Assessing the importance of mesoscale sea‐surface temperature variations for surface turbulent cooling of the Kuroshio Extension in wintertime

Abstract

Western boundary currents are well known to exhibit a strong eddy field and meandering on subseasonal timescales and wavelengths of a few hundreds of kilometers. However, the extent to which the ocean mesoscale activity associated with these motions can enhance the turbulent air–sea heat flux averaged over a large spatial domain has not been fully characterized. This study aims to do so during the cold season using reanalysis data and simplified air–sea interaction models. The correlation between sea-surface height anomaly and the wintertime mean heat fluxes does not indicate any significant relations between eddy activity and large-scale surface heat flux in the Kuroshio Extension during winter over the 2003–2018 period. The results from simple models designed to isolate the contributions from the eddies suggest that the eddy enhancement of the heat flux via a rectified effect (a bit more anomalous cooling over a warm mesoscale feature than anomalous heating over a cold one) is small compared with the long-time, large-spatial scale mean in the reanalysis data, especially along the Kuroshio Extension. It is found larger north of it, where it can reach 5 W · $$ \cdotp $$ m − 2 $$ {}^{-2} $$ . Although different datasets might disagree about the level of energy of the sea-surface temperature field at the mesoscale, a simple scaling analysis gives confidence in the relatively small values of the rectified effect found here.