Interhemispheric Teleconnections from Tropical Heat Sources in Intermediate and Simple Models

Abstract

he mechanisms that control the interhemispheric teleconnections from tropical heat sources are investigated using an intermediate complexity model [a quasi-equilibrium tropical circulation model (QTCM)] and a simple linear two-level model with dry dynamics. Illustrating the interhemispheric teleconnection process with an Atlantic warm pool principal case, the heat source directly excites a baroclinic response that spreads across the equator. Then, three processes involving baroclinic?barotropic interactions?shear advection, surface drag, and vertical advection?force a cross-equatorial barotropic Rossby wave response. An analysis of these processes in QTCM simulations indicates that 1) shear advection has a pattern that roughly coincides with the baroclinic signal in the tropics and subtropics, 2) surface drag has large amplitude and spatial extent and can be very effective in forcing barotropic motions around the globe, and 3) vertical advection has a significant contribution locally and remotely where large vertical motions and vertical shear occur. The simple model is modified to perform experiments in which each of these three mechanisms may be included or omitted. By adding surface drag and vertical advection, and comparing each to shear advection, the effects of the three mechanisms on the generation and propagation of the barotropic Rossby waves are shown to be qualitatively similar to the results in QTCM. It is also found that the moist processes included in the QTCM can feed back on the teleconnection process and alter the teleconnection pattern by enlarging the prescribed tropical heating in both intensity and geographical extent and by inducing remote precipitation anomalies by interaction with the basic state.