Initialization of the HIRLAM model using a digital filter

Abstract

The method uses a digital filter applied to time series of the model variables generated by short-range forward and backward integrations from the initial time. The digital filtering technique is applied to initializer data for the High-Resolution Limited-Area Model (HIRLAM). The method is shown to have the three characteristics essential to any satisfactory initialization scheme; i) high-frequency noise is effectively removed from the forecast; ii) changes made to the analyzed fields are acceptably small; iii) the forecast is not degraded by application of the initialization. The digital filtering initialization (DFI) technique is compared to the standard nonlinear normal-mode initialization (NMI) used with the HIRLAM model. Both methods yield comparable results, though the filtering appears more effective in suppressing noise in the early forecast hours. -from Authors