1.2.1 Global atmosphere: `Held-Suarez' benchmark

A novel feature of MITgcm is its ability to simulate, using one basic algorithm, both atmospheric and oceanographic flows at both small and large scales.

Figure 1.4 shows an instantaneous plot of the 500 temperature field obtained using the atmospheric isomorph of MITgcm run at 2.8 resolution on the cubed sphere. We see cold air over the pole (blue) and warm air along an equatorial band (red). Fully developed baroclinic eddies spawned in the northern hemisphere storm track are evident. There are no mountains or land-sea contrast in this calculation, but you can easily put them in. The model is driven by relaxation to a radiative-convective equilibrium profile, following the description set out in Held and Suarez; 1994 designed to test atmospheric hydrodynamical cores - there are no mountains or land-sea contrast.

Figure 1.4: Instantaneous plot of the temerature field at 500mb obtained using the atmospheric isomorph of MITgcm

As described in Adcroft (2001), a `cubed sphere' is used to discretize the globe permitting a uniform griding and obviated the need to Fourier filter. The `vector-invariant' form of MITgcm supports any orthogonal curvilinear grid, of which the cubed sphere is just one of many choices.

Figure 1.5 shows the 5-year mean, zonally averaged zonal wind from a 20-level configuration of the model. It compares favorable with more conventional spatial discretization approaches. The two plots show the field calculated using the cube-sphere grid and the flow calculated using a regular, spherical polar latitude-longitude grid. Both grids are supported within the model.

Figure 1.5: Five year mean, zonally averaged zonal flow for latitude-longitude simulation (bottom) and cube-sphere simulation(top) using Held-Suarez forcing. Note the difference in the solutions over the pole - the cubed sphere is superior.

Copyright © 2002 Massachusetts Institute of Technology