Characterizing Temperature and Aerosol Variability during Jupiter's 2006‐07 Equatorial Zone Disturbance

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 NH4SH 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.