Difference between revisions of "Building Opacity Tables"
(→Calculation of high-resolution spectra) |
|||
| Line 5: | Line 5: | ||
* (2) convert these high-resolution spectra into correlated-k tables | * (2) convert these high-resolution spectra into correlated-k tables | ||
* (3) add continuum opacity tables | * (3) add continuum opacity tables | ||
| + | |||
== Calculation of high-resolution spectra == | == Calculation of high-resolution spectra == | ||
| Line 10: | Line 11: | ||
=== Line Lists === | === 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 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 your atmosphere. |
| − | For temperate planets (Earth, Mars, etc.), the best line lists are provided | + | For temperate planets (Earth, Mars, etc.), the best line lists are usually provided in HITRAN: https://hitran.org |
| − | For hot planets (Venus, etc.), the best line lists are provided | + | For hot planets (Venus, etc.), the best line lists are usually provided in 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. | + | These two databases (HITRAN and HITEMP) however often miss some molecules, or some line list parameters (broadening coefficients, temperature dependencies, etc.). If you reach such problem, ExoMOL (https://www.exomol.com) can be a good resource to look at. 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. For instance and for this reason, ExoMOL is often used to simulate opacity tables for hot, gas giant exoplanets. |
=== Tools to generate high-resolution absorption spectra === | === Tools to generate high-resolution absorption spectra === | ||
| Line 21: | Line 22: | ||
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. | 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/ | + | 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) and include more subtle spectroscopic effects (broadening coefficients for multiple collisional partners), which is essential if you want to use big line lists like HITEMP (that contain many, and more more lines and parameters). | |
| − | + | As of April 2025, speCT should be the reference code to use to compute high-resolution spectra for H2O, CO2 and N2. For the other gases, you should use kspectrum. In the coming years, speCT should be able to handle more and more gases so it is intended to eventually replace kspectrum. | |
| − | |||
== Building correlated-k tables == | == Building correlated-k tables == | ||
| Line 42: | Line 38: | ||
* The units of correlated-k tables is cm^2/molec. | * 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) | * The format of correlated-k tables is (n_temperature, n_pressure, n_vmr, n_band, n_gauss) | ||
| + | |||
| + | === Note on how to modify existing correlated-k tables === | ||
== Adding continuum opacities == | == Adding continuum opacities == | ||
Revision as of 11:31, 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
Contents
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 your atmosphere.
For temperate planets (Earth, Mars, etc.), the best line lists are usually provided in HITRAN: https://hitran.org For hot planets (Venus, etc.), the best line lists are usually provided in HITEMP: https://hitran.org/hitemp/
These two databases (HITRAN and HITEMP) however often miss some molecules, or some line list parameters (broadening coefficients, temperature dependencies, etc.). If you reach such problem, ExoMOL (https://www.exomol.com) can be a good resource to look at. 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. For instance and for this reason, ExoMOL is often used to simulate opacity tables for hot, gas giant exoplanets.
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) and include more subtle spectroscopic effects (broadening coefficients for multiple collisional partners), which is essential if you want to use big line lists like HITEMP (that contain many, and more more lines and parameters).
As of April 2025, speCT should be the reference code to use to compute high-resolution spectra for H2O, CO2 and N2. For the other gases, you should use kspectrum. In the coming years, speCT should be able to handle more and more gases so it is intended to eventually replace kspectrum.
describe the tools we used:
- home-made scripts
- exo-k (http://perso.astrophy.u-bordeaux.fr/~jleconte/exo_k-doc/index.html)
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
