Impact of Altika Sea Level Anomaly Data on a Variational Assimilation System

Altimeter data provide measurements of dynamic topography over the global ocean and is useful for the constraining numerical ocean modeling systems through data assimilation. In this study, sensitivity experiments are carried out to understand the relative impact of Sea Level Anomaly (SLA) extracted from satellite data on a variational assimilation system for the month of August 2013. A first experiment, without assimilation of SLA observations is called CNTR while a second experiment assimilating Ka band Altika SLA into the variational assimilation system is called ALTK. Both experiments assimilated all other observations such as surface and in situ observations of temperature and salinity as well as sea ice concentration. To understand the impact of altimeter observations, we computed the root mean square difference (RMSD) of analyzed temperature from both experiments and showed that the maximum impact is over the Indian Ocean, North Atlantic Ocean and tropical Pacific Ocean regions due to the large displacement change applied to the thermocline depth in the ALTK experiment. We also note that the impact of altimeter on analyzed temperature is over different depths. Finally, the analyzed SSH has less root mean square error (RMSE) with respect to the altimeter observations for ALTK experiment than CNTR experiment over the global ocean and shallow water over the Indian Region (60-105 degrees E, 5-40 degrees N).