Why the Solar Corona is Hotter than the Sun's Surface?

In a study published in "The Astrophysical Journal", a researcher from The University of Alabama in Huntsville (UAH) explores critical aspects of kinetic Alfvén waves (KAWs) to provide insights into the longstanding heliophysics mystery of why the solar corona is far hotter than the sun's surface. Syed Ayaz, a graduate research assistant at UAH's Center for Space Plasma and Aeronomic Research (CSPAR), examined the crucial role of KAWs in heating the solar corona, contributing significantly to understanding this perplexing phenomenon.

"For decades, Alfvén waves have been recognized as key candidates for energy transport," Ayaz says, highlighting the potential of KAWs in driving coronal heat.

"This study adopts a novel modeling approach to energetic particles in space plasmas, as observed by satellites like Viking and Freja, illuminating how the waves' electromagnetic energy transforms into heat during the damping process," he explains.

The corona surrounds the sun, extending 8 million kilometers beyond its visible disk and exhibiting exceptionally high temperatures, a mystery that has intrigued astrophysicists for nearly seventy years.

Dr. Gary Zank, CSPAR director and chair of the UAH Department of Space Science, notes, "Syed’s work, sparked by his mentor Dr. Imran A. Kahn back in Pakistan, probes Alfvén waves at kinetic scales, significantly contributing to our understanding of plasma heating."

KAWs, prevalent across the plasma universe, oscillate ions and magnetic fields. These waves originate from motions in the photosphere, the sun's light-radiating outer shell. Initiatives like the Parker Solar Probe and Solar Orbiter missions have fueled interest in how the solar corona is heated. "We investigate KAW heating within 0–10 solar radii range," adds Ayaz.

"KAWs' ability to transport energy has been consistently demonstrated," Ayaz continues, "making them crucial for energy exchange between electromagnetic fields and plasma particles."

KAWs, operating on small kinetic scales, support field fluctuations that facilitate energy transfer via Landau interactions—a process where particles matching the wave's phase velocity exchange energy, a resonant condition. "This results in energy transfer through Landau damping, where KAWs dissipate energy into plasma heating," Ayaz notes.

This study's insights will advance our understanding of solar atmosphere phenomena, particularly highlighting the role of non-thermal particles in heating processes.

Earlier, SSP wrote about the Panathenaic Prize Amphora unveiling the Ancient Greek Olympic rewards.