What is it about?
Planetary scientists have been trying to establish the length of Saturn's day since 1794. Independently, fluid dynamicists have been trying to find the on-off switch for shear instability since the 19th Century. A recent breakthrough regarding the latter led to an appreciation of the importance of the analog of the Mach number for a class of waves called vorticity waves (Rossby waves). This review explains this theory from first principles, and illustrates how it has yielded the first clear, connected, and calibrated measurement of Saturn's rotation period.
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Why is it important?
Progress in the field of shear instability theory has been slow since the 19th Century, to the point of being called out by science historians. However, the pace has recently picked up, in large measure because of the appreciation of the importance of the analog of the Mach number for vorticity waves. This has led to the identification of the long-sought on-off switch for shear instability.
Perspectives
Saturn's length of day provides a clear example of how the emergence of the prodigal "Mach" number for vorticity waves removes much of the guesswork from the prediction and control of shear instability, which is paving the way towards answers to fluid-mechanical questions that have been open for centuries.
Professor Timothy E. Dowling
University of Louisville
Read the Original
This page is a summary of: SATURN'S LONGITUDE: RISE OF THE SECOND BRANCH OF SHEAR-STABILITY THEORY AND FALL OF THE FIRST, International Journal of Modern Physics D, March 2014, World Scientific Pub Co Pte Lt,
DOI: 10.1142/s0218271814300067.
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