The Wide-field Imager for Parker Solar Probe (WISPR) Science Team, led by the U.S. Naval Research Laboratory (NRL), captured the event of turbulence as a Coronal Mass Ejection (CME) interacted with the ambient solar wind within the circumsolar space. This discovery is reported within the Astrophysical Journal.
Making the most of its unique location contained in the Sun’s atmosphere, the NRL-built WISPR telescope on NASA’s Parker Solar Probe (PSP) mission, operated by the Johns Hopkins University Applied Physics Laboratory (JHUAPL), captured in unparalleled detail the interaction between a CME and the background ambient solar wind. To the surprise of the WISPR team, images from one in all the telescopes showed what appeared like turbulent eddies, so-called Kelvin-Helmholtz instabilities (KHI). Such structures have been imaged within the terrestrial atmosphere as trains of crescent wave-like clouds and are the outcomes of strong wind shear between the upper and lower levels of the cloud. This phenomenon, while rarely imaged, is believed to occur usually on the interface of fluid flows when the appropriate conditions arise.
“We never anticipated that KHI structures could develop to large enough scales to be imaged in visible light CME images within the heliosphere after we designed the instrument,” said Angelos Vourlidas, Ph.D., JHUAPL and WISPR Project Scientist. “These wonderful detail observations show the facility of the WISPR high sensitivity detector combined with the close-up vantage point afforded by Parker Solar Probe’s unique sun-encounter orbit,” said Mark Linton, Ph.D., head, NRL Heliophysics Theory and Modeling Section and Principal Investigator for the WISPR instrument.
The KHI structures were detected by the keen eye of an early profession member of the WISPR team, Evangelos Paouris, Ph.D., George Mason University. Paouris, and his WISPR colleagues, undertook a radical investigation to confirm that the structures were indeed KHI waves. The outcomes not only report an especially rare phenomenon, even at Earth, but additionally open a brand new window of investigation with necessary consequences for the civilian and Department of Defense (DOD) communities.
“The turbulence that provides rise to KHI plays a fundamental role in regulating the dynamics of CMEs flowing through the ambient solar wind. Hence, understanding turbulence is vital in achieving a deeper understanding of CME evolution and kinematics,” said Paouris. By extension, this data will result in more accurate forecasting of the arrival of CMEs in Earth’s vicinity and their effects on civilian and DOD space assets, thus safeguarding society and the warfighter.
“The direct imaging of extraordinary ephemeral phenomena like KHI with WISPR/PSP is a discovery that opens a brand new window to higher understand CME propagation and their interaction with the ambient solar wind,” Paouris said.
WISPR is the one imaging instrument aboard the NASA Parker Solar Probe mission. The instrument, designed, developed and led by NRL, records visible-light images of the solar corona and solar outflow in two overlapping cameras that together observe greater than 100-degrees angular width from the Sun. This NASA mission travels closer to the Sun than another mission. PSP uses a series of Venus flyby’s to steadily reduce its perihelion from 36 solar radii in 2018 to 9.5 in 2025. The mission is approaching its nineteenth perihelion on March 30, 2024 at a distance of 11.5 solar radii from Sun center.
By observing the information the team found the Kelvin-Helmholtz instability is happy on the boundary between the CME and the ambient wind, because the two are flowing at distinctly different velocities. The resulting vortex-like structures are analyzed with respect to what the Kelvin-Helmholtz instability predicts, and inferences are presented about what the local magnetic field strength and density should be to permit such an instability on this environment.
