AbstractA two-dimensional discrete spatial filter was developed. It serves as a means to classify meteorological fields on a limited-area grid according to their spatial dimensions by filtering certain wavenumber ranges. Thereby it performs an isotropic spatial-scale separation of the atmospheric fields. A general algorithm was developed, which allows the construction of a filter that closely approximates a specific isotropic response function. The filter is simple in the construction and easy to apply while giving reasonable results. The method allows for considerable flexibility in choosing this specific response. This way, low-, band-, and high-pass filters are obtained. Examples show an effective scale separation of atmospheric fields on limited-area grids that can be used for process studies, model evaluation, or comparisons.