THE CHARACTERISTICS OF SPRING AND SUMMER SUBTROPICAL CIRCULATION DURING PROLONGED DROUGHTS AND FLOODS IN SUMMER IN MIDDLE AND LOWER CHANGJIANG VALLEYS

In this paper, using monthly mean vertical circulation maps in April and July of 1969, 1980, 1972, 1978 and 10-year mean maps of April and July, we have investigated the relationship between the subtropical circulation and the persistent droughts and floods in summer in middle and lower Changjiang valleys.It is found that the subtropical high between the east of the West Pacific and the Middle Pacific in lower troposphere during spring and summer of flood years in middle and lower Changjiang valleys is stronger than that of drought years.
The zonal vertical circulation of subtropical zone in the Middle Pacific has persistent characters from spring to summer during flood years.Besides, owing to the fact that the zonal vertical circulation from the South China Sea to the Middle Pacific in spring of drought and flood years has significant difference, we can use the vertical circulation map of spring along with their climate mean to revise the forecasts issued last winter.