Jupiter’s Equatorial Atmosphere Observations

Introduction

Continued monitoring of Jupiter during the past four decades from Earth-based observatories, the Hubble Space Telescope, and visiting spacecraft has provided essential insights on Jupiter's belt/zone structure from the upper stratosphere to the deeper levels (~100 bar), allowing us to further our knowledge of Jupiter’s climatology, chemistry, and the coupling between the observed atmospheric dynamics and the unseen deeper levels.

Jupiter’s equatorial atmosphere is particularly interesting when investigating the atmospheric dynamics and climatology in the giant planets, as its equatorial temperatures and aerosols display remarkable quasi-periodic oscillations from the stratosphere (~1 mbar, e.g. Leovy et al., 1991, Orton et al., 1991) to below the thick ammonia clouds (5-7 bar, Antuñano et al., 2018, 2020).

 

Ground-Based Observations

Our study uses almost four decades of ground-based mid-infrared observations (1983 to 2019) captured at NASA’s Infrared Telescope Facility, the Very Large Telescope and the Subaru Telescope at 8 different wavelengths ranging between 7.9 µm and 24.5 µm, to analyse the long-term variability of upper tropospheric and stratospheric equatorial temperatures and aerosol opacity.  Examples of Jupiter images over the three decades are shown in Figure 1.

Figure 1. Examples of Jupiter images captured at 8.6 µm, over the three decades.

In this study, zonal-mean radiance profiles at different wavelengths are stacked together to form 5-point (7.9 µm, 8.6 µm, 10.7 µm, 18.7 µm and 20.5 µm) and 8-point (same as above plus 13.0 µm, 17.6 µm and 24.5 µm) spectral image cubes between 1983-2019 and 1996-2019, respectively. These spectral image cubes are then inverted using the radiative-transfer and retrieval codes NEMESIS (Irwin et al., 2008) to retrieve stratospheric and tropospheric temperatures and tropospheric aerosol-opacity.

 

Troposphere-Stratosphere Coupling

Jupiter’s equatorial stratosphere displays a remarkable periodic oscillation, where a vertical alternating pattern in the zonally-averaged temperature and winds is observed between 3 and 20 mbar, both at the equator and off-equatorial latitudes (±12° latitude, Leovy et al., 1991, Cosentino et al., 2017). In our study, we perform a cross-correlation analysis between the retrieved upper-tropospheric and stratospheric temperatures, revealing the extend of Jupiter’s Equatorial Stratospheric Oscillation (JESO) and showing a potential anticorrelation equatorial stratospheric and upper-tropospheric temperature, hinting to a potential troposphere-stratosphere coupling at Jupiter´s equatorial region.

 

Temperature and Aerosol Variability

Jupiter´s Equatorial Zone (EZ) undergoes a rare 7-year cyclic disturbance, where the typically white, NH₃ cloud-covered, and cold EZ shows a 5-µm bright, NH₃ cloud-free region encircling the planet south of the equator, accompanied by a strong coloration event at visible wavelengths (Antuñano et al., 2018). By analysing the long-term temporal variation of the retrieved tropospheric temperatures and aerosol opacity at these latitudes, our study reveals that the equatorial tropospheric aerosol opacity is not only modulated by the Equatorial Zone disturbances, but also by a wave with half the period of the Equatorial Zone disturbances. Our study also presents a quantitative study of the temporal lag between temperature and aerosol opacity changes at these latitudes.