Similarities as well as differences between summer monsoons over SoutheastAsia and the Western North Pacific

The life cycles of SEAM (Southeast Asian Monsoon) and WNPM (Western North P acific Monsoon) are monitored by the climatological pentad mean OLR and 850 hPa [u, v], as well as utilizing the vertically integrated moisture flux v ector [Q(lambda), Q(phi)] and associated precipitation minus evaporation (P - E). SEAM reaches its peak in late July in conjunction with full establis hment of a gigantic heat low over the Asian Continent due to surface heatin g. The height of WNPM occurs two to three weeks later due to the delayed in tensification of the monsoon trough not directly by in Situ surface warming , but indirectly by remote influence of the Asian heat low. SEAM owes its e xistence to the westerly moisture influx from the Arabian Sea and further u pstream. On the other hand, the easterly moisture influx from the Eastern P acific is the major contributor to WNPM, relegating the role of moisture im port from the SEAM domain to that of secondary importance. The climatological pentad mean data are then partitioned into symmetric and asymmetric components with reference to the equator. SEAM is characterized by dominance of the asymmetric mode, an implication that it is essentially an asymmetric monsoon system regulated by north-south heat contrast. The c ontribution of the asymmetric mode to the summer mean moisture budget of SE AM is as high as 82 %, while the corresponding contribution due to the symm etric mode is only 18 %. In comparison, the asymmetric and symmetric modes equally contribute to WNPM and as such, it is an asymmetric and symmetric m ixed, hybrid monsoon system. The summer mean moisture budget of WNPM is acc omplished by almost equally significant contributions of the symmetric and asymmetric modes, i.e., 58 % from the former, while 42 % from the latter mo de. The symmetric mode exerts a strong influence on the maintenance of the clim atological equatorial Walker circulation. It is the asymmetric Hadley circu lation that furnishes moisture to equatorial convections over the updraft p ortion of the Walker circulation in the eastern Indian ocean. Activated con vections then enhance the symmetric zonal flow along the equator, which is westerly over the Indian Ocean while easterly over the western Pacific.