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Atmospheric confinement of jet streams on Uranus and Neptune

2013; Nature Portfolio; Volume: 497; Issue: 7449 Linguagem: Inglês

10.1038/nature12131

1476-4687

Yohai Kaspi, Adam P. Showman, W. B. Hubbard, O. Aharonson, Ravit Helled,

Geology and Paleoclimatology Research

On Uranus and Neptune, the measured fourth-order gravity harmonic, J4, constrains the atmospheric dynamics to the outermost 0.15 per cent and 0.2 per cent, respectively, of the planetary mass, indicating that these dynamics are confined to a thin weather layer no more than 1,000 kilometres deep on both planets. The depth to which the atmospheric circulation and climate extends on the giant planets has been a subject of debate for several decades. On the basis of Voyager 2 and Hubble Space Telescope measurements of wind speed on Uranus and Neptune, combined with gravity field data and atmospheric modelling, Yohai Kaspi et al. calculate that the winds on both planets are confined to a thin 'weather layer' no more than 1,000 km deep. This finding implies that the dynamics controlling these winds derive from come from shallow processes rather than deep atmospheric circulation. The methodology used here should also be applicable to the detailed gravity field data for Jupiter and Saturn anticipated from the low-flying Juno and Cassini orbiters. The observed cloud-level atmospheric circulation on the outer planets of the Solar System is dominated by strong east–west jet streams. The depth of these winds is a crucial unknown in constraining their overall dynamics, energetics and internal structures. There are two approaches to explaining the existence of these strong winds. The first suggests that the jets are driven by shallow atmospheric processes near the surface1,2,3, whereas the second suggests that the atmospheric dynamics extend deeply into the planetary interiors4,5. Here we report that on Uranus and Neptune the depth of the atmospheric dynamics can be revealed by the planets’ respective gravity fields. We show that the measured fourth-order gravity harmonic, J4, constrains the dynamics to the outermost 0.15 per cent of the total mass of Uranus and the outermost 0.2 per cent of the total mass of Neptune. This provides a stronger limit to the depth of the dynamical atmosphere than previously suggested6, and shows that the dynamics are confined to a thin weather layer no more than about 1,000 kilometres deep on both planets.