Characterizing Jovian Tropospheric Ammonia via Ground-based Imaging

Continuum-divided ammonia and methane absorption images of Jupiter provide a revealing perspective on atmospheric features including belts and zones, the Great Red Spot, plumes in the northern equatorial zone, along with extra-tropical storms. As a condensable gas, the distribution of ammonia vapor is an important tracer of Jovian tropospheric meteorology. Current understanding of this distribution and its relationship to aerosol opacity, cloud height, and circulation is provided by atmospheric retrieval models using observations from major ground-based facilities or from spacecraft. While these techniques recover high fidelity information on the ammonia distribution, they are limited in spatial and temporal coverage. An economical, lower fidelity approach to filling part of the coverage gap, specifically the upper tropospheric ammonia distribution, is possible using continuum-divided ammonia and methane absorption images. Two years of data have now been gathered and analyzed with a Reflecting Layer Model (RLM) approach. Positive correlations between ammonia absorption and methane absorption variations across the disk are consistent with cloud height (scattering path length) variations. Negative correlations are indicative of relative enrichment or depletion of ammonia along the scattering path. Initial results show positive correlation for the GRS, suggesting that reflecting layer height dominates. The north equatorial belt was seen to be dark in methane and bright in ammonia, suggesting a deep reflecting layer and a depletion of ammonia. The northern equatorial zone shows a mix of positive and negative correlations indicating a complex relationship between reflecting layer height and ammonia abundance. During the 2021 observing season, the number and intensity of localized peaks of ammonia absorption decreased as the number and intensity of bright plumes decreased. A few smaller features at higher latitudes were also studied. The technique and results presented here show that meaningful ammonia monitoring can be performed economically and can provide synoptic coverage and continuity between spacecraft or major ground-based facility campaigns.