Energy and water transport in climates simulated by a general circulation model that includes dynamic sea ice

We analyze energy and water transport in present, doubled CO 2 , and tripled CO 2 climates simulated by the Mark 2 CSIRO nine-level general circulation model with a mixed layer ocean. The model differs from the Mark 1 version by the inclusion of dynamic sea ice, a semi-Lagrangian water vapor transport, and an enhanced land-surface scheme, and it includes prescribed ocean heat transport. We describe a 30-year climatology of the 1xCO 2 simulation, emphasizing the sea ice and the mean meridional energy and water transport. The ice depths, concentrations, and velocities are moderately realistic in both hemispheres. Poleward energy transport is inferred (calculated indirectly from vertical energy fluxes) for both the atmosphere and ocean, although the oceanic flux is much weaker than observational estimates for the southern hemisphere. Atmospheric water transport is also poleward outside the tropics and compares well with observations. Energy transport within the ice layer has been evaluated by both direct and indirect methods. As it is largely due to the latent heat of ice formation, it is closely proportional to the water transport by ice. The meridional transports by ice of both energy and water are relatively important at high latitudes. The divergence of the ice energy transport corresponds to a significant component of the surface energy budget, reaching ±10 W m -2 or more at some polar locations. The equilibrated doubled CO 2 global mean surface warming of the Mark 2 mixed layer model is 4.3°C. The reduction from the Mark 1 result (4.8°C) follows largely from a 40% reduction of the warming over high-latitude oceans. This is attributed to the presence of dynamically induced leads in the ice cover. The equilibrated warming for 3 x CO 2 is 6.8°C. The model atmosphere transports less heat poleward in the doubled CO 2 climate, largely as a response to increased solar radiation absorbed at high latitudes. This behavior contrasts with the change at CO 2 doubling in a transient simulation by the Mark 2 model coupled to a full ocean model, in which heat is taken up in the midlatitudes, particularly by the Southern Ocean, and supplied by a net top-of-atmosphere radiative imbalance distributed over all latitudes (global mean, 1.8 W m -2 ). The atmospheric water transport is enhanced by 10-20% in the warmer climates at most latitudes.

[1]  W. Hibler.  A Dynamic Thermodynamic Sea Ice Model , 1979 .

[2]  W. Washington,et al.  A large-scale numerical model of sea ice , 1979 .

[3]  John F. B. Mitchell,et al.  Modeling climate change: An assessment of sea ice and surface albedo feedbacks , 1989 .

[4]  Ian Simmonds,et al.  The physical basis for a dynamic Antarctic sea-ice model for use with an atmospheric GCM , 1991, Annals of Glaciology.

[5]  On a simple sea-ice dynamics model for climate studies , 1990 .

[6]  P. Heil,et al.  Seasonal and interannual variations of the oceanic heat flux under a landfast Antarctic sea ice cover , 1996 .

[7]  K. Trenberth,et al.  The global heat balance: heat transports in the atmosphere and ocean , 1994 .

[8]  J. Thuburn.  Data sampling strategies for general circulation models , 1991 .

[9]  C. Covey.  Global ocean circulation and equator-pole heat transport as a function of ocean GCM resolution , 1995 .

[10]  C. Kottmeier,et al.  Atmospheric and oceanic forcing of Weddell Sea ice , 1996 .

[11]  J. Peixoto,et al.  Physics of climate , 1992 .

[12]  Barry Saltzman,et al.  Equilibrium Climate Statistics of a General Circulation Model as a Function of Atmospheric Carbon Dioxide. Part I: Geographic Distributions of Primary Variables , 1992 .

[13]  S. Power,et al.  Annual mean meridional energy transport modelled by a general circulation model for present and 2 × CO2 equilibrium climates , 1994 .

[14]  D. Ramsden,et al.  Use of a coupled ice-ocean model to investigate the sensitivity of the Arctic ice cover to doubling atmospheric CO2 , 1995 .

[15]  J. Walsh.  The Arctic as a bellwether , 1991, Nature.

[16]  S. O’Farrell,et al.  Transient Climate Change in the CSIRO Coupled Model with Dynamic Sea Ice , 1997 .

[17]  B. Hunt,et al.  Climatic variability within an equilibrium greenhouse simulation , 1994 .

[18]  Some dynamical consequences of Greenhouse gas warming , 1995 .

[19]  Donald J. Cavalieri,et al.  NASA Sea Ice Validation Program for the Defense Meteorological Satellite Program Special Sensor Microwave Imager , 1991 .

[20]  E. Kowalczyk,et al.  Implementation of a soil-canopy scheme into the CSIRO GCM -- regional aspects of the model response , 1994 .

[21]  R. Sausen,et al.  The impact of sub-grid scale sea-ice inhomogeneities on the performance of the atmospheric general circulation model ECHAM3 , 1996 .

[22]  David Rind,et al.  The role of sea ice in 2 x CO2 climate model sensitivity. Part 1: The total influence of sea ice thickness and extent , 1995 .

[23]  A. Weaver,et al.  On the incompatibility of ocean and atmosphere models and the need for flux adjustments , 1996 .

[24]  W. Brechner Owens,et al.  Coupled sea ice-mixed layer simulations for the southern ocean , 1990 .

[25]  D. Randall,et al.  Cloud-radiative effects on implied oceanic energy transports as simulated by Atmospheric General Circulation Models , 1995 .

[26]  J. McGregor,et al.  Economical Determination of Departure Points for Semi-Lagrangian Models , 1993 .

[27]  G. Meehl,et al.  A world ocean model for greenhouse sensitivity studies: resolution intercomparison and the role of diagnostic forcing , 1994 .

[28]  T. H. Haar,et al.  Estimating the Meridional Energy Transports in the Atmosphere and Ocean , 1985 .

[29]  S. Ackley,et al.  Numerical simulation of the Weddell Sea pack ice , 1983 .

[30]  A. Semtner.  A MODEL FOR THE THERMODYNAMIC GROWTH OF SEA ICE IN NUMERICAL INVESTIGATIONS OF CLIMATE , 1975 .

[31]  D. Pollard,et al.  Sea‐ice dynamics and CO2 sensitivity in a global climate model , 1994 .