Impact of a New Sea Ice Thermodynamic Formulation in the CESM2 Sea Ice Component
We investigate the role of a new approach for sea ice thermodynamics in the Community Earth System Model, based on mushy‐layer theory. The new approach predicts salinity changes within the ice and produces thicker sea ice in the Arctic, with subsequent impacts on the atmosphere and ocean, than the previous thermodynamics approach with a fixed salinity profile. The primary factor producing the difference between simulations using the two thermodynamic schemes is the fraction of snow on the ice.
Changes in the thermodynamics and resulting ice state due to the new physical parameterization for thermodynamics modify the simulated ice‐ocean‐atmosphere fluxes in the fully coupled CESM2 model, with impacts on the atmosphere and ocean states, particularly temperature.
The mushy-layer thermodynamic scheme produces thicker and more extensive ice overall in both hemispheres relative to the Bitz and Lipscomb (BL99) thermodynamics used in earlier CESM versions. In contrast to stand-alone simulations in which formulations for melt pond drainage, shortwave radiation, and thickness changes drove differences between the two thermodynamic schemes, in coupled simulations, the snow fraction is the main factor driving differences, with additional contributions from surface melt and melt pond coverage, frazil ice formation, and congelation growth. The balance of melt and growth leads to thicker ice in the mushy simulation. Despite the thicker sea ice in the mushy run, the impacts on the rest of the coupled system are relatively minor, with small differences in the surface air temperature over the sea ice and the sea surface salinity and temperature. These differences in the atmosphere and ocean also feedback on the sea ice in the coupled system.