def _rso_simple(ra, elev):
    """Simplified daily/hourly clear sky solar formulation (Eqs. 19 & 45)

    Parameters
    ----------
    ra : ee.Image or ee.Number
        Extraterrestrial radiation [MJ m-2 d-1 or MJ m-2 h-1].
    elev : ee.Image or ee.Number
        Elevation [m].

    Returns
    -------
    rso : ee.Image or ee.Number
        Clear sky solar radiation [MJ m-2 d-1 or MJ m-2 h-1].
        Output data type will match "ra" data type.

    Notes
    -----
    rso = (0.75 + 2E-5 * elev) * ra

    """
    return ra.multiply(elev.multiply(2E-5).add(0.75))