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Published February 2020 | Supplemental Material + Published
Journal Article Open

Seed Population Preconditioning and Acceleration Observed by the Parker Solar Probe


A series of solar energetic particle (SEP) events was observed by the Integrated Science Investigation of the Sun (IS⊙IS) on the Parker Solar Probe (PSP) during the period from 2019 April 18 through 24. The PSP spacecraft was located near 0.48 au from the Sun on Parker spiral field lines that projected out to 1 au within ~25° of the near-Earth spacecraft. These SEP events, though small compared to historically large SEP events, were among the largest observed thus far in the PSP mission and provide critical information about the space environment inside 1 au during SEP events. During this period, the Sun released multiple coronal mass ejections (CMEs). One of these CMEs observed was initiated on 2019 April 20 at 01:25 UTC, and the interplanetary CME (ICME) propagated out and passed over the PSP spacecraft. Observations by the Electromagnetic Fields Investigation show that the magnetic field structure was mostly radial throughout the passage of the compression region and the plasma that followed, indicating that PSP did not directly observe a flux rope internal to the ICME, consistent with the location of PSP on the ICME flank. Analysis using relativistic electrons observed near Earth by the Electron, Proton and Alpha Monitor on the Advanced Composition Explorer demonstrates the presence of electron seed populations (40–300 keV) during the events observed. The energy spectrum of the IS⊙IS-observed proton seed population below 1 MeV is close to the limit of possible stationary-state plasma distributions out of equilibrium. IS⊙IS observations reveal the enhancement of seed populations during the passage of the ICME, which likely indicates a key part of the preacceleration process that occurs close to the Sun.

Additional Information

© 2020. The American Astronomical Society. Received 2019 September 13; revised 2019 November 4; accepted 2019 November 5; published 2020 February 3. Early Results from Parker Solar Probe: Ushering a New Frontier in Space Exploration We are deeply indebted to everyone who helped make the Parker Solar Probe (PSP) mission possible. We thank all of the outstanding scientists, engineers, technicians, and administrative support people across all of the IS⊙IS, FIELDS, and SWEAP institutions that produced and supported the IS⊙IS, FIELDS, and SWEAP instrument suites, support its operations and the scientific analysis of its data. This work was supported as a part of the PSP mission under contract NNN06AA01C. The ISʘIS data and visualization tools are available to the community at: https://spacephysics.princeton.edu/missions-instruments/isois; data are also available via the NASA Space Physics Data Facility (https://spdf.gsfc.nasa.gov/). Parker Solar Probe was designed, built, and is now operatedby the Johns Hopkins Applied Physics Laboratory aspart of NASA's Living with a Star (LWS) program (contract NNN06AA01C). Support from the LWS management and technical team has played a critical role in the success of the Parker Solar Probe mission. We thank and acknowledge Dr. X.P. Zhao for providing the CSSS model.

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August 22, 2023
October 23, 2023