Recently, scientists from the Indian Institute of Astrophysics (IIA), an autonomous institute of the Department of Science and Technology (DST), used over 100 years of archival solar observations from the Kodaikanal Solar Observatory (KSO) to uncover new clues about how the Sun’s surface convection patterns respond to its 11-year activity cycle.
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About the Study
- Study Basis: Researchers analysed about 34,000 Ca II K spectroheliograms recorded between 1907 and the present, covering more than nine solar cycles.
- Ca II K Spectroheliograms: Images of the Sun taken in the calcium-II K spectral line, useful for studying magnetic activity and solar networks.
- Supergranulation and EUV Network: The study examined large-scale convection cells (supergranules) that form the chromospheric network, which extends into the transition region as the Extreme UltraViolet (EUV) network.
Key Findings of the Study
- Linked to Solar Activity: Surface convection features on the Sun closely follow the 11-year solar cycle, especially in regions located about 11°–22° north and south of the equator.
- Different Latitudes Behave Differently: No single latitude perfectly reflects solar activity, indicating that the Sun’s surface responds differently across regions.
- Time Lag Observed: Changes in convection-cell widths occur around the solar maximum, while changes in network brightness appear 1.25–1.5 years later.
- Variable Response Across Latitudes: The time lag differs across latitudes, suggesting complex interactions between solar magnetic fields and convection patterns.
- Role of Magnetic Flux: Supergranular properties appear to be influenced by local magnetic flux concentrations and changing solar activity levels.
About Supergranulation
- Supergranules are large convective cells on the Sun’s surface with an average size of about 30,000 km and a lifetime of around 24 hours.
- Magnetic Network Formation: Their boundaries contain concentrated magnetic fields, forming the chromospheric network visible in Ca II K observations.
- Role in Magnetic Flux Transport: They play an important role in transporting magnetic flux across the solar surface.
About Kodaikanal Solar Observatory (KSO)
- Location: Situated in the Palani Hills of Tamil Nadu and operated by the Indian Institute of Astrophysics.
- Established: Founded in 1899 for systematic solar observations.
- Long-Term Solar Records: Maintains one of the world’s longest continuous series of solar observations, spanning over 100 years.
- Multi-Wavelength Observations: Conducts simultaneous observations of the Sun in different wavelengths, making its dataset uniquely suited for multi-wavelength solar studies.
- Global Research Resource: Its century-long records provide valuable insights into long-term changes in solar behaviour across multiple solar cycles.
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Significance of the Study
- Improves Solar Cycle Understanding: Provides new insights into how supergranulation and the Extreme UltraViolet (EUV) network evolve during the 11-year solar activity cycle.
- Supports Solar Activity Prediction: Understanding the correlation between supergranulation and sunspot activity can improve future solar cycle forecasts.
- Helps Study Solar Irradiance: Findings are relevant for understanding variations in solar ultraviolet radiation that affect Earth’s upper atmosphere.
- Advances Solar Physics: Contributes to resolving the long-standing puzzle of the origin and evolution of supergranulation.
- Value of Long-Term Data: Demonstrates the scientific importance of century-long observations maintained by the Kodaikanal Solar Observatory.
- Future Research Potential: High-resolution observations from the National Large Solar Telescope (NLST) are expected to further improve understanding of supergranular dynamics.
6 Jun 2026
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