Sensitivity of sea ice to physical parameterizations in the GISS global climate model

Abstract

The GISS coupled model is used to investigate the sensitivity of sea ice to each of the following parameterizations: (1) two sea ice dynamics (CF: cavitating fluid; VP: viscous-plastic), (2) the specification of oceanic isopycnal mixing coefficients in the Gent and McWilliams isopyncal mixing (GM), and (3) the wajsowicz viscosity diffusion (WV). The large-scale sea ice properties are highly sensitive to sea ice dynamics. With the inclusion of resistance to shear stress, VP captures the major observed sea ice drift features and improves the simulations of sea ice concentrations, thickness, and export through Fram Strait relative to CF. GM significantly improves the simulation of vertical temperature distributions in the Southern Ocean, although it leads to a dramatic reduction of Antarctic sea ice cover. The reduced oceanic isopycnal mixing coefficients lead to Arctic sea ice that tends to be less and thinner in almost the entire Arctic except in the North Pacific and Labrador Sea, while Antarctic sea ice that extends more equatorward throughout the circumpolar regions. The responses of sea ice to WV show an enlargement and thickening of sea ice in the Arctic, within the ice packs around the Antarctic and a reduction and thinning of sea ice in the northern Weddell and Ross Seas. On the basis of these experiments, two composite experiments with the best parameterizations are investigated. The atmospheric responses associated with sea ice changes are discussed. While improvements are seen, there are still many unrealistic aspects that will require further improvements to sea ice and ocean components.