Nonlinear Damping of ITCZ Migrations Due to Ekman Ocean Energy Transport

The role of tropical wind-driven ocean circulation in setting the position of the Intertropical Convergence Zone (ITCZ) is studied using an atmospheric model coupled to a slab ocean with parameterized Ekman energy transport. Unlike previous studies, the parameterized cross-equatorial ocean energy transport, which is critical for the coupled response, is explicitly represented as the curl of the wind stress at the equator. A nonlinear sensitivity of the ITCZ position to hemispherically asymmetric heating and ocean stratification is seen, which is primarily linked to the partitioning of cross-equatorial energy transport between (i) the atmosphere and ocean and (ii) atmospheric mean and transient eddy components. Due to the nonmonotonic response of transient eddies to the asymmetric heating, amplified or damped response is possible. The common assumption of a linear relation between the ITCZ position and hemispherically asymmetric heating is therefore found to be inadequate when large climatic variations are considered.