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Planetary Science and Exploration Seminar, David Stevenson: "Jupiter Winds: A magnetic story"

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The zonal flows (differential rotation) of Jupiter have long been known. Jupiter's magnetic field has also long been known, and the associated rotation of the dominant part (the tilted dipole) was determined by radio astronomy. Relative to this essentially rigid rotation deep down, the equatorial atmosphere of Jupiter flows prograde at around 100 m/s, a value that is very stable over time. The winds die to zero at around 16 degrees north and south of the equator, and form an oscillating pattern at higher latitudes. It is natural (but far from established) to associate this pattern at least in part with an equator to pole temperature difference. However, Jupiter has no surface so this leaves unresolved the issue of flow at a depth beneath what is normally thought of as atmosphere (e.g., pressure less than of order a kilobar) but above the metallic fluid in which most of the field is generated. Gravity data from Juno, a spacecraft still in orbit around Jupiter, supports truncation of the winds at perhaps 3000 km in depth, at a pressure and temperature that are well above the metallic region but nonetheless at a place where there is significant electrical conductivity of the hydrogen of order 1S/m because of thermal excitation of the primarily bound electrons. The depth limit is set by Ohmic dissipation but the underlying dynamics is still imperfectly understood. I will discuss this and possible paths forward.

 

Professor David Stevenson is the Marvin L. Goldberger Professor of Planetary Science, Emeritus at California Institute of Technology. Professor David Stevenson’s work focuses on the internal structure and evolution of both major and terrestrial planets; application of fluid dynamics and magnetohydrodynamics to planetary interiors and the origin of the solar system. Originally from New Zealand, he received his Ph.D. from Cornell University in physics, where he proposed a model for the interior of Jupiter.


 

 

 

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