Form of the anomalous cosmic ray spectrum at the solar wind termination shock

Steenberg, Conrad; Moraal, H.

doi:10.1029/1999ja900336

Cited by 34 publications

(33 citation statements)

References 19 publications

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“…More realistic parameters would yield results that are quantitatively different, but still qualitatively similar. This paper is an extension of the work published in [17,20].…”

Section: Introductionmentioning

confidence: 82%

“…It was found that for a wide range of parameters [17,20] that the cutoff in the shock spectrum occurs where (6) …”

Section: Transport and Acceleration Of Cosmic Raysmentioning

confidence: 99%

“…This number is higher than the lower limit of C c -1, in (5), which may be due to the effects of adiabatic energy losses not being taken into account in that estimate, or may simply be dependent on the criterion used to determine the cutoff energy. In comparison [17,20] obtained a value of C « 10, by essentially taking the smallest detectable deviation from a power law to indicate a cutoff. ACR O + shock spectra (top) and at 60 AU (bottom) for (i) baseline solution with 5 -4, (ii) s = 2.5, (iii) solution with X rr0 = 1.…”

Section: The Power Law Spectrum and Cutoffmentioning

confidence: 99%

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The morphology of anomalous cosmic rays in the outer heliosphere

Steenberg¹

2000

AIP Conference Proceedings

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Abstract. The well established cosmic ray transport equation describes the physics of cosmic ray modulation in the heliosphere and is thought to be complete. Its solution for anomalous cosmic rays has special characteristics due to the local acceleration of these particles at the solar wind termination shock. Some of these characteristics are demonstrated here, namely effects by the strength of the shock, shock drift, the cutoff in the spectrum at the shock, species scaling, drift, and ionization.

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“…More realistic parameters would yield results that are quantitatively different, but still qualitatively similar. This paper is an extension of the work published in [17,20].…”

Section: Introductionmentioning

confidence: 82%

“…It was found that for a wide range of parameters [17,20] that the cutoff in the shock spectrum occurs where (6) …”

Section: Transport and Acceleration Of Cosmic Raysmentioning

confidence: 99%

Section: The Power Law Spectrum and Cutoffmentioning

confidence: 99%

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The morphology of anomalous cosmic rays in the outer heliosphere

Steenberg¹

2000

AIP Conference Proceedings

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“…Near the equatorial plane, θ > 60 • , this power law persists up to ∼10 MeV nuc −1 in the equatorial plane, where the ACR rollover is observed. This almost exponential decay in intensity is believed to occur predominantly due to the curvature of the TS (Steenberg & Moraal 1999) leading to ineffective Fermi I acceleration above these energies. Near the polar regions however, the spectra exhibit a highly modulated form for E > 0.1 MeV nuc −1 .…”

Section: Latitude Dependent S(θ) and I(θ)mentioning

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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“…With increasing energy, intensities eventually start to fall away almost exponentially. The energy at which this deviation in the power law spectrum occurs is referred to as the cut-off or roll-over energy determined by, amongst others, the curvature of the shock front (Steenberg & Moraal 1999;Langner & Potgieter 2007). The spectra at Earth illustrate the corresponding modulated roll-over intensities; below ∼10 MeV nuc −1 these spectra are dominated by adiabatic cooling giving rise to the well-known j ∝ E spectral shapes.…”

Section: Modelling Results and Discussionmentioning

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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Form of the anomalous cosmic ray spectrum at the solar wind termination shock

Cited by 34 publications

References 19 publications

The morphology of anomalous cosmic rays in the outer heliosphere

The morphology of anomalous cosmic rays in the outer heliosphere

Modelling anomalous cosmic ray oxygen in the heliosheath

The heliospheric transport and modulation of multiple charged anomalous oxygen revisited

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