Abstract
The seasonal cycle and the onset and retreat dates in the summer monsoon in Indonesia, Australia and New Guinea are analyzed using 15-year (April 1978-December 1992)-averaged 5-day mean 1-degree latitude-longitude gridded GMS high-cloud-amount data. An analysis of these data shows seasonal cycles of the convective zone (ITCZ) cloud defined by regions with more than 30 percent of the mean high-cloud amount. The high clouds associated with the ITCZ increase in Java and northern New Guinea during November and subsequently spread to the eastern Indonesian and Australian regions during December and January.
Comparision of the dates of the onset of the summer monsoon winds defined as simultaneous observations of westerly wind at 850hPa and easterly wind at 200hPa derived from the 9-year (1980-88) mean of the 5-day mean 2.5-degree latitude-longitude ECMWF 850hPa and 200hPa wind data showed that convective clouds are enhanced over the land areas over northern Australia, New Guinea, Sulawesi and southern Borneo, where a tendency for early onset and late retreat of the summer monsoon clouds is observed.
The onset and retreat dates as derived from this study fill a major gap in these dates over Indonesia, Australia and New Guinea, where determination of onset (retreat) dates has been hindered by poor rainfall data coverage.
