A First Look at Satellite-Derived Sea Surface Density and its Applications
[26-Feb-2016] Schanze, J. and Lagerloef, G.
Presented at the 2016 Ocean Sciences Meeting
With the recent advent of remotely sensed sea-surface salinity (SSS) data from missions such as Aquarius/SAC-D and Soil Moisture and Ocean Salinity (SMOS), it has become possible to compute sea surface density from these data in conjunction with existing remotely sensed sea surface temperature (SST) data. The International Thermodynamic Equation of Seawater - 2010 (TEOS-2010) is used with Aquarius SSS and the Aquarius ancillary SST product to compute sea surface density.
The Aquarius sea surface density product provides a higher resolution of features than existing in-situ systems such as Argo or shipborne measurements. To validate the product, we compare the data with the in-situ-based MetOffice EN4 (4.1.1) objectively analyzed surface fields and find generally good agreement (< ±1 kg m-3), even including a slight seasonal bias. This bias appears as denser water in the Northern Hemisphere and lighter waters in the Southern Hemisphere during boreal summers. Most small-scale differences are located in areas of known mesoscale features, such as western boundary currents, the ITCZ, and riverine plumes. These differences are thus likely caused by the difference in resolution between the two products.
Preliminary comparisons with other in-situ platforms in the North Atlantic, which were deployed during the Salinity Processes in the Upper Ocean Regional Study (SPURS) between 2012 and 2013, also show good agreement with Aquarius-derived density.
A number of features, which are also present in the EN4 data, are more pronounced in the Aquarius-derived density product. This includes a band of lighter water that appears in the months of August and September and extends from the Subtropical Pacific Ocean around 30°N, 180°W towards the North American coast at approximately 45°N, 125°W. The progression of the Amazon River outflow is evident in sea surface density in Aquarius, but is largely undefined or altogether obscured in EN4 due to undersampling. To elucidate the relative contributions of SST and SSS on sea surface density, we present maps of both haline and thermal density components relative to standard seawater at S=35 and T=15°C.
We thus show that remotely sensed sea surface density can provide a new insight into oceanographic processes, including water-mass transformation and the influence of salinity on ocean dynamics.