Near-Surface Shear Layer(NSSL) – UPSC Prelims

Near-Surface Shear Layer(NSSL)?
  • It has long been known that the sun’s equator spins faster than the poles.
  • However, a peek into the internal rotation of the sun using sound waves revealed the existence of an intriguing layer where its rotation profile changes sharply.
  • This layer is called the near-surface shear layer(NSSL) and exists very close to the solar surface, within which the angular velocity decreases rapidly with radius.
  • Angular velocity is the time rate at which an object rotates or revolves, about an axis, or at which the angular displacement between two bodies changes.
  • Significance: Understanding NSSL is crucial for the study of several solar phenomena like sunspot formation and solar cycle.
Explanation for the existence of Near-Surface Shear Layer(NSSL):
  • Astronomers have provided an explanation of NSSL based on the thermal wind balance equation. It explains how the slight difference in temperature between solar poles and equator called thermal wind term is balanced by the centrifugal force appearing due to solar differential rotation.
  • Most scientists believe that this condition is true only in the interior of the Sun, and it does not hold near the solar surface.
  • But in this study, astronomers have shown that this belief actually holds near the solar surface as well. Hence, this is the reason for the existence of the Near-Surface Shear Layer(NSSL).
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