HITRAN

The current version of the database, HITRAN2024, contains 61 molecules in the line-by-line portion of HITRAN along with some of their most significant isotopologues (156 isotopologues in total). These data are archived as a multitude of high-resolution line transitions, each containing many spectral parameters required for high-resolution simulations. ==Absorption Cross-Sections==

In addition to the traditional line-by-line spectroscopic absorption parameters, the HITRAN database contains information on absorption cross-sections where the line-by-line parameters are absent or incomplete. Typically HITRAN includes absorption cross-sections for heavy polyatomic molecules (with low-lying vibrational modes) which are difficult for detailed analysis due to the high density of the spectral bands/lines, broadening effects, isomerization, and overall modeling complexity. There are 644 molecular species in the current edition of the database provided as cross-section files. The cross-section files are provided in the HITRAN format described on the official HITRAN website. ==Collision-Induced Absorption==

The HITRAN compilation also provides collision-induced absorption (CIA) that was first introduced into HITRAN in the 2012 edition. CIA refers to absorption by transient electric dipoles induced by the interaction between colliding molecules. Instructions for accessing the CIA data files can be found on HITRAN/CIA. ==MT_CKD Water Vapor Continuum==

The MT_CKD (Mlawer-Tobin-Clough-Kneizys-Davies) Water Vapor Continuum Model provides water vapor absorption coefficients that should be added to the local contributions of water vapor transitions, such as those available in the HITRAN line-by-line section, in order to obtain the total absorption due to water vapor. Compared to line absorption, the continuum absorption varies more slowly across the spectrum. The MT_CKD Water Vapor Continuum provides absorption coefficients for both the self continuum (arising from interactions between water molecules) and the foreign continuum (arising from interactions between water vapor and other atmospheric gases). These coefficients are distributed in a netCDF file at a reference density corresponding to a pressure of 1013 mbar and temperature of 296 K for both the self and foreign continuum. This file also contains the temperature-dependence coefficients for the self continuum, allowing users to adjust the reference values for temperatures other than 296 K. The accompanying code performs the appropriate scaling and interpolation to compute the continuum absorption coefficients at arbitrary pressures, temperatures, and wavenumbers. The MT_CKD Water Vapor Continuum Model is constrained to remain consistent with high-quality analyses of atmospheric and laboratory measurements. Keeping the MT_CKD continuum consistent with current observational studies requires periodic updates to the continuum coefficients. A record of revisions to the MT_CKD Water Vapor Continuum Model can be found on the model's GitHub page. The associated code and data are available through the HITRAN website at hitran.org/mtckd and at the AER GitHub site at github.com/AER-RC/MT_CKD_H2O. ==Aerosol Refractive Indices==

HITRAN2024 also has an aerosols refractive indices section, with data in the visible, infrared, and millimeter spectral ranges of many types of cloud and aerosol particles. Knowledge of the refractive indices of the aerosols and cloud particles and their size distributions is necessary in order to specify their optical properties. ==HITEMP==

HITEMP is the molecular spectroscopic database analogous to HITRAN for high-temperature modeling of the spectra of molecules in the gas phase. HITEMP encompasses many more bands and transitions than HITRAN for eight absorbers: H2O, CO2, N2O, CO, CH4, NO, NO2 and OH. Due to the extremely large number of transitions required for high-temperature simulations, it was necessary to provide the HITEMP data as separate files to that of HITRAN. The HITEMP line lists retain the same 160-character format that was used for earlier editions of HITRAN. analysis of combustion processes, and modeling spectra of atmospheres in the Solar System, exoplanets, brown dwarfs, and stars. ==HAPI==

A Python library HAPI (HITRAN Application Programming Interface) has been developed which serves as a tool for absorption and transmission calculations as well as comparisons of spectroscopic data sets. The following spectral functions can be calculated in the current version #1 of HAPI: • absorption coefficient • absorption spectrum • transmittance spectrum • radiance spectrum ==See also==