Hydrogen and the Abundances of Elements in Impulsive Solar Energetic-Particle Events

Abstract

Hydrogen has been almost completely ignored in studies of the abundance patterns of the chemical elements in solar energetic particles (SEPs). We seek to find impulsive events where H fits these abundance patterns and document the events that do not, suggesting possible reasons for the disparity. For 24 % of the smaller impulsive SEP events, the relative abundance of H fits within one standard deviation of the power-law fit of the abundances of elements 6 ≤ Z ≤ 56, relative to coronal abundances. In impulsive events with high intensities, H can be 10 to 100 times its expected value. In a few of these larger events, increased scattering at high wavenumber may preferentially detain H, perhaps with self-amplified waves; in some events pre-event proton background may contribute. In most large impulsive SEP events, however, associated shock waves must play a much greater role than previously thought; fast (>500km s -1 ) coronal mass ejections contribute to 62 % of impulsive events. Shocks may sample protons from the ambient coronal plasma or residual background as well as reaccelerating heavier impulsive SEP ions injected from the region of magnetic reconnection in solar jets. Excess H may be a signature of shock acceleration.

Four Distinct Pathways to the Element Abundances in Solar Energetic Particles

“…It is only when we include the abundance of the element H, which significantly extends the span of A/Q, that we find revealing upward breaks in the power-law dependence that could be direct evidence of two-component seed population for shock acceleration, at least for weak shocks, and is therefore a signature of shock-acceleration itself (Reames 2019b(Reames , 2019c(Reames , 2019d. The intermediate energies we study allow us to exploit the simple power-law behavior in A/Q, avoiding high-energy spectral breaks (e.g.…”

“…The apparent coupling among these three events is remarkable and of unknown origin; the proton excess increases while the He suppression decreases. We should caution, however, that Events 34 and 35 (Reames 2019b) have the opposite behavior, the proton excess decreases and the He suppression increases with time, so any apparent coupling may be coincidental. Note also that Event 14, shown in Fig.…”

“…Measurements have progressed for individual elements up through Fe (Teegarden et al 1973;McGuire et al 1979;Cook et al 1984;Meyer 1985;Reames 1995aReames , 2014Reames , 2017aReames , 2018aMewaldt et al 2002) and groups of elements throughout the rest of the periodic table (Reames 2000;Mason et al 2004;Reames and Ng 2004;Reames et al 2014a). Yet, surprising new patterns have begun to emerge only recently as we extended abundances down to H (Reames 2019b(Reames , 2019c(Reames , 2019d.…”

Element Abundances of Solar Energetic Particles and the Photosphere, the Corona, and the Solar Wind

“…Presumably, these shock waves in larger impulsive events sample protons from the ambient plasma in addition to favoring the high intensities of preaccelerated SEPs that are already enhanced, as shown in Figure 5. ions, plus additional protons from the ambient coronal plasma to produce the observed proton excesses [74,75].…”

Excess H, Suppressed He, and the Abundances of Elements in Solar Energetic Particles

“…High-FIP (>10 eV) elements are neutral atoms in the chromosphere while low-FIP elements are ions that are preferentially enhanced by a factor of ≈4, probably by the action of Alfvén waves (Laming, 2015;Reames, 2018a;Laming et al, 2019), when swept up into the corona and later sampled as SEPs (Webber, 1975;Meyer, 1985;Reames, 1995aReames, , 2014. After acceleration, ion scattering, depending upon magnetic rigidity, hence upon A/Q at a given velocity (Parker, 1963;Ng, Reames, and Tylka, 1999, 2001Reames, 2016aReames, , 2019b, can also lead to power-law dependence, i.e. since Fe scatters less than O, for example, Fe/O is enhanced early but depleted later in an event, producing power-law enhancements that in-Excess H and Suppressed He Abundances in SEPs D. V. Reames 3 crease and then decrease with A/Q (e.g.…”