Seasonal variations in size and intensity of the Indo-western Pacific warm pool in different sectors

Abstract

The present study investigates the roles of solar radiation and monsoon wind in annual and semiannual variations of size and intensity of the Indo-western Pacific warm pool. The Indo-western Pacific warm pool is divided into four sectors with the equator and 100°E (north of the equator) and 135°E (south of the equator) longitude as the demarcations. These sectors display different seasonal variations in size and intensity and different roles of surface heat flux and oceanic processes. The size of the North Indian Ocean warm pool displays a semiannual variation with two peaks in May and October, while that in the other three sectors shows an annual variation. These features are attributable to a dominant role of solar radiation in the four sectors and an additional effect of the Asian monsoon in the North Indian Ocean sector. The intensity of the warm pool displays semianunal variations, with two peaks in May and August in the North Indian Ocean sector, April and November in the South Indian Ocean sector, May–June and September in the North Pacific Ocean sector and December and April in the South Pacific Ocean sector. The semiannual feature is associated with two effects of monsoon winds: wind-induced ocean advection and convection-related cloud-radiation changes. These two changes induce a decrease of sea surface temperature during the monsoon period, leading to the formation of semiannual variations in the size and intensity of the warm pool.