Effects of particle drift on cosmic-ray transport. I - General properties, application to solar modulation

Jokipii, J. R.; Levy, E. H.; Hubbard, W. B.

doi:10.1086/155218

Cited by 465 publications

(252 citation statements)

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“…Because the sign of the helium gradient at that time was opposite to that of ACR oxygen reported here, it suggests that curvature and gradient drifts, which are field-polarity dependent, are important in the propagation of cosmic rays as suggested by Jokipii et al [1977].…”

Section: Discussionmentioning

confidence: 46%

Latitudinal and radial gradients of anomalous and galactic cosmic rays in the outer heliosphere

Cummings

Stone

Webber

1987

Geophysical Research Letters

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Abstract. We have used measurements from instruments on Voyagers 1 and 2 and Pioneer 10 to derive simultaneous radial and latitudinal gradients of anomalous cosmic-ray oxygen during the latter part of 1985. We find that in the energy interval from 7.1-30.6 Me V /nucleon the latitudinal gradient is -3 to -4 %/deg. The sign of the latitudinal gradient is opposite to that reported for the last solar cycle when the solar magnetic field polarity was reversed, as predicted by propagation models in which curvature and gradient drifts are significant. The ratios of the radial and latitudinal gradients of anomalous oxygen, anomalous helium, and galactic cosmic rays are similar, also in agreement with drift theory ·predictions. Based on drift theory, these observed ratios, which are near unity, lead to estimates of Kif~ in the range of 3-8 x 10 22 cm 2 /sec at 24.9 AU for particles with rigidities of -2-3 GV.

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Section: Discussionmentioning

confidence: 46%

Latitudinal and radial gradients of anomalous and galactic cosmic rays in the outer heliosphere

Cummings

Stone

Webber

1987

Geophysical Research Letters

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“…We suggest that the 22-year cycle in GCR flux may be partly due to direct heliospheric modulation, although drift effects (Jokipii, Levy, and Hubbard, 1977;Ferreira and Potgeiter, 2004) will still play a role, particularly during the end of the polarity cycle (i.e., the rise phase of the solar cycle), when differences in heliospheric parameters are less apparent. Of course, while changes in heliospheric structure are coincident with the differing behaviour in cosmic ray flux in alternate polarity cycles, it still remains to be shown that they are of sufficient magnitude to effect the required modulation.…”

Section: Discussionmentioning

confidence: 88%

The 22-Year Hale Cycle in Cosmic Ray Flux – Evidence for Direct Heliospheric Modulation

2013

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The ability to predict times of greater galactic cosmic ray (GCR) fluxes is important for reducing the hazards caused by these particles to satellite communications, aviation, or astronauts. The 11-year solar cycle variation in cosmic rays is highly correlated with the strength of the heliospheric magnetic field. Differences in GCR flux during alternate solar cycles yield a 22-year cycle, known as the Hale Cycle, which is thought to be due to different particle drift patterns when the northern solar pole has predominantly positive (denoted a qA>0 cycle) or negative (qA<0) polarities. This results in the onset of the peak cosmic ray flux at Earth occurring earlier during qA>0 cycles than for qA<0 cycles and hence the peak being more domed for qA>0 and more sharply peaked for qA<0. In this study, we demonstrate that properties of the large-scale heliospheric magnetic field are different during the declining phase of the qA<0 and qA>0 solar cycles, when the difference in GCR flux is most apparent. This suggests that particle drifts may not be the sole mechanism responsible for the Hale Cycle in GCR flux at Earth. However, it is also demonstrated that these polarity-dependent heliospheric differences are evident during the space-age but much less clear in earlier data: using geomagnetic reconstructions, it is shown that for the period of 1905 -1965, alternate polarities do not give as significant a difference during the declining phase of the solar cycle. Thus we suggest that the 22-year cycle in cosmic ray flux is at least partly the result of direct modulation by the heliospheric magnetic field and that this effect may be primarily limited to the grand solar maximum of the space-age.

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“…Therefore, we can consider the HCS as a plane with TA = 0, i.e., the heliosphere is divided into two symmetric parts (hemispheres) by the HCS coinciding with the Sun's equatorial plane. We implement in our model the drift velocities due to the large-scale curvature and gradient of the average IMF on the HCS, which are represented by the derivative of the anti-symmetric part of the anisotropic diffusion tensor (Jokipii, Levy, and Hubbard, 1977;Jokipii and Kopriva, 1979). The ratios of the perpendicular (κ ⊥ ) and drift (κ d ) diffusion coefficients to the parallel (κ ) diffusion coefficient are assumed to have the forms β = κ ⊥ /κ = (1 + ω 2 τ 2 ) −1 and β 1 = κ d /κ = ωτ (1 + ω 2 τ 2 ) −1 , where τ is the collision time and ω = qB/mc is the gyro-frequency (q and m are particle's charge and mass, respectively, and c is the speed of light).…”

Section: Model Of the 27-day Variation Of The Gcr Intensity; Results mentioning

confidence: 99%

Theoretical and Experimental Studies of the Rigidity Spectrum of the 27-Day Variation of the Galactic Cosmic Ray Intensity in Different Epochs of Solar Activity

Gil

Alania

2012

Sol Phys

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We consider the recent, very exceptional, 11-year cycle (2003 -2009) of solar activity and confirm that the relative amplitude in rigidity spectrum, δD(R)/D(R), which can be approximated by a power law in rigidity R, of the first three harmonics of the 27-day variation of the galactic cosmic ray (GCR) intensity is hard in the maximum and soft in the minimum epochs of solar activity, as was found by neutron monitor data for the period of 1965 -2002. This property is seen not only in separate minimum and maximum epochs but in individual intervals of a solar Carrington rotation as well: There exist many individual intervals of solar rotation when the expected rigidity spectrum of the 27-day variation of the GCR intensity indeed is hard in the maximum epoch of solar activity and is soft in the minimum epoch. We then construct a three-dimensional model of the 27-day variation of the GCR intensity based on Parker's transport equation, by implementing in situ measurements of the changes in heliographic longitude of the solar wind velocity and interplanetary magnetic field for different epochs of solar activity.Keywords 27-days variation of the galactic cosmic rays intensity · Epochs of solar activity · Rigidity spectrum

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Effects of particle drift on cosmic-ray transport. I - General properties, application to solar modulation

Cited by 465 publications

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Latitudinal and radial gradients of anomalous and galactic cosmic rays in the outer heliosphere

Latitudinal and radial gradients of anomalous and galactic cosmic rays in the outer heliosphere

The 22-Year Hale Cycle in Cosmic Ray Flux – Evidence for Direct Heliospheric Modulation

Theoretical and Experimental Studies of the Rigidity Spectrum of the 27-Day Variation of the Galactic Cosmic Ray Intensity in Different Epochs of Solar Activity

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