13 research outputs found
Recent Advances in Understanding Particle Acceleration Processes in Solar Flares
We review basic theoretical concepts in particle acceleration, with
particular emphasis on processes likely to occur in regions of magnetic
reconnection. Several new developments are discussed, including detailed
studies of reconnection in three-dimensional magnetic field configurations
(e.g., current sheets, collapsing traps, separatrix regions) and stochastic
acceleration in a turbulent environment. Fluid, test-particle, and
particle-in-cell approaches are used and results compared. While these studies
show considerable promise in accounting for the various observational
manifestations of solar flares, they are limited by a number of factors, mostly
relating to available computational power. Not the least of these issues is the
need to explicitly incorporate the electrodynamic feedback of the accelerated
particles themselves on the environment in which they are accelerated. A brief
prognosis for future advancement is offered.Comment: This is a chapter in a monograph on the physics of solar flares,
inspired by RHESSI observations. The individual articles are to appear in
Space Science Reviews (2011
Contributions to the cross shock electric field at supercritical perpendicular shocks: Impact of the pickup ions
A particle-in-cell code is used to examine contributions of the pickup ions
(PIs) and the solar wind ions (SWs) to the cross shock electric field at the
supercritical, perpendicular shocks. The code treats the pickup ions
self-consistently as a third component. Herein, two different runs with
relative pickup ion density of 25% and 55% are presented in this paper. Present
preliminary results show that: (1) in the low percentage (25%) pickup ion case,
the shock front is nonstationary. During the evolution of this perpendicular
shock, a nonstationary foot resulting from the reflected solar wind ions is
formed in front of the old ramp, and its amplitude becomes larger and larger.
At last, the nonstationary foot grows up into a new ramp and exceeds the old
one. Such a nonstationary process can be formed periodically. hen the new ramp
begins to be formed in front of the old ramp, the Hall term mainly contributed
by the solar wind ions becomes more and more important. The electric field Ex
is dominated by the Hall term when the new ramp exceeds the old one.
Furthermore, an extended and stationary foot in pickup ion gyro-scale is
located upstream of the nonstationary/self-reforming region within the shock
front, and is always dominated by the Lorentz term contributed by the pickup
ions; (2) in the high percentage (55%) pickup ion case, the amplitude of the
stationary foot is increased as expected. One striking point is that the
nonstationary region of the shock front evidenced by the self-reformation
disappears. Instead, a stationary extended foot dominated by Lorentz term
contributed by the pickup ions, and a tationary ramp dominated by Hall term
contributed by the solar wind ions are clearly evidenced. The significance of
the cross electric field on ion dynamics is also discussed.Comment: 11 pages, 6 figs and 1 table. This paper will be published in the
journal: Astrophysics and Space Scienc
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PSP/IS⊙IS Observation of a Solar Energetic Particle Event Associated with a Streamer Blowout Coronal Mass Ejection during Encounter 6
In this paper we examine a low-energy solar energetic particle (SEP) event observed by IS⊙IS's Energetic Particle Instrument-Low (EPI-Lo) inside 0.18 au on 2020 September 30. This small SEP event has a very interesting time profile and ion composition. Our results show that the maximum energy and peak in intensity are observed mainly along the open radial magnetic field. The event shows velocity dispersion, and strong particle anisotropies are observed throughout the event, showing that more particles are streaming outward from the Sun. We do not see a shock in the in situ plasma or magnetic field data throughout the event. Heavy ions, such as O and Fe, were detected in addition to protons and 4He, but without significant enhancements in 3He or energetic electrons. Our analysis shows that this event is associated with a slow streamer blowout coronal mass ejection (SBO-CME), and the signatures of this small CME event are consistent with those typical of larger CME events. The time-intensity profile of this event shows that the Parker Solar Probe encountered the western flank of the SBO-CME. The anisotropic and dispersive nature of this event in a shockless local plasma gives indications that these particles are most likely accelerated remotely near the Sun by a weak shock or compression wave ahead of the SBO-CME. This event may represent direct observations of the source of the low-energy SEP seed particle population. © 2022. The Author(s). Published by the American Astronomical Society.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]