Sensitivities and mechanisms of the zonal mean atmospheric circulation response to tropical warming

Using an idealized dry atmospheric model, the zonal mean circulation changes are investigated with respect to different patterns of tropical warming. Generally speaking, an equatorward shift in circulation takes place in the presence of enhanced tropical temperature gradient or narrow tropical warming, similar to the changes associated with El Niño events.

In contrast, the zonal mean atmospheric circulations expand or shift poleward in response to upper-tropospheric warming or broad tropical warming, resembling the changes under future global warming. The mechanisms underlying these opposite changes in circulation are investigated by comparing the dry dynamical responses to a narrow tropical warming and a broad warming as analogs for El Niño and global warming. When running the idealized model in a zonally symmetric configuration in which the eddy feedback is disabled, both the narrow and broad warmings give rise to an equatorward shift of the subtropical jet.