Using Sea Surface Height to Examine Air–Sea Interaction in the North Atlantic Ocean in Winter

As a proxy for upper ocean heat content, the 22 year record of sea surface height (SSH) allows an examination of the interaction of heat stored below the seasonal thermocline with the atmosphere. We use monthly averaged sea level from AVISO, turbulent fluxes of heat (latent plus sensible heat flux, Q) and sea surface temperature (SST) from OAflux, ISCCP (International Satellite Cloud Climatology Project) Cloud Fraction, and ERA-20C precipitation to investigate seasonal variability in air-sea interaction. Lagged correlation analysis shows that SSH has longer persistence than SST throughout the North Atlantic. In both the Northern and Southern Recirculation gyres of the Gulf Stream, early summer SSH is correlated with surface flux in winter while SST is correlated with surface flux one month in advance. In the recirculation gyres, the SSH anomalies are not forced locally by surface flux; instead they result from oceanic heat transport convergence.

There is also evidence for stored heat forcing changes in the atmosphere. Turbulent flux of heat Q out of the ocean is linked to an increase in mid-level (tropospheric) cloud fraction in winter over the Gulf Stream, as well as changes in precipitation. These relationships are consistent with the climatological analysis of atmospheric conditions over the Gulf Stream in winter by Minobe and co-workers. In addition, early summer SSH is correlated with winter cloud cover, giving predictive skill for winter cloud cover over portions of the Eastern seaboard; at the same time, SST does not have this predictive skill. This suggests that the persistence of SSH may be useful seasonal forecasts of along the Eastern Seaboard.