SHDOM: Correlated K-distribution File Format

The CKD file has the correlated k-distribution information for a series of spectral bands for a particular atmospheric profile. This file is made by another program (e.g. ckdfu.f) from a profile. Each band, i.e. a range of wavenumbers, has a k-distribution associated with it. The k-distibution is performed as a discrete sum over probability intervals (the delta g in the notation of Fu and Liou, 1993). A radiative transfer calculation is done for each "k" in the sum, which represents the gaseous absorption. The distribution of gases in the atmosphere is assumed to horizontally uniform, and so the absorption coefficients depend only on height. Thus the CKD file specifies the absorption coefficient (in km^-1) for each height, "k" in the sum, and each band. The delta g's are the weights with which the separate radiative transfer results are added together.

There are three sections in the CKD file.

  1. The band information.
  2. The atmosphere information.
  3. The absorption coefficients for each band and g range.

The format is:

   Comment line
   Number of bands
   Comment line
   For each band: 
     band num, waveno1, waveno2, solar flux, number of k's, all the delta g's
   Number of z levels
   Two comment lines
   For each atmospheric level from the top down:
     height, (other profile information is not used)
   Comment line
   For each band and level:
     band number, level number, all the k_i's
 
Notes: waveno1 and waveno2 are the starting and ending wave numbers in cm^-1 of the bands; solar flux is the top of the atmosphere solar irradiance in W/m^2 for overhead sun. The level numbers start with 1 at the top of the atmosphere. The levels in the CKD file are completely independent of the levels in the SHDOM run, though they should cover the SHDOM levels. The k-distributions should start with the lowest k's (they are used in the reverse order in the program).