Radiation-circulation Destabilization of ITCZ Latitude in an Idealized GCM: Response to External Forcing (Invited Presentation)

We have found that an idealized aquaplanet moist global atmospheric model (GCM) with realistic clear-sky radiative transfer but no cloud radiative effects and no convective parameterization possesses multiple climate equilibria. When forced symmetrically about the equator, the ITCZ can migrate to an off-equatorial equilibrium position, provided a slab ocean boundary condition has sufficiently large heat capacity. Mechanism denial experiments prescribing relative humidity suggest that radiation-circulation coupling is essential to this instability. Having enumerated requisite aspects of model configuration and sensitivity to parameters in Zurita-Gotor et al. 2023, I will present new GCM simulations where we i) alter the carbon dioxide concentration and ii) impose hemispheric asymmetry in the boundary conditions. Starting from a control simulation that exhibits the ITCZ destabilization, multiple equilibria persist under perturbed carbon dioxide concentration. The simulations with imposed hemispheric asymmetry are used to investigate whether the ITCZ always resides in the higher-energy hemisphere (or can multiple equilibria persist?) and quantify how ITCZ location differs from model configurations that do not exhibit multiple equilibria (i.e., is there an amplification of the equilibrated degree of hemispheric asymmetry?). These results probe the potential for non-uniqueness of climate states to complicate studies with idealized models of the tropical response to perturbations for two key classes of forcing.