Development of an isentropic coordinate model of the middle atmosphere

We have developed a model for the middle atmosphere based on an isentropic vertical coordinate, which is especially advantageous for studying the stratospheric dynamics.

The model is a generalization of Hsu and Arakawa (1990) to the global domain, in which the conservation properties of the potential vorticity are still maintained. The vertical domain covers the middle atmosphere above the 400-K isentropic surface. At the lower boundary, the Montgomery potential is prescribed from observation for an upward propagating wave component and extrapolated from the interior for a downward propagating wave component to minimize the spurious reflection of downward propagating waves. At present, the physical processes are represented by a simple Newtonian type heating/cooling.

The model is used to simulate the entire evolution of sudden warming of February 1979. This paper presents the design of the model and its performance in simulating that event. A detailed analyses of the simulated results will be presented in a companion paper.