Shock Geometry, Seed Populations, and the Origin of Variable Elemental Composition at High Energies in Large Gradual Solar Particle Events

Tylka, A. J.; Cohen, C. M. S.; Dietrich, William F.; Lee, M. A.; Maclennan, C. G.; Mewaldt, R. A.; Ng, C. K.; Reames, D. V.

doi:10.1086/429384

Cited by 367 publications

(370 citation statements)

References 77 publications

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“…Many of these shock-related parameters (geometry, compression ratio, speed) are available or can be deduced from in-situ measurements at 1 AU. None, however, is actually measured in the low corona where the highest energy particles originate (≤10 R s , Tylka 2005). Moreover, the large scatter in the correlation between CME speeds and SEP peak intensities suggests a complex interplay among the CME speed, the acceleration mechanism(s) and the ambient environment.…”

Section: Science Question 6: 'What Are the Roles Of Shocks Reconnectmentioning

confidence: 99%

“…Fermi acceleration is the likely acceleration mechanism for quasi-parallel shocks while gradient-drift acceleration operates at quasi-perpendicular shocks (e.g., Lee 2000). The geometry of the shock seems to play a further role in the observed variability of the spectral characteristics and composition of SEPs (Tylka 2005). The shock compression ratio determines the power law index of the SEP spectrum under some simplifying assumptions such as equilibrium conditions.…”

Section: Science Question 6: 'What Are the Roles Of Shocks Reconnectmentioning

confidence: 99%

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The Wide-Field Imager for Solar Probe Plus (WISPR)

et al. 2015

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mission designed to orbit as close as 7 million km (9.86 solar radii) from Sun center. WISPR employs a 95 • radial by 58 • transverse field of view to image the fine-scale structure of the solar corona, derive the 3D structure of the large-scale corona, and determine whether a dust-free zone exists near the Sun. WISPR is the smallest heliospheric imager to date yet it comprises two nested wide-field telescopes with large-format (2 K × 2 K) APS CMOS detectors to optimize the performance for their respective fields of view and to minimize the risk of dust damage, which may be considerable close to the Sun. The WISPR electronics are very flexible allowing the collection of individual images at cadences up to 1 second at perihelion or the summing of multiple images to increase the signal-to-noise when the spacecraft is further from the Sun. The dependency of the Thomson scattering emission of the corona on the imaging geometry dictates that WISPR will be very sensitive to the emission from plasma close to the spacecraft in contrast to the situation for imaging from Earth orbit. WISPR will be the first 'local' imager providing a crucial link between the large-scale corona and the in-situ measurements.

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Section: Science Question 6: 'What Are the Roles Of Shocks Reconnectmentioning

confidence: 99%

Section: Science Question 6: 'What Are the Roles Of Shocks Reconnectmentioning

confidence: 99%

The Wide-Field Imager for Solar Probe Plus (WISPR)

et al. 2015

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“…However, not all CMEs that satisfy the two factors can lead to large SEP events or GLEs (e.g., Kahler & Vourlidas 2005;Ding et al 2013), indicating other processes are important for producing large SEP events as well. The proposed factors include the background energetic particles that provide seed particles for the shock acceleration to high energies (e.g., Kahler et al 2000;Kahler 2001;Cliver 2006), preceding CMEs that may provide both seed particles and enhanced turbulence for more efficient particle acceleration (e.g., Gopalswamy et al 2004;Li et al 2012;Ding et al 2013;Zhao & Li 2014), and the CME shock geometry that allows a perpendicular shock region to rapidly accelerate particles to high energies (e.g., Tylka et al 2005). …”

Section: Introductionmentioning

confidence: 99%

“…Note, however, that self-excited waves produced by streaming energetic particles may further enhance particle acceleration at parallel shocks (e.g., Lee 1983Lee , 2005Li et al 2003;Rice et al 2003). When a CME-driven shock develops in the corona, the nonplanar shock front sweeps through the coronal magnetic field with a range of different shock angles, which has been proposed to have significant effects on particle acceleration (e.g., Giacalone 2005aGiacalone , 2005bTylka et al 2005). By including large-scale magnetic field variation, the transport effect is found to be important in the shock region, creating hot spots where most high-energy particles are concentrated (Guo et al 2010).…”

Section: Introductionmentioning

confidence: 99%

The Acceleration of High-energy Protons at Coronal Shocks: The Effect of Large-scale Streamer-like Magnetic Field Structures

Kong

Guo

Giacalone

et al. 2017

ApJ

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Recent observations have shown that coronal shocks driven by coronal mass ejections can develop and accelerate particles within several solar radii in large solar energetic particle (SEP) events. Motivated by this, we present an SEP acceleration study that including the process in which a fast shock propagates through a streamer-like magnetic field with both closed and open field lines in the low corona region. The acceleration of protons is modeled by numerically solving the Parker transport equation with spatial diffusion both along and across the magnetic field. We show that particles can be sufficiently accelerated to up to several hundred MeV within 2-3 solar radii. When the shock propagates through a streamer-like magnetic field, particles are more efficiently accelerated compared to the case with a simple radial magnetic field, mainly due to perpendicular shock geometry and the natural trapping effect of closed magnetic fields. Our results suggest that the coronal magnetic field configuration is an important factor for producing large SEP events. We further show that the coronal magnetic field configuration strongly influences the distribution of energetic particles, leading to different locations of source regions along the shock front where most high-energy particles are concentrated. This work may have strong implications for SEP observations. The upcoming Parker Solar Probe will provide in situ observations for the distribution of energetic particles in the coronal shock region, and test the results of the study.

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“…At higher energies the gradual SEP events start to show substantial event-to-event variations (Tylka et al 2005), especially in abundance ratios and charge states. It has been debated that in some cases these variations are caused either by a particle component accelerated at a solar flare accompanying the CME (Cane et al 2006), or that the DSA accelerates a mixed seed particle population that contains remnant flare suprathermals in addition to the coronal material (Tylka et al 2005).…”

Section: Introductionmentioning

confidence: 99%

Diffusive shock acceleration to relativistic energies in the solar corona

Sandroos

Vainio²

2009

A&A

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Aims. We study the effect of magnetic geometry on the efficiency of diffusive shock acceleration (DSA) of protons in the solar corona with emphasis on conditions that may lead to the formation of so-called ground level enhancements (GLEs) where the protons are accelerated into energies 1 GeV. Methods. We use Monte Carlo simulations of DSA in a semirealistic large scale coronal magnetic field near a bipolar active region. This active region is assumed to be the source region of a coronal mass ejection (CME) driving a shock wave in the corona. The shock geometry evolves in time, and the obliquity angle goes through a wide range of values from perpendicular to quasi-parallel. We consider the effect of the evolving magnetic geometry on the acceleration efficiency in five selected field lines. Results. In most of the considered field lines the maximum proton energies are of the order of 100 MeV, which is rather typical for gradual solar energetic particle (SEP) events. We find that the DSA can be more effective on field lines where the shock starts out by being oblique and gradually turns quasi-perpendicular than on field lines where the shock starts perpendicularly.

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Shock Geometry, Seed Populations, and the Origin of Variable Elemental Composition at High Energies in Large Gradual Solar Particle Events

Cited by 367 publications

References 77 publications

The Wide-Field Imager for Solar Probe Plus (WISPR)

The Wide-Field Imager for Solar Probe Plus (WISPR)

The Acceleration of High-energy Protons at Coronal Shocks: The Effect of Large-scale Streamer-like Magnetic Field Structures

Diffusive shock acceleration to relativistic energies in the solar corona

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