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

Roux, J. A. le; Zank, G. P.; Птускин, В. С.

doi:10.1029/1999ja900318

Cited by 74 publications

(52 citation statements)

References 51 publications

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“…With these observations, the rigidity dependence h of the mean free path can be determined for each ACR pair, , , to 3000 MV O data) that we used above to study the change of L between solar cycle extrema. These values for the rigidity power-law index are in agreement with the aforementioned numerical modeling of le Roux et al (1999), in which the use of the NPT turbulence model (Zank et al 1998) yielded values for h of about 1.2 for rigidities from ∼400 to 2000 MV and approaching for rigidities below and above this range. h p 2 4.…”

Section: Discussionsupporting

confidence: 88%

“…With a nonperturbative theory (NPT) for the evolution of magnetohydrodynamic turbulence in the solar wind (Zank et al 1998 and references therein), the radial dependence of k was found to be weak and nonmonotonic. Using a spherically symmetric modulation model, le Roux, Zank, & Ptuskin (1999) compared NPT with two other theories, found that NPT performed best, and demonstrated the roughly constant radial mean free path for modeled 28 MeV nucleon Ϫ1 ACR He ϩ over a large range of helioradii. Nonetheless, by making these assumptions, some significant effects could be neglected in our estimates.…”

Section: Discussionmentioning

confidence: 99%

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Evolution of Anomalous Cosmic-Ray Oxygen and Helium Energy Spectra during the Solar Cycle 22 Recovery Phase in the Outer Heliosphere

Hill

Hamilton

Krimigis

2002

The Astrophysical Journal

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We present annual 0.3-40 MeV nucleon Ϫ1 anomalous cosmic-ray (ACR) oxygen and helium energy spectra from the 1991-1999 cosmic-ray recovery phase of solar cycle 22. These observations were made with the Low Energy Charged Particle instruments aboard the Voyager 1 and Voyager 2 spacecraft while at helioradial positions ranging from 34 to 76 AU. The peak intensities of both species increased by 2 orders of magnitude during this period, while the energies of peak O and He intensity decreased from ∼9 to 1.3 MeV nucleon Ϫ1 and from ∼35 to 6 MeV nucleon Ϫ1 , respectively. Using these observations along with published O measurements from the Solar Anomalous Magnetospheric Particle Explorer at 1 AU, we investigate ACR transport phenomena. We make estimates related to transport parameters such as the relative change in the scattering mean free path over time, the rigidity dependence of the mean free path, and the distance between the Sun and the solar wind termination shock.

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Section: Discussionsupporting

confidence: 88%

Section: Discussionmentioning

confidence: 99%

Evolution of Anomalous Cosmic-Ray Oxygen and Helium Energy Spectra during the Solar Cycle 22 Recovery Phase in the Outer Heliosphere

Hill

Hamilton

Krimigis

2002

The Astrophysical Journal

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“…For perpendicular diffusion, it was shown using simulations that K ⊥r and K ⊥θ scale as the parallel coefficient (le Roux, Zank, and Ptuskin, 1999;Giacalone and Jokipii, 1999;Qin, Matthaeus, and Bieber, 2002) so it is assumed that:…”

Section: Recent Theoretical Advances In the Transport Coefficientsmentioning

confidence: 99%

Time-Dependent Modulation of Cosmic Rays in the Heliosphere

2013

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The time-dependent modulation of galactic cosmic rays in the heliosphere is studied by computing intensities using a time-dependent modulation model. By introducing recent theoretical advances in the transport coefficients in the model, computed intensities are compared with Voyager 1, International Monitoring Platform (IMP) 8, and Ulysses proton observations in search of compatibility. The effect of different modulation parameters on computed intensities is also illustrated. It is shown that this approach produces, on a global scale, realistic cosmic-ray proton intensities along the Voyager 1 spacecraft trajectory and at Earth upto ∼2004, whereafter the computed intensities recovers much slower towards solar minimum than observed in the inner heliosphere. A modified time dependence in the diffusion coefficients is proposed to improve compatibility with the observations at Earth after ∼2004. This modified time dependence led to an improved compatibility between computed intensities and the observations along the Voyager 1 trajectory and at Earth even after ∼2004. An interesting result is that the cosmic-ray modulation during the present polarity cycle is not determined only by changes in the drift coefficient and tilt angle of the wavy current sheet, but is also largely dependent on changes in the diffusion coefficients.

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“…As input for κ || various turbulence quantities are needed, most notable the HMF variance δB 2 . The magnitude and spatial dependences of these turbulence parameters are taken from Burger et al (2000), with the HMF variance assumed to scale as δB 2 ∼ B 2 in the heliosheath (le Roux et al 1999;Florinski & Pogorelov 2009), where B is the HMF magnitude. The profiles of B, the solar wind velocity V sw and the Alfvén speed V A in the heliosheath are discussed in the next section.…”

Section: The Modulation Modelmentioning

confidence: 99%

Modelling anomalous cosmic ray oxygen in the heliosheath

Strauss

Potgieter

Ferreira

et al. 2010

A&A

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This paper discusses a numerical modulation model to describe anomalous cosmic ray acceleration and transport in the heliosheath, the portion of the heliosphere between the termination shock and the heliopause. The model is based on the well known Parker transport equation and includes, in addition to diffusive shock acceleration at the solar wind termination shock, momentum diffusion (Fermi II, stochastic acceleration) and adiabatic heating occurring in the heliosheath together with both a latitude dependent compression ratio and injection efficiency as inferred from hydrodynamic heliospheric models. The model is applied to the study of anomalous cosmic ray oxygen, with the resulting intensities compared to recent Voyager 1 spacecraft observations in the heliosheath.Comparison shows that the model is able to very satisfactorily reproduce these observations, which includes a modulated spectral form at the termination shock and subsequent unfolding into the heliosheath. It is concluded that a combination of momentum diffusion and adiabatic heating, under certain realistic assumption of the solar wind speed in the heliosheath, form a viable re-acceleration mechanism, or continuous acceleration process, to explain the very contentious anomalous cosmic ray observations in the heliosheath.

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

Cited by 74 publications

References 51 publications

Evolution of Anomalous Cosmic-Ray Oxygen and Helium Energy Spectra during the Solar Cycle 22 Recovery Phase in the Outer Heliosphere

Evolution of Anomalous Cosmic-Ray Oxygen and Helium Energy Spectra during the Solar Cycle 22 Recovery Phase in the Outer Heliosphere

Time-Dependent Modulation of Cosmic Rays in the Heliosphere

Modelling anomalous cosmic ray oxygen in the heliosheath

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