A lateral boundary formulation for multi‐level prediction models

TLDR

The paper proposes an expedient method for treating lateral boundaries in limited‑area prediction models. The method relaxes interior flow near the boundary to match externally prescribed flow, and is evaluated through systematic studies with a linear primitive‑equation model and numerical experiments. Analytical and numerical results show the method effectively dissipates gravity‑wave energy and errors at the boundary, accurately represents outgoing gravity waves, and preserves balanced flow, indicating it is a promising lateral‑boundary treatment.

Abstract

Abstract An expedient method is proposed for the lateral boundary treatment of a limited‐area prediction model. The method involves the relaxation of the interior flow in the vicinity of the boundary to the external fully prescribed flow. A systematic study of the method is undertaken with an (x, z) , linear, primitive equation model. Analytical considerations of the method for the continuous equations demonstrate the manner in which the method consumes gravity wave energy, error and fine spatial scale potential vorticity near the lateral boundaries. Numerical experiments are also undertaken to assess the usefulness of the method. The results indicate that the method gives an adequate representation of outgoing gravity waves with and without an ambient shear flow, and also allows the substantially undistorted transmission of geostrophically balanced flow out of the interior of the limited domain. On the basis of these results, it is suggested that the method constitutes a promising utilitarian treatment of the lateral boundaries.