Radiative Transfer model of Jupiter’s atmosphere in ASIMUT-ALVL

The composition, evolution, distribution, structure, and dynamics of Jupiter’s atmosphere are of interest to the scientific community. The JUICE (JUpiter ICy moons Explorer) mission from the European Space Agency (ESA) launched in April 2023, will make detailed observations to characterize Jupiter’s atmosphere that are complementary to those from Juno. In preparation for its arrival to the Jovian System in July 2031, we would like to assess the visible and near-infrared (VIS-NIR) capabilities of the Moons And Jupiter Icy Moons Spectrograph (MAJIS), onboard JUICE. This is only possible by knowing the actual performances of the MAJIS VIS-NIR channel implemented in a radiometric model, and by simulating the radiative processes of Jupiter’s atmosphere in a Radiative Transfer (RT) model. Here we discuss the radiative transfer model, which was validated against observational data from Jupiter’s Great Red Spot (GRS) taken by the Visible and Infrared Mapping Spectrometer (VIMS), on board the Cassini mission, during its journey to Saturn. The line-by-line RT software ASIMUT-ALVL developed by BIRA-IASB, has been extensively used for the study of the atmospheres of Venus, Mars and Earth (Vandaele et al., 2006), and now has been upgraded for the modelling of Jupiter’s atmosphere. Since Jupiter’ upper atmosphere is mainly composed of hydrogen (H2), helium (He), and minor traces of other gases such as methane (CH4), water (H2O) and ammonia (NH3), its VIS-NIR spectrum is dominated by the absorption bands due to the CH4, H2O and NH3; Rayleigh scattering due to the dominant atmospheric species (H2 and He); Mie scattering due to aerosols and haze; and Collision-Induced Absorption (CIA) due to H2-H2 and H2-He molecular systems (Lopez-Puertas et al., 2005). We included the typical temperature profile from Moses et al. (2005) in our model, which covers data down to a pressure level of 1 bar, supplemented with data from Seiff et al. (1998) for pressure levels down to 20 bar. The initial atmospheric composition was obtained from González et al. (2011) and extrapolated with constant values below the pressure level of 1 bar. The required spectroscopic line lists were implemented as Look Up Tables (LUTs) for different pressure and temperature values, using data from Chubb et al. (2021), after realizing that the HITRAN 2020 database does not extend in the visible spectral range for all species. In the case of CH4 and NH3, the LUTs have been derived from the band models of Karkoschka et al. (2010) and Coles et al. (2018), respectively. Finally, to model the atmospheric aerosols and hazes, including the chromophores, the microphysical parameters were obtained as described by Baines et al., (2019) for the Crème Brulée model. Additionally, aerosols and hazes as defined by Lopez-Puertas et al., (2005) are also available. It is already possible to perform inverse models and retrieve physical parameters. Moreover, the RT model can now be used in combination with the radiometric model of MAJIS to assess the optical performances of the VIS-NIR channel.