A compact wave pattern has been identified on Jupiter ’ s fastest retrograding jet at 20 ^ { \circ } 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 - 10.0 ^ { \circ } 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 17 ^ { \circ } 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 can not 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 .