Sensitivity of Asian summer monsoon and tropical circulations to 1987 and 1988 sea surface temperature anomalies

In this work, the impact of Sea Surface Temperatures (SSTs) during 1987 and 1988 on the Northern Hemisphere summer mean monsoon is studied using an At mospheric General Circulation Model. Four model experiments were carried ou t to assess the relative impacts of observed SST fields of global(E1), trop ical(E2), tropical Pacific(E3) and tropical central and eastern Pacific(E4) oceans. It was seen that in El, the model captured a number of important o bserved circulation and precipitation features of 1987 and 1988 monsoons. T he upper tropospheric outflow during 1988 was strong over India, Indian oce an and western Australia and the inflow was strong over central and eastern Pacific oceans. During 1987, the upper tropospheric velocity potential min imum over western Pacific shifted east by 20 degrees of its 1988 position. The Tropical Easterly Jet (TEJ) over equatorial Africa was stronger in 1988 than in 1987. The precipitation maximum over western Pacific shifted to ce ntral and eastern Pacific during 1987. Over southern India, south west Indi an ocean and parts of Sahel, there was increased rainfall during 1988 compa red to 1987. However, it was less over northeast India in 1988 than in 1987 . In experiments E2, E3 and E4, the large-scale structures of the upper tropo spheric velocity potential difference between 1987 and 1988 were similar to those in E1. However, some important changes were seen in E3 and E4. The d ivergent flow during 1988 was weaker over Indian ocean and monsoon region w ith the center of velocity potential differences shifted to the east in E3 and E4 than in E1. Consistent changes were seen in the wind fields also. Th e TEJ was weaker during both the years 1987 and 1988 in E3 and E4 than in E 1.