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

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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 E −4–E 6; and (5) maximum energies E X increase with the ion’s charge-to-mass (Q/M) ratio as E X / E H ∝ ( Q X / M X ) 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.
Funding Information
  • National Aeronautics and Space Administration (NNN06AA01C)
  • NASA ∣ Science Mission Directorate (80NSSC20K1815)
  • NASA ∣ Science Mission Directorate (80NSSC18K1446)
  • NASA ∣ Science Mission Directorate (80NSSC21K0112)
  • NASA ∣ Science Mission Directorate (80NSSC20K1255)
  • NASA ∣ Science Mission Directorate (80NSSC21K0971)

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