Summary of Abstract Submission

Abstract Submission No. IO50-07-0038PresentationOral

IS THERE AN EFFECT OF BAY OF BENGAL SALINITY ON THE INDIAN OCEAN CLIMATE?

Vialard, J. *1, Krishnamohan, K.S.2, Lengaigne, M.3, Masson, S.1, Samson, G.4, Durand, F.5, Shenoi, S.6

1 LOCEAN, France
2 IRD/LOCEAN, France
3 IRD/LOCEAN, NIO, France
4 LEGOS, France
5 IRD/LEGOS, France
6 INCOIS, India

ABSTRACT :

The Indian monsoon drives a considerable amount of freshwater flux into the Bay of Bengal (BoB) through river runoffs (Ganges, Brahmaputra, Irrawady) and oceanic rainfall. As a result, the BoB exhibits some of the lowest near-surface salinities in the tropics. The resulting strong salinity stratification inhibits thermal exchanges between the mixed layer and sub-surface and results in a shallow mixed layer that is responsive to atmospheric forcing. Shenoi et al. (2002) proposed that these salinity effects may feedback onto summer monsoon precipitations, by allowing high surface temperatures, conducive to deep atmospheric convection over the BoB. In the present study, we evaluate the effect of BoB salinity on the Indian Ocean climate through experiments with a 25 km resolution Indian Ocean configuration of the NOW (Nemo-Oasis-WRF) regional coupled model. The model simulates the main features of the Northern Indian Ocean seasonal cycle and circulation reasonably well. Sensitivity experiments that neglect the effect of salinity on vertical mixing in the BoB display relatively small changes in both surface temperature and rainfall over the Northern Indian Ocean. Physically, this small effect is a result of the competing effects of salinity on the fraction of solar heat flux absorbed by the mixed layer and on vertical mixing of heat. The effects of salinity may however also be underestimated because of overestimated wind and vertical mixing in the model, in particular during the summer monsoon.