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Evolution of the Suprathermal Proton Population at Interplanetary ShocksWe investigate the evolution of the suprathermal (ST) proton population as interplanetary shocks cross 1 au. The variability of the ST proton intensities and energy spectra upstream of the shocks is analyzed in terms of the shock parameters, upstream magnetic field configurations, and preexisting upstream populations. Propitious conditions for the observation of ST particles at distances far upstream from the shock occur in parallel shock configurations when particles can easily escape from the shock vicinity. In this situation, ST intensity enhancements show onsets characterized by velocity dispersion effects and energy spectra that develop into a “hump” profile peaking around ∼10 keV just before the arrival of the shock. The observation of field-aligned proton beams at low energies (5–10 keV) is possible under conditions that facilitate the scatter-free propagation of the particles streaming out of the shock. Upstream of perpendicular shocks, ST intensity enhancements are only observed in close proximity to the shock. Power-law proton spectra develop downstream of the shocks. The functional form for the downstream phase-space density proportional to v(exp -5) is observed only over a limited range of ST energies. The absence of ST populations observed far upstream of interplanetary shocks raises questions about whether ST protons contribute as a seed particle population in the processes of particle acceleration at shocks.
Document ID
20190028780
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
Authors
Lario, D. ORCID
(Johns Hopkins Univ. Baltimore, MD, United States)
Berger, L.
(Institut für Experimentelle und Angewandte Physik Kiel, Germany)
Decker, R. B.
(Johns Hopkins Univ. Baltimore, MD, United States)
Wimmer-Schweingruber, R. F. ORCID
(Institut für Experimentelle und Angewandte Physik Kiel, Germany)
Wilson, L. B., III ORCID
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Giacalone, J.
(Arizona Univ. Tucson, AZ, United States)
Roelof, E. C.
(Johns Hopkins Univ. Baltimore, MD, United States)
Date Acquired
August 6, 2019
Publication Date
June 11, 2019
Publication Information
Publication: Astronomical Journal
Publisher: American Astronomical Society
Volume: 158
Issue: 1
ISSN: 0004-6256
e-ISSN: 1538-3881
Subject Category
Astrophysics
Report/Patent Number
GSFC-E-DAA-TN70043
Funding Number(s)
CONTRACT_GRANT: NNX15AD03G
CONTRACT_GRANT: NNX16AF73G
CONTRACT_GRANT: NNX10AT75G
Distribution Limits
Public
Copyright
Use by or on behalf of the US Gov. Permitted.
Technical Review
NASA Technical Management
Keywords
Shock waves
Interplanetary medium
Acceleration of particles
Solar wind
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