def GlobalRadiation(ra, z):
    """Reduce extraterrestrial radiation to in-atmosphere value

    Parameters
    ----------

    ra : numpy.array(double)
        Estimate of extraterrestrial radiation (W/m2)

    z : double
        Height above mean sea level (m)

    Returns
    -------

    numpy.array(double)
        Estimate of global solar radiation (W/m2)
    """

    rg = ra * (0.75 + 2.0e-5*z)

    return rg