Role of Asian and African orography in Indian summer monsoon

Abstract

Role of Asian and African orography in the Indian summer monsoon has been investigated using a general circulation model. Orography of Asian region west of 80°E appears to have more impact on the Indian summer monsoon rainfall than the orography to the east of 80°E. It has been found that removal of the African orography increases the seasonal precipitation over the Indian sub-continent by 28%, whereas removal of orography over the entire globe reduces it by 25%. Moreover, there was a substantial delay in all-India monsoon onset in the experiment in which mountains were removed globally, mainly due to the intrusion of midlatitude dry air west of 80°E. The increase in precipitation in which orography over Africa was removed was due to the positive feedback between the wind over the East African coast/Arabian Sea and precipitation over Bay of Bengal, with the latter leading the former by about 2 days.