By using a new heat budget equation that is closely related to the sea surface temperature (SST) and a dataset from an ocean general circulation model (MOM2) with 10-a integration (1987-1996), the relative importance of various processes determining SST variations in two regions of the Indian Ocean is compared. These regions are defined by the Indian Ocean Dipole Index and will be referred to hereafter as the eastern (0°-10°S, 90°-110°E) and western regions (10°S-10°N, 50°-70°E), respectively. It is shown that in each region there is a falling of SST in boreal summer and a rising in most months of other seasons, but the phases are quite different. In the eastern region, maximum cooling rate occurs in July,whereas in the western region it occurs in June with much larger magnitude. Maximum heating rate occurs in November in the eastern region, but in March in the western one. The western region exhibits another peak of increasing rate of SST in October, indicating a typical half-year period. Net surface heat flux and entrainment show roughly the same phases as the time-varying term, but the former has much larger contribution in most of a year, whereas the latter is important in the boreal summer. Horizontal advection, however, shows completely different seasonal variations as compared with any other terms in the heat budget equation. In the eastern region, it has a maximum in June/November and a minimum in March/September, manifesting a half-year period; in the western region, it reaches the maximum in August and the minimum in November. Further investigation of the horizontal advection indicates that the zonal advection has almost the opposite sign to the meridional advection. In the eastern region, the zonal advection is negative with a peak in August, whereas the meridional one is positive with two peaks in June and October. In the western region, the zonal advection is negative from March to November with two peaks in June and November, whereas the meridional one is positive with one peak in July.Diffe
Based on the daily outgoing longwave radiation (OLR) data from National Oceanic and At- mospheric Administration (NOAA) satellites, the Cli- mate Prediction Center’s merged analysis of pre- cipitation (CMAP) data and the National Centers for Environmental Prediction/National Center for At- mospheric Research (NCEP/NCAR) reanalysis dataset, the mean intraseasonal variability of the Asian summer monsoon (ASM) is investigated by using power spectrum analysis, band-pass filter, and diagnostic analyses. The processes of the onset and advance of monsoon over the southern part of Indo- china Peninsula, the east coast of Bay of Bengal, the South China Sea and the Indian subcontinent are explored. It is found that there is an abrupt change in OLR, precipitation and zonal wind during the onset and advance of the ASM. It is also indicated that the southern part of Indochina Peninsula and the adja- cent Andaman Sea is the region where the earliest onset of the ASM occurs in the 2nd pentad of May.
