Importance of Intraseasonal Oscillation for the Regional Extreme Consecutive dry Days Events in Spring Over Southern China

This study investigates the influences of intraseasonal oscillation on two types of regional extreme consecutive dry days events (RECDD) in spring over Southern China (SC). For type-1 RECDD occurring in entire SC, the 7–25 days and 25–90 days high over Lake Balkhash-Baikal are important. The 7–25 days high first causes lower-tropospheric northerlies and moisture deficit in SC, then propagates to Yangtze River Basin and causes lower-tropospheric warming and decaying moisture deficit in SC. These processes favor dry condition in SC for 1 week. In comparison, the 25–90 days high and associated lower-tropospheric warming and moisture deficit in SC favor dry condition there for more than one week. For type-2 RECDD occurring in the southern part of SC, the 7–25 days and 25–90 days high over Northeast Asia are important. The 7–25 days high contributes for one week. It first causes lower-tropospheric anticyclone around the East China Sea and south-negative–north-positive moisture pattern in SC, then propagates to the Sea of Japan and causes lower-tropospheric south-warming–north-cooling pattern and decaying south-negative–north-positive moisture pattern in SC. In comparison, the 25–90 days high and associated lower-tropospheric south-warming–north-cooling pattern and south-negative–north-positive moisture pattern in SC favor south-dry–north-wet pattern there for more than one week. Moreover, the 7–25 days low and decaying 25–90 days high over Lake Balkhash-Baikal, concurring with 7–25 days low over Bay of Bengal, favor the end of type-1 RECDD; the 7–25 days low and decaying 25–90 days high over Northeast Asia favor the end of type-2 RECDD.