3He-rich Solar Energetic Particle Events Research Articles

Source investigation of impulsive 3He-rich particle events

We have investigated the source characteristic and coronal magnetic field structure of six impulsive solar energetic particle (SEP) events selected from Wang et al. [Wang, Y.-M., Pick, M., Mason, G.M. Coronal holes, jets, and the origin of 3He-rich particle events. ApJ 639, 495, 2006] and Pick et al. [Pick, M., Mason, G.M., Wang, Y.-M., Tan, C., Wang, L. Solar source regions for 3He-rich solar energetic particle events identified using imaging radio, optical, and energetic particle observations. ApJ 648, 1247, 2006]. Some results are obtained: first, 2 events are associated with wide (≈100°) CMEs (hereafter wide CME events), another 4 events are associated with narrow (⩽40°) CMEs (hereafter narrow CME events); second, the coronal magnetic field configuration of narrow CME events appear more simple than that of the wide CME events; third, the photospheric magnetic field evolutions of all these events show new emergence of fluxes, while one case also shows magnetic flux cancellation; fourth, the EUV jets usually occurred very close to the footpoint of the magnetic field loop, while meter type III bursts occurred near or at the top of the loop and higher than EUV jets. Furthermore, the heights of type III bursts are estimated from the result of the coronal magnetic field extrapolations.

Solar Source Regions for3He‐rich Solar Energetic Particle Events Identified Using Imaging Radio, Optical, and Energetic Particle Observations

We have identified the sources of six impulsive 3He-rich solar energetic particle events using imaging radio, optical, and energetic ion and electron data, together with calculated coronal fields obtained from extrapolating photospheric magnetograms using a potential field source surface (PFSS) model. These events were all studied in 2006 by Wang et al., who identified the particle sources as typically small, flaring active regions lying next to a coronal hole containing Earth-directed open field lines, located between W33° and W65°. By introducing radio imaging data we were able in one case to conclusively identify which of two simultaneous EUV jets was associated with the particle source. In addition, type III radio burst and energetic electron data introduced in this study constrain the injection times much more accurately than possible with low-energy ion data used in Wang et al. These new observations confirm the source identifications of Wang et al. and remove many of the remaining uncertainties. All of these events were associated with narrow, fast coronal mass ejections (CMEs), which are unusual for 3He-rich solar energetic particle (SEP) events. Although the CMEs generally were ejected in directions well off the ecliptic plane, the PFSS calculations show the presence of magnetic field lines that made it possible for the energetic particle to quickly reach Earth. Some of these impulsive events were observed during periods in which 3He was observed continuously over several days.

Abundances of Heavy and Ultraheavy Ions in3He‐rich Solar Flares

We have surveyed 3He-rich solar energetic particle (SEP) events over the period 1997 September-2003 April in order to characterize abundances of heavy ions near 400 keV nucleon-1. The first part of the study focuses on 20 distinct SEP events that show the previously observed pattern in which, relative to O, heavy ions through Fe are enriched, with the enrichment increasing with mass. We find that these enrichments are well correlated such that 3He-rich SEP events with high Fe/C also show larger enrichments in other heavy ions. Ultraheavy (UH; taken as 78-220 amu) ions are routinely seen in these events with abundance enhancements correlating with Fe/C but with even larger flare-to-flare variations. In one event with unusually little interplanetary scattering, we are able to estimate the time of heavy- and UH-ion injections at the Sun and find them to be simultaneous. The second part of the study sums up many impulsive-event time periods in order to construct a mass histogram of UH nuclei; this histogram shows broad mass peaks similar to those in compilations of solar system abundances. In this summed period, relative to O, the average enhancement of heavy nuclei increases with mass with values of ~7 for Fe, ~40 for mass 78-100 amu, ~120 for mass 125-150 amu, and ~215 for 180-220 amu. The maximum UH enhancements seen in the most-enriched events are at least a factor of 5 larger. The enhancements are approximately proportional to the particle charge-to-mass ratio raised to a power, as seen previously in large, shock-associated SEP events.