From Ship to Model: Assessing SST and SSS with TSG Data

In situ obsersavations collected by thermosalinographs (TSG) provide valuable information on sea surface temperature (SST) and salinity (SSS) in coastal and shelf regions, where strong spatial gradiants and short-scale variability occur. TSG measurements offer high resolution along survey transects, capturing small scale fluctuations and offers a valuable opportunity for evaluating ocean models and satellite products.

In this study, TSG data aquired during multiple fisheries monitoring surveys from 2019 to 2024 along the Portuguese coast are used to assess the accuracy of SST and SSS fields from the Iberian-Biscay-Irish (IBI) reanlysis, provided by the Copernicus Marine Service, and a dedicated regional CROCO ocean model simulation specifically configured for western iberia. Satellite SST products from the Multiscale Ultrahigh Resolution (MUR) and Mediterranean Sea Ultra High Resolution (MED - UHR) are also compared with in situ observations to examine consistency across observation plataforms. For all surveys, model and satellite data are extracted at the nearest spatial and temporal points matching the TSG measurements processed at the appropriate spatial scales. Statistical skill metrics (bias, correlation coefficient, RMSD, MAE, and Skill score) are applied systematecally across all surveys.

The results show that, although SST is generally well reproduced, SSS displays larger discrepancies in IBI reanalysis, which tends to underestimate nearshore salinity. To improve the representation of nearshore SSS, sensitivity simulations were conducted using the CROCO model with prescribed riverine salinity and daily river discharge. These simulations highlight the importance of ensuring accurate river discharge and salinity values to represent coastal SSS variability and riverine low-salinity plumes along the Portuguese margin.

This evaluatin provides insight into the strengths and limitations of existing models and satellite products, guiding our ongoing efforts to improve our regional simulations of the Ibearin margin and to investigate its physical and biogeochemical processes.