Modeling Planetary Opacities with HITRAN and HAPI: Test case of Ammonia Microwave Absorption Spectra Under Jovian Condition

Abstract:

HITRAN (high-resolution transmission molecular spectroscopic database) is an international standard for reference molecular spectroscopy, particularly in simulating planetary atmospheric spectra [Gordon et al., 2017]. HITRAN recently added parameters for broadening of ammonia lines not only by “traditional” air and self, but also by H₂, He, CO₂ [Wilzewski et al., 2016] and H₂O [Tan et al., 2019]. With these additional broadening parameters applied to HITRAN, the efficacy of their application on the inversion spectrum of ammonia in the microwave region has been tested by using the HITRAN Application Programming Interface (HAPI) [Kochanov et al., 2016] and comparing it with modern widely used models and laboratory data. In particular, this work is comparing to the laboratory studies and empirical MATLAB models utilized by the Juno mission for interpretation of Jupiter’s atmospheric composition. The Juno spacecraft carries with it a microwave radiometer which operates in the 0.02-0.73 cm^-1 range to retrieve the abundance of molecular constituents from the microwave signature of Jupiter [Janssen et al., 2017, Bolton et al., 2017]. At these frequencies, the microwave opacity of the Jovian atmosphere is dominated by the inversion of the ammonia (NH₃) molecule. To make accurate comparisons to laboratory data and corresponding MATLAB models of NH₃ opacities, this work required three new line shapes to be incorporated into HAPI (the Ben-Reuven [1966], Gross [1955] and Van Vleck and Weisskopf [1945] line shapes). The results of this work demonstrate that using HAPI and HITRAN data, with a Ben-Reuven [1966] line shape, can accurately reproduce the opacity of NH₃ under Jovian conditions.

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