A Spatial Filter for Use in Finite Area Calculations

Abstract

A multidimensional filter which selectively removes 2?x and 2?y noise is introduced. The filter is designed to be effective in finite area models with nonperiodic horizontal boundary conditions. An economical splitting technique, requiring an intermediate boundary condition, is utilized in the calculations. The filter is tested on a finite difference representation of two-dimensional linear advection and compared with the Shapiro eighth-order filter. Tests on both uniform and variable grid configurations are conducted, as well as a finite element calculation. Influence of repeated applications of the filters upon a rectangular column is analyzed and comparisons between filter factors are made. Lastly, the proposed filter is inserted into the three-dimensional Penn State-NCAR regional model to test its performance in a state-of-the-art model and to study the importance of horizontal diffusion.