First-of-its-kind study of Alfven waves possibly key to mystery of solar corona heating
by Russ Nelson
Huntsville AL (SPX) Nov 15, 2024
Syed Ayaz, a researcher at The University of Alabama in Huntsville (UAH), has published a paper in Scientific Reports that builds on an earlier first-of-its-kind study that examined kinetic Alfven waves (KAW) as a possible explanation for why the solar corona, the outermost layer of the sun’s atmosphere, is approximately 200 times hotter than the surface of the sun itself. The new study, also a first, further confirms that these electromagnetic phenomena – abundant throughout the plasma universe – could prove vital to unlocking the biggest mystery of heliophysics.
“In our earlier work, we explored wave-particle interactions, focusing on the dynamics of kinetic Alfven waves in plasmas,” notes Ayaz, a graduate research assistant in the Center for Space Plasma and Aeronomic Research (CSPAR) at UAH, a part of The University of Alabama System. “However, certain critical aspects – such as the energy distribution of KAWs, the net resonance speed of particles and the characteristic damping length of KAWs – remained unexplored.”
Kinetic Alfven waves are oscillations of the charged particles and magnetic field as they move through the solar plasma. The waves are formed by motions in the photosphere, the sun’s outer shell that radiates visible light. “Damping” is a physical phenomenon that occurs in plasmas when charged particles interact with wave electric fields where KAWs transfer energy to particles, leading to plasma heating over extended distances.
“In this new study, we addressed these critical issues, which have not been investigated in existing literature,” Ayaz says. “By comparing our analytical findings with data from NASA’s Parker Solar Probe and the European Space Agency’s Solar Orbiter missions, we found strong consistency validating our theoretical results. Notably, this work represents the first investigation of these phenomena in non-thermal plasma, marking a significant advancement in understanding KAW dynamics in the solar corona and solar wind.”
A need for speed
“Group velocity,” the speed at which the energy of a wave propagates through a medium, is a key factor in understanding how KAWs transport energy across different spatial regions, such as the solar corona and solar wind – regions central to Ayaz’s research. This velocity helps researchers examine the flow and distribution of wave energy, enabling a better understanding of its role in energy transfer in astrophysical environments.
One critical piece of the puzzle is the precise velocity of the particles – called the resonance speed – after they gain energy from waves such as KAWs.
“When particles absorb energy from KAWs, at what speed do they move? The resonance velocity provides crucial insights into the flow and distribution of particle acceleration, enabling a better understanding of its role in energy transfer in astrophysical environments,” says Ayaz. “In our current study, we derive analytical expressions for the net resonance speed of particles, offering a quantitative measure of particle acceleration. The new study also reveals the damping length of KAWs, a parameter that derives the distance over which these waves can transport energy before being damped, providing valuable insights into the efficiency and reach of energy transfer mediated by KAWs in space plasmas.”
All three aspects – the group velocity of KAWs, the net resonance speed of particles and the damping length of KAWs – play pivotal roles in understanding wave-particle interactions in space plasmas.
“The phenomenon of the net resonance speed of particles stands out as especially significant,” Ayaz says. “This is because it directly quantifies how particles gain energy from KAWs and how their motion evolves in response to this energy transfer. For the first time, we have derived generalized analytical expressions for the net resonance speed of particles, providing a robust framework for understanding particle acceleration and heating mechanisms in non-thermal plasmas, offering insights into both localized and large-scale dynamics in the solar corona and solar wind.”
“Syed has undertaken an extensive and very important investigation into the direct mechanism by which ions, especially protons, are heated by magnetic fluctuations that terminate the cascade of energy from large to small scales,” says Dr. Gary Zank, Aerojet/Rocketdyne Chair in Space Science, as well as director of the Center for Space Physics and Aeronomic Research (CSPAR). “KAWs have long been regarded as the mechanism by which magnetic energy at small scales is converted to heat, but the precise mechanism by which this process occurs has not been understood. Syed’s work offers a clear path for how this process occurs.”
Looking ahead, this revolutionary work lays the foundation for future research projects aimed at deepening the understanding of the intricate processes at play in space plasma environments.
“The derived expressions have significant practical value for the broader scientific community, especially for data simulation experts,” Ayaz concludes. “By incorporating these generalized formulas into their coding frameworks, researchers can simulate more accurate models of wave-particle interactions, improving predictions of space weather phenomena. This interdisciplinary applicability underscores the potential of our findings to advance not only theoretical plasma physics but also its practical applications in computational astrophysics and beyond.”
Research Report:Alfven waves in the solar corona: resonance velocity, damping length, and charged particles acceleration by kinetic Alfven waves
Related Links
The Center for Space Plasma and Aeronomic Research
Solar Science News at SpaceDaily
