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

Desai, M. I. and Mitchell, D. G. and McComas, D. J. and Drake, J. F. and Phan, T. and Szalay, J. R. and Roelof, E. C. and Giacalone, J. and Hill, M. E. and Christian, E. R. and Schwadron, N. A. and McNutt, R. L. and Wiedenbeck, M. E. and Joyce, C. and Cohen, C. M. S. and Davis, A. J. and Krimigis, S. M. and Leske, R. A. and Matthaeus, W. H. and Malandraki, O. and Mewaldt, R. A. and Labrador, A. and Stone, E. C. and Bale, S. D. and Verniero, J. and Rahmati, A. and Whittlesey, P. and Livi, R. and Larson, D. and Pulupa, M. and MacDowall, R. J. and Niehof, J. T. and Kasper, J. C. and Horbury, T. S. (2022) Suprathermal Ion Energy Spectra and Anisotropies near the Heliospheric Current Sheet Crossing Observed by the Parker Solar Probe during Encounter 7. Astrophysical Journal, 927 (1). Art. No. 62. ISSN 0004-637X. doi:10.3847/1538-4357/ac4961.

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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–E⁶; and (5) maximum energies EX 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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper ItemIS⊙IS data
Desai, M. I.0000-0002-7318-6008
Mitchell, D. G.0000-0003-1960-2119
McComas, D. J.0000-0001-6160-1158
Drake, J. F.0000-0002-9150-1841
Phan, T.0000-0002-6924-9408
Szalay, J. R.0000-0003-2685-9801
Roelof, E. C.0000-0002-2270-0652
Giacalone, J.0000-0002-0850-4233
Hill, M. E.0000-0002-5674-4936
Christian, E. R.0000-0003-2134-3937
Schwadron, N. A.0000-0002-3737-9283
McNutt, R. L.0000-0002-4722-9166
Wiedenbeck, M. E.0000-0002-2825-3128
Joyce, C.0000-0002-3841-5020
Cohen, C. M. S.0000-0002-0978-8127
Davis, A. J.0000-0002-9922-8915
Krimigis, S. M.0000-0003-2781-2386
Leske, R. A.0000-0002-0156-2414
Matthaeus, W. H.0000-0001-7224-6024
Malandraki, O.0000-0002-4751-6835
Mewaldt, R. A.0000-0003-2178-9111
Labrador, A.0000-0001-9178-5349
Stone, E. C.0000-0002-2010-5462
Bale, S. D.0000-0002-1989-3596
Verniero, J.0000-0003-1138-652X
Rahmati, A.0000-0003-0519-6498
Whittlesey, P.0000-0002-7287-5098
Livi, R.0000-0002-0396-0547
Larson, D.0000-0001-5030-6030
Pulupa, M.0000-0002-1573-7457
MacDowall, R. J.0000-0003-3112-4201
Niehof, J. T.0000-0001-6286-5809
Kasper, J. C.0000-0002-7077-930X
Horbury, T. S.0000-0002-7572-4690
Additional Information:© 2022. The Author(s). Published by the American Astronomical Society. 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. Received 2021 October 25; revised 2021 December 1; accepted 2021 December 10; published 2022 March 4. This work was supported by NASA's Parker Solar Probe Mission, contract NNN06AA01C. We thank all the scientists and engineers who have worked hard to make PSP a successful mission, in particular the engineers, scientists, and administrators who designed and built IS⊙IS/EPI-Lo, IS⊙IS/EPI-Hi, FIELDS, and SWEAP instrument suites and support their operations and the scientific analysis of its data. For their contributions to the scientific configuration and instrumental analysis, we owe special thanks to P. Kollmann, J. Peachy, and J. Vandegriff at JHU/APL for EPI-Lo. The IS⊙IS data are available at as well as at the NASA Space Physics Data Facility. Work at SwRI is supported in part under NASA grant Nos. 80NSSC20K1815, 80NSSC18K1446, 80NSSC21K0112, 80NSSC20K1255, and 80NSSC21K0971.
Group:Astronomy Department, Space Radiation Laboratory
Funding AgencyGrant Number
Subject Keywords:The Sun; Solar magnetic reconnection; Interplanetary particle acceleration; Interplanetary magnetic fields; Heliosphere
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: The Sun (1693); Solar magnetic reconnection (1504); Interplanetary particle acceleration (826); Interplanetary magnetic fields (824); Heliosphere (711)
Record Number:CaltechAUTHORS:20220307-189632000
Persistent URL:
Official Citation:M. I. Desai et al 2022 ApJ 927 62
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:113774
Deposited By: George Porter
Deposited On:09 Mar 2022 15:39
Last Modified:09 Mar 2022 15:39

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