Abundances of Heavy and Ultraheavy Ions in³He‐rich Solar Flares

Abstract

We have surveyed 3 He-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 À1 . 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 3 He-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.

Source Regions of the Interplanetary Magnetic Field and Variability in Heavy-Ion Elemental Composition in Gradual Solar Energetic Particle Events

“…In fact, as shown in Figure 15, the ratio of the A-CH to Q-CH values is reasonably well organized by the charge-to-mass ( q /M) ratio, where q values are the gradual SEP averages measured by Luhn et al (1984) at ∼0.5-2.5 MeV nucleon −1 . 13 The q /M ordering shown in Figure 15 is reminiscent of what is observed in impulsive SEP events (Reames 2000;Reames & Ng 2004;Mason et al 2004), suggesting that the same physical processes governing composition in those events are also affecting the suprathermal seed particles for gradual SEP events. 3.…”

“…Any magnetic reconnection within areas containing such large, complex, and dynamic magnetic fields might reasonably be expected to be much more effective in producing suprathermal ions that could subsequently become seeds for shock acceleration. Moreover, if these reconnection processes are similar to those that produce impulsive SEP events (Drake et al 2009;Knizhnik et al 2011), the suprathermals may have impulsive-like enhancements in heavy ions (Reames 2000;Reames & Ng 2004;Mason et al 2004). We now explore that notion more fully by examining the complete event sample, using not only hourly averaged abundance ratios, but also interval-integrated ratios and ensemble-averages of events in the two classes.…”

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

“…6 The metric radio images show a source moving outward at about the same position angle as the CME with a speed of about 1470 km s À1 ( Pick et al 2003). This event has been widely studied (e.g., Mason et al 2000Mason et al , 2002Kahler 2001;Pick et al 2003;Maia & Pick 2004;Klein & Posner 2005).…”

“…The low-energy ion data used here are from the Ultra Low Energy Isotope Spectrometer (ULEIS; Mason et al 1998) on the Advanced Composition Explorer (ACE ) spacecraft, which was launched into a halo orbit around the sunward Lagrangian point in 1997 (Stone et al 1998). ULEIS covers the energy range $0.2Y10 MeV nucleon À1 and identifies periods when 3 He is enriched.…”

Seed Populations for Large Solar Particle Events Of Cycle 23

“…We chose to plot the event-averaged abundances of S, Ca, and Fe (i.e., low FIP elements) relative to C and O (i.e., high FIP elements) to minimize the so-called FIP fractionation effect seen in large SEP events [19]. Figure 3 also compares the LSEP abundances with those seen in IP shock events of [20] and ^He-rich SEP events of [21]. The dashed line represents a linear fit to the LSEP data with slope m and intercept c. We remark that the slopes and intercepts of the hnear fits obtained independently by fitting the data for IP shocks (blue) and Herich events (green) are well within the respective la error limits of the fit parameters for the three types of events.…”