Why in News?
A team using the Daniel K. Inouye Solar Telescope in Hawaii recently reported clear evidence of torsional Alfvén waves twisting through the Sun’s outer atmosphere. The observations, released in October 2025, show small‑scale red and blue Doppler shifts in coronal loops that match theoretical predictions for these magnetised waves. Understanding Alfvén waves is crucial for explaining why the corona is millions of degrees hotter than the solar surface and for improving forecasts of space weather.
Background
Alfvén waves are a type of magnetohydrodynamic (MHD) wave first theorised by Swedish physicist Hannes Alfvén in 1942. They occur when a magnetic field line in a plasma oscillates and carries disturbances along its length, much like waves travelling on a stretched string. In the Sun, these waves propagate along magnetic flux tubes from the photosphere into the corona. Because the corona is much hotter than the solar surface, scientists have long suspected that MHD waves could transfer energy upward. Earlier observations hinted at the presence of Alfvénic motions, but directly measuring them in the corona remained challenging due to faint signals and instrument limitations.
Key findings of the study
- Clear Doppler signatures: Using the Cryogenic Near‑Infrared Spectropolarimeter (Cryo‑NIRSP), researchers measured alternating red and blue shifts that indicate plasma rotating around magnetic field lines. These torsional motions match the theoretical signature of Alfvén waves.
- Energy contribution to coronal heating: Estimates suggest that such waves could supply up to half of the energy required to keep the corona at temperatures exceeding one million degrees Celsius. They likely work in concert with other processes like magnetic reconnection.
- Implications for solar wind: Alfvén waves may accelerate charged particles away from the Sun, contributing to the solar wind. Better understanding these waves can improve models that predict geomagnetic storms affecting satellites, power grids and communications on Earth.
- Advancement in instrumentation: The DKIST, with its 4‑metre mirror and advanced infrared detectors, offers unprecedented spatial and spectral resolution, allowing scientists to probe the fine structure of the corona.
Why it matters
- Solving a long‑standing mystery: Coronal heating has puzzled physicists for decades. Direct observations of Alfvén waves lend support to theories that waves play a major role in transporting energy from the Sun’s interior to its outer atmosphere.
- Improving space weather forecasting: By quantifying how much energy these waves carry, researchers can refine models of solar eruptions and their effects on Earth, helping to protect infrastructure and astronauts.
- Advancing plasma physics: The findings have broader relevance for understanding magnetised plasmas in fusion reactors, astrophysical jets and planetary magnetospheres.
Sources: The Indian Express