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

Abstract

Context. The tropospheric wind pattern in Jupiter consists of alternating prograde and retrograde zonal jets with typical velocities of up to 100 m s−1 around the equator. At much higher altitudes, in the ionosphere, strong auroral jets have been discovered with velocities of 1−2 km s−1. There is no such direct measurement in the stratosphere of the planet. Aims. In this Letter, we bridge the altitude gap between these measurements by directly measuring the wind speeds in Jupiter’s stratosphere. Methods. We use the Atacama Large Millimeter/submillimeter Array’s very high spectral and angular resolution imaging of the stratosphere of Jupiter to retrieve the wind speeds as a function of latitude by fitting the Doppler shifts induced by the winds on the spectral lines. Results. We detect, for the first time, equatorial zonal jets that reside at 1 mbar, that is, above the altitudes where Jupiter’s quasi-quadrennial oscillation occurs. Most noticeably, we find 300−400 m s−1 nonzonal winds at 0.1 mbar over the polar regions underneath the main auroral ovals. They are in counterrotation and lie several hundred kilometers below the ionospheric auroral winds. We suspect them to be the lower tail of the ionospheric auroral winds. Conclusions. We directly detect, for the first time, strong winds in Jupiter’s stratosphere. They are zonal at low-to-mid latitudes and nonzonal at polar latitudes. The wind system found at polar latitudes may help increase the efficiency of chemical complexification by confining the photochemical products in a region of large energetic electron precipitation.