Signatures of Air–Sea Interactions in a Coupled Atmosphere–Ocean GCM

Abstract

Various types of air?sea interactions are studied based on the general properties of cross-covariance function and the well-defined shapes of these functions obtained from conceptual models. The analysis is applied to sea surface temperature and surface fluxes obtained from a long integration with the coupled ECHAM3/LSG model. The results suggest that the atmosphere plays a dominant role in generating the coupled variability. Covariances between SST and wind stress in the extratropics are close to zero when SST leads, suggesting that SST anomalies, once being generated, do not feed back to the atmosphere. The interactions between SST and tropical wind stress involve various types of feedbacks. For heat flux, the antisymmetric shape of cross-covariance functions indicates that heat flux anomalies generate SST variations and the interaction tends to reverse the sign of the earlier SST anomalies. The atmosphere plays also an important role in generating coupled variations of SST and evaporation, and of SST and extratropical precipitation. The most dominant role of the ocean is found in the Tropics. The results can be used to verify simple atmospheric models that are used in ocean-only modeling studies. Cross-covariance functions found in such simple coupled models should be similar to those found in a fully coupled atmosphere?ocean GCM, if the simple models produce the same interactions found in fully coupled GCMs.