The bands of Jupiter represent a global system of powerful winds. Broad eastward equatorial jets are flanked by smaller-scale, higher-latitude jets flowing in alternating directions. Jupiter's large thermal emission suggests that the winds are powered from within, but the zonal flow depth is limited by increasing density and electrical conductivity in the molecular hydrogen-helium atmosphere towards the centre of the planet. Two types of planetary flow models have been explored: shallow-layer models reproduce multiple high-latitude jets, but not the equatorial flow system, and deep convection models only reproduce an eastward equatorial jet with two flanking neighbours. Here we present a numerical model of three-dimensional rotating convection in a relatively thin spherical shell that generates both types of jets. The simulated flow is turbulent and quasi-two-dimensional and, as observed for the jovian jets, simulated jet widths follow Rhines' scaling theory. Our findings imply that Jupiter's latitudinal transition in jet width corresponds to a separation between the bottom-bounded flow structures in higher latitudes and the deep equatorial flows.

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Spacecraft data reveal a very Earth-like Jovian magnetic field. This is surprising since numerical simulations have shown that the vastly different interiors of terrestrial and gas planets can strongly affect the internal dynamo process. Here we present the first numerical dynamo that manages to match the structure and strength of the observed magnetic field by embracing the newest models for Jupiter's interior. Simulated dynamo action primarily occurs in the deep high electrical conductivity region while zonal flows are dynamically constrained to a strong equatorial jet in the outer envelope of low conductivity. Our model reproduces the structure and strength of the observed global magnetic field and predicts that secondary dynamo action associated to the equatorial jet produces banded magnetic features likely observable by the Juno mission. Secular variation in our model scales to about 2000 nT per year and should also be observable during the one year nominal mission duration.Comment: 7 pages, 4 figures, accepted for publication in Geophysical Research Letter

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Jupiter and Saturn exhibit similar large‐scale dynamical features. Each planet has a prograde equatorial jet and a deeply seated dipolar magnetic field. Compared to Jupiter, Saturn's jet is broader and faster, while its magnetic field is weaker and more axially symmetric. The Sun also has prograde equatorial flow and a large‐scale axial magnetic field. While the depth of the Sun's differential rotation is well constrained by helioseismology, the depth to which the zonal winds penetrate in the giant planets is not known and has been a subject of debate. Although magnetic braking has been invoked as the mechanism to slow the winds at depth, such a mechanism has not previously been demonstrated. Here we present the first self‐consistent numerical planetary dynamo models in which slow convection in the interior dynamo source region coexists with strong zonal flow near the outer surface. The models include radially variable electrical conductivity and show that prograde zonal flow penetrates to a depth where Lorentz forces balance the Reynolds stress, which drives the equatorial jet. Our results imply that major differences between the surface zonal flows of Jupiter and Saturn arise from the different depths and conditions of a transition layer analogous to the solar tachocline. This transition layer, the planetary tachocline, separates the high velocity, semiconducting molecular envelope from the slow moving liquid metal interior dynamo.