Led by Dr. Keiichi Ogasawara, the study shows that helium pickup ions play a crucial role in the formation of solar energetic particles (SEPs), a high-energy class of particles including electrons, protons, and heavy ions that arise during solar flares and coronal mass ejections (CMEs). SwRI scientists used observations from NASA's Solar TErrestrial RElations Observatory (STEREO) to trace the acceleration profiles of these ions across multiple CME events.
"We carefully identified the specific properties of the ions and used them to trace the physical energy transfer processes," said Ogasawara. "We also considered the roles played by different types of interplanetary shocks, when fast-moving solar wind disturbances collide with slower-moving solar wind plasmas."
The team found that helium pickup ions often travel at velocities up to twice that of the ambient solar wind-even during quiet solar conditions. Their higher energy levels make them especially susceptible to further acceleration in the dynamic environment of CME-driven shocks.
The SwRI study also analyzed how these particles behave relative to local magnetic field orientations and shock structures. By isolating different heliospheric regions, such as turbulent zones and CME sheaths, the researchers developed a new method for mapping particle evolution. This approach enabled them to distinguish between energy-gaining, energy-losing, and energy-conserving mechanisms.
"The velocity distribution of pickup ions is quite different from that of the solar wind," Ogasawara noted. "Because of this difference, pickup ions are more effectively accelerated to even higher energies than normal solar wind particles."
Understanding the acceleration of SEPs is vital, as their high energy levels can pose significant radiation risks to astronauts and spacecraft. The new tracking method enhances scientists' ability to predict where and how these particles gain energy within the heliosphere.
"This study examined particle behavior across a broad range of structures in the heliosphere including magnetic structures, interplanetary shocks and the sheath region that forms in advance of a CME," added Ogasawara.
Research Report:Helium Pickup Ion Velocity Distributions Observed in Interplanetary Coronal Mass Ejection Structures
Related Links
Southwest Research Institute
Solar Science News at SpaceDaily
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