A New Approach for Estimating Salinity in the Southwest Atlantic and Its Application in a Data Assimilation Evaluation Experiment

Abstract

A new method for generating synthetic salinity (SS) profiles in the Southwest Atlantic was developed and applied in data assimilation experiments. This method was based on the smallest integrated values of root mean square deviation (RMSD)—with respect to observations—to infer salinity through climatological data and by regressive methods on temperature (T) using a five‐order polynomial function (P5). In the 14 delimited subregions, the averaged RMSD of P5 was 45% smaller than interpolated climatological data. However, climatological salinity presented better results in the first top layers while P5 presented smaller errors in higher depths. Therefore, by joining the best that P5 and climatology may offer, a new hybrid approach was used to generate SS based on T from XBT profiles. The SS would allow more T profiles to be employed in the Oceanographic Modeling and Observation Network (REMO) data assimilation system, called RODAS, into the Hybrid Coordinate Ocean Model (HYCOM). The use of SS estimates has potential to improve model outputs, in which the presence of the T‐S pair is quite necessary. Three integrations were performed: one run without assimilation (FREE), one assimilating sea surface temperature, Argo profilers, and sea level anomaly (RODAS) and one similar to RODAS, but with added XBTs with SS (RODAS_XBT). The inclusion of XBT data in the HYCOM + RODAS system improved the position and magnitude of the Brazil Current (BC). It was shown that SS is feasible for producing ocean reanalysis and initial conditions for ocean forecast systems requiring very low computational cost.

Estimation of Seawater Hydrophysical Characteristics from Thermistor Strings and CTD Data in the Sea of Japan Shelf Zone

“…In the case of a hypothetical ideal CTD profiling at τ 2 = τ T , procedure (10) leads to the complete elimination of dynamic errors T(t) = T 2 (t). However, in real conditions, this is not the case for the following reasons.…”

“…To reduce the levels of dynamic errors in CTD data as much as possible, we will continue to use an alternative processing scheme everywhere. To do this, we replace the smoothing of the profile T 1 (t) by filter (9) with the "recovery" procedure (10), preserving its equalization (8) and smoothing of the profile E 1 (t) (9). In this case, we will select the optimal values of the "recovery" processing parameters τ 2 , displacement nδt, and smoothing τ 3 according to the criterion of minimum dispersion of high-frequency salinity fluctuations on scales of up to 2 s [27,36].…”

“…Dynamic correction of the data obtained with RBR profilers (XR-620, XR-620, and RBRconcerto) was carried out according to the scheme proposed above ( 8)- (10). Its efficiency is demonstrated by the results presented in Figure 5.…”

“…Stommel proposed a solution to the problem only for a limited class of fairly homogeneous water masses with clearly defined Ts structure. In subsequent years, many authors proposed both various modifications of the Stommel method and new approaches based on the analysis of the statistical relationship between T and s, for example, [8][9][10]. We will not dwell here on the review and analysis of these methods, since it is beyond the scope of our proposed discussion.…”

“…We will not dwell here on the review and analysis of these methods, since it is beyond the scope of our proposed discussion. The current state of this problem can be found, for example, in [10]. Let us focus only upon some publications, in which the regression of T and s was used, which corresponds to the topic of this article.…”