Distinct Quasi-Biweekly Variations of the subtropical East Asian monsoon during early and late summers

Using Global Precipitation Climatology Project daily rainfall and ERA interim reanalysis data, we investigate the distinct characteristic of quasi-biweekly variation (QBV: 12-20 day) over East Asia (EA) during the early (June1-July 20) and late (July 21-August 31) summer. The QBV maximum variance is found over the core region (30-40N, 110-130E) of EA, which covers the eastern China (lower reaches of Yellow River, Huaihe River, and Yangtze River) as well as Korean peninsula. At its peak wet/dry phases, the QBV over the core region features a baroclinic structure but different spatial distributions in two subseasons. Although the processes of the local initiation and the dissipation that are linked to QBV of the core region are almost similar in two subseasons, different source regions and propagating tracks before peak phase are identified in early and late summers. Furthermore, during the transition from the peak dry to peak wet phase, the tropical monsoon trough extends eastward in early summer while retreats westward in late summer; the South Asia High and western North Pacific subtropical High move toward each other in early summer while moves away from each other in late summer. And the linkage between South Asian Monsoon and EA summer monsoon related to the QBV over the core region occurs only in early summer. The abrupt change of mean state in mid- to late-July is considered as the root cause of the different behavior of QBV. We also investigate the source for the QBV over EA, in an attempt to provide useful guidance for the intraseasonal prediction.