Characterizing Temperature and Aerosol Variability During Jupiter's 2006–2007 Equatorial Zone Disturbance

Abstract

We use ground-based mid-infrared (8-20 μm) data acquired by three different instruments between 2005 and 2008 to characterize the variability of tropospheric temperature and aerosol opacity during the 2006-2007 Equatorial Zone disturbance. This disturbance is part of a repeating pattern of cloud-clearing events at Jupiter's equator, observed as a significant brightening at 5 μm (sensing the 2-to 7-bar region) and darkening at visible wavelengths (sensing the ∼0.7-bar pressure level). The data reveal a brightness temperature increase of ∼3.1 K between 2005 and February 2007 at 8.6-μm sensing tropospheric aerosol opacity and temperature near 0.6-0.8 bar. At wavelengths sensing tropospheric ammonia and temperatures between 150 and 600 mbar, the brightness temperature remains largely invariant between 2005 and 2008. The tropospheric vertical temperature profile and the tropospheric aerosol opacity were derived from images captured in different filters on four different dates, one for each year. The retrieved aerosol opacity at ∼0.6-0.8 bar shows a decrease at 2-5 • S of ∼45% in 2006 and ∼65% in 2007, with respect to 2008. This is consistent with cloud clearing/thinning during the coloration of the Equatorial Zone at visible wavelengths. This brightening at 8.6 μm started in 2005 and preceded the brightening at 5 μm, which started in April 2006. The results also suggest that cloud clearing during the Equatorial Zone disturbances is not simply the result of tropospheric warming, at least at p < 0.7 bar. We propose that cloud clearing occurs due to a decrease in the ammonia gas upwelling at the equator. Plain Language Summary Jupiter's equatorial latitudes between ∼7 • , known as the Equatorial Zone (EZ), undergo dramatic planetary-scale disturbances that completely alter its appearance at different altitudes of the troposphere between 0.7 and 4 bar. Here we characterize the last EZ disturbance, observed in 2006-2007, to investigate what atmospheric conditions vary during these disturbances. Retrieved aerosol opacity at ∼0.6 bar shows a decrease at 2-5 • S of ∼45% in 2006 and ∼65% in 2007, with respect to 2008, consistent with cloud clearing/thinning during these events. This removal of aerosol opacity is observed to start in 2005, a year before the deeper clouds are cleared. These results indicate that the EZ disturbance involves the clearing of both the ammonia ice cloud near 0.7 bar and the deeper NH 4 SH clouds with each cloud deck responding at different times. Results also suggest that cloud clearing during the EZ disturbances is not simply the result of tropospheric warming in the middle-to-high troposphere. We propose that cloud clearing occurs due to a decrease in the ammonia gas upwelling from deeper levels.

Long-Term Behavior of Tropospheric Temperatures in Jupiter: Evidence for Quasi-Seasonal and Non-Seasonal Variability

“…Equatorial Zone (EZ) disturbances 17,18 in 1992, 1999-2000 and 2006-2007 (denoted by the black horizontal bars in Fig. 2A) appear to be contemporaneous with decreases in 330-mbar temperatures, in general agreement with a detailed study of atmospheric properties for the 2006-2007 event 29 . This cadence is also consistent with the 6-7 year period of these events 12 , even though not all of the equatorial temperature changes are tied to full-scale cloud-disturbance events.…”

Jupiter's Multi‐Year Cycles of Temperature and Aerosol Variability From Ground‐Based Mid‐Infrared Imaging

“…In particular, we (a) characterize the long-term variability of Jupiter's atmosphere in each of the wavelengths analyzed; (b) retrieve stratospheric and tropospheric temperatures, as well as tropospheric aerosol opacity, to explore hemispherical asymmetries, both seasonal and non-seasonal changes, and equatorial oscillations; and (c) investigate thermal and aerosol opacity changes during cyclic and non-cyclic disturbances of the belt/zone structure. Although some of the mid-infrared images used in this study have been previously published (e.g., Antuñano et al, 2021;Fletcher, Orton, Sinclair, et al, 2017, Orton et al, 1994, 2023, this is the first study that analyses simultaneously long-term ground-based images captured in 5 and 8 filters in a systematic fashion. The conclusions of this study are summarized below:…”

Mid-Infrared Observations of the Giant Planets

“…In all cases, hydrogen and helium are assumed to be uniformly well mixed throughout the atmosphere below the homopause, and so the observed spatial structure can be explained by spatially varying temperatures. On Jupiter and Saturn, methane is likewise considered well mixed, and thus the 7.9-µm observations are again indicative of temperatures structure [53,54], but at lower pressures. However, on Uranus and Neptune, it is cold enough for methane to condense in the troposphere, and therefore methane cannot necessarily be assumed to be uniformly well mixed [70,74].…”

“…N-band (8-14 µm) spectroscopy and imaging have been used in numerous investigations to infer temperatures, chemistry, and aerosol abundances in the troposphere and stratosphere of Jupiter (e.g., [49][50][51][52][53][54]) and Saturn (e.g., [55][56][57][58][59][60][61][62][63][64][65]). For Uranus and Neptune, the N band has been used to measure stratospheric emission associated with hydrocarbons (e.g., [33,[66][67][68][69][70][71][72][73][74]), but interpretations have been limited by larger uncertainties in both temperatures and chemical abundances.…”

“…Data have revealed gradual changes in low latitude temperatures, with little seasonal or short-term variation [384]. Emission at 5-µm has been used to reveal significant variability in the cloud opacity [54,289,385], while stratospheric temperatures, appear more variable and complicated on shorter timescales [50,386].…”