Four Distinct Pathways to the Element Abundances in Solar Energetic Particles

2021

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We have used abundance measurements to identify the sources and the physical processes of acceleration and transport of SEPs. Here we study energetic particles themselves as samples of the solar corona that is their origin, distinguishing the corona from the photosphere and the SEPs from the solar wind. Theoretically, differences in the first ionization potential “FIP effect” may distinguish closed- and open-field regions at the base of the corona, which may also distinguish SEPs from the solar wind. There is not a single coronal FIP effect, but two patterns, maybe three. Are there variations? What about He?

Section: Fip Theory: the Sources Of Seps And The Solar Windmentioning

confidence: 99%

Element Abundances and FIP: SEPs, Corona, and Solar Wind

2021

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“…Helium may receive comparable contributions from both sources in this event (Reames 2019b, d). Panel (b) shows possible selection of seed particle H (solid) and O (dashed) from ambient (red) and harder pre-accelerated impulsive (blue SEP1) spectra by shock waves with different threshold energies (Reames 2020a) list in Reames et al 2014) with a CME of 954 km s À1 may include shock-accelerated protons predominantly from the ambient corona (red source) plus ions with Z ! 2 mainly from a local impulsive jet magnetic-reconnection source (blue source labeled SEP1).…”

Section: Compound Seed Particlesmentioning

confidence: 99%

Hydrogen Abundances and Shock Waves

2021

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How well do protons fit into the abundance patterns of the other elements? Protons have Q = 1 and A/Q = 1 at all temperatures of interest. When does their relative abundance fit on the power law in A/Q defined by the elements with A/Q > 2? For small “pure” impulsive events, protons fit well, but for larger CME-associated impulsive events, where shock waves boost the intensities, protons are enhanced a factor of order ten by addition of seed protons from the ambient plasma. During most large gradual SEP events with strong shock waves, protons again fit the power law, but with weaker or quasi-perpendicular shock waves, dominated by residual impulsive seed particle abundances at high Z, again protons are enhanced. Proton enhancements occur when moderately weak shock waves happen to sample a two-component seed population with dominant protons from the ambient coronal plasma and impulsive suprathermal ions at high Z; thus proton-enhanced events are a surprising new signature of shock acceleration in jets. A/Q measures the rigidity dependence of both acceleration and transport but does not help us distinguish the two. Energy-spectral indices and abundances are correlated for most gradual events but not when impulsive ions are present; thus we end with powerful new correlations that probe both acceleration and transport.

“…The SEP abundances in Table 1.1 can serve as reference abundances for discussion of "enhancements" throughout this book. Table 1.1 lists the photospheric (Asplund et al 2009) and the reference SEP (Reames 1995(Reames , 2014(Reames , 2020) abundances that we can use. A likely correction to the Fig.…”

Section: Abundancesmentioning

confidence: 99%

Introducing the Sun and SEPs

2021

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The structure of the Sun, with its energy generation and heating, creates convection and differential rotation of the outer solar plasma. This convection and rotation of the ionized plasma generates the solar magnetic field. This field and its variation spawn all of the solar activity: solar active regions, flares, jets, and coronal mass ejections (CMEs). Solar activity provides the origin and environment for both the impulsive and gradual solar energetic particle (SEP) events. This chapter introduces the background environment and basic properties of SEP events, time durations, abundances, and solar cycle variations.