Orbit 16 observations of SEP events from Parker Solar Probe to STEREO and ACE

Abstract

During Parker Solar Probe’s 16th orbit, two solar energetic particle (SEP) events were detected by the Integrated Science Investigation of the Sun (ISʘIS). The spacecraft measuring these SEP events were oriented near-perfectly along the same nominal Parker spiral magnetic field line which connected Earth to the solar source for ambient solar wind speeds. Both events were also observed by STEREO and ACE, which provided the opportunity to examine how SEP velocity dispersion, CME shock arrival, energy spectra, and elemental composition varied during transport from 0.65 and 0.76 AU to ~1 AU. On 17 July 2023, near the southwestern face of the Sun, the solar magnetic active region 13363 underwent considerable evolution which resulted in the largest SEP event of orbit 16 measured by ISʘIS. Two M5.0+ flares at 23:34 and 00:06 UT coincided with a confined prominence eruption and major halo coronal mass ejection (CME). A similar magnetic evolution occurred on 7 August 2023, at the northwestern limb of the Sun, in the solar magnetic active region 13386 when an M1.4 and X1.4 flare at 19:37 and 20:30, respectively, coincided with a confined prominence eruption and large CME. We utilized a variety of remote observations from GOES, SDO, and SOHO to characterize the magnetic configuration of the local active regions, estimate low coronal temperature, and discuss confined prominence eruptions as a key particle injection source. The notable result from this multi-spacecraft alignment is that SEP fluence appears qualitatively similar at different radial distances, but heavy ions, such as O and Fe, are depleted in comparison to lighter ions during transport.