Suprathermal Ion Energy Spectra and Anisotropies near the Heliospheric Current Sheet Crossing Observed by the Parker Solar Probe during Encounter 7

M. I. Desai, D. G. Mitchell, D. J. McComas, J. F. Drake, T. Phan, J. R. Szalay, E. C. Roelof, J. Giacalone, M. E. Hill, E. R. Christian, N. A. Schwadron, R. L. McNutt, M. E. Wiedenbeck, C. Joyce, C. M.S. Cohen, A. J. Davis, S. M. Krimigis, R. A. Leske, W. H. Matthaeus, O. MalandrakiR. A. Mewaldt, A. Labrador, E. C. Stone, S. D. Bale, J. Verniero, A. Rahmati, P. Whittlesey, R. Livi, D. Larson, M. Pulupa, R. J. Macdowall, J. T. Niehof, J. C. Kasper, T. S. Horbury

Research output: Contribution to journalArticlepeer-review

3 Scopus citations

Abstract

We present observations of ≳10-100 keV nucleon-1 suprathermal (ST) H, He, O, and Fe ions associated with crossings of the heliospheric current sheet (HCS) at radial distances of <0.1 au from the Sun. Our key findings are as follows: (1) very few heavy ions are detected during the first full crossing, the heavy-ion intensities are reduced during the second partial crossing and peak just after the second crossing; (2) ion arrival times exhibit no velocity dispersion; (3) He pitch-angle distributions track the magnetic field polarity reversal and show up to ∼10:1 anti-sunward, field-aligned flows and beams closer to the HCS that become nearly isotropic farther from the HCS; (4) the He spectrum steepens either side of the HCS, and the He, O, and Fe spectra exhibit power laws of the form ∼E -4-E 6; and (5) maximum energies E X increase with the ion's charge-to-mass (Q/M) ratio as EX/EH∝ (QX/MX)δ, where δ ∼0.65-0.76, assuming that the average Q states are similar to those measured in gradual and impulsive solar energetic particle events at 1 au. The absence of velocity dispersion in combination with strong field-aligned anisotropies closer to the HCS appears to rule out solar flares and near-Sun coronal-mass-ejection-driven shocks. These new observations present challenges not only for mechanisms that employ direct parallel electric fields and organize maximum energies according to E/Q but also for local diffusive and magnetic-reconnection-driven acceleration models. Reevaluation of our current understanding of the production and transport of energetic ions is necessary to understand this near-solar, current-sheet-associated population of ST ions.

Original languageEnglish (US)
Article number62
JournalAstrophysical Journal
Volume927
Issue number1
DOIs
StatePublished - Mar 1 2022

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Fingerprint

Dive into the research topics of 'Suprathermal Ion Energy Spectra and Anisotropies near the Heliospheric Current Sheet Crossing Observed by the Parker Solar Probe during Encounter 7'. Together they form a unique fingerprint.

Cite this