Use of the Temperature–Salinity Relation in a Data Assimilation Context

Abstract

A data analysis using conductivity?temperature?depth (CTD) measurements in the western tropical Pacific is carried out to get an estimate of the timescale over which temperature?salinity (T?S) relationships are preserved. Results show that the T?S preservation holds for periods on the order of a few weeks. A new method for assimilating upper-ocean temperature profiles with salinity adjustments into numerical ocean models is then proposed. The approach would use a T?S relation that is more local in space and time than is the climatological T?S relation used in previous studies. The assimilation method avoids convective instability as the temperature data are introduced. The CTD data and instantaneous fields from an ocean model are used to test the assimilation method by combining one profile with another. These tests recover the salinity profiles and the 0?500-m dynamic height very well (differences are smaller than 1 dyn cm). By contrast, analyses that used a climatological T?S relation did not provide a good salinity profile or dynamic height (errors were greater than 3 dyn cm). If used for data assimilation, the method would allow the recovery of a good salinity and density field when only temperature data were available, at intervals of, say, two to four weeks. There is evidence that the same conclusions could be drawn for many other oceanic areas.