Difference between revisions of "Building Opacity Tables"

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(→‎Calculation of high-resolution spectra)
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== Calculation of high-resolution spectra ==
 
== Calculation of high-resolution spectra ==
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=== Line Lists ===
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The first thing you need to compute high-resolution spectra is to get line lists of the molecules (and/or atoms) that you want to simulate in the atmosphere.
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For temperate  planets (Earth, Mars, etc.), the best line lists are provided by HITRAN: https://hitran.org
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For hot planets (Venus, etc.), the best line lists are provided by HITEMP: https://hitran.org/hitemp/
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These two databases (HITRAN and HITEMP) however often miss some molecules, or some line list parameters. If you reach such problem, ExoMOL (https://www.exomol.com) can be a good resource. It is less reliable than HITRAN and HITEMP because it is based on theoretical calculations, but it can be extremely useful to get line list/parameters where HITRAN and HITEMP have no data.
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=== Tools to generate high-resolution absorption spectra ===
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Once you have your line lists for all the molecules/atoms you want to simulate, you need to use tools to compute high-resolution absorption spectra.
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 +
Historically, we have been using the code ''k-spectrum'' to compute high-resolution spectra. We have stored an historical version of the code here: http://svn.lmd.jussieu.fr/KSPECTRUM/trunk/kspectrum/
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More recently, we have developed (Guillaume Chaverot et al.) a new tool, called speCT (linked to be added here soon), to produce high-resolution spectra. Compared to k-spectrum, this new code is much more efficient (written and parallelized more efficiently), which is essential if you want to
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describe the tools we used :
 
describe the tools we used :

Revision as of 11:00, 30 April 2025

This page describes the main steps required to build new opacity tables for the Generic PCM.

There are three important steps to consider:

  • (1) calculate high-resolution spectra for a grid of pressures, temperatures and mixing ratios.
  • (2) convert these high-resolution spectra into correlated-k tables
  • (3) add continuum opacity tables

Calculation of high-resolution spectra

Line Lists

The first thing you need to compute high-resolution spectra is to get line lists of the molecules (and/or atoms) that you want to simulate in the atmosphere.

For temperate planets (Earth, Mars, etc.), the best line lists are provided by HITRAN: https://hitran.org For hot planets (Venus, etc.), the best line lists are provided by HITEMP: https://hitran.org/hitemp/

These two databases (HITRAN and HITEMP) however often miss some molecules, or some line list parameters. If you reach such problem, ExoMOL (https://www.exomol.com) can be a good resource. It is less reliable than HITRAN and HITEMP because it is based on theoretical calculations, but it can be extremely useful to get line list/parameters where HITRAN and HITEMP have no data.

Tools to generate high-resolution absorption spectra

Once you have your line lists for all the molecules/atoms you want to simulate, you need to use tools to compute high-resolution absorption spectra.

Historically, we have been using the code k-spectrum to compute high-resolution spectra. We have stored an historical version of the code here: http://svn.lmd.jussieu.fr/KSPECTRUM/trunk/kspectrum/

More recently, we have developed (Guillaume Chaverot et al.) a new tool, called speCT (linked to be added here soon), to produce high-resolution spectra. Compared to k-spectrum, this new code is much more efficient (written and parallelized more efficiently), which is essential if you want to


describe the tools we used :

  • k-spectrum
  • home-made scripts

Building correlated-k tables

describe the tools we used:

Several important notes:

  • The units of correlated-k tables is cm^2/molec.
  • The format of correlated-k tables is (n_temperature, n_pressure, n_vmr, n_band, n_gauss)

Adding continuum opacities

Explain strategies to calculate continuum opacities

  • Usually the continuum units used as input in the GCM is cm-1 amagat-2
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