Definition and Features of the North Edge of the East Asian Summer Monsoon

By using daily total precipitable water (TPW) amount from the ECMWF reanalysis (ERA-44a) data in 1958-2001, the north edge of the Asian sub-tropical summer monsoon is defined by a normalized precipitable water index (NPWI), and its climatology and interannual/interdecadal variability are examined. The results show that two monsoon systems (the Indian and East Asian monsoon systems) can be identified in terms of monsoon edge defined by the NPWI over Asia. The mean north edge goes in the west-east direction along the south side of the Tibetan Plateau over the area west of 100°E, and then turns northeastward along the northeast side of the Tibetan Plateau via the east of Northwest China, the north of North China,the west of Northeast China to Northeast Asia over the region east of 100°E. The north edge of the East Asian monsoon system has distinct interannual and interdecadal variabilities in the area east of 100°E while that of the Indian monsoon does not show obvious interannual or interdecadal variation in the area west of 100°E.