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

Creators: Giacalone, Joe¹; Cohen, C. M. S.²; McComas, D. J.³; Chen, X.¹; Dayeh, M. A.^{4, 5}; Matthaeus, W. H.⁶; Klein, K. G.¹; Bale, S. D.⁷; Christian, E. R.⁸; Desai, M. I.^{4, 5}; Hill, M. E.⁹; Khoo, L. Y.³; Lario, D.⁸; Leske, R. A.²; McNutt, R. L.⁹; Mitchell, D. G.⁹; Mitchell, J. G.⁸; Malandraki, O.¹⁰; Schwadron, N. A.^{3, 11}

1. University of Arizona
2. California Institute of Technology
3. Princeton University
4. Southwest Research Institute
5. The University of Texas at San Antonio
6. University of Delaware
7. University of California, Berkeley
8. Goddard Space Flight Center
9. Johns Hopkins University Applied Physics Laboratory
10. National Observatory of Athens
11. University of New Hampshire

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 10²⁰ cm² 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.

Copyright and License

Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Acknowledgement

This project was supported by the IS⊙IS instrument suite on NASA's Parker Solar Probe Mission, contract NNN06AA01C. Parker Solar Probe was designed, built, and is now operated by the Johns Hopkins Applied Physics Laboratory as part of NASA's Living with a Star program. Support from the LWS management and technical team has played a critical role in the success of the Parker Solar Probe mission. J.G. also acknowledges support from the NSF/AGS under grant 1931252, and NASA under grants 80NSSC20K1283, 80NSSC18K1213, and 80NSSC21K0119.

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