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D V Reames - One of the best experts on this subject based on the ideXlab platform.
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hydrogen and the abundances of elements in gradual solar Energetic Particle events
2019Co-Authors: D V ReamesAbstract:Despite its dominance, hydrogen has been largely ignored in studies of the abundance patterns of the chemical elements in gradual solar Energetic Particle (SEP) events; those neglected abundances show a surprising new pattern of behavior. Abundance enhancements of elements with $2\leq Z \leq 56$, relative to coronal abundances, show a power-law dependence versus their average mass-to-charge ratio $A/Q$, which varies from event to event and with time during events. The ion charge states $Q$ depend upon the source plasma temperature $T$. For most gradual SEP events, shock waves have accelerated ambient coronal material with $T 2$ down to hydrogen at $A/Q = 1$. Thus the abundances of the elements with $Z \geq 6$ fairly accurately predict the observed abundance of H, at a similar velocity, in most SEP events. However, for those gradual SEP events where ion enhancements follow positive powers of $A/Q$, especially those with $T > 2~\mbox{MK}$ where shock waves have reaccelerated residual suprathermal ions from previous impulsive SEP events, proton abundances commonly exceed the extrapolated expectation, usually by a factor of order ten. This is a new and unexpected pattern of behavior that is unique to the abundances of protons and may be related to the need for more streaming protons to produce sufficient waves for scattering and acceleration of more heavy ions at the shock.
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spatial distribution of element abundances and ionization states in solar Energetic Particle events
2017Co-Authors: D V ReamesAbstract:We have studied the spatial and temporal distribution of abundances of chemical elements in large “gradual” solar Energetic-Particle (SEP) events, and especially the source plasma temperatures, derived from those abundances, using measurements from the Wind and Solar TErrestrial RElations Observatory (STEREO) spacecraft, widely separated in solar longitude. A power-law relationship between abundance enhancements and mass-to-charge ratios [\(A/Q\)] of the ions can be used to determine \(Q\)-values and source plasma temperatures at remote spacecraft with instruments that were not designed for charge-state measurements. We search for possible source variations along the accelerating shock wave, finding one clear case where the accelerating shock wave appears to dispatch ions from \(3.2\pm 0.8~\mbox{MK}\) plasma toward one spacecraft and those from \(1.6\pm 0.2~\mbox{MK}\) plasma toward another, 116∘ away. The difference persists for three days and then fades away. Three other SEP events show less-extreme variation in source temperatures at different spacecraft, in one case observed over 222∘ in longitude. This initial study shows how the power-law relation between abundance enhancements and ion \(A/Q\)-values provides a new technique to determine \(Q\) and plasma temperatures in the seed population of SEP ions over a broad region of space using remote spacecraft with instruments that were not originally designed for measurements of ionization states.
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variations in abundance enhancements in impulsive solar Energetic Particle events and related cmes and flares
2014Co-Authors: D V Reames, E W Cliver, S W KahlerAbstract:We study event-to-event variations in the abundance enhancements of the elements He through Pb for Fe-rich impulsive solar Energetic-Particle (SEP) events, and their relationship with properties of associated coronal mass ejections (CMEs) and solar flares. Using a least-squares procedure we fit the power-law enhancement of element abundances as a function of their mass-to-charge ratio A/Q to determine both the power and the coronal temperature (which determines Q) in each of 111 impulsive SEP events identified previously. Individual SEP events with the steepest element enhancements, e.g. ~(A/Q)^6, tend to be smaller, lower-fluence events with steeper energy spectra that are associated with B- and C-class X-ray flares, with cooler (~2.5 MK) coronal plasma, and with narrow ( 0.1 are even more strongly associated with narrow, slow CMEs, with cooler coronal plasma, and with B- and C-class X-ray flares than are other Fe-rich impulsive SEP events with smaller enhancements of 3He.
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abundance enhancements in impulsive solar Energetic Particle events with associated coronal mass ejections
2014Co-Authors: D V Reames, E W Cliver, S W KahlerAbstract:We study the abundances of the elements He through Pb in Fe-rich impulsive solar Energetic-Particle (SEP) events with measurable abundances of ions with atomic number Z>2 observed on the Wind spacecraft, and their relationship with coronal mass ejections (CMEs) observed by the Large Angle and Spectrometric Coronagraph (LASCO) onboard the Solar and Heliospheric Observatory (SOHO). On average the element abundances in these events are similar to coronal abundances at low Z but, for heavier elements, enhancements rise as a power law in the mass-to-charge ratio A/Q of the ions (at coronal temperatures of 2.5-3 MK) to a factor of 3 at Ne, 9 at Fe, and 900 for 75 700 km/s), wider CMEs in our sample are related to SEPs with coronal abundances indicating hot coronal plasma with fully ionized He, C, N and O and moderate enhancements of heavier elements, relative to He, but slower (<700 km/s), narrower CMEs emerge from cooler plasma where higher SEP mass-to-charge ratios, A/Q, yield much greater abundance enhancements, even for C/He and O/He. Apparently, the open magnetic-reconnection region where the impulsive SEPs are accelerated also provides the energy to drive out CME plasma, accounting for a strong, probably universal, impulsive SEP-CME association.
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solar Energetic Particle release times in historic ground level events
2009Co-Authors: D V ReamesAbstract:Ground-level events (GLEs) are large solar Energetic-Particle events with sufficiently hard spectra for GeV protons to be detected by neutron monitors at ground level. For each of 30 well-observed historic GLEs from four solar cycles, extending back to 1973, I have plotted onset times versus velocity–1 for Particles observed on the IMP-7 and 8, ISEE-3, Wind, and GOES spacecraft and by neutron monitors. A linear fit on such a plot for each GLE determines the initial solar Particle release (SPR) time, as the intercept, and the magnetic path length traversed, as the slope, of the fitted line. Magnetic path lengths and SPR times are well determined by the fits and cannot be used as adjustable parameters to make Particle and photon emission times coincide. SPR times follow the onsets of shock-induced type II radio bursts and the coronal height of the coronal mass ejection (CME)-driven shock at SPR time can be determined for GLEs spanning an interval of solar longitude of ~140 deg. For a given GLE, all Particle species and energies diverge from a single SPR point at a given coronal height and footpoint longitude of the field line to the Earth. These heights tend to increase with longitudinal distance away from the source, a pattern expected for shock acceleration. Acceleration for magnetically well-connected large GLEs begins at ~2 solar radii, in contrast to non-GLEs that have been found to be strongly associated with shocks above ~3 solar radii. The higher densities and magnetic field strengths at lower altitudes may be responsible for the acceleration of higher-energy Particles in GLEs, while those GLEs that begin above 3R S may compensate by having higher shock speeds. These results support the joint dependence of maximum Particle energy on magnetic field strength, injected Particle density, and shock speed, all predicted theoretically.
Alessandro Biancalani - One of the best experts on this subject based on the ideXlab platform.
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gyrokinetic investigation of the nonlinear interaction of alfven instabilities and Energetic Particle driven geodesic acoustic modes
2021Co-Authors: F Vannini, Alessandro Biancalani, E Poli, Ph Lauber, A Bottino, T Haywardschneider, A Mishchenko, G VladAbstract:This paper presents a study of the interaction between Alfven modes and zonal structures, considering a realistic ASDEX Upgrade equilibrium. The results of gyrokinetic simulations with the global, electromagnetic, Particle-in-cell code ORB5 are presented, where the modes are driven unstable by Energetic Particles with a bump-on-tail equilibrium distribution function, with radial density gradient. Two regimes have been observed. At low Energetic Particle concentration, the zonal structure (identified as an Energetic Particle-driven geodesic acoustic mode) is more unstable than the Alfven mode. In the regime at high Energetic Particle concentration, the Alfven mode is more unstable than the zonal structure. The interplay between the modes leads to a modification of their growth rates as well as to a modification of their saturation levels. The theoretical explanation of the mode interaction is given in terms of three-wave coupling of the Energetic Particle-driven geodesic acoustic mode and Alfven mode, mediated by the curvature–pressure coupling term of the Energetic Particles.
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nonlinear dynamics of Energetic Particle driven geodesic acoustic modes in asdex upgrade
2020Co-Authors: I Novikau, Alessandro Biancalani, E Poli, Ph Lauber, A Bottino, A Di Siena, P Manz, G D Conway, N Ohana, Emmanuel LantiAbstract:Turbulence in tokamaks generates radially sheared zonal flows. Their oscillatory counterparts, geodesic acoustic modes (GAMs), appear due to the action of the magnetic field curvature. The GAMs can be driven unstable by an anisotropic Energetic Particle (EP) population leading to the formation of global radial structures, called Energetic-Particle-driven geodesic acoustic modes (EGAMs). The EGAMs can redistribute EP energy to the bulk plasma through collisionless wave-Particle interaction. In such a way, the EGAMs might contribute to the plasma heating. Thus, investigation of EGAM properties, especially in the velocity space, is necessary for precise understanding of the transport phenomena in tokamak plasmas. In this work, the nonlinear dynamics of EGAMs without considering the mode interaction with the turbulence is investigated with the help of a Mode-Particle-Resonance (MPR) diagnostic implemented in the global gyrokinetic Particle-in-cell code ORB5. An ASDEX Upgrade discharge is chosen as a reference case for this investigation due to its rich EP nonlinear dynamics. An experimentally relevant magnetic field configuration, thermal species profiles, and an EP density profile are taken for EGAM chirping modeling and its comparison with available empirical data. The same magnetic configuration is used to explore energy transfer by the mode from the Energetic Particles to the thermal plasma including kinetic electron effects. For a given EGAM level, the plasma heating by the mode can be significantly enhanced by varying the EP parameters. Electron dynamics decreases the EGAM saturation amplitude and consequently reduces the plasma heating, even though the mode transfers its energy to thermal ions much more than to electrons.
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electromagnetic turbulence suppression by Energetic Particle driven modes
2018Co-Authors: A Di Siena, Alessandro Biancalani, Tobias Görler, E Poli, Banon A Navarro, F JenkoAbstract:In recent years, a strong reduction of plasma turbulence in the presence of Energetic Particles has been reported in a number of magnetic confinement experiments and corresponding gyrokinetic simulations. While highly relevant to performance predictions for burning plasmas, an explanation for this primarily nonlinear effect has remained elusive so far. A thorough analysis finds that linearly marginally stable Energetic Particle driven modes are excited nonlinearly, depleting the energy content of the turbulence and acting as an additional catalyst for energy transfer to zonal modes (the dominant turbulence saturation channel). Respective signatures are found in a number of simulations for different JET and ASDEX Upgrade discharges with reduced transport levels attributed to Energetic ion effects.
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effect of elongation on Energetic Particle induced geodesic acoustic mode
2018Co-Authors: Alberto Siena, Alessandro Biancalani, Tobias Görler, H Doerk, I Novikau, Pierre Lauber, Alberto Bottino, E PoliAbstract:The effect of the plasma elongation on the Energetic-Particle-induced geodesic acoustic mode (EGAM) dynamics is studied with numerical simulations performed with the gyrokinetic codes GENE and ORB5 and assessed with analytical models. The former code has been recently extended to support non-Maxwellian distribution functions and for the first time global results are shown here and benchmarked against the code ORB5. Taking advantage of these recent developments in GENE, which allow a joint investigation with ORB5, linear electrostatic simulations with adiabatic electrons have been performed. The impact of the elongation on the EGAM dynamics and excitation mechanism is investigated through the study of the energy exchange terms between the Particle and the mode for different plasma geometry. Finally, the results are applied to the study of an ASDEX Upgrade discharge with strongly elongated plasma employing realistic density and temperature profiles.
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saturation of Energetic Particle driven geodesic acoustic modes due to wave Particle nonlinearity
2017Co-Authors: Alessandro Biancalani, A Bottino, Zhiyong Qiu, I Chavdarovski, D Del Sarto, Alain Ghizzo, O D Gurcan, P Morel, I NovikauAbstract:The nonlinear dynamics of Energetic-Particle (EP) driven geodesic acoustic modes (EGAM) is investigated here. A numerical analysis with the global gyrokinetic Particle-in-cell code ORB5 is performed, and the results are interpreted with the analytical theory, in close comparison with the theory of the beam-plasma instability. Only axisymmetric modes are considered, with a nonlinear dynamics determined by wave-Particle interaction. Quadratic scalings of the saturated electric field with respect to the linear growth rate are found for the case of interest. As a main result, the formula for the saturation level is provided. Near the saturation, we observe a transition from adiabatic to non-adiabatic dynamics, i.e., the frequency chirping rate becomes comparable to the resonant EP bounce frequency. The numerical analysis is performed here with electrostatic simulations with circular flux surfaces, and kinetic effects of the electrons are neglected.
E Poli - One of the best experts on this subject based on the ideXlab platform.
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gyrokinetic investigation of the nonlinear interaction of alfven instabilities and Energetic Particle driven geodesic acoustic modes
2021Co-Authors: F Vannini, Alessandro Biancalani, E Poli, Ph Lauber, A Bottino, T Haywardschneider, A Mishchenko, G VladAbstract:This paper presents a study of the interaction between Alfven modes and zonal structures, considering a realistic ASDEX Upgrade equilibrium. The results of gyrokinetic simulations with the global, electromagnetic, Particle-in-cell code ORB5 are presented, where the modes are driven unstable by Energetic Particles with a bump-on-tail equilibrium distribution function, with radial density gradient. Two regimes have been observed. At low Energetic Particle concentration, the zonal structure (identified as an Energetic Particle-driven geodesic acoustic mode) is more unstable than the Alfven mode. In the regime at high Energetic Particle concentration, the Alfven mode is more unstable than the zonal structure. The interplay between the modes leads to a modification of their growth rates as well as to a modification of their saturation levels. The theoretical explanation of the mode interaction is given in terms of three-wave coupling of the Energetic Particle-driven geodesic acoustic mode and Alfven mode, mediated by the curvature–pressure coupling term of the Energetic Particles.
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nonlinear dynamics of Energetic Particle driven geodesic acoustic modes in asdex upgrade
2020Co-Authors: I Novikau, Alessandro Biancalani, E Poli, Ph Lauber, A Bottino, A Di Siena, P Manz, G D Conway, N Ohana, Emmanuel LantiAbstract:Turbulence in tokamaks generates radially sheared zonal flows. Their oscillatory counterparts, geodesic acoustic modes (GAMs), appear due to the action of the magnetic field curvature. The GAMs can be driven unstable by an anisotropic Energetic Particle (EP) population leading to the formation of global radial structures, called Energetic-Particle-driven geodesic acoustic modes (EGAMs). The EGAMs can redistribute EP energy to the bulk plasma through collisionless wave-Particle interaction. In such a way, the EGAMs might contribute to the plasma heating. Thus, investigation of EGAM properties, especially in the velocity space, is necessary for precise understanding of the transport phenomena in tokamak plasmas. In this work, the nonlinear dynamics of EGAMs without considering the mode interaction with the turbulence is investigated with the help of a Mode-Particle-Resonance (MPR) diagnostic implemented in the global gyrokinetic Particle-in-cell code ORB5. An ASDEX Upgrade discharge is chosen as a reference case for this investigation due to its rich EP nonlinear dynamics. An experimentally relevant magnetic field configuration, thermal species profiles, and an EP density profile are taken for EGAM chirping modeling and its comparison with available empirical data. The same magnetic configuration is used to explore energy transfer by the mode from the Energetic Particles to the thermal plasma including kinetic electron effects. For a given EGAM level, the plasma heating by the mode can be significantly enhanced by varying the EP parameters. Electron dynamics decreases the EGAM saturation amplitude and consequently reduces the plasma heating, even though the mode transfers its energy to thermal ions much more than to electrons.
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electromagnetic turbulence suppression by Energetic Particle driven modes
2018Co-Authors: A Di Siena, Alessandro Biancalani, Tobias Görler, E Poli, Banon A Navarro, F JenkoAbstract:In recent years, a strong reduction of plasma turbulence in the presence of Energetic Particles has been reported in a number of magnetic confinement experiments and corresponding gyrokinetic simulations. While highly relevant to performance predictions for burning plasmas, an explanation for this primarily nonlinear effect has remained elusive so far. A thorough analysis finds that linearly marginally stable Energetic Particle driven modes are excited nonlinearly, depleting the energy content of the turbulence and acting as an additional catalyst for energy transfer to zonal modes (the dominant turbulence saturation channel). Respective signatures are found in a number of simulations for different JET and ASDEX Upgrade discharges with reduced transport levels attributed to Energetic ion effects.
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effect of elongation on Energetic Particle induced geodesic acoustic mode
2018Co-Authors: Alberto Siena, Alessandro Biancalani, Tobias Görler, H Doerk, I Novikau, Pierre Lauber, Alberto Bottino, E PoliAbstract:The effect of the plasma elongation on the Energetic-Particle-induced geodesic acoustic mode (EGAM) dynamics is studied with numerical simulations performed with the gyrokinetic codes GENE and ORB5 and assessed with analytical models. The former code has been recently extended to support non-Maxwellian distribution functions and for the first time global results are shown here and benchmarked against the code ORB5. Taking advantage of these recent developments in GENE, which allow a joint investigation with ORB5, linear electrostatic simulations with adiabatic electrons have been performed. The impact of the elongation on the EGAM dynamics and excitation mechanism is investigated through the study of the energy exchange terms between the Particle and the mode for different plasma geometry. Finally, the results are applied to the study of an ASDEX Upgrade discharge with strongly elongated plasma employing realistic density and temperature profiles.
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analytic dispersion relation of Energetic Particle driven geodesic acoustic modes and simulations with nemorb
2014Co-Authors: D Zarzoso, Alessandro Biancalani, E Poli, Ph Lauber, A Bottino, J B Girardo, X Garbet, R DumontAbstract:Recent progress regarding the excitation of Energetic-Particle driven geodesic acoustic modes (EGAMs) in Particle-in-cell simulations is presented in this paper. The exact dispersion relation with adiabatic electrons is derived and solved. The origin of the so-called EGAM is briefly analysed and we show that its nature changes, at least, with the safety factor. A simple expression for the GAM frequency modified in the presence of a small concentration of Energetic Particles is given in the fluid limit. We show that gyrokinetic simulations with Nemorb in the presence of adiabatic electrons are able to reproduce the analytic predictions. Also, different energy channels are analysed by means of dedicated energy diagnostics characterizing the wave-Particle interaction. Finite Larmor radius and finite orbit width effects are studied regarding the excitation of geodesic acoustic modes, showing that these effects are likely to be negligible for sufficiently high concentration of Energetic Particles, but significant when approaching the threshold of excitation.
N Thakur - One of the best experts on this subject based on the ideXlab platform.
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large solar Energetic Particle events associated with filament eruptions outside active regions
2015Co-Authors: N Gopalswamy, H Xie, S Yashiro, Pia Makela, S Akiyama, N ThakurAbstract:We report on four large filament eruptions (FEs) from solar cycles 23 and 24 that were associated with large solar Energetic Particle (SEP) events and interplanetary type II radio bursts. The post-eruption arcades corresponded mostly to C-class soft X-ray enhancements, but an M1.0 flare was associated with one event. However, the associated coronal mass ejections (CMEs) were fast (speeds ~ 1000 km s−1) and appeared as halo CMEs in the coronagraph field of view. The interplanetary type II radio bursts occurred over a wide wavelength range, indicating the existence of strong shocks throughout the inner heliosphere. No metric type II bursts were present in three events, indicating that the shocks formed beyond 2–3 Rs. In one case, there was a metric type II burst with low starting frequency, indicating a shock formation height of ~2 Rs. The FE-associated SEP events did have softer spectra (spectral index >4) in the 10–100 MeV range, but there were other low-intensity SEP events with spectral indices ≥4. Some of these events are likely FE-SEP events, but were not classified as such in the literature because they occurred close to active regions. Some were definitely associated with large active region flares, but the shock formation height was large. We definitely find a diminished role for flares and complex type III burst durations in these large SEP events. Fast CMEs and shock formation at larger distances from the Sun seem to be the primary characteristics of the FE-associated SEP events.
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ground level enhancement in the 2014 january 6 solar Energetic Particle event
2014Co-Authors: N Thakur, N Gopalswamy, H Xie, Pertti Makela, S Yashiro, Sachiko AkiyamaAbstract:We present a study of the 2014 January 6 solar Energetic Particle event which produced a small ground level enhancement (GLE), making it the second GLE of this unusual solar cycle 24. This event was primarily observed by the South Pole neutron monitors (increase of approximately 2.5 percent) while a few other neutron monitors recorded smaller increases. The associated coronal mass ejection (CME) originated behind the western limb and had a speed of 1960 kilometers per second. The height of the CME at the start of the associated metric type II radio burst, which indicates the formation of a strong shock, was measured to be 1.61 solar radii using a direct image from STEREO-A/EUVI. The CME height at the time of the GLE Particle release (determined using the South Pole neutron monitor data) was directly measured as 2.96 solar radii based on STEREO-A/COR1 white-light observations. These CME heights are consistent with those obtained for GLE71, the only other GLE of the current cycle, as well as cycle-23 GLEs derived using back-extrapolation. GLE72 is of special interest because it is one of only two GLEs of cycle 24, one of two behind-the-limb GLEs, and one of the two smallest GLEs of cycles 23 and 24.
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ground level enhancement in the 2014 january 6 solar Energetic Particle event
2014Co-Authors: N Thakur, N Gopalswamy, H Xie, Pertti Makela, S Yashiro, Sachiko AkiyamaAbstract:We present a study of the 2014 January 6 solar Energetic Particle (SEP) event, which produced a small ground level enhancement (GLE), making it the second GLE of this unusual solar cycle 24. This event was primarily observed by the South Pole neutron monitors (increase of ~2.5%) whereas a few other neutron monitors recorded smaller increases. The associated coronal mass ejection (CME) originated behind the western limb and had the speed of 1960 km/s. The height of the CME at the start of the associated metric type II radio burst, which indicates the formation of a strong shock, was measured to be 1.61 Rs using a direct image from STEREO-A/EUVI. The CME height at the time of GLE Particle release (determined using the South Pole neutron monitor data) was directly measured as 2.96 Rs, from the STEREO-A/COR1 white-light observations. These CME heights are consistent with those obtained for the GLE71, the only other GLE of the current cycle as well as cycle-23 GLEs derived using back-extrapolation. GLE72 is of special interest because it is one of the only two GLEs of cycle 24, one of the two behind-the-limb GLEs and one of the two smallest GLEs of cycles 23 and 24.
G M Mason - One of the best experts on this subject based on the ideXlab platform.
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observations of euv waves in 3he rich solar Energetic Particle events
2015Co-Authors: R Bucik, G M Mason, D E Innes, Lijia Guo, M E WiedenbeckAbstract:Small 3He-rich solar Energetic Particle (SEP) events with their anomalous abundances, markedly different from solar system, provide evidence for a unique acceleration mechanism that operates routinely near solar active regions. Although the events are sometimes accompanied by coronal mass ejections (CMEs) it is believed that mass and isotopic fractionation is produced directly in the flare sites on the Sun. We report on a large-scale extreme ultraviolet (EUV) coronal wave observed in association with 3He-rich SEP events. In the two examples discussed, the observed waves were triggered by minor flares and appeared concurrently with EUV jets and type III radio bursts but without CMEs. The energy spectra from one event are consistent with so-called class-1 (characterized by power laws) while the other with class-2 (characterized by rounded 3He and Fe spectra) 3He-rich SEP events, suggesting different acceleration mechanisms in the two. The observation of EUV waves suggests that large-scale disturbances, in addition to more commonly associated jets, may be responsible for the production of 3He-rich SEP events.
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case studies of multi day 3he rich solar Energetic Particle periods
2015Co-Authors: Naihwa Chen, Davina Innes, R Bucik, G M MasonAbstract:Context. Impulsive solar Energetic Particle events in the inner heliosphere show the long-lasting enrichment of 3He. Aims. We study the source regions of long-lasting 3He-rich solar Energetic Particle (SEP) events Methods. We located the responsible open magnetic field regions, we combined potential field source surface extrapolations (PFSS) with the Parker spiral, and compared the magnetic field of the identified source regions with in situ magnetic fields. The candidate open field regions are active region plages. The activity was examined by using extreme ultraviolet (EUV) images from the Solar Dynamics Observatory (SDO) and STEREO together with radio observations from STEREO and WIND. Results. Multi-day periods of 3He-rich SEP events are associated with ion production in single active region. Small flares or coronal jets are their responsible solar sources. We also find that the 3He enrichment may depend on the occurrence rate of coronal jets.
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long lived Energetic Particle source regions on the sun
2015Co-Authors: R Bucik, R Gomezherrero, G M Mason, Naihwa Chen, D E Innes, M E WiedenbeckAbstract:Discovered more than 40 years ago, impulsive solar Energetic Particle (SEP) events are still poorly understood. The enormous abundance enhancement of the rare 3He isotope is the most striking feature of these events, though large enhancements in heavy and ultra-heavy nuclei are also observed. Recurrent 3He-rich SEPs in impulsive events have only been observed for limited time periods, up to a few days which is typically the time that a single stationary spacecraft is magnetically connected to the source active regions on the Sun. With the launch of the two STEREO spacecraft we now have the possibility of longer connection time to solar active regions. We examined the evolution of source regions showing repeated 3He-rich SEP emissions for relatively long time periods. We found that recurrent 3He-rich SEPs in these long-lived sources occur after the emergence of magnetic flux.
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3he enhancements in large solar Energetic Particle events
1999Co-Authors: G M Mason, J E Mazur, J R DwyerAbstract:We have measured the 3He abundance from approximately 0.5 to 2 MeV nucleon-1 in 12 large solar Energetic Particle (SEP) events during the period 1997 November-1999 June. In five of the events, the 3He time-intensity profile is similar to the 4He time-intensity profile, indicating a common acceleration and transport origin for the two species. The average 3He/4He ratio during these events is p1.9+/-0.2px10-3, a factor of approximately 5 enhancement over the solar wind value. During this same survey period, we have also measured the low-energy ion intensities during quieter periods in between the large-Particle events. We find 3He and Fe remnants from impulsive events present on a majority of the days, implying that they fill a substantial volume (>50%) of the in-ecliptic interplanetary medium during our survey. We suggest that these suprathermal ions may therefore be a source population that is available for further acceleration by interplanetary shocks that accompany large SEP events, thereby leading to the 3He enhancements in a significant fraction of large SEP events. This impulsive SEP event material might also account for recent observations of large solar Particle events with Energetic Particle ionization states that have a wide range of ionization states that encompass values expected for both gradual and impulsive solar SEP events.