High-Order Low-Pass Implicit Tangent Filters for Use in Finite Area Calculations

High-order implict tangent filters are developed. The implicit tangent filters possess a highly selective amplitude response function and they can be applied relatively close to a boundary. Comparisons are made between the implict and the traditional or explict filters. Numerical simulations are performed to test the response in a limited-area model. An algorithm to maximize computing efficiency is presented. All tests indicate the desirability and utility of the implicit tangent filter.