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Register a new userJupiters Mesoscale Waves Observed at 5 $mu$m by Ground-Based Observations and Juno JIRAM
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We characterise the origin and evolution of a mesoscale wave pattern in Jupiters North Equatorial Belt (NEB), detected for the first time at 5 $mu$m using a 2016-17 campaign of `lucky imaging from the VISIR instrument on the Very Large Telescope and the NIRI instrument on the Gemini observatory, coupled with M-band imaging from Junos JIRAM instrument during the first seven Juno orbits. The wave is compact, with a $1.1-1.4^circ$ longitude wavelength (wavelength 1,300-1,600 km, wavenumber 260-330) that is stable over time, with wave crests aligned largely north-south between $14$ and $17^circ$N (planetographic). The waves were initially identified in small ($10^circ$ longitude) packets immediately west of cyclones in the NEB at $16^circ$N, but extended to span wider longitude ranges over time. The waves exhibit a 7-10 K brightness temperature amplitude on top of a $sim210$-K background at 5 $mu$m. The thermal structure of the NEB allows for both inertio-gravity waves and gravity waves. Despite detection at 5 $mu$m, this does not necessarily imply a deep location for the waves, and an upper tropospheric aerosol layer near 400-800 mbar could feature a gravity wave pattern modulating the visible-light reflectivity and attenuating the 5-$mu$m radiance originating from deeper levels. Strong rifting activity appears to obliterate the pattern, which can change on timescales of weeks. The NEB underwent a new expansion and contraction episode in 2016-17 with associated cyclone-anticyclone formation, which could explain why the mesoscale wave pattern was more vivid in 2017 than ever before.
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Jupiters banded structure undergoes strong temporal variations, changing the visible and infrared appearance of the belts and zones in a complex and turbulent way due to physical processes that are not yet understood. In this study we use ground-based 5-$mu$m infrared data captured between 1984 and 2018 by 8 different instruments mounted on the Infrared Telescope Facility in Hawaii and on the Very Large Telescope in Chile to analyze and characterize the long-term variability of Jupiters cloud-forming region at the 1-4 bar pressure level. The data show a large temporal variability mainly at the equatorial and tropical latitudes, with a smaller temporal variability at mid-latitudes. We also compare the 5-$mu$m-bright and -dark regions with the locations of the visible zones and belts and we find that these regions are not always co-located, specially in the southern hemisphere. We also present Lomb-Scargle and Wavelet Transform analyzes in order to look for possible periodicities of the brightness changes that could help us understand their origin and predict future events. We see that some of these variations occur periodically in time intervals of 4-8 years. The reasons of these time intervals are not understood and we explore potential connections to both convective processes in the deeper weather layer and dynamical processes in the upper troposphere and stratosphere. Finally we perform a Principal Component analysis to reveal a clear anticorrelation on the 5-$mu$m brightness changes between the North Equatorial Belt and the South Equatorial Belt, suggesting a possible connection between the changes in these belts.
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