Improved representation of sea‐ice processes in climate models

The apparent sensitivity of high latitudes to climate perturbations has spurred the development of global climate model components with improved parametrizations of sea-ice related processes.We focus on two of these.The first involves the ocean component in which we generalize a recently developed parametrization of brine rejection during sea-ice formation for use in a multi-category sea-ice model (i.e., one that resolves the thickness distribution function).The parametrization employs initial subsurface mixing of brine-enriched surface waters resulting from sea-ice growth.It is implemented in the University of Victoria coupled model, and numerical experiments are performed to highlight the physical processes and feedbacks involved.It is shown that a better representation of brine rejection improves the simulation of intermediate and deep ocean waters.Over the Arctic Ocean it also improves the simulation of the warm Atlantic Layer and sharpens the halocline.The second part of this paper focuses on the sea-ice component.We perform a series of stand-alone sea-ice model experiments comparing a recently developed multi-layer energy-conserving thermodynamic scheme with the simplified scheme used in many existing climate models.Experiments are done with and without the inclusion of dynamic processes (ice motion and deformation).Of particular interest is the impact of changes in the representation of dynamic and thermodynamic processes on the response of sea ice to climate perturbations.This is accomplished by comparing results obtained with present-day and future climate forcing, the latter obtained from the Canadian Centre for Climate Modelling and Analysis (CCCma) coupled climate model.We find that the more sophisticated thermodynamic scheme increases the sensitivity of ice volume, but decreases the sensitivity of ice area.As in previous studies, the introduction of ice dynamics tends to reduce sensitivity relative to a thermodynamic-only model.