Solar wind electron halo depletions at 90° pitch angle

Gosling, J. T.; Skoug, R. M.; Feldman, W. C.

doi:10.1029/2001gl013758

Cited by 82 publications

(111 citation statements)

References 10 publications

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“…The D μμ minimum in μ = 0, predicted by the quasilinear theory for the resonant wave-particle interaction (Jokipii 1966), was consistent with the observations of particle PA distributions (PADs) that are anisotropic, and in many instances even strongly beamed along the magnetic field (e.g., suprathermal electrons by EPAM on ACE, Gosling et al 2001Gosling et al , 2002Simnet et al 2002;; nearrelativistic electrons by 3DP on WIND, Kahler et al 2007; also, Lin 1985). An early issue with quasilinear theory was the exact cancellation of the scattering coefficient in μ = 0, but that issue was resolved by a number of nonlinear and higher-order corrections of the theoretical predictions (e.g., Völk 1973; Lee & Völk 1975;Jones et al 1978;Smith et al 1990; Jaekel & Schlickeiser 1992;Achatz et al 1991Achatz et al , 1993Bieber et al 1994;Dröge 1994;Ng & Reames 1995;Shalchi 2005), allowing for a slow scattering across μ = 0, from one hemisphere of the velocity space to the other.…”

Section: Introductionsupporting

confidence: 57%

“…Perhaps magnetic focusing between the particle injection back to the Sun and about 0.3 AU, where stronger MFL wandering should limit magnetic focusing, already produces beamed distributions of impulsive SEPs, but in the absence of significant near-gyroscale turbulence, nonresonant filtering is sure to only let through those particles that are sufficiently aligned with the local MFL. Nonresonant interactions with low-frequency turbulence are also likely responsible for the observed reflections of particle beams in the SW (e.g., counterstreaming suprathermal electrons, Gosling et al 2001Gosling et al , 2002; SEP ion/electron beams, Tan et al 2009). …”

Section: Resultsmentioning

confidence: 99%

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Nonresonant Interaction of Charged Energetic Particles With Low-Frequency Noncompressive Turbulence: Numerical Simulation

Ragot

2012

ApJ

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A new method for simulating the three-dimensional dynamics of charged energetic particles in very broadband noncompressive magnetic turbulence is introduced. All scales within the primary inertial range of the turbulence observed in the solar wind near 1 AU are now included for the independent computations of both the particle dynamics and the turbulent magnetic field lines (MFLs). While previous theories of resonant particle pitch-angle (PA) scattering and transport in interplanetary magnetic fields had favored interpreting the observed depletions in the electron PA distributions (PADs) around 90 • PA as evidence of poor scattering at low PA cosines, the computed particle dynamics reveal a very different reality. The MFL directions now vary on many scales, and the PADs are depleted around 90 • PA due to nonresonant filtering of the particles that propagate at too large an angle to the local magnetic field. Rather than being too weak, the scattering through 90 • PA is actually so strong that the particles (electrons and protons/ions) are reflected and trapped in the turbulent magnetic fields. While the low-frequency nonresonant turbulence produces ubiquitous magnetic traps that only let through particles with the most field-aligned velocities, higher-frequency near-gyroscale turbulence, when present, enhances particle transport by allowing the particles to navigate between magnetic traps. Finally, visualizing both particle trajectories and MFLs in the very same turbulence reveals a powerful tool for understanding the effects of the turbulent fields on the particle dynamics and cross-field transport. Some cross-field-line scattering, strongly amplified by MFL dispersal, results in a strong cross-field scattering of the particles. From this visualization, it also appears that near-gyroscale turbulence, previously known as gyroresonant turbulence, does not resonantly interact with the particles. The interaction between particles and fields at or near the gyroscale, though potentially strong, does not actually involve the periodic driving of a true resonance.

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Section: Introductionsupporting

confidence: 57%

Section: Resultsmentioning

confidence: 99%

Nonresonant Interaction of Charged Energetic Particles With Low-Frequency Noncompressive Turbulence: Numerical Simulation

Ragot

2012

ApJ

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“…Note the sudden appearance (within a single 10-minute interval) of the dip at 90¨and the extreme symmetry of the beams aligned and anti-aligned with the field once the depletion is fully developed. Although this might arise from bidirectional streaming on a closed field line, mirroring of an outward-going beam on an open field line at a magnetic field enhancement beyond the spacecraft, as proposed to account for observed 90d epletions in solar wind suprathermal electrons [5,6], might also be responsible. Similar 90¨depletions in energetic ion anisotropies have been used to infer the presence of reflecting boundaries in particle reservoirs [7].…”

Section: Observationsmentioning

confidence: 99%

A survey of anisotropic energetic particle flows observed by STEREO

Leske¹,

Cohen²,

Dotson³

et al. 2013

AIP Conference Proceedings

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Abstract. The Low Energy Telescopes (LETs) onboard the twin STEREO spacecraft have been measuring the anisotropies of energetic particles since before the beginning of solar cycle 24. Large unidirectional anisotropies often appear at the onset of magnetically well-connected solar energetic particle (SEP) events, suggesting beamed particles with relatively little scattering. Also, long-lasting bidirectional flows are seen during the decay phase of several SEP events. Some of these instances appear to be within interplanetary coronal mass ejections (ICMEs), as indicated by characteristics such as magnetic field rotations or bidirectional suprathermal electrons. We present preliminary findings from a survey of LET proton anisotropy observations, which illustrate that bidirectional flows appear more likely to come from directions far from the nominal Parker spiral direction than do unidirectional beams, consistent with previous studies. Individual cases that show unusual intensity depletions perpendicular to the magnetic field or pitch angle distributions otherwise indicative of magnetic mirroring are presented in more detail.

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“…Another prominent feature often detected in the pitch angle spectrograms of 1 AU suprathermal electrons is the depletion at 90 • pitch angles. When such a depletion is observed on open field lines, it arises from a combination of adiabatic focusing and mirroring of backstreaming halo electrons from a magnetic field enhancement farther out in the heliosphere (Gosling et al, 2001). In turn, Gosling et al (2002) suggested that 90 • pitch angle depletion observed on closed field lines arises primarily from the double magnetic connection to the Sun.…”

Section: Introductionmentioning

confidence: 99%

Analysis of the substructure within a complex magnetic cloud on 3–4 September 2008

et al. 2013

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In this paper we have analyzed a substructure found within a leading part of a north–south-oriented magnetic cloud (MC) observed on 3–4 September 2008 in the near-Earth solar wind by multiple spacecraft (ACE, Wind, THEMIS B and C). The MC was preceded by a stream interface (SI) and followed by a high-speed stream (HSS). The identified substructure featured a strong depletion of suprathermal halo electrons and showed distinct magnetic field and plasma signatures. It occurred where suprathermal electron flow within a cloud changed from bidirectional to unidirectional, indicating change in the field line connectivity to the Sun. We found that the substructure maintained roughly its integrity from the first Lagrangian point to the vicinity of the Earth's bow shock in the front edge of the MC, but revealed small changes in the structure which could be explained either by temporal evolution or spatial configuration of the spacecraft

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Solar wind electron halo depletions at 90° pitch angle

Cited by 82 publications

References 10 publications

Nonresonant Interaction of Charged Energetic Particles With Low-Frequency Noncompressive Turbulence: Numerical Simulation

Nonresonant Interaction of Charged Energetic Particles With Low-Frequency Noncompressive Turbulence: Numerical Simulation

A survey of anisotropic energetic particle flows observed by STEREO

Analysis of the substructure within a complex magnetic cloud on 3–4 September 2008

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