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.