Indian Astronomers Solve Solar Radio Mystery, Unlock Clues to Space Weather Prediction

In a breakthrough that advances our understanding of solar activity and its impact on Earth, researchers from the Indian Institute of Astrophysics (IIA) have resolved a long-standing scientific puzzle related to solar radio bursts triggered by coronal shocks.

The study sheds new light on how solar flares and coronal mass ejections (CMEs) generate radio emissions and how these signals propagate through the Sun's outer atmosphere, or corona—an advance that could significantly improve space weather forecasting capabilities.

Decoding the Mystery of Solar Radio Emissions

Solar coronal shocks often produce Type II solar radio bursts, also known as slow-drifting bursts, which travel outward from the Sun at speeds of around 1,000 km per second. These bursts are critical indicators of solar disturbances that can affect satellite communications, navigation systems, and power grids on Earth.

Type II bursts typically exhibit two components:

• Fundamental emission (base frequency)

• Harmonic emission (higher-frequency overtone)

Conventional theory suggests that the fundamental emission should be stronger. However, observations over decades have shown inconsistencies, with harmonic emissions sometimes appearing stronger—posing a persistent scientific puzzle.

Key Discovery: Solar Location Determines Signal Strength

The IIA-led research team has now identified the root cause behind this variation. By analysing 58 Type II solar radio bursts, scientists discovered that the relative strength of fundamental and harmonic emissions depends on the location of the solar event.

According to the study:

• Solar events originating beyond 75° heliographic longitude (near the Sun's limb) tend to show stronger harmonic emissions

• Events closer to the solar disk center (less than 75°) exhibit stronger fundamental emissions

Explaining the phenomenon, Dr. K. Sasikumar Raja, Principal Investigator of the study, noted:

"The variation is primarily due to refractive effects in the solar corona, as well as the directivity and viewing angle of radio emissions. Fundamental emissions from regions beyond 75° often fail to reach Earth effectively, whereas harmonic emissions, with broader cone angles, are more likely to be detected."

Global Data and Advanced Instrumentation

The research leveraged data from a global network of CALLISTO (Compound Astronomical Low Frequency Low Cost Instrument for Spectroscopy and Transportable Observatory) instruments, enabling comprehensive tracking of solar radio events.

Additionally, high-resolution observations were obtained from the Gauribidanur Low Frequency Solar Spectrograph (GLOSS), operated by IIA, which played a crucial role in analysing the spectral characteristics of the bursts.

This combination of global observational data and indigenous instrumentation allowed researchers to systematically decode the emission patterns.

Implications for Space Weather Forecasting

Understanding how solar radio waves behave is essential for predicting space weather events, which can have far-reaching consequences, including:

• Disruptions to satellite communications and GPS systems

• Impacts on aviation and maritime navigation

• Risks to power grids and critical infrastructure

By clarifying the mechanisms behind radio wave propagation, the study enhances scientists' ability to:

• Accurately interpret solar signals

• Improve early warning systems for solar storms

• Develop more reliable space weather prediction models

Future Directions: AI and Big Data in Solar Science

Highlighting the next phase of research, Rishikesh G. Jha, first author of the study, emphasized the potential of advanced analytics:

"CALLISTO and other spectrometers worldwide have generated vast datasets. Applying machine learning techniques could help uncover deeper patterns and solve more such mysteries in solar physics."

Published in Leading Journal

The findings have been published in the internationally reputed journal Solar Physics, with contributions from:

• Rishikesh G. Jha, K. Sasikumar Raja, R. Ramesh, and C. Kathiravan (IIA)

• Christian Monstein (IRSOL, Università della Svizzera italiana, Switzerland)

A Step Forward in Solar Science

This discovery marks a significant step in bridging theoretical predictions and observational evidence in solar physics. As solar activity continues to influence modern technological systems, such insights are vital for strengthening India's capabilities in space science and global scientific leadership.