Tuesday, 16 January 2007

A Geodesic Atmospheric Model With A Quasi-Lagrangian Vertical Coordinate

Exhibit Hall C (Henry B. Gonzalez Convention Center)

A geodesic atmospheric model with a quasi-Lagrangian vertical coordinate is being developed as a part of the “Coupled Colorado State Model (CCoSM)”. Each component of CCoSM is based on geodesic grids. The geodesic grid eliminates the pole problem while providing approximately homogeneous resolution and isotropic distribution of grid points over the entire sphere. The advantages of using the geodesic grid are enhanced with the use of vorticity-divergence equations. The atmosphere model makes use of quasi-Lagrangian vertical coordinates known as the generalized vertical coordinate. The generalized vertical coordinate is configured as a hybrid isentropic-sigma type in the free atmosphere. The isentropic surfaces, which are surfaces of constant potential temperature, are quasi-Lagrangian surfaces in the atmosphere because the potential temperature is entirely conserved for adiabatic motion and nearly conserved under diabatic processes. Because of the reduced truncation errors due to minimized vertical advection with the quasi-Lagrangian coordinate, we expect the model to more accurately predict moisture and cloud distribution than a pressure based coordinate model. The atmospheric model combines this dynamical core with the physics package previously developed at CSU.

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