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A dispersive wave pattern on Jupiter's fastest retrograde jet at 20S

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journal contribution
posted on 08.06.2016 by J. H. Rogers, Leigh N. Fletcher, G. Adamoli, M. Jacquesson, M. Vedovato, G. S. Orton
A compact wave pattern has been identified on Jupiter’s fastest retrograding jet at 20°S (the SEBs) on the southern edge of the South Equatorial Belt. The wave has been identified in both reflected sunlight from amateur observations between 2010 and 2015, thermal infrared imaging from the Very Large Telescope and near infrared imaging from the Infrared Telescope Facility. The wave pattern is present when the SEB is relatively quiescent and lacking large-scale disturbances, and is particularly notable when the belt has undergone a fade (whitening). It is generally not present when the SEB exhibits its usual large-scale convective activity (‘rifts’). Tracking of the wave pattern and associated white ovals on its southern edge over several epochs have permitted a measure of the dispersion relationship, showing a strong correlation between the phase speed (−−43.2 to −−21.2 m/s) and the longitudinal wavelength, which varied from 4.4 to 10.0° longitude over the course of the observations. Infrared imaging sensing low pressures in the upper troposphere suggest that the wave is confined to near the cloud tops. The wave is moving westward at a phase speed slower (i.e., less negative) than the peak retrograde wind speed (−−62 m/s), and is therefore moving east with respect to the SEBs jet peak. Unlike the retrograde NEBn jet near °N, which is a location of strong vertical wind shear that sometimes hosts Rossby wave activity, the SEBs jet remains retrograde throughout the upper troposphere, suggesting the SEBs pattern cannot be interpreted as a classical Rossby wave. 2D windspeeds and thermal gradients measured by Cassini in 2000 are used to estimate the quasi-geostrophic potential vorticity gradient as a means of understanding the origin of the a wave. We find that the vorticity gradient is dominated by the baroclinic term and becomes negative (changes sign) in a region near the cloud-top level (400–700 mbar) associated with the SEBs. Such a sign reversal is a necessary (but not sufficient) condition for the growth of baroclinic instabilities, which is a potential source of the meandering wave pattern.
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Citation

Icarus, 2016, 277, pp. 354–369

Author affiliation

/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy

Version

VoR (Version of Record)

Published in

Icarus

Publisher

Elsevier for Academic Press

issn

0019-1035

Acceptance date

19/05/2016

Copyright date

2016

Available date

27/05/2017

Publisher version

http://www.sciencedirect.com/science/article/pii/S0019103516302330

Language

en

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