Atmospheric radiative transfer calculations require information about the spectral absorption properties of all relevant gases in the atmospheric path. For years, much of the atmospheric community has relied on the HITRAN molecular spectroscopic database for absorption line information and the MT_CKD (Mlawer-Tobin-Clough-Kneizys-Davies) water vapor continuum model, developed by scientists at AER, to specify water vapor continuum absorption. AER Principal Scientist Eli Mlawer recently published a study that reported on efforts related to the recent inclusion of the MT_CKD water vapor continuum model as a component of HITRAN. Details were provided about the restructuring of the MT_CKD model to separate its code and data and simplify the code structure. Also described was the reformulation of the temperature dependence of the water vapor self-continuum in MT_CKD, motivated both by improvements to the model’s accuracy at high temperatures and greater consistency with HITRAN. Other recent updates to the MT_CKD water vapor continuum model were described and perspective was provided on the need for future water vapor continuum measurements.
Figure 1. The schematic diagram illustrates the MT_CKD water vapor continuum model and its relationship with the HITRAN molecular spectroscopic database and AER radiative transfer models. The purple (lower right) section shows the MT_CKD water vapor continuum model (MT_CKD_H2O), which is common to both HITRAN (red) and what is distributed with AER radiative transfer models like LBLRTM (blue). For both HITRAN and the AER models, MT_CKD_H2O takes as input the water vapor abundance, pressure, temperature, and wavenumber specifications, and returns the water vapor continuum absorption coefficients. In its calculation, the mt_ckd_h2o_absco code accesses the continuum data stored in absco-ref_wv-mt-ckd.nc, which is created by the AER internal water vapor continuum code (yellow box).
Citation: The inclusion of the MT_CKD water vapor continuum model in the HITRAN molecular spectroscopic database
E.J. Mlawer, K. E. Cady-Pereira, J. Mascio, I. E. Gordon
Journal of Quantitative Spectroscopy & Radiative Transfer, 306, (2023) 108645.
doi.org/10.1016/j.jqsrt.2023.108645