Energetic Perspectives on the Changing Tropical Circulation (Invited Presentation)

Changes in energy transport by the atmospheric circulation are related to meridional gradients in climate feedbacks, radiative forcing, and ocean heat uptake, providing the basis for a diagnostic decomposition of the response of the tropical mean circulation to anthropogenic forcing in CMIP5 and idealized aquaplanet simulations. The robust weakening of the tropical circulation is found to be characterized by an increase in gross moist stability, by an increase in poleward eddy heat flux, and by positive extratropical feedbacks, such as associated with lapse rate and sea ice response. However, feedbacks do not act in isolation: Only half of the range of Hadley cell weakening exhibited in the aquaplanet experiments is attributable to systematic variations in the surface albedo feedback. Changes in extratropical clouds that accompany the albedo changes explain the remaining spread. Through comparison of tropical circulation changes in models of various complexities, these findings provide insights into the hemispheric asymmetries in Hadley cell structure and subtropical precipitation trends.