A STRATIFIED SPECTRAL MODEL FOR STABLE AND CONVECTIVE ATMOSPHERES

In our solar system, convective atmospheres are as common as those tha t are stable, and convective and stable regions sometimes coexist in t he same atmosphere. There is a need to develop circulation models that can handle convection and stable-layer flows simultaneously and effic iently. This paper represents an approach to the construction of such a model. Taking advantages of the simplicity of implementing implicit time stepping in spectral models, we solve a non-hydrostatic, fully co mpressible version of the hydrodynamic equations without the time step restrictions imposed by acoustic and gravity waves. To simplify the n onlinear terms and to conserve the total mass and total angular moment um to round-off accuracy, we introduce a ''stratified'' approximation which limits the nonlinearity of the equations to quadratic. The linea r terms remain intact so that all the linear waves are preserved. The set of assumptions made by the ''stratified'' approximation is a subse t of those of the anelastic approximation. It offers more generality a nd accuracy while the computational overhead is relatively low. Tests are presented to illustrate the capabilities and advantages of the pre sent model. (C) 1994 Academic Press, Inc.