Narrowing of the ITCZ in a warming climate: Physical mechanisms
The Intertropical Convergence Zone (ITCZ) narrows in response to global warming in both observations and climate models. However, a physical understanding of this narrowing is lacking. Here we show that the narrowing of the ITCZ in simulations of future climate is related to changes in the moist static energy (MSE) budget. MSE advection by the mean circulation and MSE divergence by transient eddies tend to narrow the ITCZ, while changes in net energy input to the atmosphere and the gross moist stability tend to widen the ITCZ. The narrowing tendency arises because the meridional MSE gradient strengthens with warming, whereas the largest widening tendency is due to increasing shortwave heating of the atmosphere. The magnitude of the ITCZ narrowing depends strongly on the gross moist stability and clouds, emphasizing the need to better understand these fundamental processes in the tropical atmosphere.
© 2016 American Geophysical Union. Received 11 JUL 2016; Accepted 14 OCT 2016; Accepted article online 22 OCT 2016; Published online 9 NOV 2016. We thank Paulo Ceppi, Angie Pendergrass, and Robert Wills for helpful discussions. We also thank two anonymous reviewers for their comments and suggestions.
Supplemental Material - grl55148-sup-0001-supplementary.pdf