AAS Nova

Selections from 2024: First Images of Turbulent Eddies in the Outer Corona

By on Features
Share:
photograph of clouds exhibiting the kelvin-helmholtz instability
The Kelvin–Helmholtz instability, which plays an important role in the atmospheres of stars and planets alike, is revealed by rare, wave-like patterns in clouds. [UCAR]

Editor’s Note: For the remainder of 2024, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded articles published in AAS journals this year. The usual posting schedule will resume January 3rd.

First Direct Imaging of a Kelvin–Helmholtz Instability by PSP/WISPR

Published March 2024

Main takeaway:

solar Kelvin-Helmholtz instability

One of several frames in which the turbulent eddies are clearly visible in images from the Wide-field Imager for Parker Solar Probe (WISPR). Each vortex-like feature is labeled. Click to enlarge. [Adapted from Paouris et al. 2024]

Evangelos Paouris (George Mason University; The Johns Hopkins University Applied Physics Laboratory) and collaborators discovered evidence of the Kelvin–Helmholtz instability in the outer solar corona. This is likely the first time this phenomenon has been directly imaged so far out in the Sun’s atmosphere, and this groundbreaking observation was made possible by the unique vantage point and sensitive instruments of the Parker Solar Probe.

Why it’s interesting:

The Kelvin–Helmholtz instability arises at the interface between two fluids, or between fluid regions that are moving at different velocities. While that might sound obscure, Kelvin–Helmholtz instabilities are thought to be common throughout planetary and stellar atmospheres, and you may have seen images of the wave-like clouds (pictured above) that form through the instability. Although researchers knew that the Kelvin–Helmholtz instability happens in the Sun’s atmosphere, they didn’t expect to see evidence of it in the Sun’s middle and outer corona — the hot and tenuous upper atmosphere. They believed that the wave-like pattern of the instability would simply be too small to pick out, even from a nearby spacecraft like the Parker Solar Probe.

More about the discovery and what it might enable:

Paouris and collaborators spotted the instability at the boundary between the solar corona and a coronal mass ejection: a massive outburst of solar plasma and magnetic fields. The team applied multiple tests to the data to confirm that the observed pattern of eddies was consistent with expectations for the Kelvin–Helmholtz instability. This discovery opens up the possibility of using these observations to study the rarefied plasma of the solar corona, as well as the movement of coronal mass ejections through the corona and the outflowing solar wind. Understanding the motions of coronal mass ejections is important for forecasting whether these destructive events might strike Earth, which has practical value: the energetic particles of a coronal mass ejection threaten spacecraft electronics, power grids, and astronauts floating beyond the protective shield of Earth’s magnetic field.

Citation

Evangelos Paouris et al 2024 ApJ 964 139. doi:10.3847/1538-4357/ad2208