The Hough functions in applied mathematics are the eigenfunctions of Laplace's tidal equations which govern fluid motion on a rotating sphere. As such, they are important in geophysics and meteorology where they form part of the solutions for atmospheric and ocean waves.
Each Hough mode is a function of latitude and longitude; the functions are orthogonal over the sphere in the continuous case. Thus they can also be thought of as a generalized Fourier series in which the basis functions are the normal modes of a resting atmosphere.
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