Continuum Database
As of February 2025, we have now implemented a new continuum database in the Generic PCM. The continuum files are provided here (please contact Martin if you have any suggestion, question, new additions you want to make): https://web.lmd.jussieu.fr/~lmdz/planets/LMDZ.GENERIC/datagcm/continuum_data/
Contents
File format and location
The files are stored here: https://web.lmd.jussieu.fr/~lmdz/planets/LMDZ.GENERIC/datagcm/continuum_data/
The first line of the file (header) list the grid of temperatures. For the next lines, the first column corresponds to the wavenumber (in cm-1), then the absorption coefficient at the first temperature, etc.
Note : We have stored all the ancient continuum files (e.g., HITRAN format) in the https://web.lmd.jussieu.fr/~lmdz/planets/LMDZ.GENERIC/datagcm/continuum_data/pre-2025_continua/ directory.
Units
The continuum absorption a_normXY units of the tables is cm-1 amagat-2. This is a standard units for continuum absorption.
The absorption coefficient a_XY (m-1) </math> for molecules X and Y can then be computed from the following equation:
a_XY = 100.0 * a_normXY * amagat_X * amagat_Y !
with amagat_X = (273.15/T)*(P_X/101325.0) with amagat_Y = (273.15/T)*(P_Y/101325.0)
with T the temperature (in K), P_X and P_Y the partial pressure of the molecules X and Y (in Pascal units).
Note : The HITRAN continuum files are in cm^5 molecule-2 units. You can convert HITRAN continuum data into cm-1 amagat-2 by dividing them by \(1.385 \times 10^{-39}\)
List of continua in the database
Below we provide the list of continua included in the database, with some details on how they were computed.
CO2-CO2
The CO2-CO2 continuum file combines:
- the COA CIA band at 0-250cm-1 (Gruszka and Borysow, 1997), extrapolated down to 100K.
- All CIA and dimer bands listed in Tran et al. 2024 (see Table), using the functional formula for the shape and band intensity (as a function of temperature). Temperature dependency is extended from 100 to 800K.
N2-N2
The N2-N2 continuum file combines all data (roto-translational, fundamental and first overtone bands) from Karman+2019: https://hitran.org/cia/ (N2-N2_2021.cia file).
The temperature dependency is extrapolated from 70 to 500K.
O2-O2
The O2-O2 continuum file combines all data from Karman+2019: https://hitran.org/cia/ (O2-O2_2018b.cia and O2-O2_theory_temp_2018.cia files).
The temperature dependency is extrapolated from 100 to 400K.
CH4-CH4
The CH4-CH4 continuum file combines all data from Karman+2019: https://hitran.org/cia/ (CH4-CH4_2011.cia file). Only a single CH4 CIA band has been characterized so far (see Borysow & Frommhold 1987).
The temperature dependency is extrapolated from 40 to 500K.
H2O-H2O
The H2O-H2O continuum is taken and interpolated from the MT_CKD continuum v_4.0.1 (https://github.com/AER-RC/MT_CKD_H2O). The H2O-H2O MT_CKD continuum is frequently updated, but most of the time the changes are very minor.
Note that the H2O-H2O MT_CKD continuum includes CIA and dimer bands, but also the absorption from the far wing (anything that absorbs beyond +/- 25cm-1 of each H2O line) and the plinth (the absorption at +/- 25cm-1) of H2O monomers (broadened by H2O).
Note that give the assumption of the MT_CKD continuum (continuum above 25cm-1), it is required that a 25cm-1 cutoff is applied to the absorption by the H2O monomers, and that the plinth is removed.
H2-H2
The H2-H2 continuum file combines the H2-H2 file previously used for temperate-to-hot gas giants (H2-H2_2011_extended.cia.txt extended to wavelengths > 10,000cm-1 and temperatures up to 10,000K ; work done by Lucas Teinturier using codes provided by Bruno Bézard) and the (low-temperature) H2-H2 file used for solar system giant planets (provided by Gwenael Milcareck). The first file is used for T>400K and the second file for T<=400K.
We took the "equilibrium" files which is the most accurate choice in general for most of our giant planet (H2-rich atmospheres) applications. Differences between "equilibrium" and "norm" appear at temperatures << 100K.
CO2-H2
The CO2-H2 continuum file combines all data from Turbet+20, Mondelain+21 and Fakhardji+21.
The temperature dependency is extrapolated from 100 to 800K.
CO2-CH4
The CO2-H2 continuum file is built from Turbet+20.
The temperature dependency is extrapolated from 100 to 800K.
CO2-O2
The CO2-O2 continuum file combines all data from Karman+2019: https://hitran.org/cia/ (O2-CO2_2011.cia file) and data from Baranov et al. 2004 (digitized from Fig. 7).
The temperature dependency is extrapolated from 100 to 600K.
O2-N2
The O2-N2 continuum file combines all data from Karman+2019: https://hitran.org/cia/ (O2-N2_2021.cia and O2-N2_theory_temp_2018.cia).
The temperature dependency is extrapolated from 100 to 500K.
H2O-AIR (H2O-O2 / H2O-N2)
The H2O-AIR continuum is taken and interpolated from the MT_CKD continuum v_4.0.1 (https://github.com/AER-RC/MT_CKD_H2O)
Note that the H2O-AIR MT_CKD continuum includes CIA and dimer bands, but also the absorption from the far wing (anything that absorbs beyond +/- 25cm-1 of each H2O line) and the plinth (the absorption at +/- 25cm-1) of H2O monomers (broadened by "air").
Note that "AIR" here corresponds to the present-day Earth mixture of O2 and N2. In practice in the model, we will use the H2O-AIR continuum for both H2O-O2 and H2O-N2 continuum.
Note that give the assumption of the MT_CKD continuum (continuum above 25cm-1), it is required that a 25cm-1 cutoff is applied to the absorption by the H2O monomers, and that the plinth is removed.
In practice, we take the H2O-O2 continuum equal to the MT_CKD H2O-AIR continuum. The H2O-N2 continuum is taken equal to the H2O-AIR MT_CKD continuum + the CIA band of Baranov+2012/Hartmann+2017 near 2400cm-1.
H2O-CO2
The H2O-CO2 continuum file was recalculated following the procedure described in Tran, Turbet et al. 2018 (using HITRAN 2016 line list modified with CO2-broadening coefficient) and extended up to 20,000cm-1. The temperature dependency was calculated using Ma & Tipping 1992 results (only from 0-10000cm-1, because we have no data above).
We also added the H2O-CO2 CIA band from Fleurbaey et al. 2022 (but the temperature dependency is not known).
Note that we followed the MT_CKD framework (continuum above 25cm-1), so it is required that a 25cm-1 cutoff is applied to the absorption by the H2O monomers, and that the plinth is removed.
CH4-N2
The CH4-N2 continuum file combines all data from Karman+2019: https://hitran.org/cia/ (N2-CH4_2011.cia file).
The temperature dependency is extrapolated from 40 to 600K.
H2-N2
The H2-N2 continuum file combines all data from Karman+2019: https://hitran.org/cia/ (N2-H2_2011.cia).
The temperature dependency is extrapolated from 40 to 600K.
H2-He
The H2-He continuum file combines the H2-He file previously used for temperate-to-hot gas giants (H2-He_2011.cia file provided in HITRAN) and the (low-temperature) H2-He file used for solar system giant planets (provided by Gwenael Milcareck ; file name was H2-He_eq_0-15000cm-1_40-400K.cia) and that we extended up to 20,000cm-1. The first file is used for T>400K and the second file for T<=400K.
We took the "equilibrium" file which is the most accurate choice in general for most of our giant planet (H2-rich atmospheres) applications. Differences between "equilibrium" and "norm" appear at temperatures << 100K.
H2-CH4
The H2-CH4 continuum file combines all data from Karman+2019: https://hitran.org/cia/ (H2-CH4_eq_2011.cia). We took the "equilibrium" file which is the most accurate choice in general for most of our giant planet (H2-rich atmospheres) applications. Differences between "equilibrium" and "norm" appear at temperatures << 100K.
The temperature dependency is extrapolated from 40 to 600K.
Words of caution
Beware that some of the correlated-k tables do already include some of the continuum terms here. For instance CO2_H2Ovar correlated-k table (and most of the CO2-thick historical correlated-k table) include the 0-250cm-1 CIA band and the Fermi doublet of CO2-CO2. For these "old" tables, we recommend that you switch back to the old continuum tables, to avoid counting some terms twice.
