Lateral Boundary Conditions for Tropical Cyclone Models

Abstract

Under certain circumstances a large fraction of the energy generated by the release of latent heat in a tropical cyclone cab be partitioned to gravity-inertia wave motion rather than to balanced flow. In this way most of the generated energy is radiated away to the far field. If a primitive equation tropical cyclone model is to successfully simulate this process, its lateral boundary condition must be able to transmit the gravity-inertia wave energy generated in the interior of the model. Most present models seem deficient in this regard. As an improvement we explore the possibility of using a cylindrical, pure gravity wave radiation condition. Since there is a wide range of gravity wave phase velocities in a stratified atmosphere, it is necessary to apply the radiation condition vertical mode by vertical mode rather than level by level. The usefulness of this radiation condition and several other conditions in present use is tested both by a reflectivity analysis and by simple numerical time integrations.