A high-resolution atmospheric general circulation model (GCM) is used to evaluate the atmospheric response to North Atlantic sea surface temperature (SST) anomalies. The transient evolution of the response is studied in detail. The linear and nonlinear effects can thus be contrasted and separated by their different time scales. Baroclinic patterns related directly to the surface anomalies quickly reach their maximum manifestation. However, barotropic patterns related to the mid- and upper troposphere eddy vorticity fluxes have longer time scales with much more important amplitude, able to gradually replace the initial baroclinic response. This study thus provides an evolutional picture of the two types of response in a GCM.