Interhemispheric teleconnections from Atlantic Warm Pool heat source in intermediate and simple models

The mechanisms that control the interhemispheric teleconnections from tropical heat sources are investigated using a moist dynamical intermediate complexity model (a Quasi-Equilibrium Tropical Circulation Model, QTCM) and a simple linear two-level model with dry dynamics. As a case study, here we examine Atlantic Warm Pool (AWP) heating as a source of interhemispheric teleconnection wave dynamics. The AWP heating directly excites a baroclinic response that is trapped within the tropics yet spreads across the equator. The cross-equatorial barotropic Rossby waves that penetrate into mid- and high-latitudes in both hemispheres are excited by three processes involving baroclinic-barotropic interactions—shear advection, surface drag, and vertical advection. 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 both locally and remotely where large vertical motions and vertical shear occur. 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. The simple model is modified to perform experiments in which each of the three mechanisms may be included or omitted. Addition of the surface drag mechanism results in a strong amplification and extension of the barotropic response in the southern hemisphere. The vertical advection amplifies the barotropic response locally around the heating area, and spreads the barotropic signals into the southern hemisphere, although the impact is moderate compared to the surface drag mechanism. Thus, the effects of the three mechanisms on the generation and propagation of the barotropic Rossby waves in the simple model are shown to be qualitatively similar to the results in QTCM.