Hainan,an island province of China in the northern South China Sea,experienced two sustained rainstorms in October 2010,which were the most severe autumn rainstorms of the past 60 years.From August to October 2010,the most dominant signal of Hainan rainfall was the 10-20-day oscillation.This paper examines the roles of the 10-20-day oscillation in the convective activity and atmospheric circulation during the rainstorms of October 2010 over Hainan.During both rainstorms,Hainan was near the center of convective activity and under the influence of a lower-troposphere cyclonic circulation.The convective center was initiated in the west-central tropical Indian Ocean several days prior to the rainstorm in Hainan.The convective center first propagated eastward to the maritime continent,accompanied by the cyclonic circulation,and then moved northward to the northern South China Sea and South China,causing the rainstorms over Hainan.In addition,the westward propagation of convection from the tropical western Pacific to the southern South China Sea,as well as the propagation farther northward,intensified the convective activity over the northern South China Sea and South China during the first rainstorm.
