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Energetic Particle Increases Associated with Stream Interaction Regions

Cohen, C. M. S. and Christian, E. R. and Cummings, A. C. and Davis, A. J. and Desai, M. I. and Giacalone, J. and Hill, M. E. and Joyce, C. J. and Labrador, A. W. and Leske, R. A. and Matthaeus, W. H. and McComas, D. J. and McNutt, R. L., Jr. and Mewaldt, R. A. and Mitchell, D. G. and Rankin, J. S. and Roelof, E. C. and Schwadron, N. A. and Stone, E. C. and Szalay, J. R. and Wiedenbeck, M. E. and Allen, R. C. and Ho, G. C. and Jian, L. K. and Lario, D. and Odstrcil, D. and Bale, S. D. and Badman, S. T. and Pulupa, M. and MacDowall, R. J. and Kasper, J. C. and Case, A. W. and Korreck, K. E. and Larson, D. E. and Livi, Roberto and Stevens, M. L. and Whittlesey, Phyllis (2020) Energetic Particle Increases Associated with Stream Interaction Regions. Astrophysical Journal Supplement Series, 246 (2). Art. No. 20. ISSN 1538-4365. doi:10.3847/1538-4365/ab4c38.

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The Parker Solar Probe was launched on 2018 August 12 and completed its second orbit on 2019 June 19 with perihelion of 35.7 solar radii. During this time, the Energetic Particle Instrument-Hi (EPI-Hi, one of the two energetic particle instruments comprising the Integrated Science Investigation of the Sun, IS⊙IS) measured seven proton intensity increases associated with stream interaction regions (SIRs), two of which appear to be occurring in the same region corotating with the Sun. The events are relatively weak, with observed proton spectra extending to only a few MeV and lasting for a few days. The proton spectra are best characterized by power laws with indices ranging from −4.3 to −6.5, generally softer than events associated with SIRs observed at 1 au and beyond. Helium spectra were also obtained with similar indices, allowing He/H abundance ratios to be calculated for each event. We find values of 0.016–0.031, which are consistent with ratios obtained previously for corotating interaction region events with fast solar wind ≤ 600 km s⁻¹. Using the observed solar wind data combined with solar wind simulations, we study the solar wind structures associated with these events and identify additional spacecraft near 1 au appropriately positioned to observe the same structures after some corotation. Examination of the energetic particle observations from these spacecraft yields two events that may correspond to the energetic particle increases seen by EPI-Hi earlier.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Cohen, C. M. S.0000-0002-0978-8127
Christian, E. R.0000-0003-2134-3937
Cummings, A. C.0000-0002-3840-7696
Desai, M. I.0000-0002-7318-6008
Hill, M. E.0000-0002-5674-4936
Joyce, C. J.0000-0002-3841-5020
Labrador, A. W.0000-0001-9178-5349
Leske, R. A.0000-0002-0156-2414
Matthaeus, W. H.0000-0001-7224-6024
McComas, D. J.0000-0001-6160-1158
Mewaldt, R. A.0000-0003-2178-9111
Mitchell, D. G.0000-0003-1960-2119
Rankin, J. S.0000-0002-8111-1444
Schwadron, N. A.0000-0002-3737-9283
Stone, E. C.0000-0002-2010-5462
Szalay, J. R.0000-0003-2685-9801
Wiedenbeck, M. E.0000-0002-2825-3128
Allen, R. C.0000-0003-2079-5683
Jian, L. K.0000-0002-6849-5527
Lario, D.0000-0002-3176-8704
Bale, S. D.0000-0002-1989-3596
Badman, S. T.0000-0002-6145-436X
Pulupa, M.0000-0002-1573-7457
MacDowall, R. J.0000-0003-3112-4201
Kasper, J. C.0000-0002-7077-930X
Case, A. W.0000-0002-3520-4041
Korreck, K. E.0000-0001-6095-2490
Stevens, M. L.0000-0002-7728-0085
Additional Information:© 2020. The American Astronomical Society. Received 2019 September 13; revised 2019 October 4; accepted 2019 October 7; published 2020 February 3. Early Results from Parker Solar Probe: Ushering a New Frontier in Space Exploration 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, we thank B. Kecman and W.R. Cook, without whom the EPI-Hi instrument would not be possible. S.D.B. acknowledges support of the Leverhulme Trust Visiting Professorship program. We gratefully acknowledge the test and calibration support provided by Michigan State University's National Superconducting Cyclotron Laboratory, Texas A&M University's Cyclotron Institute, and the Lawrence Berkeley National Laboratory's 88-inch Cyclotron Laboratory.
Group:Space Radiation Laboratory
Funding AgencyGrant Number
Leverhulme TrustUNSPECIFIED
Subject Keywords:Solar energetic particles ; Solar activity ; Fast solar wind
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Solar energetic particles (1491); Solar activity (1475); Fast solar wind (1872)
Record Number:CaltechAUTHORS:20200203-104219201
Persistent URL:
Official Citation:C. M. S. Cohen et al 2020 ApJS 246 20
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:101069
Deposited By: George Porter
Deposited On:03 Feb 2020 19:10
Last Modified:16 Nov 2021 17:58

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