CROSS-FIELD DIFFUSION OF ENERGETIC (100 keV to 2 MeV) PROTONS IN INTERPLANETARY SPACE

Costa, Edio da; Tsurutani, B. T.; Alves, M. V.; Echer, E.; Lakhina, G. S.

doi:10.1088/0004-637x/778/2/180

Cited by 8 publications

(4 citation statements)

References 20 publications

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“…In contrast, the cross-field diffusion coefficient resulting from charged-particle motion in meandering magnetic fields can be 2-5 % of the parallel diffusion coefficient, which is much larger. In a recent paper, Costa et al (2013) noted that the frequent occurrence of a phenomenon known as "magnetic holes", which are rather small pressure-balanced regions of the solar wind where the magnetic field decreases significantly from the background, can lead to a non-resonant process whereby particles are displaced normal to the average magnetic field.…”

Section: Cross-field Diffusion Including Field-line Random Walkmentioning

confidence: 99%

Large gradual solar energetic particle events

Desai

Giacalone

2016

Living Rev. Sol. Phys.

379

305

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Solar energetic particles, or SEPs, from suprathermal (few keV) up to relativistic (∼few GeV) energies are accelerated near the Sun in at least two ways: (1) by magnetic reconnection-driven processes during solar flares resulting in impulsive SEPs, and (2) at fast coronal-mass-ejection-driven shock waves that produce large gradual SEP events. Large gradual SEP events are of particular interest because the accompanying high-energy (>10s MeV) protons pose serious radiation threats to human explorers living and working beyond low-Earth orbit and to technological assets such as communications and scientific satellites in space. However, a complete understanding of these large SEP events has eluded us primarily because their properties, as observed in Earth orbit, are smeared due to mixing and contributions from many important physical effects. This paper provides a comprehensive review of the current state of knowledge of these important phenomena, and summarizes some of the key questions that will be addressed by two upcoming missions-NASA's Solar Probe Plus and ESA's Solar Orbiter. Both of these missions are designed to directly and repeatedly sample the near-Sun environments where interplanetary scattering and transport effects are significantly reduced, allowing us to discriminate between different acceleration sites and mechanisms and to isolate the contributions of numerous physical processes occurring during large SEP events.

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Section: Cross-field Diffusion Including Field-line Random Walkmentioning

confidence: 99%

Large gradual solar energetic particle events

Desai

Giacalone

2016

Living Rev. Sol. Phys.

379

305

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“…The 1,000 values of λ i were then used to empirically calculate the cross-field diffusion rates. A detailed description of the analysis can be found in Da Costa et al (2013). At the left side of the plot, the cross-field diffusion for~100 keV particles is noted to be~11% of the Bohm rate.…”

Section: 1002/2017ja024203mentioning

confidence: 99%

“…The red dots represent 100 particle-magnetic decrease (MD) interaction runs and the blue triangles 200 particle-MD interaction runs. Taken from DaCosta et al (2013).…”

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confidence: 99%

A Review of Alfvénic Turbulence in High‐Speed Solar Wind Streams: Hints From Cometary Plasma Turbulence

et al. 2018

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Solar wind turbulence within high‐speed streams is reviewed from the point of view of embedded single nonlinear Alfvén wave cycles, discontinuities, magnetic decreases (MDs), and shocks. For comparison and guidance, cometary plasma turbulence is also briefly reviewed. It is demonstrated that cometary nonlinear magnetosonic waves phase‐steepen, with a right‐hand circular polarized foreshortened front and an elongated, compressive trailing edge. The former part is a form of “wave breaking” and the latter that of “period doubling.” Interplanetary nonlinear Alfvén waves, which are arc polarized, have a ~180° foreshortened front and with an elongated trailing edge. Alfvén waves have polarizations different from those of cometary magnetosonic waves, indicating that helicity is a durable feature of plasma turbulence. Interplanetary Alfvén waves are noted to be spherical waves, suggesting the possibility of additional local generation. They kinetically dissipate, forming MDs, indicating that the solar wind is partially “compressive” and static. The ~2 MeV protons can nonresonantly interact with MDs leading to rapid cross‐field (~5.5% Bohm) diffusion. The possibility of local (~1 AU) generation of Alfvén waves may make it difficult to forecast High‐Intensity, Long‐Duration AE Activity and relativistic magnetospheric electrons with great accuracy. The future Solar Orbiter and Solar Probe Plus missions should be able to not only test these ideas but to also extend our knowledge of plasma turbulence evolution.

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“…For example, Tsurutani et al (1999) showed magnetic field decreases (MDs), which is a common feature associated with the HCS, can cause displacements of particle guiding center, thus resulting in cross-field diffusion. A cross-field diffuse rate for 100 keV-2 MeV protons due to MDs was estimated to be ∼0.1 Bohm diffusion rate (Costa et al 2013). Anomalous cross-field diffusion of charged particles can also occur by cyclotron-resonant scattering and has been used to explain the low-latitude boundary layer (Tsurutani & Thorne 1982).…”

Section: Introductionmentioning

confidence: 99%

Solar Energetic Particle and the Heliospheric Current Sheet

Liou,

2024

ApJ

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The effect of the heliospheric current sheet (HCS) on the propagation of solar energetic particles (SEPs) remains poorly known. In this study we address this question by surveying energetic (∼2.0–9.6 MeV nucleon–1) helium data acquired by the energetic particle acceleration, composition, and transport (EPACT) sensor on board the Wind spacecraft. A superposed epoch analysis of 319 HCS crossings made by Wind reveals a sharp drop in the SEP fluxes at the HCS for the low-energy channels and little change across the HCS for the high-energy channels. To help understand the statistical result, we studied a total of 15 SEP flux dropout (a decrease of ∼50% or more) events that coincided with the crossing of the HCS. One of the common features of these SEP events is that they were initiated in the western hemisphere but far away from the longitude of HCS crossings, suggesting that the source of SEPs was well connected initially but was cut off later after Wind moved to the opposite hemisphere (e.g., HCS crossing). Further analysis of the events suggests that the percentage of flux dropouts decreases with increasing energy. It is suggested that a strong scattering of MeV helium may have occurred as the particle gyroradius is comparable to the thickness of the current sheet. This study clearly provides solid evidence for the HCS as a barrier to suppressing SEP flux of MeV energies from the onset hemisphere to the other.

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CROSS-FIELD DIFFUSION OF ENERGETIC (100 keV to 2 MeV) PROTONS IN INTERPLANETARY SPACE

Cited by 8 publications

References 20 publications

Large gradual solar energetic particle events

Large gradual solar energetic particle events

A Review of Alfvénic Turbulence in High‐Speed Solar Wind Streams: Hints From Cometary Plasma Turbulence

Solar Energetic Particle and the Heliospheric Current Sheet

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