Seasonal Change in the Deep Atmosphere of Uranus, 1981 to 2021

Our team is using radio observations of Uranus, collected with the Very Large Array (VLA) telescope, to track seasonal changes in the deep troposphere of Uranus between 1981 and the present. In Hofstadter, Akins, and Butler (https://doi.org/10.5194/egusphere-egu21-1374), we reviewed evidence for seasonal changes in Uranus’ atmosphere from a record of VLA observations between 1981 and 2012. We found that large scale latitude structure has remained essentially similar for the bulk of the record with the exception of the pole-equator contrast differences between mid-summer observations in 1985 and late summer observations in 1994. This record has been extended to the present (close to ½ a Uranian year) with VLA observations in 2015 (published in Molter et al. 2021 https://doi.org/10.3847/PSJ/abc48a) and in late 2021 (and early 2022). Here, we will discuss our analysis of data obtained between 2012 and the present. All observations during this period were made with the upgraded Jansky VLA receivers and thus obtain higher sensitivities than those obtained before this time. This sensitivity permits resolution of zonal banding in the deep atmosphere, with bands observed between 0 and 20 degrees with 2 K brightness temperature contrasts at depths between 1-10 bar. These variations are likely driven by small-scale circulation patterns and associated condensation effects similar to those associated with the large pole-to-equator variations. We will discuss the consistency of these datasets and inferred distribution of opacity sources (NH₃ or H₂S). As we approach winter solstice in 2030, it will be particularly important to monitor Uranus’ deep atmosphere to provide further evidence for near-solstice changes in the deep atmosphere structure or composition as a seasonal phenomenon. Confirmation would provide insight into how varying insolation due to Uranus’ obliquity drives atmospheric changes in a manner unlike other giant planets.