The role of diurnal processes in the seasonal evolution of sea ice and its snow cover

Diagnostic comparisons between hourly and daily average forcing simulations using a one-dimensional thermodynamic sea-ice model show significant differences due to diurnal changes in the surface energy balance that directly affect the snow layer and indirectly affect modeled ice conditions. Hourly forcing produced sooner onset of snow melt compared to daily average forcing and a 21 day longer open water duration. These differences are due to non-linearities associated with absorbed shortwave radiation as well as latent and sensible heat fluxes. The accuracy of model parameterizations of downwelling shortwave (K down arrow) and longwave (K down arrow) fluxes and albedo over diurnal time scales is assessed by comparison to field observations made during the Seasonal Ice Monitoring and Modeling Site (SIMMS) 1992/93 field experiments near Resolute Bay, NWT. Mean K down arrow errors (modeled-observed) were -23 W m(-2) with a standard deviation of 89 W m(-2) and mean L down arrow errors were -1 W m(-2) with a standard deviation of 18.8 W m(-2). Modeled dry/new snow and wet snow albedos were about 0.1 and 0.05, respectively, lower than those observed, allowing greater amounts of shortwave energy absorption into the snowpack. Using SIMMS'92 on-ice field data as replacement for model K down arrow, L down arrow and albedo parameterizations shows very different spring period simulations compared to using hourly forcing from Resolute land-based observations. Simulated net surface flux, surface temperature and snow/ice ablation were significantly improved..