A SEEK filter assimilation of sea surface salinity from Aquarius in an OGCM: Implication for surface dynamics and thermohaline structure

Singular Evolutive Extended Kalman (SEEK) filter has been used to assimilate Aquarius-derived sea surface salinity (SSS) in a near-global ocean general circulation model (OGCM). Advanced Very High Resolution Radiometer (AVHRR)-derived sea surface temperature (SST) has also been assimilated in conjunction. The primary aim of the study is to investigate the improvement in simulation of global ocean surface currents as a result of this assimilation. The route of empirical orthogonal function (EOF) analysis has been taken for an efficient assessment of this impact separately in the space and time domains and satellite-derived surface current has been used as a benchmark. As expected, the assimilation has been found to impart significant positive impact in both the domains. Also, joint assimilation of SSS and SST has been found to be better than standalone SSS assimilation. These results have been further corroborated by a comparison with buoy-derived surface currents. Further emphasis has been laid on the simulation of Wyrtki and monsoon jets in the equatorial Indian Ocean, because of their importance in the climate of this region and again it has been found that assimilation guides the simulation toward realism in both the cases. Finally, impact on the SSS and SST fronts and their zonal displacements in the western Pacific has been investigated and here again the assimilation has led to an improvement in simulation of these features.