scholarly journals What Are the Sources of Solar Energetic Particles? Element Abundances and Source Plasma Temperatures

2015 ◽  
Vol 194 (1-4) ◽  
pp. 303-327 ◽  
Author(s):  
Donald V. Reames
Keyword(s):  
Energetic Particles ◽  
Solar Energetic Particles ◽  
Element Abundances

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

Atoms ◽  
2019 ◽  
Vol 7 (4) ◽  
pp. 104 ◽  
Author(s):  
Donald V. Reames
Keyword(s):  
Solar Wind ◽  
Shock Waves ◽  
Solar Corona ◽  
Plasma Temperature ◽  
Energetic Particles ◽  
Solar Energetic Particles ◽  
Charge Ratio ◽  
Ambient Plasma ◽  
Element Abundances ◽  
Resonant Wave

From a turbulent history, the study of the abundances of elements in solar energetic particles (SEPs) has grown into an extensive field that probes the solar corona and physical processes of SEP acceleration and transport. Underlying SEPs are the abundances of the solar corona, which differ from photospheric abundances as a function of the first ionization potentials (FIPs) of the elements. The FIP-dependence of SEPs also differs from that of the solar wind; each has a different magnetic environment, where low-FIP ions and high-FIP neutral atoms rise toward the corona. Two major sources generate SEPs: The small “impulsive” SEP events are associated with magnetic reconnection in solar jets that produce 1000-fold enhancements from H to Pb as a function of mass-to-charge ratio A/Q, and also 1000-fold enhancements in 3He/4He that are produced by resonant wave-particle interactions. In large “gradual” events, SEPs are accelerated at shock waves that are driven out from the Sun by wide, fast coronal mass ejections (CMEs). A/Q dependence of ion transport allows us to estimate Q and hence the source plasma temperature T. Weaker shock waves favor the reacceleration of suprathermal ions accumulated from earlier impulsive SEP events, along with protons from the ambient plasma. In strong shocks, the ambient plasma dominates. Ions from impulsive sources have T ≈ 3 MK; those from ambient coronal plasma have T = 1 – 2 MK. These FIP- and A/Q-dependences explore complex new interactions in the corona and in SEP sources.

scholarly journals The Evolution of Research on Abundances of Solar Energetic Particles

Universe ◽  
2021 ◽  
Vol 7 (8) ◽  
pp. 292
Author(s):  
Donald V. Reames
Keyword(s):  
Shock Waves ◽  
Power Laws ◽  
Energetic Particles ◽  
Solar Energetic Particles ◽  
Charge Ratio ◽  
Particle Interactions ◽  
Solar Cosmic Rays ◽  
Element Abundances ◽  
Resonant Wave ◽  
Field Lines

Sixty years of study of energetic particle abundances have made a major contribution to our understanding of the physics of solar energetic particles (SEPs) or solar cosmic rays. An early surprise was the observation in small SEP events of huge enhancements in the isotope 3He from resonant wave–particle interactions, and the subsequent observation of accompanying enhancements of heavy ions, later found to increase 1000-fold as a steep power of the mass-to-charge ratio A/Q, right across the elements from H to Pb. These “impulsive” SEP events have been related to magnetic reconnection on open field lines in solar jets; similar processes occur on closed loops in flares, but those SEPs are trapped and dissipate their energy in heat and light. After early controversy, it was established that particles in the large “gradual” SEP events are accelerated at shock waves driven by wide, fast coronal mass ejections (CMEs) that expand broadly. On average, gradual SEP events give us a measure of element abundances in the solar corona, which differ from those in the photosphere as a classic function of the first ionization potential (FIP) of the elements, distinguishing ions and neutrals. Departures from the average in gradual SEPs are also power laws in A/Q, and fits of this dependence can determine Q values and thus estimate source plasma temperatures. Complications arise when shock waves reaccelerate residual ions from the impulsive events, but excess protons and the extent of abundance variations help to resolve these processes. Yet, specific questions about SEP abundances remain.

scholarly journals Sixty Years of Element Abundance Measurements in Solar Energetic Particles

2021 ◽  
Vol 217 (6) ◽  
Author(s):  
Donald V. Reames
Keyword(s):  
Solar Corona ◽  
Magnetic Reconnection ◽  
Extreme Ultraviolet ◽  
Chemical Elements ◽  
Energetic Particles ◽  
Solar Energetic Particles ◽  
Charge Ratio ◽  
Element Abundance ◽  
Shock Acceleration ◽  
Element Abundances

AbstractSixty years ago the first observation was published showing solar energetic particles (SEPs) with a sampling of chemical elements with atomic numbers $6 \leq Z \leq 18$ 6 ≤ Z ≤ 18 above 40 MeV amu−1. Thus began study of the direct products of dynamic physics in the solar corona. As we have progressed from 4-min sounding-rocket samples to continuous satellite coverage of SEP events, we have extended the observations to the unusual distribution of element abundances throughout the periodic table. Small “impulsive” SEP events from islands of magnetic reconnection on open magnetic-field lines in solar jets generate huge enhancements in abundances of 3He and of the heaviest elements, enhancements increasing as a power of the ion mass-to-charge ratio as ($A$ A /$Q$ Q )3.6, on average. Solar flares involve the same physics but there the SEPs are trapped on closed loops, expending their energy as heat and light. The larger, energetic “gradual” SEP events are accelerated at shock waves driven by fast, wide coronal mass ejections (CMEs). However, these shocks can also reaccelerate ions from pools of residual suprathermal impulsive ions, and CMEs from jets can also drive fast shocks, complicating the picture. The underlying element abundances in SEP events represent the solar corona, which differs from corresponding abundances in the photosphere as a function of the first ionization potential (FIP) of the elements, distinguishing low-FIP (<10 eV) ions from high-FIP neutral atoms as they expand through the chromosphere. Differences in FIP patterns of SEPs and the solar wind may distinguish closed- and open-field regions of formation at the base of the corona. Dependence of SEP acceleration upon $A$ A /$Q$ Q allows best-fit estimation of ion $Q$ Q -values and hence of the source plasma temperature of ∼1 – 3 MK, derived from abundances, which correlates with recent measures of temperatures using extreme ultraviolet emission from jets. Thus, element abundances in SEPs have become a powerful tool to study the underlying solar corona and to probe physical processes of broad astrophysical significance, from the “FIP effect” to magnetic reconnection and shock acceleration. New questions arise, however, about the theoretical basis of correlations of energy-spectral indices with power-laws of abundances, about the coexistence of separate resonant and non-resonant mechanisms for enhancements of 3He and of heavy elements, about occasional events with unusual suppression of He and about the overall paucity of C in FIP comparisons.

Assessing the Predictability of Solar Energetic Particles with the Use of Machine Learning Techniques

Solar Physics ◽  
2021 ◽  
Vol 296 (7) ◽  
Author(s):  
E. Lavasa ◽  
G. Giannopoulos ◽  
A. Papaioannou ◽  
A. Anastasiadis ◽  
I. A. Daglis ◽  
...  
Keyword(s):  
Machine Learning ◽  
Energetic Particles ◽  
Solar Energetic Particles ◽  
Machine Learning Techniques ◽  
Learning Techniques

scholarly journals Evidence for Remnant Flare Suprathermals in the Source Population of Solar Energetic Particles in the 2000 Bastille Day Event

2001 ◽  
Vol 558 (1) ◽  
pp. L59-L63 ◽  
Author(s):  
A. J. Tylka ◽  
C. M. S. Cohen ◽  
W. F. Dietrich ◽  
C. G. Maclennan ◽  
R. E. McGuire ◽  
...  
Keyword(s):  
Energetic Particles ◽  
Solar Energetic Particles ◽  
Source Population
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