Vol. 647
1. Letters

First direct measurement of auroral and equatorial jets in the stratosphere of Jupiter

by T. Cavalié, B. Benmahi, V. Hue, et al. 2021, A&A, 647, L8

The circulation in Jupiter's upper troposphere at cloud level has been measured for decades using the cloud-tracking technique. It consists of alternating prograde and retrograde zonal jets (i.e., east-west) with velocities up to ~100m/s that peak at low latitudes. More than 1000 km higher, in the ionosphere, supersonic jets have been discovered at polar latitudes in the auroral region. In this paper, Cavalié and collaborators use the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to discover jets 150-200 km above the clouds in the stratosphere. Benefiting from the combination of high spectral and spatial resolving powers as well as high sensitivity and near instantaneous imaging with ALMA, they directly probe the wind speeds using Doppler shifts induced by the winds on spectral lines formed in the stratosphere. They discover strong nonzonal jets located under the main auroral ovals with velocities of 300-400 m/s. Auroral jets may thus extend from the ionosphere down to the stratosphere, forming huge vortices in which chemical compounds may be dynamically confined and bombarded by energetic magnetospheric electrons, resulting in a richer chemical inventory. In addition, zonal jets with velocities peaking at 150 m/s were found around Jupiter’s equator, the first direct measurement of the winds generated by the quasi-quadrennial oscillation in Jupiter’s equatorial stratosphere.