Parallel Climate Model Effort (Version 1)

This is a joint effort to develop a DOE-sponsored parallel climate model between Los Alamos National Laboratory (LANL), the Naval Postgraduate School (NPG), the US Army Corps of Engineers' Cold Regions Research and Engineering Lab (CRREL) and the National Center for Atmospheric Research (NCAR). We have coupled the NCAR Community Climate Model version 3, the LANL Parallel Ocean Program, and a sea ice model from the Naval Postgraduate School together in a massively parallel computer environment. This is Version 1 of the PCM (PCM1).

Our target machines were the CRAY T3D/T3E and SGI Origin 2000. With the close cooperation and assistance of NCAR's Scientific Computing Division, the PCM1 model code has been ported to the Hewlett-Packard, the SGI Origin 2000, the IBM SP2, and Compaq.

Based on the experience with the NCAR Climate System Model, in order to minimize the initial drift of the coupled system, the ocean/ice can be spun-up with forcing from previous CCM3 runs with prescribed ocean temperatures. This has also been useful in demonstrating and improving the kind of adjustments that occur in the ocean and ice due to coupling the CCM3, without having to run the more expensive coupled system. The full system has been in full production with several control experiments and many ensemble climate change simulations in progress and completed.

Atmospheric Component

The atmospheric component is the massively parallel version of the NCAR Community Climate Model version 3.2 (CCM3). This model includes the latest versions of radiation, boundary physics, and precipitation physics and is a state-of-the-art atmospheric component. The CCM3 also includes the land surface model (LSM) which takes into account soil physics and vegetation.

Ocean Component

We have a limited spin-up of a moderate resolution global ocean model with a displaced pole grid using the POP (Parallel Ocean Program) model. The grid is 384 x 288 x 32, with an average resolution of 2/3 degree latitude and longitude with increased latitudinal resolution near the equator of approximately 1/2 degree. Because of the displaced pole, there is relatively higher horizontal resolution in the eastern North Pacific, in the Arctic Straits near northern Canada and Greenland, and in the Gulf Stream area. Also, the continents and bottom topography were carefully modified to obtain realistic flow in many regions throughout the globe. This model is being spun up with observed surface and subsurface forcing in preparation for coupling. We also plan to add more realistic ocean parameterizations to the model. The model in its present form yields an extraordinary simulation of the Arctic Ocean, tropical Pacific, and boundary currents, such as the Gulf Stream, with eddies solved in most basins. We have developed tools to interpolate the model output to regular grids. Integrations have been run on the T3D and SGI Origin at NCAR, National Energy Research Supercomputing Center's T3E, and an SGI Origin at LANL.
More documentation on the POP model can be found in Los Alamos report LA-UR-95-1146 by Richard D. Smith, Samuel Kortas, Bertrand Meitz, Curvilinear Coordinates for Global Ocean Models, pp 38.

Sea Ice Component

The PCTM dynamic-thermodynamic sea ice model has been developed by combining two existing sea ice models from collaborating institutions: the ice dynamics of the elastic-viscous-plastic model of Hunke and Dukowicz (Los Alamos CICE model, 1997) with the thermodynamics and ice thickness distribution model from the University of Washington (Bitz 2000; and Bitz and Lipscomb, 1999). The PCTM ice model contains the same physics as the 2001 version of the NCAR CCSM sea ice component, although the two models have different adaptations for time-sequence in coupling to the other components and for separate execution on parallel processors.

The ice thermodynamics have been completely replaced from what was in PCM-1 (see description) to a more complete thermodynamic treatment. The ice thermodynamics include: (i) the energy- and mass-conserving 1-D thermodynamics of Bitz and Lipscomb (1999), (ii) four vertical layers to resolve vertical temperature gradients in the ice, and (iii) temperature and salinity-dependent thermal properties for sea ice derived from a fixed salinity profile. The model also calculates a ice-state-dependent ice thickness distribution based on the treatment of Bitz et al. (1999). Thickness distribution calculations will normally use 5 thickness categories where separate thermodynamic calculations determine, for each category, quantities such as average albedo, rates of ice growth or melt, vertical heat exchange at the surface, and transmission of solar radiation to the ocean.

The ice dynamics use the Hunke (2001) updated version of the elastic-viscous-plastic (EVP) rheology to solve the ice momentum equation, which balance the forces on the ice: wind stress, ocean currents, Coriolis force, gravitational tilt of the ocean surface, inertia, and internal stress of the ice pack. The ice pack resists compression and shear stress, and divergence under shear, and follows the elliptical yield curve of the Hibler (1979) model. The EVP approach is an explicit solution of the ice stress tensor, as opposed to the implicit iterative solution of the Hibler or more recent Hibler and Zhang (1997) model. The EVP solution velocities compare very closely to those of the Hibler and Zhang model, with a considerable improvement in the parallel performance.

The Hunke and Dukowicz ice model is written in general orthogonal coordinates, so it runs on the same dipole grid as the ocean component (POP). This provides a resolution of ranging between 25 km and 60 km over much of the Arctic, and resolves not only the Fram Strait and Bering Strait, but also much of the Canadian Archipelago.

Early results of ice simulation from the PCTM are shown in the papers linked below (PDF format):

Weatherly, J.W., and C. M. Bitz, 2001: Natural and Anthropogenic Climate Change in the Arctic. 12th Symposium on Global Change and Climate Variations, AMS.

Weatherly, J. W., C. M. Bitz, and E. C. Hunke, 2001: Parallel Climate Model Simulations with a Dynamic-Thermodynamic Ice Thickness Distribution Model. Sixth Conference on Polar Meteorology and Oceanography, American Meteorol. Soc., Boston. (submitted).

River Transport Component

The river transport model (RTM) was developed by Marcia Branstetter and Jay Famiglietti, researchers at the University of Texas, Austin, based on the work of Vörösmarty (1989) and Miller (1994). This river routing scheme uses the atmospheric T42 grid. The RTM takes into account river flow mass and river direction in each watershed to pass water to the oceans.

Images of the RTM's river basins with vectors representing river flow direction
Global Asia Europe N America S America
Global Asia Europe North America South America

Flux Coupler

The method of tying the components together and allowing the exchange of fluxes and variables is the flux coupler. The flux coupler is fully implemented. Since the grid components are different, there is an interpolation scheme for passing information between the atmospheric component grid and the ocean/sea ice grid that has been developed by P. Jones of LANL.

Present and Future Experiments

An important part of the IPCC debate (IPCC, 1994) is the concept of stabilizing CO2 and trace gas emissions at some reference level. Depending on the reference level of stabilization, various climate change patterns could result. We have run many experiments with greenhouse gas concentrations and sulfate aerosol scenarios We have been asked to perform some National Assessment simulations that can be used by the climate impacts community. All of these experiments are related to the energy mission of the DOE.

We also intend to perform climate change detection/attribution experiments with various combinations of forcing from ozone changes, biomass burning, and solar forcing, in addition to increased greenhouse gases and sulfate aerosols. Some of the experiments will start from the 1870 initial condition and run to the present, and then extended to the year 2100.