Simulations of Snow, Ice, and Near-Surface Atmospheric Processes on Ice Station Weddell

Abstract

The 4-month drift of Ice Station Weddell (ISW) produced over 2000 h of nearly continuous measurements in the atmospheric surface layer and in the snow and sea ice in the western Weddell Sea. This paper reports simulations, based on these data, of processes in the air, snow, and sea ice at ISW using SNTHERM, a one-dimensional mass and energy balance model. An earlier version of SNTHERM had to be adapted, however, to treat the flooding that often occurs on sea ice in the western Weddell Sea. To treat this layer of slush and brine, SNTHERM holds the brine salinity constant at its initial value of 31.5 psu until 80% of this slush layer freezes. The current version of SNTHERM also incorporates a new parameterization for the roughness length for wind speed, z0, derived from analyses of ISW eddy-covariance data. SNTHERM's simulations are validated with temperature measurements within the ice and snow and with eddy-covariance measurements of the surface momentum and sensible and latent heat fluxes. The simulated turbulent fluxes agree fairly well with the measured fluxes, except the simulated sensible heat flux is biased low by 4?5 W m?2 for both stable and unstable stratification. The simulated temperature profiles in the snow and ice also agree well with the measured temperatures. In particular, allowing seawater to flush the slush layer until it is 80% frozen delays the freezing of this layer such that its behavior mirrors the data.