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New Insights on Solar Wind Acceleration from Alfvén Waves

Recent research utilizing data from NASA’s Parker Solar Probe and the European Space Agency’s Solar Orbiter has unveiled significant insights into the mechanisms driving the acceleration and heating of the solar wind. This collaborative study led by an international team of astrophysicists has confirmed the role of Alfvén waves—electromagnetic plasma waves—as a primary energy source influencing solar wind behavior.

Published in the journal Science, the study illustrates how the alignment of the two spacecraft allowed for a unique observational opportunity. The Parker Solar Probe, positioned closer to the sun, recorded numerous high-energy magnetic waves at the edge of the solar corona. Meanwhile, the Solar Orbiter, situated beyond Venus’s orbit, captured data indicating the absence of these waves, which suggests they had dissipated their energy to heat and accelerate the outbound solar wind.

Key researchers, Luca Sorriso-Valvo from the CNR–Institute for Plasma Science and Technology in Sweden, and Francesco Malara from the University of Calabria in Italy, contributed a Perspective piece alongside the main findings, further contextualizing the implications of their research.

Previous studies have established that the solar wind, as it departs from the sun’s corona, tends to cool and accelerate—a process that traditionally seemed to occur faster than expected. Researchers postulated that an additional heat source was necessary to explain this discrepancy. Alfvén waves were suspected to play a key role in this dynamic, prompting the current research team’s efforts to investigate their influence more closely.

Observations and Findings

During a carefully staged alignment, data collected from Parker Solar Probe revealed significant Alfvén wave activity just before the solar wind interacted with the Solar Orbiter approximately 40 hours later. The initial probe’s measurements indicated that these waves were exerting force on the solar wind, causing directional shifts. Interestingly, data from the Solar Orbiter showed these wave influences were no longer detectable, and the solar wind was noticeably warmer.

To quantify the energy variations, the researchers compared the losses attributed to Alfvén waves with the thermal energy required for the observed heating and acceleration of the solar wind collected by the second probe. This analysis substantiated the hypothesis that Alfvén waves are indeed responsible for initiating the processes that heat and accelerate solar wind particles.

Conclusion and Implications

The findings present a compelling argument in favor of Alfvén waves serving as a critical driver for solar wind dynamics. This research not only advances our understanding of solar phenomena but also underscores the intricate connections between solar activity and space weather, which can significantly impact satellite operations and communication systems on Earth.

More information:
Yeimy J. Rivera et al, In situ observations of large-amplitude Alfvén waves heating and accelerating the solar wind, Science (2024). DOI: 10.1126/science.adk6953

Luca Sorriso-Valvo et al, Interplanetary rendezvous at a solar wind stream, Science (2024). DOI: 10.1126/science.adr5854

Source
phys.org