Zonal Profiles of Jupiter's Tropospheric Abundances from Near-Infrared Juno JIRAM Spectroscopy

The polar orbit of the Juno spacecraft provides an unprecedented view of Jupiter's atmosphere as it passes above the cloud tops every 53 days. The spectrum in the near infrared is dominated by reflected sunlight from aerosols (both condensate clouds and hazes) in the troposphere, as well as absorptions by the molecular species present. In addition, thermal emission longward of 4.5 µm provides access to the gaseous composition and aerosols below the top-most clouds.  Of particular importance in shaping the spectra are ammonia, phosphine and water, in addition to minor contributions from species such as arsine, germane and carbon monoxide. These regions also include emissions by ionospheric H₃⁺. Here, we produce meridionally averaged zonal profiles from the Juno-JIRAM observations obtained during PJ3, which provide almost complete latitude coverage. To analyse the observations, we use the radiative transfer and retrieval code NEMESIS (Irwin et al., 2008), which has been updated to cover this wavelength with the latest line-data from HITRAN. Our aim is to analyse both the reflected-sunlight region (2-4 µm) and the thermal emission region (4-5 µm) simultaneously for the first time, building on the work of Grassi et al. (2019) and Grassi et al. (2020).  We investigate the appropriate set of aerosol and haze layers, starting with NH4SH at 1.3 bars, NH3 and 0.7 bars and two grey hazes: one in the troposphere and one in the stratosphere.  The optical properties of these aerosols are tested to find the optimal cloud structure to reproduce the full JIRAM spectrum. From the retrievals of the zonally-averaged spectra we investigate whether spatial variations of tropospheric composition are truly required to fit the data, comparing gaseous contrasts to the expected circulation patterns associated with Jupiter’s belts and zones.