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Time evolution of stream interaction region energetic particle spectra in the inner heliosphere

Joyce, C. J. and McComas, D. J. and Schwadron, N. A. and Christian, E. R. and Wiedenbeck, M. E. and McNutt, R. L. and Cohen, C. M. S. and Leske, R. A. and Mewaldt, R. A. and Stone, E. C. and Labrador, A. W. and Davis, A. J. and Cummings, A. C. and Mitchell, D. G. and Hill, M. E. and Roelof, E. C. and Allen, R. C. and Szalay, J. R. and Rankin, J. S. and Desai, M. I. and Giacalone, J. and Matthaeus, W. H. and Bale, S. D. and Kasper, J. C. (2021) Time evolution of stream interaction region energetic particle spectra in the inner heliosphere. Astronomy and Astrophysics, 650 . Art. No. L5. ISSN 0004-6361. doi:10.1051/0004-6361/202039330.

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We analyze an energetic proton event associated with a stream interaction region (SIR) that was observed at Parker Solar Probe on day 320 of 2018 when the spacecraft was just 0.34 AU from the Sun. Using the Integrated Science Investigation of the Sun instrument suite, we perform a spectral analysis of the event and show how the observed spectra evolve over the course of the event. We find that the spectra from the first day of the event are much more consistent with local acceleration at a weak compression, while spectra from later on are more typical of SIR-related events in which particles accelerated at distant shocks dominate. After the first day, the spectra remain approximately constant, which indicates that the modulation of energetic particles during transit from the presumed source region is weaker than previously thought. We argue that these observations can be explained by a sub-Parker spiral magnetic field structure connecting the spacecraft to a source region in the SIR that is relatively close to the Sun. We further propose that acceleration at weak, pre-shock compressions likely plays an important role in observations of SIR-related events in the inner heliosphere and that future modelling of such events should consider acceleration all along the compression region, not just at the distant shock region.

Item Type:Article
Related URLs:
URLURL TypeDescription ItemIS⊙IS data and visualization tools
https://spdf.gsfc.nasa.govRelated ItemNASA Space Physics Data Facility
Joyce, C. J.0000-0002-3841-5020
McComas, D. J.0000-0001-6160-1158
Schwadron, N. A.0000-0002-3737-9283
Christian, E. R.0000-0003-2134-3937
Wiedenbeck, M. E.0000-0002-2825-3128
McNutt, R. L.0000-0002-4722-9166
Cohen, C. M. S.0000-0002-0978-8127
Leske, R. A.0000-0002-0156-2414
Mewaldt, R. A.0000-0003-2178-9111
Stone, E. C.0000-0002-2010-5462
Labrador, A. W.0000-0001-9178-5349
Davis, A. J.0000-0002-9922-8915
Cummings, A. C.0000-0002-3840-7696
Mitchell, D. G.0000-0003-1960-2119
Hill, M. E.0000-0002-5674-4936
Roelof, E. C.0000-0002-2270-0652
Allen, R. C.0000-0003-2079-5683
Szalay, J. R.0000-0003-2685-9801
Rankin, J. S.0000-0002-8111-1444
Desai, M. I.0000-0002-7318-6008
Giacalone, J.0000-0002-0850-4233
Matthaeus, W. H.0000-0001-7224-6024
Bale, S. D.0000-0002-1989-3596
Kasper, J. C.0000-0002-7077-930X
Additional Information:© ESO 2021. Article published by EDP Sciences. Received 2 September 2020; Accepted 30 March 2021. Published online 02 June 2021. This work was supported as a part of the Integrated Science Investigations of the Sun on NASA’s Parker Solar Probe mission, under contract NNN06AA01C. The IS⊙IS data and visualization tools are available to the community at:; data are also available via the NASA Space Physics Data Facility (
Group:Space Radiation Laboratory
Funding AgencyGrant Number
Subject Keywords:acceleration of particles – solar wind – magnetic fields
Record Number:CaltechAUTHORS:20210608-095304738
Persistent URL:
Official Citation:Time evolution of stream interaction region energetic particle spectra in the inner heliosphere. C. J. Joyce, D. J. McComas, N. A. Schwadron, E. R. Christian, M. E. Wiedenbeck, R. L. McNutt, C. M. S. Cohen, R. A. Leske, R. A. Mewaldt, E. C. Stone, A. W. Labrador, A. J. Davis, A. C. Cummings, D. G. Mitchell, M. E. Hill, E. C. Roelof, R. C. Allen, J. R. Szalay, J. S. Rankin, M. I. Desai, J. Giacalone, W. H. Matthaeus, S. D. Bale and J. C. Kasper. A&A, 650 (2021) L5; DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:109438
Deposited By: Tony Diaz
Deposited On:09 Jun 2021 18:44
Last Modified:09 Jun 2021 18:44

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