ILWR all sky parametrization Using air temperature (TA) and relative humidity (RH) and optionnally cloud transmissivity (TAU_CLD), this offers the choice of several all-sky parametrizations:
- OMSTEDT – from Omstedt, "A coupled one-dimensional sea ice-ocean model applied to a semi-enclosed basin", Tellus, 42 A, 568-582, 1990, DOI:10.1034/j.1600-0870.1990.t01-3-00007.
- KONZELMANN – from Konzelmann et al., "Parameterization of global and longwave incoming radiation
for the Greenland Ice Sheet." Global and Planetary change 9.1 (1994): 143-164.
- UNSWORTH – from Unsworth and Monteith, "Long-wave radiation at the ground", Q. J. R. Meteorolo. Soc., Vol. 101, 1975, pp 13-24 coupled with a clear sky emissivity following (Dilley, 1998).
- CRAWFORD – from Crawford and Duchon, "An Improved Parametrization for Estimating Effective Atmospheric Emissivity for Use in Calculating Daytime
Downwelling Longwave Radiation", Journal of Applied Meteorology, 38, 1999, pp 474-480
If no cloud transmissivity is provided in the data, it is calculated from the solar index (ratio of measured iswr to potential iswr, therefore using the current location (lat, lon, altitude) and ISWR to parametrize the cloud cover). This relies on (Kasten and Czeplak, 1980) except for Crawford that provides its own parametrization. The last evaluation of cloud transmissivity is used all along during the times when no ISWR is available if such ratio is not too old (ie. no more than 1 day old). If only RSWR is measured, the measured snow height is used to determine if there is snow on the ground or not. In case of snow, a snow albedo of 0.85 is used while in the abscence of snow, a grass albedo of 0.23 is used in order to compute ISWR from RSWR. Finally, it is recommended to also use a clear sky generator (declared after this one) for the case of no available short wave measurement (by declaring the ClearSky generator after AllSky).
ILWR::generators = allsky_LW
ILWR::allsky_lw = Omstedt