Tropical Dynamics and Warming in Simplified Atmosphere-Ocean Simulations.

(Tuckman, P.J., and Marshall, J.), Journal of Climate, vol. 39, no. 1, pp. pages, 2026.

Abstract

The Hadley circulation, tropical sea surface temperatures (SSTs), and the tropical rain belt are key features of the tropical climate. In this work, we use simplified atmosphere–ocean simulations with no continents to study these phenomena and their response to greenhouse warming in an idealized setting. Without ocean dynamics, tropical precipitation strengthens with warming, while the Hadley circulation weakens but transports more energy out of the tropics. Meanwhile, the intertropical convergence zone (ITCZ) moves sinusoidally north and south following solar insolation over the seasonal cycle, and the meridional extent of this annual oscillation decreases with warming. In simulations with ocean dynamics, the ocean exports energy from the deep tropics, smoothing tropical SST gradients and creating an SST minimum at the equator. This leads to an ITCZ which straddles the equator in the annual mean and has a square-wave-like seasonal cycle, with rapid fall and spring transitions of peak precipitation between the hemispheres. Atmosphere and ocean changes with warming, as well as associated shifts in SST structure, are examined using an analytic framework based on a tropical energy balance model constructed from simple relationships between SST, mass transport, and energy transport. The simplified simulations and analytic model used here have implications for important features of the tropical climate such as the double-ITCZ bias, monsoon onset, and changes to the Hadley cells under greenhouse warming.

doi = 10.1175/JCLI-D-24-0685.1