The Effect of Atmosphere-Ocean Coupling on the Sensitivity of the ITCZ to Convective Mixing

The 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 idealised modelling 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, whilst 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 analysed 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 parameterisation or atmospheric forcing. Future modelling studies investigating the precipitation response to such changes should be aware of the potential sensitivity of their results to atmosphere-ocean interactions.