[A-CG29] Extratropical oceans and atmosphere

[ACG29-06] Co-variability in sea surface temperature and salinity in the midlatitude ocean and its scale-dependent features

*Shoichiro Kido¹, Masami Nonaka¹, Youichi Tanimoto^1,2 (1.JAMSTEC Application Lab, 2.Faculty of Environmental Earth Science, Hokkaido University)

Keywords:Sea surface temperature, Salinity variability, Midlatitude ocean

Sea surface temperature (SST) and salinity (SSS) are key variables for understanding the role of ocean in the climate system. Since variations in surface density, which affect a variety of dynamical and thermodynamical processes in the ocean, are determined by combinations of SST and SSS variability, an integrated description of the linkage between these two surface variables are of particular importance. However, little is known about features and mechanisms of SST-SSS covariability, because SST and SSS variability in the global ocean have been separately investigated so far. Through analysis of available observational datasets and outputs from high-resolution general circulation models, we found that correlations between SST and SSS in the global oceans exhibit coherent patterns with different signs and distinct spatial-scale dependence, particularly in the midlatitude oceans. At spatial scale smaller than 1,000 km, prominent covariability between SST and SSS are primarily caused by ocean dynamical processes such as meanders of currents and eddies, and their spatial pattern can be reasonably explained by the climatological SST and SSS fields. Specifically, positive (negative) SST-SSS correlations are found over regions where the horizontal gradients of climatological SST and SSS are in the same (opposite) directions. In contrast, SST–SSS covariations at larger spatial scale (>1,000 km) are caused by combinations of changes in local atmospheric conditions and large-scale ocean circulations; in regions with weak ocean currents, large-scale SST and SSS anomalies are negatively correlated due to negative correlations between surface heat and freshwater fluxes anomalies, but this fundamental interpretation is not applicable in locations where ocean dynamical processes play an important role (e.g., the western boundary current regions). Such distinct SST-SSS covariations are underestimated by the current generation of climate models, suggesting the role of salinity may not be faithfully represented as observed.