Observations of atmosphere‐ocean coupling in midlatitude western boundary currents

Abstract

Oceanographic fields derived from the Geosat altimeter and atmospheric fields from the European Centre for Medium‐Range Weather Forecasts (ECMWF) were examined for both the western North Pacific Ocean and the western North Atlantic Ocean to determine the nature of the coupling. Despite the short data records, approximately 2.5 years, correlation analyses of nonseasonal fluctuations showed similar relationships for both oceans. Correlations between the height difference across the jets (surface transport) and the path of the western boundary currents suggested that there is a structural change of the recirculation gyres, associated with a path change, with timescales of 5–9 months. Both wind stress and wind stress curl were clearly correlated with the surface transport and path in each ocean. Although net surface heat flux and wind stress were correlated, there was no clear correlation between net surface heat flux from ECMWF and surface transport over the entire study region. Additional regional analyses of the North Atlantic showed a consistent relationship between cooling, sea surface temperature (SST), and surface transport west of 62°W; anomalous cooling (accompanied by cyclonic wind anomalies) corresponds to a weaker SST gradient across the Gulf Stream and decreasing surface transport. Because the surface transport fluctuations to the west and east of 62°W in the western North Atlantic are not correlated, structural changes in the recirculation gyres, which have their maximum variations east of 62°W, may not be related to surface heat flux variations.