Influence of the Sea Ice Thickness Distribution on Polar Climate in CCSM3

Abstract

The sea ice simulation of the Community Climate System Model version 3 (CCSM3) T42-gx1 and T85-gx1 control simulations is presented and the influence of the parameterized sea ice thickness distribution (ITD) on polar climate conditions is examined. This includes an analysis of the change in mean climate conditions and simulated sea ice feedbacks when an ITD is included. It is found that including a representation of the subgrid-scale ITD results in larger ice growth rates and thicker sea ice. These larger growth rates represent a higher heat loss from the ocean ice column to the atmosphere, resulting in warmer surface conditions. Ocean circulation, most notably in the Southern Hemisphere, is also modified by the ITD because of the influence of enhanced high-latitude ice formation on the ocean buoyancy flux and resulting deep water formation. Changes in atmospheric circulation also result, again most notably in the Southern Hemisphere.There are indications that the ITD also modifies simulated sea ice-related feedbacks. In regions of similar ice thickness, the surface albedo changes at 2XCO 2 conditions are larger when an ITD is included, suggesting an enhanced surface albedo feedback. The presence of an ITD also modifies the ice thickness-ice strength relationship and the ice thickness-ice growth rate relationship, both of which represent negative feedbacks on ice thickness. The net influence of the ITD on polar climate sensitivity and variability results from the interaction of these and other complex feedback processes.

Simulation of the Global Hydrological Cycle in the CCSM Community Atmosphere Model Version 3 (CAM3): Mean Features

“…As the ice volume flux depends on both the thickness and velocity of the sea ice, the good agreement with observations suggests that both of these properties are reasonably simulated. This does appear to be the case, as discussed further in Holland et al (2005) and DeWeaver and Bitz (2005). On the long-term average, the northern hemisphere CCSM3 sea ice covers 10 million km with a mean thickness of approximately 2 m. Accounting for the ice salinity, this represents a freshwater storage of 18,450 km .…”

“…This corresponds to an annual average area of 12 million km with an average thickness of approximately 1.4 m and a salinity of 4ppt. As discussed in Holland et al (2005), the simulated area of Antarctic sea ice is large compared to observations, which have an annual average of approximately 9-10 million km .…”

“…However, the ice thickness is excessive, particularly in the Weddell Sea (Holland et al 2005), resulting in the high meridional transport. This excessive ice transport and melting along the ice edge, modifies the ocean sea surface salinity conditions, resulting in a fresh bias along the Antarctic sea ice edge in the south-western Atlantic.…”

Inherent sea ice predictability in the rapidly changing Arctic environment of the Community Climate System Model, version 3

“…Holland et al 2006a;Gerdes and Koberle 2007). This includes a realistic mean and spatial distribution of Arctic ice thickness and reasonable ice mass budget terms (Holland et al 2008a), although the Fram Strait ice volume transport is about 50% higher than observed (Holland et al, 2006b). The summer ice extent is very well simulated compared to satellite observations (Fig.…”

“…The ocean model (Smith and Gent 2004) includes an isopycnal transport parameterization (Gent and McWilliams 1990) and a surface boundary layer formulation following Large et al (1994). The dynamic-thermodynamic sea ice model (Briegleb et al 2004;Holland et al 2006b) uses the elasticviscous-plastic rheology (Hunke and Dukowicz 1997), a sub-gridscale ice thickness distribution (Thorndike et al 1975;Lipscomb 2001) and the thermodynamics of Bitz and Lipscomb (1999). Both the ice and ocean models use a nominally 1-degree resolution grid in which the north pole is displaced into Greenland.…”