A "Classic" Z-Rich Solar Energetic Particle Event Observed by Parker Solar Probe at 0.2AU (April 2-3, 2019)
Abstract
An impulsive solar energetic particle event displaying enhanced abundances of heavy ions was observed on 02 April 2019 from 0.2 AU by the EPI-Lo ion spectrometer of the ISOIS instrument suite on the Parker Solar Probe (PSP). It was associated with brightenings and south-westerly surges from the active region (2738) east of central meridian as viewed in 193 nm images from STEREO-A (fortuitously only10.7deg eastward of PSP). Compared to a subsequent impulsive SEP event observed by ISOIS/EPI-Hi/EPI-Lo (only two days later on 04 April 2019), the enhancements (by species) were: 1-to-1 for ~60 keV H; 20-fold for ~210 keV He; and >50-fold for both ~375 keV O and ~1500 keV Fe (i.e., unmeasurable above background on 04 April). The velocity-dispersed ion onset ~1200 UT on 02 April implied that impulsive ion injection began at about same time as a type iii burst group (0850-1905 UT) observed by PSP/FIELDS. The ion event began with beam-like pitch-angle anisotropies. The event was abruptly terminated by a dramatic flux dropout ~0750 UT on 03 April, in close coincidence with what appears to be a tangential discontinuity (or separatrix) in the local magnetic field lines at PSP. We seem to have observed a "classic" Z-rich ion event, as first identified during the decline of Solar Cycle 20 (Hurford et al., ApJLett, 1975; Zwickl et al., ApJ, 1978). These were characterized by normal ion spectra, normal SW conditions, association with small H-alpha flares, but with long-lasting (~1 day) beam-like highly anisotropic pitch-angle distributions. Because the ion spectra were similar to impulsive events with normal ion abundances, Zwickl et al. argued that these events were Z-rich as a consequence of enhanced abundances in the seed population, rather than differences in the acceleration mechanism itself. Recently, Mason and Klecker (ApJ, 2017) have suggested a very efficient abundance enrichment process, whereby propagation of all ions through a material thickness of ~20 micrograms/cm2 produces a selective (Z-rich) enhancement, because of the heavies' greater affinity for electrons that mitigates the Z^2/A energy loss rate. At low-coronal H-densities of 10^8-10^9 /cc, this thickness would imply an ion path length of 0.2-2.0 solar radii, which might produce a seed population consistent with the constraints of our PSP observations.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMSH21B..09R
- Keywords:
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- 7514 Energetic particles;
- SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMY;
- 7519 Flares;
- SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMY;
- 7845 Particle acceleration;
- SPACE PLASMA PHYSICS;
- 7859 Transport processes;
- SPACE PLASMA PHYSICS