Below is a brief overview of the GEWEX Longwave and Shortwave Algorithms, and
the Langley Parameterized Longwave and Shortwave Algorithms. A more detailed
description of these algorithms is available in the Model Documentation.
GEWEX Longwave (LW) Algorithm uses the Fu et al., (1997, JAS, Vol. 54,
2799-2812) Thermal Infrared radiative transfer code with cloud and surface
parameters requiring cloud, atmospheric profile information, and surface
properties. Inputs to the algorithm were obtained from the following sources:
The ISCCP DX cloud pixels were separated into categories of high, middle and low
where middle and low clouds could be composed of ice or water. Cloud fractions
and cloud optical depths were determined within these categories. Cloud particle
sizes were assumed and cloud physical thicknesses were also designed based upon
information from literature. Random overlap is used between the high, middle and
low layers to better approximate undercast conditions.
Langley Parameterized Longwave algorithm (LPLA) Detailed descriptions of
this algorithm can be found in:
- Gupta et al. (1992) - J. Appl.
Meteor., 31, 1361-1367.
- Gupta (1989) - J. Climate, 2, 305-320.
- Wilber et al. (1999) - NASA/TP-1999-209362. (available here )
GEWEX Shortwave (SW) Algorithm The shortwave parameters in this data
file were generated using the Pinker/Laszlo shortwave algorithm (R.T. Pinker and
I. Laszlo, 1992: Modeling Surface Solar Irradiance for Satellite Applications
on a Global Scale, J. Appl. Met., 31, 194-211).
Langley Parameterized Shortwave Algorithm (LPSA)
Detailed descriptions of the LPSA algorithm can be found in:
- Gupta et al. (2001) - NASA/TP-2001-211272, Dec. 2001.
(available here )
- Darnell et al. (1992) - J. Geophys. Res., 97, 15741-15760
- Darnell et al. (1988) - J. Climate, 1, 820-835
Each of the algorithms use cloud parameters derived from the DX data of the
International Satellite Cloud Climatology Project (ISCCP; Rossow and Schiffer,
1999, BAMS, 80, 2261-2287) and temperature and moisture profiles taken from 4-D
data assimilation products provided by the Data Assimilation Office at NASA GSFC
and produced with the Goddard Earth Observing System model version 4 (GEOS-4).
GEOS-4 is used in Rel. 3.0. Surface emissivities used in several
algorithms are taken from a map developed at NASA LaRC (Wilber et al. 1999; see
reference above). Column ozone values for the entire duration of this dataset
were obtained primarily from the Total Ozone Mapping Spectrometer (TOMS)
archive. For the early period (July 1983-November 1994), TOMS data came from
NIMBUS-7 and Meteor-3 satellites. There was an interruption of about 20 months
(December 1994-July 1996) after which TOMS data from EP-TOMS became available in
August 1996 and continued until December 2004. From January 2005 to June 2006,
Stratosphere Monitoring Ozone Blended Analysis (SMOBA) is used. All gaps in
TOMS data, including those over the polar night areas every year, were filled
with column ozone values from TIROS Operational Vertical Sounder (TOVS) data.
Surface albedos are derived with a parameterization using monthly climatological
clear-sky TOA albedos which are based on ERBE measurements during the 1985-1989