Moist convection and the 2010–2011 revival of Jupiter’s South Equatorial Belt

Abstract

The transformation of Jupiter's South Equatorial Belt (SEB) from its faded, whitened state in 2009-2010(Fletcher et al., 2011b to its normal brown appearance is documented via comparisons of thermal-infrared (5-20 µm) and visible-light imaging between November 2010 and November 2011. The SEB revival consisted of convective eruptions triggered over ∼ 100 days, potentially powered by the latent heat released by the condensation of water. The plumes rise from the water cloud base and ultimately diverge and cool in the stably-stratified upper troposphere. Thermal-IR images from the Very Large Telescope (VLT) were acquired 2 days after the SEB disturbance was first detected as a small white spot by amateur observers on November 9th 2010. Subsequent images over several months revealed the cold, putatively anticyclonic and cloudy plume tops (area 2.5 × 10 6 km 2 ) surrounded by warm, cloud-free conditions at their peripheries due to subsidence. The latent heating was not directly detectable in the 5-20 µm range. The majority of the plumes erupted from a single source near 140 − 160 • W, coincident with the remnant cyclonic circulation of a brown barge that had formed during the fade. The warm remnant of the cyclone could still be observed in IRTF imaging 5 days before the November 9th eruption. Additional plumes erupted from the leading edge of the central disturbance immediately east of the source, which propagated slowly eastwards to encounter the Great Red Spot. The tropospheric plumes were sufficiently vigorous to excite stratospheric thermal waves over the SEB with a 20 − 30 • longitudinal wavelength and 5-6 K temperature contrasts at 5 mbar, showing a direct connection between moist convection and stratospheric wave activity. The subsidence and compressional heating of dry, unsaturated air warmed the troposphere (particularly to the northwest of the central branch of the revival) and removed the aerosols that had been responsible for the fade. Dark, cloud-free lanes west of the plumes were the first to show the colour change, and elongated due to the zonal windshear to form the characteristic 'S-shape' of the revival complex. The aerosol-free air was redistributed and mixed throughout the SEB by the zonal flow, following a westward-moving southern branch and an eastwardmoving northern branch that revived the brown colouration over ∼ 200 days. The transition from the cool conditions of the SEBZ during the fade to the revived SEB caused a 2-4 K rise in 500-mbar temperatures (leaving a particularly warm southern SEB) and a reduction of aerosol opacity by factors of 2-3. Newly-cleared gaps in the upper tropospheric aerosol layer appeared different in filters sensing the ∼ 700-mbar cloud deck and the 2-3 bar cloud deck, suggesting complex vertical structure in the downdrafts. The last stage of the revival was the re-establishment of normal convective activity northwest of the GRS in September 2011, ∼ 840 days after the last occurrence in June 2009. Moist convection may therefore play an important role in controlling th...

Jupiter's North Equatorial Belt expansion and thermal wave activity ahead of Juno's arrival

“…The newly-darkened NTrZ then whitens over a 1-3 years, such that the edge of the brown belt appears to recede southwards to the normal 7 − 17 • N range. Infrared observations of the 2009-11 event demonstrated that the darkening of the NTrZ corresponded to a removal of aerosol opacity at 5 µm [Fletcher et al, 2017]. The cyclic nature of the NEB activity suggested that a new expansion phase would occur in 2015-16, which we characterize here.…”

Jupiter's Turbulent Power Spectra From Hubble Space Telescope

“…The right panel of Figure shows there is a high amount of spectral power at k = 1 across many latitudes, and sometimes spanning across shear regions. This effect is attributed to large‐scale sporadic events such as belt revivals and convective disturbances where cloud patterns dominate half the globe (Fletcher et al, ). We found that changing k low = 1 to k low = 2 had a significant impact on the calculated transition wave numbers; see panels (c) and (d) in Figure .…”

“…Jupiter's zonal wind profile is very stable with only a few locations experiencing significant changes in velocity with time, such as jet near 24°N. The continual banded appearance of light and dark clouds in Jupiter's atmosphere is occasionally disrupted by sporadic events that do not last very long (Fletcher et al, ). At the smallest scales, we see storms rapidly evolve and local cloud features get sheared apart (Gierasch et al, ).…”

Cycles of activity in the Jovian atmosphere

“…For example, material dredged upward by the erupting plumes is exposed to solar ultraviolet radiation, which may lead to a chain of photochemical pathways [e.g., Carlson et al, 2016] to produce a high-altitude haze Geophysical Research Letters 10.1002/2017GL073806 FLETCHER containing a red coloring agent. SEB revival events tend to take on an orange coloration during their latter stages [Fletcher et al, 2017a], and the Equatorial Zone periodically takes on an orange/yellow appearance ( Figure 1 and Table 1), and we speculate that similar photochemical modification of newly emplaced material could be at work. The existence of this reddened NTB band, which persists for some years before it narrows and fades away, could help to improve our understanding of the NTB life cycle.…”

“…During these fade events, the SEB can appear hidden and almost indistinguishable from the Equatorial Zone (EZ) to the north and the South Tropical Zone to the south (Figure ). The last SEB fade and revival occurred between 2009 and 2011 [ Fletcher et al , ; Pérez‐Hoyos et al , ; Fletcher et al , ], and assessment of the historical record shows that these dramatic cycles sometimes occur at intervals of about 3 years, but periods between fades can be as long as 36 years, with many intervening years of “normal” SEB activity. If Juno had been observing Jupiter during one of these events, as Pioneer 10 and 11 did, we might expect aerosol distributions (measured by JunoCam and Jovian Infrared Auroral Mapper) and gaseous distributions (e.g., ammonia measured by the microwave radiometer) to be anomalous compared to the long‐term record.…”