Observations of Jupiter in the 645nm Ammonia Absorption Band

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 such as Juno. While these techniques recover high fidelity information on the ammonia distribution, they are limited in spatial and temporal coverage due to availability and cost. To complement these measurements, a simple optical filter ratio technique leveraging the 645nm ammonia absorption band was investigated. A commercially available 647±10nm filter was used to image Jupiter in the 645nm NH3 absorption band while continuum reference images were obtained at adjacent wavelengths. The Galilean moons were used as photometric references lacking a 645nm absorption feature. This technique is insufficient to retrieve environmental conditions such as ammonia abundance, aerosol characteristics, and cloud height. However, it demonstrated accurate measurement of global absorption in the 645nm band, averaged meridional profiles showing enhanced absorption in the Equatorial Zone (EZ), and detection of localized absorption enhancements in the northern EZ. The best resolution images showed that the localized enhancements were associated with plumes and dark features, consistent with published work. Multiple potential causes for artifacts or noise that might resemble the observed absorption patterns were investigated and eliminated. This technique is low-cost and low effort, making it potentially available to large numbers of astronomers, including amateur astronomers. If the physical mechanisms behind the 645nm absorption features can be fully established, the technique could provide long-term context monitoring for more sophisticated observations.