Direct observations of the formation of the solar wind halo from the strahl

Gurgiolo, C.; Goldstein, M. L.; Viñas, A. F.; Fazakerley, A. N.

doi:10.5194/angeo-30-163-2012

Cited by 31 publications

(34 citation statements)

References 29 publications

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“…The resulting diffusion coefficients suggest the occurrence of diffusion in energy. This feature is relevant since, according to the work by Gurgiolo et al (2012), energy diffusion might be a signature of scattering of strahl electrons to the halo. In bursty conditions, however, energy diffusion should take place in higher energies.…”

Section: Numerical Approach Results and Discussionmentioning

confidence: 97%

“…These plasma waves represent an alternative mechanism to the broadening by sunward-propagating whistler waves (Vocks et al 2005;Viñas et al 2010), whose existence is speculative (Gurgiolo et al 2012). Nevertheless, considering the general existence of whistler frequency range solar wind turbulence, both mechanisms could combine to produce the observed strahl widths, since the whistler instability could be triggered by the broadened strahl.…”

Section: Numerical Approach Results and Discussionmentioning

confidence: 98%

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Solar Wind Strahl Broadening by Self-Generated Plasma Waves

Pavan

Viñas

Yoon³

et al. 2013

ApJ

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This Letter reports on the results of numerical simulations which may provide a possible explanation for the strahl broadening during quiet solar conditions. The relevant processes involved in the broadening are due to kinetic quasi-linear wave-particle interaction. Making use of static analytical electron distribution in an inhomogeneous field, it is found that self-generated electrostatic waves at the plasma frequency, i.e., Langmuir waves, are capable of scattering the strahl component, resulting in energy and pitch-angle diffusion that broadens its velocity distribution significantly. The present theoretical results provide an alternative or complementary explanation to the usual whistler diffusion scenario, suggesting that self-induced electrostatic waves at the plasma frequency might play a key role in broadening the solar wind strahl during quiet solar conditions.

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Section: Numerical Approach Results and Discussionmentioning

confidence: 97%

Section: Numerical Approach Results and Discussionmentioning

confidence: 98%

Solar Wind Strahl Broadening by Self-Generated Plasma Waves

Pavan

Viñas

Yoon³

et al. 2013

ApJ

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“…They mention no long contiguous time periods of no strahl or any correlation of the absence of the strahl with solar wind speed. Gurgiolo et al (2012) have shown observations of what appears to be strong local diffusion of the strahl within the energy range where the strahl and halo overlap, suggesting that the buildup of the halo may occur rapidly within regions where the intense disruption of the lower edge of the strahl occurs. Again, it is not certain what processes are responsible for the observations.…”

Section: Gurgiolo and M L Goldstein: Absence Of The Strahl In Slmentioning

confidence: 98%

Absence of the strahl during times of slow wind

Gurgiolo¹,

Goldstein

2017

Ann. Geophys.

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Abstract. It is not uncommon during periods when the solar wind speed is less than 425 km s −1 to observe near 1 AU no evidence of a strahl population in either the electron solar wind or within the foreshock. Estimating the fluid flow within each energy step returned from the Plasma Electron And Current Experiment (PEACE) on board Cluster-2 often finds that in slow wind the GSE spherical flow angles in energies above where there is a clear core/halo signature are often close to radial with no evidence of a field-aligned flow. This signifies the lack of a strahl presence in the electron velocity distribution function (eVDF). When there is no obvious strahl signature in the data, the electrons above the core/halo in energy appear to be unstructured and smeared in angle. This can either be interpreted as due to statistical noise in low counting rate situations or the result of intense scattering. Regions where the strahl is seen and not seen are often separated by a very thin boundary layer. These transitions in the spacecraft frame of reference can be quite rapid, generally occurring within one to two spins (4-8 s).

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“…This is seen as a slow and continual erosion of the strahl and buildup of the halo through inelastic scattering. Gurgiolo et al (2012) have shown observations of what appears to be a strong local diffusion of the strahl in a restricted energy band where the strahl and halo overlap. This is an overlap in energy but not necessarily in the angular dimensions (of velocity space) and suggests that the buildup of the halo may not be a slow and steady process but may occur in "quantum" jumps within regions where the intense disruption of the lower edge of the strahl occurs.…”

Section: Introductionmentioning

confidence: 96%

“…In the presence of nonradial magnetic field the strahl is often fully separable from the core/halo populations (see Fig. 5 in Gurgiolo et al, 2012) and the strahl moments can be computed by direct integration. At times, however, when the magnetic field has a significant radial component, the strahl will overteristics are required during these times, then numerical fitting is necessary.…”

Section: Introductionmentioning

confidence: 99%

Observations of diffusion in the electron halo and strahl

Gurgiolo¹,

Goldstein

2016

Ann. Geophys.

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Abstract. Observations of the three-dimensional solar wind electron velocity distribution functions (VDF) using φ-θ plots often show a tongue of electrons that begins at the strahl and stretches toward a new population of electrons, termed the proto-halo, that exists near the projection of the magnetic field opposite that associated with the strahl. The energy range in which the tongue and proto-halo are observed forms a "diffusion zone". The tongue first appears in energy generally near the lower-energy range of the strahl and in the absence of any clear core/halo signature. While the φ-θ plots give the appearance that the tongue and proto-halo are derived from the strahl, a close examination of their density suggests that their source is probably the upper-energy core/halo electrons which have been scattered by one or more processes into these populations.

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Direct observations of the formation of the solar wind halo from the strahl

Cited by 31 publications

References 29 publications

Solar Wind Strahl Broadening by Self-Generated Plasma Waves

Solar Wind Strahl Broadening by Self-Generated Plasma Waves

Absence of the strahl during times of slow wind

Observations of diffusion in the electron halo and strahl

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