Sensitivity of Monsoon circulations to changes in sea surface temperatures

Abstract

Sensitivity of a regional scale model to different sea surface temperatures (SSTs) in the context of short-range predicuon of monsoon rainfall is studied using a three dimensional regional scale model. For the month of July, over certam regions of Arabian Sea, Bay of Bengal and the Inchan Ocean, observed SSTs are about 1 to 2°C warmer than the chmatological SSTs. Two numerical experiments are performed using observed and chmatological SSTs for an active monsoon period. It is found that the evaporation increases over these surrounding oceans when the observed SSTs are used. As expected, warmer SSTs caused the surface pressure to decrease by 2 to 3 hPa leading to local aceeleraUons of winds. As a result, stronger circulation patterns are induced. Area-averaged evaporation is about 20% higher and the rainfall 10% higher when observed SSTs are used. Effect of an uniform increase m SST by 2°C over chmatological values is also investigated. Comparison of simulations with the climatic and the umformly mcreased SSTs indicated that the ramfall predictions are quahtattvely similar to those obtained with the observed SSTs. Area-averaged evaporation is about 40% higher and the rainfall 15% higher than those obtained with the climatic SSTs. Results from these three numerical experiments indicate that the short-range prediction of monsoon weather is sensitive to the sea surface temperature distnbution. This is mainly because of variations in mesoscale clrculatmns caused by the local gradients m the SSTs.