Solar modulation of galactic cosmic rays: 5. Time‐dependent modulation

Perko, J. S.; Fisk, L. A.

doi:10.1029/ja088ia11p09033

Cited by 98 publications

(67 citation statements)

References 16 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…In their model, the initial cosmic ray intensity, assumed to be a steady-state solution of a spherically symmetric approximation, is perturbed by increases in the IMF that propagate away from the Sun and cause a reduction in the GCR radial diffusion coefficient. The assumed inverse coupling of the IMF with cosmic ray spatial diffusion coefficients is consistent with the concept of propagating diffusive barriers first introduced theoretically by Perko and Fisk (1983). The flux decrease associated with these barriers is followed by a recovery caused by both diffusion mechanisms and the large-scale influence of drifts.…”

Section: Introductionsupporting

confidence: 53%

Oscillations in the open solar magnetic flux with a period of 1.68 years: imprint on galactic cosmic rays and implications for heliospheric shielding

Rouillard

Lockwood

2004

Ann. Geophys.

View full text Add to dashboard Cite

Abstract. An understanding of how the heliosphere modulates galactic cosmic ray (GCR) fluxes and spectra is important, not only for studies of their origin, acceleration and propagation in our galaxy, but also for predicting their effects (on technology and on the Earth's environment and organisms) and for interpreting abundances of cosmogenic isotopes in meteorites and terrestrial reservoirs. In contrast to the early interplanetary measurements, there is growing evidence for a dominant role in GCR shielding of the total open magnetic flux, which emerges from the solar atmosphere and enters the heliosphere. In this paper, we relate a strong 1.68-year oscillation in GCR fluxes to a corresponding oscillation in the open solar magnetic flux and infer cosmic-ray propagation paths confirming the predictions of theories in which drift is important in modulating the cosmic ray flux.

show abstract

Section: Introductionsupporting

confidence: 53%

Oscillations in the open solar magnetic flux with a period of 1.68 years: imprint on galactic cosmic rays and implications for heliospheric shielding

Rouillard

Lockwood

2004

Ann. Geophys.

View full text Add to dashboard Cite

show abstract

“…Concerning the theoretical description of long-term cosmic-ray modulation, it was shown by Perko and Fisk (1983) and le Roux and that in order to describe cosmic-ray modulation over long periods, some form of propagating diffusion barriers is required. This is especially true for solar maximum activity periods when step decreases in cosmic-ray intensities are observed.…”

Section: Introductionmentioning

confidence: 99%

Time-Dependent Modulation of Cosmic Rays in the Heliosphere

2013

View full text Add to dashboard Cite

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.

show abstract

“…An outstanding problem in modulation research is that what parameters vary throughout the solar cycle is not clear. Perko and Fisk [1984] have reported results of time dependent, spherically symmetric, numerical solutions of the modulation equations that begin to address this problem. The importance of drifts in the time dependence of the modulation has been emphasized by Isenberg and Jokipii (1978, 19791;Jokipii and Kopriva [1979]; and among others.…”

Section: Introductionmentioning

confidence: 99%

Power spectral signatures of interplanetary corotating and transient flows

Goldstein¹,

Burlaga²,

Matthaeus³

1984

J. Geophys. Res.

View full text Add to dashboard Cite

Recent studies of the time behavior of the galactic cosmic ray intensity have concluded that long term decreases in the intensity are generally associated with systems of interplanetary flows that contain flare‐generated shock waves, magnetic clouds, and other transient phenomena. In this paper the magnetic field power spectral signatures of such flow systems are compared to power spectra obtained during times when the solar wind is dominated by stable corotating streams that do not usually produce long‐lived reductions in the cosmic ray intensity. We find that the spectral signatures of these two types of regimes (transient and corotating) are distinct. However, the distinguishing features are not the same throughout the heliosphere. The transient flows at 1 AU tend to have smaller correlation lengths and larger magnetic helicity scale lengths than do the corotating flows. In data collected beyond 1 AU, the primary differences are in the power spectra of the magnitude of the magnetic field rather than in the power in the field components. Consequently, decreases in cosmic ray intensity are very likely due to magnetic mirror forces and gradient drifts rather than to pitch angle scattering.

show abstract

Solar modulation of galactic cosmic rays: 5. Time‐dependent modulation

Cited by 98 publications

References 16 publications

Oscillations in the open solar magnetic flux with a period of 1.68 years: imprint on galactic cosmic rays and implications for heliospheric shielding

Oscillations in the open solar magnetic flux with a period of 1.68 years: imprint on galactic cosmic rays and implications for heliospheric shielding

Time-Dependent Modulation of Cosmic Rays in the Heliosphere

Power spectral signatures of interplanetary corotating and transient flows

Contact Info

Product

Resources

About