A quasi-geostrophic coupled model (Q-GCM)

The design and implementation of a midlatitude basin-scale coupled climate model are described. The development of the model is motivated by the clear indications of important low-frequency midlatitude ocean variability in ocean-only models and the lack of the same in coupled climate models. Currently, the best comprehensive coupled climate models run at resolutions far coarser than those needed to model intrinsic ocean variability. The model presented here is an attempt to explicitly include ocean eddies within the framework of an idealized climate setting. It is proposed that the model will help resolve how intrinsic ocean variability is altered by coupling and the extent to which such variability may force the climate. The objective of this paper is to describe the theory behind the model formulation and its implementation. The basic model consists of a quasigeostrophic channel atmosphere coupled to a simple, rectangular quasigeostrophic ocean. Heat and momentum exchanges between the ocean and the atmosphere are mediated via mixed-layer models, and the system is driven by steady, latitudinally dependent incident solar radiation. Model spinup is described, some basic descriptors of the solution are discussed, and it is argued that the model exhibits skill in capturing essential features of the midlatitude climate system.