An Initialization Procedure Combining Digital Filter and Nudging Techniques

.The specification of numerical forecast initial conditions free of imbalance between mass and wind is a desirable feature to avoid large amplitude inertia-gravity waves in high frequencies and the spinup problem noted during the first hours of a numerical integration. Without a proper initialization, as the numerical integration evolves the high frequency waves are attenuated by dispersion and dumping diffusion just after a 6-12 hour period of numerical simulation.

The digital filter is an approach frequently adopted in initialization of meteorological models due to its effectiveness and easy implementation. Depending on the operational design of this scheme, its implementation can result in an initial condition where the influence of data near the time of the filtered fields is very reduced. This short-coming can be avoided with the technique presented in this research. It consists in combining the digital filter and an assimilation scheme. Its advantages are shown in a simple model, where only gravity waves are included, with the nudging assimilation scheme. Then the technique is implemented in a limited area numerical model, and applied in the simulation of an intense cyclone developing over South Atlantic