Objective analysis of a two dimensional data field by the cubic spline technique

Abstract : A procedure to use the Spline interpolation technique on an arbitrarily prescribed two-dimensional data field is described. In order to use this technique it is necessary to obtain an initial approximation to the data at the grid points. This is achieved by fitting spherical surfaces to the data. Bi-directional Spline interpolation was then applied repeatedly on the grid point estimates of the data to produce convergence to the true surface. The Spline interpolation technique and another objective analysis technique developed by Gilchrist and Cressman are tested against an exact solution and the resulting analyses are compared. Real temperature, geopotential height, and wind data for various pressure surfaces are analysed by the Spline method and the results are compared to the subjective analyses of the same data.