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Computing incoming solar radiation for each shortwave g point: The incoming solar radiation for a g point is found by integrating over the points of the Coddington et al. (BAMS 2016) reference spectrum used by CKDMIP which contribute to that g point.
ARTDECO-PyKdis
Reference: there is no publication on PyKdis, but the tool is largely based on the method described by Lacis & Oinas (1991) and Edwards & Francis (2000).
Implementation details: The code is written in Python3. Coefficients as computed with the PyKdis tools are distributed with ARTDECO. PyKdis itself is not intended to be shared for now but may be distributed as part of ARTDECO at some point.
Selecting band boundaries: PyKdis can be used to generate correlated-k coefficients for narrow bands ranging over the entire solar and thermal spectral domains. It can also be used to produce coefficients related to instrument spectral response function (e.g. 3MI, METimage, SEVIRI). No specific implementation is available in order to be able to produce full-spectrum correlated-k coefficients, in particular because we use it mostly for solar range under scattering atmosphere (Rayleigh, aerosol, cloud). In the solar range, the solar spectrum is used to weight the spectral absorption coefficients.
Line-by-line model: Either (1) the LBL tool Py4cats, written in Python under the GNU license and integrated into PyKdis, or (2) tabulated LBL spectral absorption. The spectral absorptions must be provided for each gas separately and tabulated for relevant pressures and temperatures. We developed this branch especially in order to be able to use LBL spectral absorptions from LBLRTM and ARAHMIS (the LBL code developed at LOA, http://www-loa.univ-lille1.fr/)
Reordering spectrum
The mapping from wavenumber to g space is done for each temperature and pressure separately considering a given number (depending on the k range) of log10 k sub-interval. Reordering is performed for each gas separately. As of now, possibility to use «composite gas» is not implemented.
Choosing number of g points
The number of g points for a given gas depends on its transmission over the band for airmass = 2 computed for a test atmosphere (usually US62).
l 0 < T ≤ 0.05, ng=10
l 0.05 < T ≤ 0.5, ng=20
l 0.5 < T ≤ 0.8, ng=15
l 0.8 < T ≤ 0.9, ng=10
l 0.9 < T ≤ 0.99, ng=5
l 0.99 < T ≤ 0.999, ng=3
l 0.999 < T ≤ 1.0, ng=1
Partitioning g space for one gas
For each gas, the partition of g space is obtained by first setting a Gaussian quadrature grid over the log10 k range for a refrerence pressure and temperature (most likely corresponding to an altitude where the absorption will be the most important in the atmosphere). This grid is then mapped to the g space and the corresponding g partition is then used for all other pressures and temperatures.
Partitioning g space for multiple gases
Random line position assumption and brute force approach with N g-points being the product of the Ni g-points of individual gases.
Computing absorption of one gas
G partition being known, we compute the average log10 k value in each g interval weigthed it using the probability density function of log10 k. The coefficients obtained are tabulated in pressure and temperature to produce a Look-Up Table. Molar absorption coefficients are stored. CKDMIP «Idealized» dataset would then be used to produce such LUT.
Computing combined absorption of multiple gases
Random line position assumption and brute force approach with N g-points being the product of the Ni g-points of individual gases.
Computing Planck function for each longwave g point:
Planck function is not accounted for in computing the coefficients (i.e. not accounted for in computing g).
Computing incoming solar radiation for each shortwave g point:
The incoming solar spectral flux is accounted for in compu