Interpolation of the wind field in a terrain following coordinate system over complex topography

In mesoscale modelling of the atmosphere and in dispersion calculations often a terrain following, and therefore nonrectangular, coordinate system is used. In this paper the following questions are handled in a unified scheme: interpolation on such a nonrectangular grid, definition of the boundaries of a single cell and calculation of its volume. The interpolation is done in a boundary-following way and results in a rational interpolation formula. For comparison, two classical interpolation methods are briefly reviewed.