Multiyear and SHEBA-year simulations of Arctic ocean-atmosphere-ice interactions with a single column version of CCSM2

A goal of the Surface Heat Budget of the Arctic Ocean (SHEBA) project is to improve the simulation of arctic ocean-atmosphere-ice interactions in global climate models, using observations acquired during a one-year experiment. Here we study how changes to model parameters and physical formulas affect simulations of the SHEBA year, and simulations of multidecadal average climate. Time dependent budgets of heat, moisture, and ice mass are simulated in a column representing the upper ocean, sea-ice and atmosphere of the Arctic Ocean, using a single column model (SCM) version of the Community Climate System Model version 2 (CCSM2). Atmospheric advection of heat and moisture are prescribed as forcing functions from (a) ECMWF forecast-assimilation model products following the drift of the SHEBA ice station, 1997-98, and (b) NCEP analyses for a central Arctic gridpoint during 1948-1998. For the SHEBA year, the SCM oversimulates cloud fraction in winter, cloud water content in summer, and surface albedo in summer. The model melt season begins one week later than observed and heating of the upper ocean is smaller than observed during the spring-summer transition season. Adjustments are made to physical parameters and formulas in the model in an attempt to fit the SHEBA observations more closely. The implications of these adjustments for longer term climate are explored with simulations using the NCEP forcing. Parameters and formulas considered include the relative humidity thresholds in the cloud fraction parameterization, the rate of autoconversion of cloud ice to precipitation, and the surface albedo formulation including specific dependence on melt pond area and depth.