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Published August 1994 | metadata_only
Journal Article

Baroclinic Instability in the Interiors of the Giant Planets: A Cooling History of Uranus?


We propose a quasigeostrophic, baroclinic model for heat transport within the interior of a stably stratified Jovian planet, based on motion in thin cylindrical annuli. Density decreases from the center outward and is zero at the surface of the planet. In the homogeneous case (no core), we find instability for the poles hotter than the equator, but not for the reverse. If the motion is bounded by an impenetrable core, instability occurs for both cases. Much of the behavior can be explained by analogy to conventional baroclinic instability theory. Motivated by our results, we explore a possible connection between the highly inclined rotation axis of Uranus and its anomalously low surface heat flux. We assume that the planets formed hot. Our conjecture is that heat was efficiently convected outwards by baroclinic instability in Uranus (with the poles hotter than the equator), but not in the other three Jovian planets. The surface temperature was higher for the stably stratified case (Uranus), leading to a higher rate of infrared emission and faster cooling. Therefore, we propose that Uranus lost its internal heat sooner than Neptune because baroclinic motions, permitted by its inclination to the sun, were able to extract its internal heat while the surface was still warm.

Additional Information

© 1994 Academic Press. Received December 6, 1993; revised May 23, 1994. This project was instigated and much of the work completed while A. P. I. was the principal lecturer and R. H. student at the 1992 Woods Hole Oceanographic Institution summer school in Geophysical Fluid Dynamics. This program was supported by N.S.F. through Grant OCE8901012. Further work was supported by N.A.S.A. Grants NAGW-2494 (R.H.) and NAGW-1958 (A.P.I.). We thank Glenn Flierl and Joe Keller for useful discussions and G. Wutchterl and an anonymous reviewer for significant comments on an initial draft of this paper.

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August 22, 2023
August 22, 2023