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The number and location of Jupiter’s circumpolar cyclones explained by vorticity dynamics

Abstract

The Juno mission observed that both poles of Jupiter have polar cyclones that are surrounded by a ring of circumpolar cyclones (CPCs). The north pole holds eight CPCs and the south pole possesses five, with both circumpolar rings positioned along latitude ~84° N/S. Here we explain the location, stability and number of the Jovian CPCs by establishing the primary forces that act on them, which develop because of vorticity gradients in the background of a cyclone. In the meridional direction, the background vorticity varies owing to the planetary sphericity and the presence of the polar cyclone. In the zonal direction, the vorticity varies by the presence of adjacent cyclones in the ring. Our analysis successfully predicts the latitude and number of circumpolar cyclones for both poles, according to the size and spin of the respective polar cyclone. Moreover, the analysis successfully predicts that Jupiter can hold circumpolar cyclones, whereas Saturn currently cannot. The match between the theory and observations implies that vortices in the polar regions of the giant planets are largely governed by barotropic dynamics, and that the movement of other vortices at high latitudes is also driven by interaction with the background vorticity.

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Fig. 1: Observations of the PCs and CPCs of Jupiter and Saturn.
Fig. 2: Generalized β-drift schematic.
Fig. 3: An illustration of the balance holding a CPC around the PC.
Fig. 4: Latitudes of equilibrium in the gas giants.
Fig. 5: Zonal stability of CPCs.

Data availability

No data sets were generated or analysed during the current study.

Code availability

The MATLAB codes used for calculating and plotting the figures in this paper are available on request from N.G.

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Acknowledgements

We thank K. Duer and E. Galanti for insightful conversations. This research was supported by the Minerva Foundation with funding from the Federal German Ministry for Education and Research, the Israeli Space Agency and the Helen Kimmel Center for Planetary Science at the Weizmann Institute of Science.

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N.G. designed the study, performed the calculations and wrote the paper together with Y.K.

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Correspondence to Nimrod Gavriel.

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Peer review information Primary Handling Editor: Stefan Lachowycz. Nature Geoscience thanks Yakov Afanasyev and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 Measurements of the Jovian PC velocity profiles.

The velocity profiles from Extended Data Fig. 3a, overlaid on Fig. 6 from Grassi et al., 20186 (adapted with permission), showing the observed velocities around the north (a) and south (b) poles of Jupiter. The idealized velocity profiles are calculated using the Jovian values for R and V (Methods). The green curves (vPC) represent the velocity profiles used for the analyses in this study.

Extended Data Fig. 2 Measurements of the Saturnian PC velocity profiles.

Two velocity profiles from Extended Data Fig. 3a, overlaid on Fig. 8 from Baines et al., 200912 (adapted with permission), showing the observed velocities around the north (solid) and south (dashed) poles of Saturn. Error bars are calculated as standard deviations12. The idealized velocity profiles are calculated using the Saturnian values for R and V (Methods). The green curves (vPC) represent the velocity profiles used for the analyses in this study.

Extended Data Fig. 3 Idealized profiles of velocity, vorticity, and vorticity gradient.

a, The vortex velocity profile according to the suggested piece-wise function (green solid curve) from equation (6) compared with two other ideal vortex profiles6,23 (for the Grassi curve6, γ = 1.5 is taken). b, The vorticity calculated for the same profiles as a. c, Vorticity gradient (in log scale), calculated for the same three profiles. In addition, the minus of the β profiles are shown for the northern and southern poles of Saturn and Jupiter. The 4 curves for − β differentiate as the vorticity gradient is normalized according to each polar cyclone, and as the length is scaled by the radius of maximum velocity for the respective PC. The points where the vorticity gradient curves cross the − β curves represent equilibrium. Here, 0 in the r/R axis represents the pole.

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Gavriel, N., Kaspi, Y. The number and location of Jupiter’s circumpolar cyclones explained by vorticity dynamics. Nat. Geosci. 14, 559–563 (2021). https://doi.org/10.1038/s41561-021-00781-6

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