Why are the loops in the solar atmosphere so neat and tidy?

When a solar eclipse on August 21 reveals the Sun’s normally dim atmosphere, the corona will appear as a complex and organized network of loops, fans and tapes. These features track the coronal magnetic field, which drives the coronal plasma into the tubes and flakes. This thin coronal structure arises from a magnetic field on the visible surface of the Sun or its photosphere. Unlike the corona, the magnetism of the photosphere is a mess.

“It’s not a static surface like the earth, it’s more like an ocean,” said solar physicist Amir Kaspi of the Southwest Research Institute in Boulder, Colorado. And not just the ocean. It’s like a boiling ocean. ”Since all the loops and corona tapes originate from the turbulent photosphere, the roots must twist and stretch.

“However, the structures in this corona are not entangled, entangled, or entangled like seaweeds or seaweeds in the ocean,” Kaspi said. “They seem to still have an orderly and smooth loop. No one understands why.”

To unravel the tangled photosphere mat, Kaspi said, the corona must release some of the energy stored there. Therefore, during an eclipse, he and his friends would find an exhaust valve that releases the corona.

One possibility is that the movement of waves in the corona magnetic field line helps to unravel the tangled knots. Magnetic waves in plasma, called Alfvén waves, are thought to oscillate in the line of the Sun’s magnetic field, much like a guitar string vibrates. The researchers directly observed Alfvén waves at the bottom of the corona, about half the solar radius of the surface (SN: 04/11/09, p. 12), but not further away where similar waves of higher amplitude could propagate. These nearby waves are too weak to explain the corona features, but perhaps further waves can shake the situation up enough.

Another possibility is that a small burst of hypothetical magnetic energy could help unravel the clutter. These nano flares and nanojets will be similar to solar flares, but with a billion energy. Simulations have shown that, firing all the time, nano flares and nanojets can together release enough energy to give the corona some structure.

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“Both are symptoms of a small rearrangement in a magnetic field-a magnetic reconnection,” said solar physicist Craig DeForest of the Southwest Research Institute. Solar flares and larger flames called coronal mass bounces are also signs of magnetic reconnection, but they do not occur frequently enough to explain coronal smoothness. “Nanojets and/or nanoflars in the central corona can provide irrefutable evidence of why the corona is so organized,” DeForest said.

No one sees nanoflars or nanojets. Theories suggest it’s too small and fast to be seen individually, but it should look like a small pop fuss when a solar eclipse reveals the lower corona.

The vibrations from Alfvén waves and the flicker of nano flares can not only decompose the magnetic entanglement, but also transfer high heat into the corona. Caspi, DeForest and colleagues hope to see both effects on Aug. 21 when they fly a pair of telescopes on two NASA WB-57 high-altitude research aircraft along the eclipse path (SN Online: 08/14/17).

“We’re taking high -speed video footage of the Sun and analyzing it for things that look like waves,” Kaspi said. “We’re just looking at the crown structure as a whole.”