Brief Overview of the Model

The CCM2 is primarily a spectral model, meaning that the time integration is done in the spectral domain. The physics and nonlinear advection calculations are done in the grid point domain. Moisture is handled nonspectrally, using a semi-Lagrangian solver. The version for the present study has a horizontal spectral resolution of T42 and a corresponding grid resolution of approximately 2.8 by 2.8 degrees, giving 64 by 128 horizontal grid points. CCM2 has 18 vertical levels.

Radiation calculations are performed using the delta-Eddington method for the shortwave radiation [1] and and solving the transfer equations for the longwave radiation using absorptivities and emissivities. Moist convection uses the mass flux convective parameterization of [5]. The present version of CCM2 has specified moisture over the land surface. Later versions have incorporated the Biosphere Atmosphere Transfer Scheme (BATS) as an additional option. A detailed description of the CCM2 is given in [6].

The algorithm for the climate model can be summarized as follows:

1. Compute physics and nonlinear interactions in the physical grid-space.
2. Convert the variables to spectral space.
3. Compute the tendencies, and update the variables (excluding moisture) to the latest time step.
4. Perform inverse transform of the variables to physical space.
5. Compute and update moisture in the physical space using the semi-Lagrangian method and repeat steps 1-5.