A response climatology of idealized midlatitude thermal forcing experiments with and without a storm track

Several GCM studies indicate that eddy activity may have a considerable inf luence on the atmospheric response to midlatitude sea surface temperature a nomalies. The effect of eddy activity on the atmospheric equilibrium respon se to idealized midlatitude thermal forcing is analyzed for an atmosphere w ith or without an idealized storm track. Experiments using a simplified glo bal circulation model forced by thermal anomalies of different sign and loc ation are discussed. Consistent with the linear theory the geopotential height field displays a baroclinic response with a shallow low (high) somewhat downstream of the wa rm (cold) anomaly; farther downstream an equivalent barotropic response occ urs with positive (negative) amplitude increasing with height. Eddy feedbac ks have weak impact on the baroclinic part, but the equivalent barotropic r esponse is strongly enhanced if the bandpass-filtered streamfunction tenden cy is in-phase with the linear geopotential height response. This is the ca se in an experiment with a warm anomaly near 40 degreesN, located southwest erly of the idealized storm track. In the corresponding experiment with a c old anomaly the two patterns are out-of-phase and the equivalent barotropic response is slightly reduced. It is weakened (strengthened) if a warm (col d) anomaly is shifted about 10 degrees poleward or equatorward relative to the idealized storm track. Midlatitude heat sources generate wave trains th at extend equatorward and poleward developing large-scale correlations betw een the flow at remote locations (teleconnections). The space-time variabil ity can be changed considerably by eddy feedbacks developing stronger varia nce for large-scale retrogressive traveling and standing waves. Partially, blocking-like events develop.