A GENERALIZED SLEVE COORDINATE ALLOWING FOR THIN NEAR-SURFACE LEVELS

Abstract: Smooth vertical coordinate levels in atmospheric models can considerably reduce numerical errors in the simulation of flow past complex topography. In this paper we propose a new Smooth LEvel VErtical (SLEVE) coordinate formulation with a modified vertical decay of topography, leading to a more uniform level thickness near the ground while preserving the fast transition to smooth levels in the upper atmosphere. Using numerical simulations of flow past complex topography, we demonstrate the feasibility of this approach. As a result, the new formulation allows for generally thinner near-surface levels of almost constant thickness and thus a better resolution of the boundary layer compared to the SLEVE coordinate, while retaining its advantages over classical sigma-coordinates at upper levels