Sea Surface Salinity Subfootprint Variability from a Global High-Resolution Model

We have studied the subfootprint variability (SFV) of sea surface salinity (SSS) using the LLC4320 version of the MITgcm, a very high-resolution (1/48°) global simulation. SFV is the weighted standard deviation within the footprint of an SSS satellite like Aquarius or SMAP. SFV was studied as a function of footprint size and of space and time. It was found to be large in areas of strong frontal zones such as the Gulf Stream, Antarctic front and Brazil-Malvinas Confluence. SFV also tends to be larger where rainfall is heavy. It was found to have a seasonal and hemispheric component, being generally larger in the southern hemisphere and summer than the northern hemisphere and winter. For a 100 km footprint, the most likely values of SFV are (0.05, 0.06, 0.03, 0.05) for (southern summer, northern summer, southern winter, northern summer) respectively.