Contribution of Climate Feedbacks and Ocean Heat Uptake to Tropical Atmospheric Circulation Variability

The robust weakening of the tropical atmospheric circulation in projections of anthropogenic warming is associated with substantial changes in regional and global climate. In the present study we focus on understanding the equilibrium response of the Hadley circulation from a perspective of interactions between climate feedbacks and ocean heat uptake. Simulations from an ensemble of coupled ocean-atmosphere models are used to quantify changes in Hadley cell strength in terms of feedbacks, radiative forcing, ocean heat uptake, atmospheric eddies, and gross moist stability. Climate feedbacks are calculated for the CMIP5 integrations using radiative kernels. We find that tropical mean circulation is reduced by up to 2.6%/K for an abrupt quadrupling of carbon dioxide concentration. The weakening is characterized by an increase in gross moist stability, by an increase in atmospheric eddy heat flux, and by positive extratropical feedbacks, such as associated with lapse rate and sea ice response. The weakening is partially offset by the spatial pattern of ocean heat uptake. Understanding the impact of radiative feedbacks and forcings on the large-scale circulation provides a framework for constraining uncertainty in the dynamic climate response, including the hydrological cycle.