Development of a Sea Ice Model for Use in Zonally Averaged Energy Balance Climate Models

Abstract

A sea ice model for use in zonally averaged energy balance climate models is presented which includes the following processes: surface melting, basal freezing and melting, lateral melting from ice-flee water or growth of new ice in leads, snowfall and the formation of white ice, ice advection, and a parameterized ice and snow thickness distribution which represents the effects of small-scale dynamics. The ice growth equations of Hibler are solved analytically, thereby permitting a gradual increase in zonal ice fraction in fall and winter. Both lateral and vertical melting lead to a continuous decrease of ice fraction during ice decay. The correlation between ice thickness and ice thickness sensitivity to the upward heat flux at the ice base is of opposite sign seasonally and latitudinally. The parameterized feedback between ice thickness and the minimum permitted lead fraction is found to be very important to the ice simulation, and is a process which needs to be studied using higher resolution, dynamic-thermodynamic sea ice models. The interaction between lateral melting and advection is crucial to the simulated rapid retreat of Southern Hemisphere ice area in spring. With uniform snow on ice, the introduction of an ice-thickness distribution increases mean annual ice thickness by up to 20%, but simultaneously introducing an ice and snow thickness distribution such that the ratio of snow to ice thickness is constant for each ice thickness category leads to increase of mean ice thickness of up to 90%. The effect on mean annual sea ice thickness of the parameterized surface albedo temperature dependence tends to increase with increasing latitude, even though the length of the melt season and incident solar radiation decrease with latitude. Model sensitivity to variation of time-step length from 1 to 6 days is insignificant.