An Investigation of the Structure, Color, and Potential Formation Mechanisms of Jupiter’s 2018-2022 Equatorial Zone Disturbance

Jupiter’s Equatorial Zone (EZ) undergoes quasi-periodic disturbances that typically turn the normally white cloud band a reddish hue and clear out opaque cloud layers, causing brightening at 5 μm. The most recent disturbance began in late 2018 and displayed the expected, characteristic reddening but not nearly the same degree of cloud-clearing as observed in previous disturbances. While several theories exist as to the cause of these events, the identity of the responsible dynamical mechanism is still unknown. In this work, we seek to understand the changes undergone by the EZ during the most recent disturbance and look for clues as to dynamical causes for these weather events more generally. We present the results of radiative transfer models of optical spectra of Jupiter’s EZ as captured at the 3.5-m telescope at Apache Point Observatory in Sunspot, NM before and during the most recent disturbance, in March 2017 and April 2019 respectively. These models test several parameterizations of the atmosphere, including the crème brůlée model of Sromovsky et al. (2017, Icarus 291, 232-244) and Baines et al. (2019, Icarus 330, 217-229) using the Carlson et al. (2016, Icarus 274, 106-115) chromophore coefficients, as well as several models incorporating variations of continuous cloud and chromophore profiles along the lines of those employed by Braude et al. (2020, Icarus 338, 113589) and Pérez-Hoyos et al. (2020, Icarus 352, 114031). We also test variance of the complex index of refraction of the chromophore from that reported in Carlson et al. (2016, Icarus 274, 106-115). We find that during the disturbance, our models favor a main ammonia cloud layer with an overall lower opacity, shallower base, and higher cloud top, as well as a chromophore layer with a higher total optical depth by factors of 2-4 (depending on the chromophore’s complex index of refraction spectrum). The continuous cloud models allow us to examine the changing vertical distribution of aerosols, and the combination of results from these and the crème brůlée models all provide preliminary evidence for an upwelling mechanism being responsible for the most recent EZ disturbance.