rainfall during the event.The results indicate that the entire torrential rain event can be divided into threestages based on the movement of cold front passing through the center of the total precipitation.The first stage is from08:00BT to16:00BTon21July2012and characterized by prior-frontal warm sector rainfall,in which the maximum precipitation center is located in the JumaRiver basin in Hebei province and the second large one in the southwest part of Beijing.The second stage is from16:00BT to20:00BT on21July2012and characterized by frontal rainfall when the front moves across Beijing,with the maximum precipitation center being in Fangshandistrict in the southwest part of Beijing.The last stage is from20:00BT21July to03:00BT22July2012,in which post-frontal precipitationis obvious in the southwest part of Beijing,with the maximum precipitation center being located in the junction of the southeast part of Beijingand Hebei province and corresponding to the cold front position.The precipitation in the torrential rain center for the whole event includes thewarm sector rainfall,the frontal passage rainfall and the post-frontal rainfall,which account for about40%,46%and14%of total rainfall,respectively.Precipitation in the northwestern,northeastern and southeastern parts of Beijing is mainly composed of frontal rainfall,of which theproportion of warm-vector rainfall is less than15%.The floods in the Juma River basin of Hebei province are mainly caused by warm sectorrainstorm,while those in the southwest part of Beijing are contributed to by both the warm sector rainstorm and the frontal passage rainstorm.