Impacts of Argo salinity in NCEP Global Ocean Data Assimilation System: The tropical Indian Ocean (original) (raw)

Salinity in the Surface of the Indian Ocean

Marine Science, 2022

Long-term analysis of salinity can be useful to describe the main mechanisms that operate at the surface of the ocean. Average sea surface salinity (SSS) contour plots for the Indian Ocean are produced based on the NODC_WOA94 data provided by the NOAA/OAR/ESRL PSL. Salinity, together with the independent variables wind, ndff (net-down-freshwater flow) and Ekman pumping are included in a multiple regression analysis to define the relative importance of each one of these variables in the physical processes at the surface of the Indian Ocean. The ndff data set is based on COADS (Comprehensive Ocean-Atmosphere Data Set). The wind data is obtained from the Florida State University (FSU). The harmonic terms are considered to be stationary and expressed by Fourier series as a cosine function in which the first and second harmonic terms are multiplied by the maximum amplitude of the variable and added to the mean annual parameter. The salinity contours tend to be zonally orientated away from the coast, while a meridional influence is observed close to the boundaries. A typical zonal pattern of salinity distribution is observed only south of 10°S. Maximum annual amplitude values are observed in the north of the Arabian Sea and the Bay of Bengal. The variability of the annual components is consistent with the distribution of the net-down-freshwater-flow (ndff) contours and wind direction. During the SW Monsoon, the ndff becomes gradually positive towards the east, in the direction of the west coast of India, which results in a peak of maximum salinity in August and decreasing afterwards. During the NE Monsoon, the ndff is negative elsewhere in the Arabian Sea. The annual term plays a dominant role in determining the maximum and minimum salinity observed during August and January, while the semi-annual component provides minor adjustment. The annual component shows the influence of the monsoons through the year, with a high salinity during the NE Monsoon and a secondary peak during the SW Monsoon. Although harmonic analysis can be applied to the study of salinity variability, to identify and quantify the variables related to these areas of large annual and semiannual variability, a multiple regression analysis needs to be applied.