Toward a Realistic Diffusion Tensor for Galactic Cosmic Rays

Burger, R. A.; Hattingh, M.

doi:10.1086/306152

Cited by 72 publications

(43 citation statements)

References 18 publications

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“…Since this theory applies only in the limit All << l• (R << 10 -4 GV), one may argue that this theory is ap-plicable only to energies below that of interest for CR modulation. We will nonetheless consider this possibility for the following two reasons: (1) CR modulation models which assume nñ cr •11 do well in reproducing observed GCR spectra [e.g., Burger and Hattingh, 1998]. (2) Test particle simulations in magnetic field turbulence with an assumed 80% in 2-D and 20% in slab geometry [Giacalone, 1998] …”

Section: Motivation and Structure Of Papermentioning

confidence: 99%

An evaluation of perpendicular diffusion models regarding cosmic ray modulation on the basis of a hydromagnetic description for solar wind turbulence

Roux¹,

Zank²,

Птускин³

1999

J. Geophys. Res.

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Abstract. The theory for the perpendicular diffusion of cosmic rays is not well understood which hampers our understanding of cosmic ray modulation. In this paper, a spherically symmetric cosmic ray modulation model is used to evaluate three different theories for perpendicular cosmic ray diffusion in the ecliptic plane, subject to the limitation of negligible cosmic ray transport in the polar direction. In models for the perpendicular diffusion component, it is assumed that perpendicular diffusion due to large-scale field line wandering dominates resonant perpendicular diffusion. To test these models, observations of anomalous and galactic helium

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Section: Motivation and Structure Of Papermentioning

confidence: 99%

An evaluation of perpendicular diffusion models regarding cosmic ray modulation on the basis of a hydromagnetic description for solar wind turbulence

Roux¹,

Zank²,

Птускин³

1999

J. Geophys. Res.

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“…Jokipii 1966;Bieber & Matthaeus 1997;Kóta & Jokipii 2000;Matthaeus et al 2003;Shalchi et al 2004;Webb et al 2006;Shalchi 2006), a final solution has not been provided so far. The perpendicular transport of charged particles is a central problem in astrophysics, since the knowledge of the diffusion tensor for particle transport parallel and perpendicular to the prescribed external magnetic field is essential for describing solar energetic particles (Dröge 2000), the modulation of Galactic cosmic rays (Burger & Hattingh 1998), diffusive shock acceleration, and the lifetime of cosmic rays in the Galaxy (Jokipii & Parker 1969). Furthermore, there are measurements of perpendicular mean free paths in the heliosphere (Chenette et al 1977;Palmer 1982;Burger et al 2000) that still await a theoretical explanation.…”

Section: Introductionmentioning

confidence: 99%

A new theory for perpendicular transport of cosmic rays

Shalchi¹,

Kourakis²

2007

A&A

103

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We present an improved nonlinear theory for the perpendicular transport of charged particles. This approach is based on an improved nonlinear treatment of field-line random walk in combination with a generalized compound diffusion model. The generalized compound diffusion model employed is more systematic and reliable, in comparison with previous theories. Furthermore, the theory shows remarkably good agreement with test-particle simulations and solar wind observations.

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“…It is well known that the wavy heliospheric current sheet (HCS) is a very important modulation parameter as were illustrated with drift models [dokipii and Thomas, 1981; K6ta and dokipii, 1983; le Roux and Potgieter, 1990;Burger and Hattingh, 1998]. The computed modulation effects of a are, however, dependent on other modulation parameters, in particular the parallel and perpendicular diffusion coefficients, as will be illustrated below.…”

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confidence: 94%

Modulation effects of anisotropic perpendicular diffusion on cosmic ray electron intensities in the heliosphere

Ferreira¹,

Potgieter²,

Burger³

et al. 2000

J. Geophys. Res.

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Abstract. The modulation of cosmic ray electrons provides a useful tool to study the diffusion tensor applicable to heliospheric modulation. Electron modulation responds directly to the assumed energy dependence of the diffusion coefficients below ~500 MeV in contrast to protons which experience large adiabatic energy losses below this energy. As a result of this and because drifts become unimportant for electrons at these low energies, conclusions can be made about the appropriate diffusion coefficients. Using a modulation model, we illustrate the role of anisotropic perpendicular diffusion on electron modulation. In general, we find that perpendicular diffusion dominates electron modulation below ~100 MeV. Enhancing it in the polar direction typically produced an increase in modulation for both the A > 0 (e.g., ~1990 to ~2000) and A < 0 (e.g., ~1980 to ~1990) solar magnetic polarity cycles. It also causes the radial dependence of the intensity to become more uniform throughout the heliosphere, and causes a significant reduction in the latitude dependence of the intensities at all radial distances, with the largest effects in the inner heliosphere and at low energies. This agrees with studies of cosmic ray protons, which suggest that perpendicular diffusion enhanced in the polar direction of the heliosphere is required in conventional drift models to explain the small latitudinal gradients observed for protons on board the Ulysses spacecraft. The role of enhanced perpendicular diffusion was further investigated by examining electron modulation as a function of the "tilt angle" c• of the wavy current sheet. In general, a reduction occurred between the modulation differences caused by drifts as a function of c• for both polarity cycles. This work illustrates that anisotropic perpendicular diffusion has profound effects on the modulation of galactic cosmic ray electrons during both polarity cycles.

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Toward a Realistic Diffusion Tensor for Galactic Cosmic Rays

Cited by 72 publications

References 18 publications

An evaluation of perpendicular diffusion models regarding cosmic ray modulation on the basis of a hydromagnetic description for solar wind turbulence

An evaluation of perpendicular diffusion models regarding cosmic ray modulation on the basis of a hydromagnetic description for solar wind turbulence

A new theory for perpendicular transport of cosmic rays

Modulation effects of anisotropic perpendicular diffusion on cosmic ray electron intensities in the heliosphere

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