Digital filter initialization of the National Environmental Modeling System (NEMS) employing a regional-scale nonhydrostatic multi-scale model (NMMB) dynamical core

A digital filtering capability has been developed for the National Environmental Modeling System (NEMS) with the goal of minimizing the impact that high-frequency noise, induced by initial imbalances in wind and mass quantities, may have on the cycling of forecast capabilities which are in development. The Nonhydrostatic Multi-scale Model B-Grid (NMMB) dynamical core option is selected in our experiments within the NEMS framework. Two parallel experiments are conducted with and without digital filtering implementation over a regional domain. In the former, the impact of digital filtering is assessed through the use of the Digital Filter Launch (DFL) scheme, the Diabatic Digital Filter Initialization (DDFI) scheme, and the Twice Digital Filter Initialization (TDFI) scheme. Conventional observational verification and statistical analysis are employed to ascertain what effect these methods have on forecast skill. It is hoped that this added functionality may yield improved initial conditions needed in circumstances where high frequency noise degrades NEMS forecast products.