华北地区夏季旱涝的大气环流特征诊断

利用1960-2009年华北地区17个站点的月平均降水资料以及NCEP/NCAR再分析资料中的月平均位势高度场、风场等资料，研究近50 a中国华北地区夏季旱涝对应的大气环流的异常。华北地区夏季旱、涝年份对应的大气环流存在显著差异。其中，夏季华北旱年的环流特征表现为：中层乌拉尔山附近为低槽区，贝加尔湖地区则为高压脊区，朝鲜半岛附近为槽区，华北地区处于高压控制下且西太平洋副热带高压偏南；低层蒙古反气旋很强，中国东部地区出现了明显的偏北风距平,阻挡了南方暖湿水汽向华北的输送。在涝年，中层乌拉尔山附近以及朝鲜半岛附近为高压脊,贝加尔湖地区则为很深的槽区，华北地区位于贝加尔湖至蒙古的低压槽前，西太平洋副高偏北；低层蒙古附近多低压槽活动，在我国东部地区出现了南风距平,有利于南方暖湿水汽向华北输送。华北旱、涝年前期春季的大气环流形势与同期夏季很相似。 

General Circulation over North China in Drought and Flood Summers

The abnormal atmospheric circulation related to drought and flood over north China in summer in recent 50 years was analyzed using the data of monthly precipitation at 17 weather stations in north China during the period from 1960 to 2009 and the NCEP/NCAR reanalysis data, such as the average height of potential and wind speed. The results show that there was a significant difference in atmospheric circulation between the drought and flood summers over north China.The general circulation over north China in drought summer was characterized by that, at the middle level, there was a trough of low pressure near the Ural Mountains, but a ridge of high pressure over the Lake Baikal region. There was also a trough of low pressure over the Korean Peninsula, north China was affected by a high pressure, and the Western Pacific Subtropical High was shifted southeastward. At the low level, the Mongolia cyclone was very strong, and an obvious anomaly of northerly winds over east China occurred, so the transportation of atmospheric water vapor from the south to the north was blocked. There was an opposite atmospheric circulation in the flood years. The atmospheric circulation over north China in spring was very similar to that in summer before both flood and drought years.