One-dimensional mixed layer ocean and sea ice model with prescribed oceanic heat transport

Abstract

We describe a simple two-layer thermodynamic ocean-ice model, which has been developed for coupling to an atmospheric general circulation model (GCM). The model ocean is thermally active above the annual mixed layer maximum. It consists of an upper mixed layer, which exchanges heat with the atmosphere through radiative, latent and sensible heat fluxes, and a deeper oceanic layer, which exchanges heat with the mixed layer through entrainment and detrainment. Heat transport caused by advection and diffusion is calculated as the implied oceanic heat divergence/convergence resulting from net heat flux into the ocean when the GCM is forced by observed sea surface temperature (SST). The variation in mixed layer depth is prescribed from climatology, while the SST and heat storage between the mixed layer depth and its annual maximum is predicted by the model. Cooling of sea water at its freezing point results in formation of sea ice and possible accumulation of snow. Ice and snow thickness are prognostic variables in the thermodynamic sea ice model. Results are presented from two 30 year runs with oceanic mixed layer and sea ice model coupled to the CSU GCM. One run demonstrates the ability of the coupled system to simulate the current climate while the second coupled run is an instantaneous 2 x CO2 scenario.