Ammonia Abundance Derived from Juno MWR and VLA Observations of Jupiter (2209.03513v1)

Abstract: The vertical distribution of trace gases in planetary atmospheres can be obtained with observations of the atmosphere's thermal emission. Inverting radio observations to recover the atmospheric structure, however, is non-trivial, and the solutions are degenerate. We propose a modeling framework to prescribe a vertical distribution of trace gases that combines a thermo-chemical equilibrium model {based on a vertical temperature structure and compare these results to models where ammonia can vary between pre-defined pressure nodes}. To this means we retrieve nadir brightness temperatures and limb-darkening parameters, together with their uncertainties, from the Juno Microwave Radiometer (MWR). We then apply this framework to MWR observations during Juno's first year of operation (Perijove passes 1 - 12) and to longitudinally-averaged latitude scans taken with the upgraded Very Large Array (VLA) (de Pater 2016,2019a). We use the model to constrain the distribution of ammonia between -60$^{\circ}$ and 60$^{\circ}$ latitude and down to 100 bar. We constrain the ammonia abundance to be $340.5^{+34.8}_{-21.2}$ ppm ($2.30^{+0.24}_{-0.14} \times$ solar abundance), and find a depletion of ammonia down to a depth of $\sim$ 20 bar, which supports the existence of processes that deplete the atmosphere below the ammonia and water cloud layers. At the equator we find an increase of ammonia with altitude, while the zones and belts in the mid-latitudes can be traced down to levels where the atmosphere is well-mixed. The latitudinal variation in the ammonia abundance appears to be opposite to that shown at higher altitudes, which supports the existence of a stacked-cell circulation model.