- The Association of Japanese Geographers
- 地理学評論 (ISSN:13479555)
- vol.78, no.12, pp.825-841, 2005-10-01 (Released:2008-12-25)
Observational evidence is presented to show an atmosphere-ocean coupled system in the maturing process of the Asian summer monsoon (ASM) and the western Pacific monsoon (WPM). The ASM and WPM are characterized by four abrupt seasonal changes that exhibit phase-locking features in the annual cycle. They correspond to the first transition of the ASM (mid May); the Indian monsoon onset (early June); the mature phase of ITCZ (mid June) to the east of Philippines and convection jump around 150°E (late July). The appearance of a warm pool, in excess of 29.0°C, is one of the key elements in understanding the sub-seasonal evolution of the ASM and WPM. Over the Indian Ocean, the seasonal increase of sea surface temperature (SST) follows the solar insolation and reduced evaporative cooling as well. In contrast, increase of SST over the subtropical western Pacific (SWP) lags behind those in the Indian Ocean by about one month. The heat flux analysis at the ocean surface in the SWP reveals that the delayed warming is attributed to reduced evaporative cooling, in relation to the weakening of the tropical easterlies, which is concurrent with the eastward expansion (_??_150°E) of the monsoon westerlies. These processes are also valid for interannual fluctuation; namely, the intensified ASM can induce warm SST anomalies over the SWP. Thus, these physical interpretations suggest further increase of the WPM predictability.