Overview
The Kodaikanal Solar Observatory has supplied more than a century of solar images. Researchers from the Indian Institute of Astrophysics (IIA) analysed 34,000 Ca II K spectroheliograms taken between 1907 and 2025. Their work reveals how the size (lane width) and brightness (intensity) of solar supergranulation respond to the solar cycle.
Key Developments
- Correlation between lane width and sunspot number peaks at latitudes ~18°N and ~20°S.
- Correlation between intensity and sunspot number peaks at ~13°N and ~14°S, showing different optimal latitudes for each parameter.
- Lane‑width correlation is strongest during solar maximum, while intensity correlation lags 1.25–1.5 years after the maximum.
- Time‑lag varies with latitude: near ±20° the lag is almost zero; it grows toward the equator (up to ~2.5 years for intensity).
- The study covers more than nine solar cycles, providing a rare long‑term dataset for solar dynamo research.
Important Facts
- Supergranular cells have an average lifetime of 24 hours and a typical size of 30,000 km.
- Intergranular lanes are about 6,000 km wide.
- Peak correlation latitudes differ for lane width (+/‑2°) and intensity (+/‑2°).
- Lag for lane width ranges from 0.5 to 0.8 years; for intensity it ranges from 0.3 to 2.5 years.
- Findings support the idea that local magnetic flux modulates supergranular properties.
UPSC Relevance
Understanding solar convection and magnetic flux transport is vital for space weather forecasting. The Sun’s UV spectrum variations affect satellite drag, radio communication, and climate models, all of which are part of the GS3 syllabus on environment and technology. The long‑term dataset from Kodaikanal also illustrates the importance of preserving scientific archives for policy‑relevant research.
Way Forward
Future work should:
- Investigate the physical mechanisms behind latitude‑dependent lags.
- Integrate the findings with global solar dynamo models to improve prediction of the next solar cycle.
- Utilise upcoming high‑resolution instruments like the NLST for finer measurements of supergranular dynamics.
- Link solar UV variability to atmospheric and climate impact studies, aiding interdisciplinary policy planning.
These steps will enhance India’s capability in space‑weather research and contribute to global efforts in forecasting solar activity.