Projection Methods for Error Suppression in the Meteorological Fields before Calculation of Derivatives

V. A. Gordin and A. V. Khalyavin

In finite-difference approximation of derivatives on a grid with step of h, the error decreases with decreasing h. However, if the original function is given on a grid with an error of order of ε, then the approximate differentiation error grows like Cε/hk, where k is the derivative order and C is a constant depending on a chosen finite-difference approximation. Projection methods are discussed that are designed to decrease the errors of this kind. On the latitude-longitude grids, the step near the poles along the latitude circles is very small. Methods are proposed for projecting scalar and vector meteorological fields on the subspaces of smooth fields. The projected fields obtained take into account asymptotics of the smooth fields in the vicinity of the pole in the spherical coordinates, separately for each Fourier harmonic in longitude. Results are presented of such smoothing in the polar regions on the fields of objective analysis by Hydrometeorological Center of Russia and on the first-guess fields at standard isobaric heights.

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