Flow patterns of Jupiter's south polar region

Abstract

Previous studies of Jupiter's wind patterns revealed the southernmost two prograde jets at 58°S and 64°S (planetocentric), which we designate as the S5 and S6 jets, respectively, but the jets and the wind patterns further poleward were not well defined. The Juno mission has provided the first opportunity to study the South Polar Region (SPR). Here we use images from Juno's camera, JunoCam, to characterize these jets and the wind patterns further south. We measure the main wind systems using JunoCam images taken up to two hours apart. The S5 jet coincides with a slightly sinuous boundary in methane-band images. The S6 jet is faster, broader and highly undulating in latitude, generally coinciding with the sinuous edge of the methane-bright South Polar Hood, whose wave pattern is often regular with a mean wavelength of 25.5° (±2.6°) longitude. Peak wind speeds along the S6 jet range from 42 (±12) to 49 (±11) m/s, faster than previously recognized. Poleward of the S6 jet, at ~65–70°S, there is an irregular belt of chaotic cyclonic regions termed folded filamentary regions (FFRs), with several small anticyclonic white ovals (AWOs) on or near its southern edge. Some of these FFRs appear to be extending northeast into the S6 jet. More FFRs are scattered from ~70 to 80°S. Wind speeds in the FFRs are generally ~20–60 m/s, comparable to lower-latitude cyclonic circulations. We also generate semi-quantitative maps of local vorticity, and thence, mean zonal vorticity profiles as a function of latitude. These confirm the S6 jet as sinuous and the southernmost belt of FFRs as a stable belt. Further south, there is usually a weak cyclonic vorticity maximum near 78°S, which probably represents irregular structures such as FFRs. Supplementary ground-based images, spaced by up to 4 days, show westward drifts for the ~65–70°S belt, with a mean of ~ + 0.9°/day in System III longitude. AWOs can also be tracked, for months or even years. They drift westward with a uniform speed of +0.8°/day between 69.5 and 72.4°S, but towards higher latitudes, up to 76°S, they show a steep latitudinal gradient to faster (eastward) speeds, comparable to those measured around the south polar pentagon of circumpolar cyclones at ~80°S. Overall, the ~65–70°S belt and associated AWOs show dynamical behaviour similar to lower latitudes. Further south, there are no rapid continuous jets, but the loose enhancement of cyclonic structures near 78°S suggests a trace of zonal structure extending almost as far as the polar pentagon.