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 near-surface shear layer (NSSL), and it exists very close to the solar surface, where there is an outward decrease in angular velocity.
  • The layer marks the position where the rotation profile of the Sun changes sharply adding to the already known phenomenon that the Sun’s equator spins faster than the poles. The layer is called Near-Surface Shear Layer (NSSL) existing very close to the solar surface.
  • Indian astronomers have found a theoretical explanation for its existence for the first time. In a study published in the journal Notices of the Royal Astronomical Society, researchers used helioseismology, a technique of using sound waves to peek inside the Sun.
  • Scientists from Aryabhatta Research Institute of Observational Sciences (ARIES) provide an explanation of this layer based on the thermal wind balance equation that 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.
  • While most scientists believe that the condition is true only in the interior of the Sun, and it does not hold near the solar surface, the researchers from ARIES have shown otherwise, explaining that it holds near the surface as well.
  • Understanding NSSL is crucial for the study of several solar phenomena like sunspot formation, solar cycles, and it will also help in understanding such phenomena in other stars, the researchers argue.
  • The Sun had recently erupted the biggest flare in over four years that led to blackout over the Atlantic. The sunspot AR2838 burst through the surface of the sun unleashing the strongest solar flare in four years, an X1.5-class explosion. The sunspot, which is now gone, occurred over the star’s northwestern limb. The latest eruption marked the beginning of a new solar cycle, ionizing the top of Earth’s atmosphere, causing a shortwave radio blackout over the Atlantic Ocean.