Patterns and Dynamics of SST Fronts in the California Current System

The California Current System (CCS) is one of the four major Eastern Boundary CurrentSystems, where major coastal upwelling is observed in the ocean. Oceanic fronts are abundant in the CCS,and are known to be associated with coastal upwelling. Analyses of satellite observations (altimetry andsea surface temperature, SST) of the CCS highlight the presence of SST fronts in the southern part of theCCS outside of the coastal upwelling season, which will be investigated. The submesoscale-permitting andtidal-resolving LLC4320-simulation was used to analyze the nature of these features, through the study ofthe surface density gradients, the vertical velocities and the horizontal strain. An algorithm was alsodeveloped to track SST fronts in the model. The classical scenario of coastal upwelling is confirmed in thecentral CCS (off California), with a strain field correlated to vertical velocities associated with the SSTfronts, and collocated density fronts. In contrast, in the southern CCS (off Baja California), verticalvelocities were much weaker and density gradients were not always observed where SST fronts weredetected, leading to the assumption that the fronts there may be affected by thermohaline compensationoccurring in the region. These findings confirm the existence of SST fronts in the CCS outside of thetraditional coastal upwelling framework, with part of the fronts in the southern CCS being passive andadvected by the background flow.