Summary of Abstract Submission

Abstract Submission No. IO50-04-0007PresentationPoster

THE UPPER BAY OF BENGAL SALINITY STRUCTURE IN A HIGH-RESOLUTION MODEL

Rachid BENSHILA*1, Fabien DURAND1, Sebastien MASSON2, Romain BOURDALLE-BADIE3, Clement de BOYER MONTEGUT4, Fabrice PAPA5, Gurvan MADEC2

1 LEGOS, Toulouse, France
2 LOCEAN, Paris, France
3 Mercator-Ocean, Toulouse, France
4 IFREMER, Brest, France
5 IFCWS, IISc, Bangalore, India

ABSTRACT :

Salinity in the Bay of Bengal is highly heterogeneous, with extremely fresh waters found at the surface in the Northern part of the basin, and saltier waters at subsurface as well as to the south. This study investigates the seasonal structure of sea surface salinity of the Bay in a regional high-resolution model forced by ERA-Interim reanalysis and various precipitation products. Surface circulation is believed to drive the spreading of northern Bay of Bengal fresh waters to the rest of the Indian Ocean. We first present a series of experiments to infer the sensitivity of modeled circulation to various numerical choices. Surface circulation is found to be sensitive to the horizontal resolution of the model, with the 1/12 version appearing much more realistic than the 1/4 version. The sidewall boundary condition is also drastically influencing the characteristics of the western boundary current simulated. We then investigate the sensitivity of the salinity response to the various precipitation products. We observe that ERA-Interim excess precipitation induces a fresh bias in the surface salinity response. Spaceborne precipitation products are more satisfactory. We then identify the pathways of the northern Bay freshwater mass, based on passive tracers experiments. Our model suggests that over timescales of a few months, vertical exchanges between the upper fresh layer and the underlying saltier layer appear to be the main export pathway for the freshwater. Our study highlights the need for a careful set-up of a realistic ocean numerical model (resolution, parameterization, forcing fluxes).