How Future Circulation Changes are modified by the Coupling of Atmosphere and Ocean Energy Transports.
Résumé
A number of studies have shown how in isolation the atmospheric circulation would balance changes in the top-of-atmosphere energy budget or ocean energy transport, leading to climate impacts such as shifts of the ITCZ or mid-latitude jets. The atmosphere and ocean circulation, and so their respective meridional energy transports, are however tightly coupled through the surface wind forcing of the ocean. We use here the simplest setup for including the effects of the ocean circulation : an aqua-planet with the atmosphere coupled to a 2-layer slab ocean in which the Ekman currents and eddy diffusion can be parameterized. We first show how the interactive ocean strongly damps in the Tropics the atmospheric response to a prescribed inter-hemispheric heat transport. We then apply the same method for a doubling of CO2 : the response of the total meridional energy transport remains weak in the Tropics, but with strong compensation between the atmosphere and ocean components. As a result, the classic circulation response - weaker and broader Hadley cell, poleward jet shift, precipitation changes - is significantly modified.