Modelling anomalous cosmic ray oxygen in the heliosheath

Strauss, R. D.; Potgieter, M. S.; Ferreira, S. E. S.; Hill, M. E.

doi:10.1051/0004-6361/201014528

Cited by 36 publications

(25 citation statements)

References 51 publications

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“…After the shock, the radial solar wind speed decreases according to the compression ratio of three Richardson et al, 2008) and then decreases as 1/r 2 further out in the inner heliosheath to the heliopause (e.g. Strauss et al, 2010). …”

Section: Input Parameters Used In the Modelmentioning

confidence: 99%

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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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Section: Input Parameters Used In the Modelmentioning

confidence: 99%

“…See e.g. Jokipii, Levy, and Hubbard (1977); Potgieter and Moraal (1985); Shalchi, Bieber, and Matthaeus (2004); Zhang (2006); Strauss et al (2010); Potgieter (2013a,b).…”

Section: Introductionmentioning

confidence: 99%

Time-Dependent Modulation of Cosmic Rays in the Heliosphere

2013

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“…The TPE is solved numerically using a two-dimensional (2D) drift-DSA model originally developed by le Roux et al (1996) and later modified by Langner et al (2004). Variants of this same model were successfully implemented in studying the modulation and acceleration of various species of CRs (e.g., Langner et al 2006aLangner et al , 2006bStrauss et al 2010;Ngobeni & Potgieter 2015). The model is iterated several times until sufficient convergence of the numerical solution is attained, while transport coefficients are kept timeindependent.…”

Section: A Re-acceleration Model For Electron Modulationmentioning

confidence: 99%

“…This ensures that the only particle acceleration in the model takes place as a result of DSA at the TS. For alternative SW speed scenarios in the heliosheath and their consequences, see Langner et al (2006aLangner et al ( , 2006b and Strauss et al (2010). The HMF geometry is described according to the Parker (1958) model but modified in the polar regions as proposed by Jokipii & Kóta (1989).…”

Section: Heliospheric Propertiesmentioning

confidence: 99%

The Re-Acceleration of Galactic Electrons at the Heliospheric Termination Shock

Prinsloo

Potgieter

Strauss

2017

ApJ

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Observations by the Voyagerspacecraft in the outer heliosphere presented several challenges for the paradigm of diffusive shock acceleration (DSA) at the solar wind termination shock (TS). In this study, the viability of DSA as a re-acceleration mechanism for galactic electrons is investigated using a comprehensive cosmic-ray modulation model. The results demonstrate that the efficiency of DSA depends strongly on the shape of the electron spectra incident at the TS, which in turn depends on the features of the local interstellar spectrum. Modulation processes such as drifts therefore also influence the re-acceleration process. It is found that re-accelerated electrons make appreciable contributions to intensities in the heliosphere and that increases caused by DSA at the TS are comparable to intensity enhancements observed by Voyager1 ahead of the TS crossing. The modeling results are interpreted as support for DSA as a re-acceleration mechanism for galactic electrons at the TS.

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“…They could be accelerated at the flanks, the tail, or other hotspots on the termination shock [17,18,19]. Other proposed sources include compressive acceleration near the heliopause due to increased turbulence [20], reconnection in the heliosheath and at the heliopause [21], adiabatic heating and/or stochastic acceleration in the heliosheath [22], and a focused acceleration in non-uniform magnetic fields [23]. Further observations and analyses may help determine the location and process responsible for ACR acceleration.…”

Section: Anomalous Cosmic Raysmentioning

confidence: 99%

Our heliosphere: The new view from Voyager

Stone¹

2013

AIP Conference Proceedings

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Abstract. Launched in 1977 on a journey to the giant outer planets and beyond, Voyager 1 and 2 have explored the spatial and dynamical properties of the heliosphere that modulates the inward flow of galactic cosmic rays and is the source of anomalous cosmic rays. The two spacecraft are in the heliosheath beyond the termination shock where the supersonic solar wind has slowed as it approaches the boundary of the heliosphere. The shock crossing was 10 AU closer at Voyager 2 in the south than at Voyager 1 in the north, indicating a local interstellar magnetic field pressing inward more strongly on the southern hemisphere. The expected source of anomalous cosmic rays was not observed at the shock, and their intensity has increased deeper in the heliosheath, indicating the source is elsewhere on the shock or in the heliosheath. Voyager 1, now at 121 AU at 35 degrees north, has been in a quasi-stagnation region since 2010 where there is no outward motion of the wind, the magnetic field is enhanced, and the galactic cosmic ray intensity is increasing. In contrast, the heliosheath flow at Voyager 2 at 99 AU and 30 degrees south is faster and increasingly deflected in a non-radial direction as it turns to flow tailward. These observations will be placed in the context of current models of the interaction of the solar and interstellar winds.

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Modelling anomalous cosmic ray oxygen in the heliosheath

Cited by 36 publications

References 51 publications

Time-Dependent Modulation of Cosmic Rays in the Heliosphere

Time-Dependent Modulation of Cosmic Rays in the Heliosphere

The Re-Acceleration of Galactic Electrons at the Heliospheric Termination Shock

Our heliosphere: The new view from Voyager

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