The Xiamen Symposium on Marine Environmental Sciences (XMAS 2025)

136 / 2024-09-09 15:31:57

Enhanced “wind-evaporation effect” drove the “deep-tropical contraction” in the early Eocene

the ITCZ,energy balance,early Eocene,Global Climate Change

The equatorward contraction of tropical precipitation, commonly referred to as the “deep-tropical contraction”, is witnessed in the paleoclimate simulations of the early Eocene. However, the mechanism driving this contraction is still unclear. Based on the energetics framework of the Intertropical Convergence Zone (ITCZ) and the decomposition method of the latent heat flux along with the simulations of a climate system model, CESM1.2, we proposed a novel mechanism responsible for the “deep-tropical contraction” in the early Eocene. The greenhouse gases-induced sea surface warming amplifies the sensitivity of evaporation to surface wind speed changes through Clausius-Clapeyron scaling, leading to an interhemispheric asymmetric enhancement of the latent heat flux. To maintain hemispheric energy balance, the cross-equatorial atmospheric energy transport must be reduced during the solstice seasons. As a result, the solstitial location of the ITCZ shifts equatorward, causing the “deep-tropical contraction” in the early Eocene.