An Ab Initio Model for the Modulation of Galactic Cosmic-Ray Electrons

Engelbrecht, N. E.; Burger, R. A.

doi:10.1088/0004-637x/779/2/158

Cited by 44 publications

(47 citation statements)

References 70 publications

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“…Refinements to the model are, however, necessary and in the process of being made, but the fact that computed cosmic-ray intensities for galactic electrons and positrons are also in reasonable agreement with multiple sets of spacecraft observations (see, e.g. [13]) is very encouraging.…”

Section: Discussionmentioning

confidence: 95%

Cosmic-Ray Modulation: an Ab Initio Approach

Engelbrecht

Burger

2014

Braz J Phys

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A better understanding of cosmic-ray modulation in the heliosphere can only be gained through a proper understanding of the effects of turbulence on the diffusion and drift of cosmic rays. We present an ab initio model for cosmic-ray modulation, incorporating for the first time the results yielded by a two-component turbulence transport model. This model is solved for periods of minimum solar activity, utilizing boundary values chosen so that model results are in fair to good agreement with spacecraft observations of turbulence quantities, not only in the solar ecliptic plane but also along the out-of-ecliptic trajectory of the Ulysses spacecraft. These results are employed as inputs for modelled slab and 2D turbulence energy spectra. The latter spectrum is chosen based on physical considerations, with a drop-off at the very lowest wavenumbers commencing at the 2D outerscale. There currently exist no models or observations for this quantity, and it is the only free parameter in this study. The modelled turbulence spectra are used as inputs for parallel mean free path expressions based on those derived from quasi-linear theory and perpendicular mean free paths from extended nonlinear guiding center theory. Furthermore, the effects of turbulence on cosmic-ray drifts are modelled in a self-consistent way, employing a recently developed model for drift along the wavy current sheet. The resulting diffusion coefficients and drift expressions are applied to the study of galactic cosmic-ray protons and antiprotons using a threedimensional, steady-state cosmic-ray modulation code, and sample solutions in fair agreement with multiple spacecraft observations are presented.

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Section: Discussionmentioning

confidence: 95%

Cosmic-Ray Modulation: an Ab Initio Approach

Engelbrecht

Burger

2014

Braz J Phys

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“…These authors choose an expression for t W  in orderto yield a drift coefficient in agreement with simulations performed by Minnie et al (2007), so that The quantity l u represents the 2D ultrascale, which, for the 2D turbulence spectral form used in this study, is given by Engelbrecht & Burger (2013) …”

Section: Relevance For Cosmic-ray Transport Coefficientsmentioning

confidence: 97%

“…To derive an explicit expression for the perpendicular diffusion coefficient k^,we employ an expression for the 2D modal spectrum used by Engelbrecht & Burger (2013): with l 2D and l out lengthscales at which the inertial and energycontaining ranges, respectively, commence. This spectrum has three ranges: an inertial range, an energy-containing range, and an "inner" range that decreases as a function of wavenumber.…”

Section: Relevance For Cosmic-ray Transport Coefficientsmentioning

confidence: 99%

“…This is done under the assumption that the quasi-2D and wave-like quantities provide a reasonable approximation for 2D and slab quantities, following the approach of Engelbrecht & Burger (2013) ( )( )is used (and shown in the lower left panel in Figure 5), while it is assumed that l l = 100 out 2D . Although perpendicular meanfree paths derived from the NLGC family of scattering theories are quite sensitive to choices made for the 2D outer scale (see, e.g., Engelbrecht & Burger 2015a), the choice for this quantity is rendered difficult by a lack of observations.…”

Section: Relevance For Cosmic-ray Transport Coefficientsmentioning

confidence: 99%

“…This is particularly so for the solar wind; see the review-like introductions in Usmanov et al (2011Usmanov et al ( , 2014, Zank et al (2012a), and Wiengarten et al (2015). This considerable improvement, relative to non-self-consistent modeling, is, on the one hand, necessary in order to fully understand the transport of charged energetic particles in the heliosphere (e.g., Engelbrecht & Burger 2013), and via this to explore the physics of their interactions with the plasma turbulence (e.g., Schlickeiser 2002;Shalchi 2009). On the other hand, the correct description of the transport of cosmic rays in other astrophysical systems is also of great interest.…”

Section: Introductionmentioning

confidence: 99%

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A Generalized Two-Component Model of Solar Wind Turbulence and Ab Initio Diffusion Mean-Free Paths and Drift Lengthscales of Cosmic Rays

Wiengarten

Oughton

Engelbrecht

et al. 2016

ApJ

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We extend a two-component model for the evolution of fluctuations in the solar wind plasma so that it is fully three-dimensional (3D) and also coupled self-consistently to the large-scale magnetohydrodynamic equations describing the background solar wind. The two classes of fluctuations considered are a high-frequency parallelpropagating wave-like piece and a low-frequency quasi-two-dimensional component. For both components, the nonlinear dynamics is dominanted by quasi-perpendicular spectral cascades of energy. Driving of the fluctuationsby, for example, velocity shear and pickup ionsis included. Numerical solutions to the new model are obtained using the CRONOS framework, and validated against previous simpler models. Comparing results from the new model with spacecraft measurements, we find improved agreement relative to earlier models that employ prescribed background solar wind fields. Finally, the new results for the wave-like and quasi-twodimensional fluctuations are used to calculate ab initio diffusion mean-free paths and drift lengthscales for the transport of cosmic rays in the turbulent solar wind.

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The influence of different turbulence models on the diffusion coefficients of energetic particles

2015

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We explore the influence of turbulence on the transport of energetic particles by using test particle simulations. We compute parallel and perpendicular diffusion coefficients for two‐component turbulence, isotropic turbulence, a model based on Goldreich‐Sridhar scaling, noisy reduced magnetohydrodynamic turbulence, and a noisy slab model. We show that diffusion coefficients have a similar rigidity dependence regardless which turbulence model is used, and thus, we conclude that the influence of turbulence on particle transport is not as strong as originally thought. Only fundamental quantities such as particle rigidity and the Kubo number are relevant. In the current paper we also confirm the unified nonlinear transport theory for noisy slab turbulence. To double check the validity and accuracy of our numerical results, we use a second test particle code. We show that both codes provide very similar results confirming the validity of our conclusions.

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An Ab Initio Model for the Modulation of Galactic Cosmic-Ray Electrons

Cited by 44 publications

References 70 publications

Cosmic-Ray Modulation: an Ab Initio Approach

Cosmic-Ray Modulation: an Ab Initio Approach

A Generalized Two-Component Model of Solar Wind Turbulence and Ab Initio Diffusion Mean-Free Paths and Drift Lengthscales of Cosmic Rays

The influence of different turbulence models on the diffusion coefficients of energetic particles

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