ISRO Missions and Discoveries

[pib] Near-Surface Shear Layer (NSSL) of Sun


From UPSC perspective, the following things are important :

Prelims level : Near-Surface Shear Layer

Mains level : NA

Indian astronomers have found a theoretical explanation for the existence of the Near-Surface Shear Layer (NSSL) of the Sun for the first time.

What is a Near-Surface Shear Layer?

  • It was long known 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 the rotation profile of the Sun changes sharply.
  • The layer is called as a near-surface shear layer (NSSL), and it exists very close to the solar surface, where there is an outward decrease in angular velocity.

What have researchers found?

  • They have used an equation called the thermal wind balance equation to explain how the slight difference in temperature between solar poles and equator, called thermal wind term.
  • It is balanced by the centrifugal force appearing due to solar differential rotation.
  • They have noted that if this condition is true near the solar surface, it can explain the existence of NSSL, which is inferred in helioseismology (technique of using sound waves to peek inside the Sun) based observation.

Why study NSSL?

  • Understanding NSSL is crucial for the study of several solar phenomena like sunspot formation, solar cycle, and it will also help in understanding such phenomena in other stars.
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