Abstract
AbstractThe Intertropical Convergence Zone (ITCZ) is a discontinuous, zonal precipitation band that plays a crucial role in the global hydrological cycle. Previous studies using prescribed sea surface temperature (SST) aquaplanets show the ITCZ is sensitive to convective mixing, but such a framework is energetically inconsistent. Studies also show that atmosphere‐ocean coupling reduces the sensitivity of the ITCZ to hemispherically asymmetric forcing. We investigate the effect of atmosphere‐ocean coupling on the sensitivity of the ITCZ to convective mixing using an idealized modeling framework with an Ekman‐driven ocean energy transport (OET). Coupling reduces the sensitivity of the ITCZ location to convective mixing due to SST changes. In prescribed‐SST simulations reducing convective mixing promotes a double ITCZ, while in coupled simulations, it increases the meridional SST gradient which promotes an equatorward ITCZ shift. Prescribing OET in additional experiments has a minimal effect on the sensitivity of the ITCZ location to mixing but does increase the sensitivity of the ITCZ intensity by constraining the net‐downward surface energy flux. Decreasing convective mixing increases net‐downward shortwave cloudy‐sky radiation associated with increased latent heat fluxes and an intensified ITCZ. For simulations analyzed the atmospheric energy input framework is inadequate to study ITCZ dynamics due to the contribution of transient eddies to the atmospheric energy transport. Prescribing SST or OET may strengthen the sensitivity of the ITCZ to a change in parameterization or atmospheric forcing. Future modeling studies investigating the precipitation response to such changes should be aware of the potential sensitivity of their results to atmosphere‐ocean interactions.
Highlights
The Intertropical Convergence Zone (ITCZ) is a discontinuous zonal precipitation belt with some of the heaviest rainfall observed on Earth
In this study we develop an idealized atmosphere‐ocean coupled model, with an interactive ocean energy transport (OET) based on the meridional Ekman‐driven ocean circulation, to quantify the effect of atmosphere‐ocean coupling on the sensitivity of the ITCZ to convective mixing
In this study we investigate the validity of that assumption in our idealized simulations, whether an atmospheric energy input (AEI) framework should be used to understand the sensitivity of the ITCZ structure to the representation of convection in a coupled atmosphere‐ocean modeling configuration
Summary
The Intertropical Convergence Zone (ITCZ) is a discontinuous zonal precipitation belt with some of the heaviest rainfall observed on Earth. Modeling tropical rainfall is one of the greatest challenges faced in climate science (Bush et al, 2015; Sperber et al, 2013). The latest coupled GCMs simulate similar tropical precipitation maxima in each hemisphere (Lin, 2007; Tian & Dong, 2020). This bias is commonly known as the “double ITCZ bias”; it is associated with a positive precipitation bias in the South Pacific
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