On Cosmic Ray Modulation Beyond the Heliopause: Where Is the Modulation Boundary?

Scherer, K.; Fichtner, H.; Strauss, R. D.; Ferreira, S. E. S.; Potgieter, M. S.; Fahr, H. J.

doi:10.1088/0004-637x/735/2/128

Cited by 69 publications

(62 citation statements)

References 41 publications

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“…In this context, one has to keep in mind, however, that the precise form of the low-energy LIS and its connection to the Galactic spectrum on a kpc scale is still unclear and depends on modulation effects in the heliosphere, as well as on similar effects in the local solar system environment (see, e.g., the discussion in Scherer et al 2011). Furthermore, the assumed break in the diffusion coefficient may be different or even absent in a more complete propagation scenario, since up to now it has mainly been phenomenologically motivated, to yield the expected local spectra.…”

Section: The Resulting Spatial and Spectral Cr Distributionmentioning

confidence: 99%

Anisotropic diffusion of Galactic cosmic ray protons and their steady-state azimuthal distribution

Effenberger

Fichtner

Scherer

et al. 2012

A&A

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Galactic transport models for cosmic rays involve the diffusive motion of these particles in the interstellar medium. Owing to the large-scale structured Galactic magnetic field, this diffusion is anisotropic with respect to the local field direction. We included this transport effect along with continuous loss processes in a quantitative model of Galactic propagation for cosmic ray protons that is based on stochastic differential equations. We calculated energy spectra at different positions along the Sun's Galactic orbit and compared them to the isotropic diffusion case. The results show that a larger amplitude of variation and different spectral shapes are obtained in the introduced anisotropic diffusion scenario, which in turn emphasizes the need for accurate Galactic magnetic field models.

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Section: The Resulting Spatial and Spectral Cr Distributionmentioning

confidence: 99%

Anisotropic diffusion of Galactic cosmic ray protons and their steady-state azimuthal distribution

Effenberger

Fichtner

Scherer

et al. 2012

A&A

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“…where exactly in spatial terms does the modulation begin? Recently, Scherer et al (2011) argued that the solar modulation of galactic CRs might start beyond the HP which so far has always been considered the modulation boundary. Since these issues cannot yet be settled, we continue to simply assume the HP as the boundary where the modulation of galactic CR modulation essentially starts, assumed for this work to be at 120 AU.…”

Section: Together With the Question Of What Exactly The Very Lis Is Amentioning

confidence: 99%

Modulation of Galactic Protons in the Heliosphere During the Unusual Solar Minimum of 2006 to 2009

et al. 2013

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The last solar minimum activity period, and the consequent minimum modulation conditions for cosmic rays, was unusual. The highest levels of galactic protons were recorded To simulate this effect, the rigidity dependence of the diffusion coefficients had to decrease significantly below ~3 GeV. The modulation minimum period of 2009 can thus be described as relatively more 'diffusion dominated' than previous solar minima. However, we illustrate that drifts still had played a significant role but that the observable modulation effects were not as well correlated with the waviness of the heliospheric current sheet as before. Protons still experienced global gradient and curvature drifts as the heliospheric magnetic field had decreased significantly until the end of 2009, in contrast to the moderate decreases observed during previous minimum periods. We conclude that all modulation processes contributed to the observed increases in the proton spectra for this period, exhibiting an intriguing interplay of these major mechanisms.

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“…In addition, different LIS models can produce the observed spectrum with LIS model-dependent modulation parameters [Herbst et al, 2010]. Furthermore, recent studies show that remarkable modulation exists in the outer heliosphere and even beyond the heliopause [e.g., Scherer et al, 2011;Strauss et al, 2013]. And the outer heliospheric structure and boundary of the dynamic heliosphere also change associated with the varying solar activity [Zank and Müller, 2003;Scherer and Fahr, 2003;Pogorelov et al, 2009].…”

Section: Modulation Modelmentioning

confidence: 99%

Modulation of galactic cosmic rays during the unusual solar minimum between cycles 23 and 24

et al. 2014

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During the recent solar minimum between cycles 23 and 24 (solar minimum P23/24), the intensity of galactic cosmic rays (GCR) measured at the Earth was the highest ever recorded since space age. It is the purpose of this paper to resolve the most plausible mechanism for this unusually high intensity. A GCR transport model in three‐dimensional heliosphere based on a simulation of Markov stochastic process is used to find the relation of cosmic ray modulation to various transport parameters, including solar wind (SW) speed, distance of heliospheric boundary, magnitude of interplanetary magnetic field (IMF) at the Earth, tilt angle of heliospheric current sheet, and values of parallel and perpendicular diffusion coefficients. We calculate GCR proton energy spectra at the Earth for the last three solar minima P21/22, P22/23, and P23/24, with the transport parameters obtained from observations. Besides weak IMF magnitude and slow SW speed, we find that a possible low magnetic turbulence, which increases the parallel diffusion and reduces the perpendicular diffusion in the polar direction, might be an additional possible mechanism for the high GCR intensity in the solar minimum P23/24.

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On Cosmic Ray Modulation Beyond the Heliopause: Where Is the Modulation Boundary?

Cited by 69 publications

References 41 publications

Anisotropic diffusion of Galactic cosmic ray protons and their steady-state azimuthal distribution

Anisotropic diffusion of Galactic cosmic ray protons and their steady-state azimuthal distribution

Modulation of Galactic Protons in the Heliosphere During the Unusual Solar Minimum of 2006 to 2009

Modulation of galactic cosmic rays during the unusual solar minimum between cycles 23 and 24

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