What is it about?
When different currents in a fluid slide past each other, they sometimes develop growing meanders that curl up and change the currents, a process called shear instability. Most fluid systems in science and engineering are prone to this instability, including meandering jet streams in atmospheres and oceans, planet formation in protoplanetary disks, and the confinement of hot plasmas in fusion reactors. Analysis of Jupiter's eastward and westward jet streams, which remain remarkably steady for decades, has uncovered the long-sought on-off switch for this process, and has shown how Jupiter maintains stable shears. These two lessons remove much of the guesswork from the prediction and control of shear instability, and have wide-ranging implications.
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Why is it important?
Analysis of Jupiter's jet streams, using data from the Voyager, Galileo, Cassini, and Juno spacecraft, has led to the discovery of the on-off switch of fluid shear instability. This key unlocks scientific problems that include the stability of Jupiter's belts, which were discovered in 1630, and the length of Saturn's day, which was first attempted in 1794.
Perspectives
The importance of the Mach number to sound waves and aeronautics has been known since the 19th Century, and so too the importance of its analog for water waves and hydraulics, called the Froude number. There is a third class of waves, vorticity waves (Rossby waves), for which development of the analog of the Mach number was neglected throughout the 20th Century. Analysis of Jupiter's jet streams has brought this prodigal "Mach" number back into the fold, which is now helping to propel the field into the 21st Century.
Professor Timothy E. Dowling
University of Louisville
Read the Original
This page is a summary of: Jupiter-style Jet Stability, The Planetary Science Journal, March 2020, American Astronomical Society,
DOI: 10.3847/psj/ab789d.
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