Comparison analysis between NODC in situ analyzed sea surface salinity and Aquarius sea surface salinity

The Aquarius satellite mission provides globally mapped level-3 monthly sea surface salinity (SSS) fields from August 2011 to present on a one-degree grid. The US National Oceanographic Data Center (NODC) has globally analyzed monthly SSS fields from January 2009 to present on a one-degree grid. The NODC fields were created through an objective analysis scheme utilizing calculated salinity climatologies and quality controlled in situ data. The majority of in situ SSS data was from Argo floats; however, Conductivity-Temperature-Depth (CTD), bottle, tropical moored buoy arrays, and glider data were also included. Because surface ("skin") salinity is a difficult variable to measure, all in situ profiles with a salinity observation less than 5.25m from the surface were considered to be surface observations. With two different products offering a global view of SSS at monthly time scales, a comparison analysis was conducted to look at global and regional differences as well as differences in the annual cycle. To partially eliminate systematic biases in both the Aquarius SSS and NODC SSS fields, we calculated monthly SSS anomaly fields. These fields were calculated by subtracting off the respective product's 8/2011-8/2012 SSS average from each month. From this information we investigated global and regional differences to see if they arise from a lack of in situ data in the area, inability of the objective analysis scheme to accurately depict regions of high SSS variability (e.g., Gulf Stream, Amazon River outflow), or issues with the satellite data. Furthermore, a Fourier decomposition was applied to the first year of Aquarius SSS monthly fields (08/2011 - 08/2012) and to the NODC SSS monthly fields for the same time period. The first two harmonics from the Fourier decomposition were compared to reveal any similarities and differences in the annual cycle between Aquarius SSS and NODC SSS.