Cosmic ray anisotropies in the outer heliosphere

Ngobeni, Donald; Potgieter, M. S.

doi:10.1016/j.asr.2006.11.031

Cited by 20 publications

(20 citation statements)

References 31 publications

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“…is enhanced towards the poles by a factor d with respect to the value of K || in the equatorial regions of the heliosphere (as also applied and motivated by Potgieter, 2000;Ferreira et al, 2001Ferreira et al, , 2003Moeketsi et al, 2005;Ngobeni and Potgieter, 2011 …”

Section: Numerical Model and Modulation Parametersmentioning

confidence: 99%

“…For elaborated discussions on this issue, see also Strauss, Potgieter, and Ferreira (2011) and Ngobeni and Potgieter (2010). The numerical procedure used to solve Equation (1) was described by Ferreira and Potgieter (2002) and Ferreira et al (2001Ferreira et al ( , 2003 and Nkosi, Potgieter and Ferreira (2008).…”

Section: Numerical Model and Modulation Parametersmentioning

confidence: 99%

“…It is based on the numerical solution of the well-known heliospheric transport equation (TPE;Parker, 1965)  …”

Section: Numerical Model and Modulation Parametersmentioning

confidence: 99%

“…During A < 0 cycles, such as the present cycle, positively charged particles drift in towards Earth mostly along this HCS, so that its waviness as represented by the tilt angle (Hoeksema, 1991) plays a more significant modulation role than during A > 0 cycles (Webber, Potgieter and Burger, 1990;Potgieter and le Roux, 1992;Potgieter and Ferreira, 2001). It is therefore to be expected that proton spectra for A < 0 cycles should be lower than spectra during A > 0 cycles at energies E < ~1 GeV (see examples by Langner, Potgieter and Webber, 2004;Ngobeni and Potgieter, 2008). The conceptual paradigm of particle drifts (read gradient and curvature drifts) dominating CR modulation especially during periods of solar minimum conditions, and in a different manner in consecutive solar cycles, has become widely accepted and popular.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Numerical Model and Modulation Parametersmentioning

confidence: 99%

Section: Numerical Model and Modulation Parametersmentioning

confidence: 99%

“…It is based on the numerical solution of the well-known heliospheric transport equation (TPE;Parker, 1965)  …”

Section: Numerical Model and Modulation Parametersmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

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

et al. 2013

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“…McComas & Schwadron 2006) and at the equatorial regions of the heliosphere (e.g. Ngobeni & Potgieter 2008), energy cascade processes (e.g. Fisk & Gloeckler 2009) and magnetic reconnection occurring near the heliopause (e.g.…”

Section: Introductionmentioning

confidence: 99%

The heliospheric transport and modulation of multiple charged anomalous oxygen revisited

Strauss

Potgieter

Ferreira

2010

A&A

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Context. Since the crossings of the solar wind termination shock by the Voyager 1 and 2 spacecraft, much speculation has surrounded the acceleration mechanism and region where the anomalous cosmic ray component is accelerated. A peculiar, and mostly overlooked feature of the observed anomalous oxygen spectrum near the termination shock, is the power law form of the roll-over (cut-off) at the high energy range of this spectrum. Aims. We investigate, using a numerical model, why this deviation from the expected exponential form of the cut-off part of the anomalous oxygen spectrum occurs, and if the observed power law form can be explained in terms of the acceleration of multiple charged anomalous oxygen. Methods. Multiple charged anomalous cosmic rays are incorporated in a numerical model, based on the standard Parker transport equation, including acceleration at the solar wind termination shock. This is done by specifying an energy dependent charge state, constrained by observations. Results. Comparing computational results with spacecraft observations, it is found that the inclusion of multiply charged anomalous cosmic rays in the modulation model can explain the observed spectrum of anomalous oxygen in the energy range from 10−70 MeV per nucleon. The more effective acceleration of these multiple charge anomalous particles at the solar wind termination shock causes a significant deviation from the usual exponential cut-off spectrum to display instead a power law decrease up to 70 MeV per nucleon where galactic oxygen starts to dominate. In addition, the model reproduces the features of multiple charged oxygen at Earth so that a good comparison is obtained between computations and observations.

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Is the Highest Cosmic-Ray Flux Yet to Come?

Strauss¹,

Potgieter²

2014

Coronal Magnetometry

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Cosmic ray anisotropies in the outer heliosphere

Cited by 20 publications

References 31 publications

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

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

The heliospheric transport and modulation of multiple charged anomalous oxygen revisited

Is the Highest Cosmic-Ray Flux Yet to Come?

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