Other major changes since CCSM3 include increased vertical resolution in the upper ocean, incorporation of an abyssal tidal mixing parameterization ( Jayne 2009), and new prescriptions for anisotropic horizontal viscosities ( Jochum et al. 2008), a prescription for lateral tracer diffusivities that vary in the vertical ( Danabasoglu and Marshall 2007), and a submesoscale mixed layer eddy parameterization ( Fox-Kemper et al. 2010), a near-surface eddy flux parameterization ( Danabasoglu et al. Specifically, the CPTs on gravity current entrainment and eddy–mixed layer interactions resulted in an overflow parameterization ( Danabasoglu et al. Climate Variability and Predictability (CLIVAR) Climate Process Team (CPT) activities.
A significant fraction of the new subgrid-scale parameterizations were realized through our collaborations with the university communities that participated in the U.S.
BERING WAVE BEHR SOFTWARE
(2006) used in the CCSM3 simulations the base code has been updated to POP version 2 (POP2) and many physical and numerical software developments have been incorporated. The present version differs significantly from the one described in Danabasoglu et al. The ocean component of the CCSM4 is a level-coordinate model based on the Parallel Ocean Program (POP) of the Los Alamos National Laboratory ( Smith et al. The description of the nominal 3° horizontal resolution ocean model and the results from CCSM4 simulations that use this coarser-resolution ocean coupled to a T31 atmospheric model are discussed in Shields et al. The CCSM4 coupled solutions are from the version that also uses nominal 1° horizontal resolution in its atmospheric component. Here, we focus on the nominal 1° horizontal resolution version of the ocean model. In addition, the solutions from an ocean–sea ice hindcast case forced with interannually varying atmospheric data are documented in comparison with observations as well as the 20C simulations, the former to assess the fidelity of the forced ocean simulations and the latter for possible attribution of ocean model biases in the coupled integrations. The primary purposes of this paper are i) to describe the CCSM4 ocean component, highlighting major developments since CCSM3 ii) to document the CCSM4 ocean model solutions from the twentieth-century (20C) simulations in comparison with available observations and those of CCSM3, presenting improvements as well as existing biases in CCSM4 and iii) to assess the consequences of two different spinup procedures used in CCSM3 and CCSM4 on the deep ocean properties. A general description of the CCSM4 and some of the major improvements in its solutions in comparison with its previous version CCSM3 are presented in Gent et al. The Community Climate System Model version 4 (CCSM4) was released to the community in April 2010. As a result of this latter bias in the deep North Atlantic, the parameterized overflow waters cannot penetrate much deeper than in CCSM3. There is also a deep salty bias in all basins. This heat loss largely reflects the top of the atmospheric model heat loss rate in the coupled system, and it essentially determines the abyssal ocean potential temperature biases in the 20C simulations. A major concern continues to be the substantial heat content loss in the ocean during the preindustrial control simulation from which the 20C cases start.
Despite these improvements, many of the biases present in CCSM3 still exist in CCSM4.
Other improvements include a global-mean SST that is more consistent with the present-day observations due to a different spinup procedure from that used in CCSM3. These include a better equatorial current structure, a sharper thermocline, and elimination of the cold bias of the equatorial cold tongue all in the Pacific Ocean reduced sea surface temperature (SST) and salinity biases along the North Atlantic Current path and much smaller potential temperature and salinity biases in the near-surface Pacific Ocean. In comparison with CCSM3, the new solutions show some significant improvements that can be attributed to these model changes. The improvements to the ocean model physical processes include new parameterizations to represent previously missing physics and modifications of existing parameterizations to incorporate recent new developments. The ocean component of the Community Climate System Model version 4 (CCSM4) is described, and its solutions from the twentieth-century (20C) simulations are documented in comparison with observations and those of CCSM3.
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