Atmospheric Modeling at the Climate Modeling Initiative (CMI)

The Climate Modeling Initiative (CMI) is pursuing two parallel strands in Atmospheric model development: (1) an Atmospheric model of InterMediate complexity (AIM) which has simplified physics and high computational efficiency. AIM is being coupled to an ocean and fully coupled millennial timescale integrations are underway; and (2) a 'high-end' atmospheric model which utilizes complex parameterizations of the land surface, boundary layers, convection and radiation.

Both models use the hydrodynamical core of MITgcm.
Hydrodynamical kernel based on MITgcm

MITgcm simulates atmospheric dynamics by exploiting the isomorphism between the equations governing a Boussinesq ocean in z-coordinate and the compressible (hydrostatic) atmosphere in p-coordinates (see Marshall et al, 2003). This novel approach brings a number of advantages:

(1) all the software development (muti-processor, multi-threading, post processing) is available for deployment in the simulation of both fluids
(2) algorithmic developments benefits both atmosphere and ocean, e.g., the partial cell approach developed in an oceanic context is now used in our atmospheric model in the implementation of the Eta coordinate.
(3) advection schemes suitable for highly non linear dynamics, that have been validated in an atmospheric context, can readily be used for eddy-resolving oceanic simulation. And few other advantages are expected to come from a closer interaction between atmospheric and oceanic scientists working with the same model. Here after, examples of developments that were primarily required for atmospheric dynamics are detailed.

The kernel is implemented on the cubed sphere, employs an Eta vertical coordinate with a non-linear lower boundary condition.