def _rn(rs, rnl):
    """Net daily/hourly radiation (Eqs. 15 & 16)

    Parameters
    ----------
    rs : ee.Image or ee.Number
        Measured solar radiation [MJ m-2 d-1 or MJ m-2 h-1].
    rnl : ee.Image or ee.Number
        Hourly net long-wave radiation [MJ m-2 d-1 or MJ m-2 h-1].

    Returns
    -------
    ee.Image or ee.Number
        Hourly net long-wave radiation [MJ m-2 d-1 or MJ m-2 h-1].
        Output data type will match "rnl" data type.

    Notes
    -----
    Switching calculation to work from rnl (which is computed from temperature)
    rnl = 0.77 * rs - rnl

    """
    return rnl.multiply(-1).add(rs.multiply(0.77))
