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.