Seed Population Pre-Conditioning and Acceleration Observed by Parker Solar Probe

Abstract

A series of solar energetic particle (SEP) events were observed at Parker Solar Probe (PSP) by the Integrated Science Investigation of the Sun (\ISOIS) during the period from April 18, 2019 through April 24, 2019. The PSP spacecraft was located near 0.48 au from the Sun on Parker spiral field lines that projected out to 1 au within $\sim 25^{\circ }$ of near Earth spacecraft. These SEP events, though small compared to historically large SEP events, were amongst 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 April 20, 2019 at 01:25 UTC, and the interplanetary CME (ICME) propagated out and passed over the PSP spacecraft. Observations by the Electromagnetic Fields Investigation (FIELDS) 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 (EPAM) on the Advanced Composition Explorer (ACE) demonstrates the presence of electron seed populations (40--300 keV) during the events observed. The energy spectrum of the \ISOIS~ observed proton seed population below 1 MeV is close to the limit of possible stationary state plasma distributions out of equilibrium. \ISOIS~ observations reveal the \revise{enhancement} of seed populations during the passage of the ICME, which \revise{likely indicates a key part} of the pre-acceleration process that occurs close to the Sun.

References in corpus (4)

• Direct Detection of a CME-Associated Shock in LASCO White Light Images
• Quantitative Measurements of CME-driven Shocks from LASCO Observations
• Association of 3He-Rich Solar Energetic Particles with Large-Scale Coronal Waves
• Observations of EUV Waves in 3He-Rich Solar Energetic Particle Events

Cited by in corpus (7)

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• Observation-based modelling of the energetic storm particle event of 14 July 2012
• Observations of the 2019 April 4 Solar Energetic Particle Event at the Parker Solar Probe
• Energetic Particle Observations from Parker Solar Probe using Combined Energy Spectra from the IS$\odot$IS Instrument Suite
• Widespread 1-2 MeV Energetic Particles Associated with Slow and Narrow Coronal Mass Ejections: Parker Solar Probe and STEREO Measurements
• PSP/IS$\odot$IS Observation of a Solar Energetic Particle Event Associated With a Streamer Blowout Coronal Mass Ejection During Encounter 6
• Successive Coronal Mass Ejections Associated with Weak Solar Energetic Particle Events