Why the solar corona is so much hotter than sun’s surface

In a new study printed in The Astrophysical Journal, a researcher from The College of Alabama in Huntsville (UAH), part of the College of Alabama System, explores important elements of a phenomenon known as kinetic Alfvén waves (KAWs) to offer recent insights into an age-old heliophysics thriller.

Syed Ayaz, a graduate analysis assistant on the UAH Heart for House Plasma and Aeronomic Analysis (CSPAR), examined the possibly pivotal function of KAWs in heating the solar corona, shifting science one step nearer to fixing the puzzle of why the corona is many occasions hotter than the floor of the sun itself.

“For many years, Alfvén waves have been confirmed to be the most effective candidates for transporting power from one place to a different,” Ayaz says, noting the potential function of KAWs in driving coronal warmth.

“This paper makes use of a novel method to mannequin energetic particles in space plasmas, as noticed by satellites like Viking and Freja, to reply how the electromagnetic power of the waves, interacting with particles, transforms into warmth throughout the damping course of because the waves transfer by way of space.

“Our investigation explores the perturbed electromagnetic fields, Poynting flux vector and the facility supply fee of KAWs within the solar ambiance.”

The corona, or solar ambiance, is an enigmatic area surrounding our dwelling star that extends far past the seen disk of the sun, stretching some 8 million kilometers above the sun’s floor. But, the corona can be characterised by terribly excessive temperatures, a thriller that has captivated astrophysicists for almost seventy years.

“Syed is one in every of our excellent college students who’s simply beginning out on his analysis profession,” says Dr. Gary Zank, CSPAR director and the Aerojet Rocketdyne chair of the UAH Division of House Science. “His abiding curiosity in Alfvén waves, began whereas a pupil in Pakistan when working along with his mentor, Dr. Imran A. Kahn, has now resulted in his investigation of those waves at very small scales, the so-called kinetic scale in a plasma.

“His work gives necessary insights into the important downside of how power in a magnetic field is remodeled to warmth a plasma comprising charged particles like protons and electrons. One motive Syed’s work is necessary is as a result of we nonetheless don’t perceive why the ambiance of the sun is greater than 1 million levels, in comparison with the floor of the sun, which is a relatively cool 6,500 levels.”

Kinetic Alfvén waves—ample all through the plasma universe—are oscillations of the ions and magnetic area as they transfer by way of the solar plasma. The waves are shaped by motions within the photosphere, the sun’s outer shell that radiates seen gentle.

“My major curiosity in these waves was sparked by the launches of the Parker Photo voltaic Probe and Photo voltaic Orbiter missions, which raised the essential query of how the solar corona is heated,” Ayaz says. “To date, no spacecraft mission has offered predictions relating to these phenomena near the sun, particularly, inside the 0–10 solar radii vary. Our major focus is to analyze heating by KAWs inside these ranges within the solar corona.”

“We targeted on the heating and power trade facilitated by KAWs,” the researcher notes. “The rationale for the nice curiosity in these waves lies of their capacity to move power. Observational knowledge from quite a few spacecraft and theoretical investigations have persistently demonstrated that KAWs dissipate and contribute to solar coronal heating throughout their propagation in space.”

Due to these unique properties, the waves present a important mechanism for transferring power, necessary to understanding the power trade between electromagnetic fields and plasma particles.

“KAWs function on small kinetic scales and are able to supporting parallel electrical and magnetic area fluctuations, enabling an power switch between the wave area and plasma particles by way of a phenomenon known as Landau interactions,” Ayaz says.

“The current work utilized and explores the Landau damping mechanism, which happens when particles shifting parallel to a wave have velocities corresponding to the wave’s phase velocity.”

Landau damping is an exponential lower as a perform of time of explicit waves in plasma. “When particles work together with the wave, they obtain/lose power—a time period known as ‘resonant situation,'” Ayaz says.

“This can lead to the wave both delivering its power to the particles or gaining power from them, inflicting the particles to both damp or develop. Our analysis finds that KAWs quickly dissipate, utterly transferring their power to plasma particles within the type of heating. This energy transfer accelerates the particles over longer spatial distances, considerably impacting the dynamics of the plasma.”

The analytical insights gleaned from this research will discover sensible software in understanding phenomena inside the solar atmosphere, notably shedding gentle on the numerous function performed by non-thermal particles within the heating processes.