As a proxy for upper ocean heat content, the over 20-year record of sea surface height (SSH) allows an examination of whether the atmosphere or the ocean drives air-sea interaction on seasonal time scales. Here we examine seasonal lagged correlations between sea surface temperature (SST) and SSH with turbulent flux of heat (Q) to identify where and what time of year Q is predictable from SST(SSH). The canonical view of air-sea interaction in the mid-latitudes in winter is that the atmosphere forces SST anomalies that are then damped locally by the atmosphere. However, in regions of strong currents such as the Gulf Stream, ocean heat transport convergence controls SST and upper ocean heat content anomalies, and as such we expect that surface fluxes will be correlated with SST (SSH) at zero lag such that a warm ocean (high SSH) results in heat fluxed to the atmosphere. Identifying the regions with this structure in the lagged correlations localizes those regions where heat content anomalies that result from ocean heat transport convergence drive air-sea heat exchange.
We find that near the Gulf Stream but away from the core both early summer SST and SSH predict Q the following winter in the western part of the Northern Recirculation gyre. Both fields also show predictive skill for Q in the North Atlantic current although the predictability from SSH is longer. In addition, SSH, but not SST, shows predictive skill in the Eastern end of the Southern Recirculation Gyre where Subtropical Mode Water resides after subduction.
In addition to evidence for seasonal predictability of Q, observations also suggest that there is predictability for winter mid-level (tropospheric) cloud fraction. Turbulent flux Q is positively correlated with mid-level cloud fraction in the western part of the Northern Recirculation gyre and in the North Atlantic Current in winter at zero lag. We also find that early summer SSH predicts winter mid-level cloud cover in these two regions, consistent with the relationship found between SSH and Q. The relationship between Q and mid-level cloud cover in winter is consistent with the climatological analysis of atmospheric conditions over the Gulf Stream in winter by Minobe and co-workers.