Context
A researcher, Bibhuti Kumar Jha, from Aryabhatta Research Institute of Observational Sciences (ARIES), an autonomous institute under the Department of Science and Technology, Govt. of India, along with others has for the first time given the theoretical explanation of the existence of NSSL in the Sun.
- This work has been published in the journal Monthly Notices of the Royal Astronomical Society.
About the theoretical explanation of intriguing layer
- By studying the internal rotation of the Sun using sound waves, it was revealed, an intriguing layer is present in the Sun.
- The layer is called as the near-surface shear layer (NSSL), and exists very close to the solar surface. Here, an outward decrease in angular velocity is observed.
- At this layer the rotation profile of the Sun changes sharply.
- It was long known that the Sun’s equator spins faster than the poles. But, the Indian astronomers have found a theoretical explanation for the existence of this layer for the first time.
How the study was conducted?
- In the study researcher used an equation called the thermal wind balance equation.
- This shows that how the slight difference in temperature between solar poles and the equator, called thermal wind term, is balanced by the centrifugal force which appears due to solar differential rotation.
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The Thermal Wind Equation:
- The Relation between the Horizontal Temperature Gradient and the Vertical Wind Shear.
- The vector of geostrophic wind velocity Vgcan be expressed as
- Vg = (1/ρf)k×∇H(p)
- where k is the unit vertical vector, ∇H(p) is the horizontal gradient of air pressure, ρ is the mass density of air, f is the Coriolus parameter and × is the vector cross product.
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- Earlier it was believed that this condition is true only for the interior of the Sun, and does not hold near the solar surface.
- In this work, the researchers have shown that the belief holds true near the surface as well.
Significance of the finding:
- Understanding NSSL is important for the study of several solar phenomena such as sunspot formation and solar cycle.
- It will also help in understanding such phenomena in other stars.
- If the condition is true near the solar surface, it can explain the existence of NSSL, which is inferred in helioseismology based observation.
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Helioseismology
- The technique of using sound waves to peek inside the Sun.
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