Analyses of ∼0.05–2 MeV Ions Associated with the 2022 February 16 Energetic Storm Particle Event Observed by Parker Solar Probe

• Published in: The Astrophysical journal Vol. 958; no. 2; pp. 144 - 159
• Main Authors: Giacalone, Joe, Cohen, C. M. S., McComas, D. J., Chen, X., Dayeh, M. A., Matthaeus, W. H., Klein, K. G., Bale, S. D., Christian, E. R., Desai, M. I., Hill, M. E., Khoo, L. Y., Lario, D., Leske, R. A., McNutt, R. L., Mitchell, D. G., Mitchell, J. G., Malandraki, O., Schwadron, N. A.
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 01-12-2023; IOP Publishing
• Subjects: Astrophysics; Coefficients; Coronal mass ejection; Diffusion coefficient; Energetic particles; Interplanetary particle acceleration; Interplanetary shocks; Ion flux; Ion fluxes; Ions; Jupiter; Particle intensity; Solar coronal mass ejections; Solar energetic particles; Solar probes; Solar wind
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/acfb86

Abstract
We present analyses of 0.05–2 MeV ions from the 2022 February 16 energetic storm particle event observed by Parker Solar Probe's (PSP) IS⊙IS/EPI-Lo instrument at 0.35 au from the Sun. This event was characterized by an enhancement in ion fluxes from a quiet background, increasing gradually with time with a nearly flat spectrum, rising sharply near the arrival of the coronal mass ejection (CME)–driven shock, becoming nearly a power-law spectrum, then decaying exponentially afterward, with a rate that was independent of energy. From the observed fluxes, we determine diffusion coefficients, finding that far upstream of the shock the diffusion coefficients are nearly independent of energy, with a value of 10
20
cm
2
s
−1
. Near the shock, the diffusion coefficients are more than 1 order of magnitude smaller and increase nearly linearly with energy. We also determine the source of energetic particles, by comparing ratios of the intensities at the shock to estimates of the quiet-time intensity to predictions from diffusive shock acceleration theory. We conclude that the source of energetic ions is mostly the solar wind for this event. We also present potential interpretations of the near-exponential decay of the intensity behind the shock. One possibility we suggest is that the shock was overexpanding when it crossed PSP and the energetic particle intensity decreased behind the shock to fill the expanding volume. Overexpanding CMEs could well be more common closer to the Sun, and this is an example of such a case.