Solar modulation of cosmic ray protons, helium nuclei, and electrons: A comparison of experiment with theory

Lezniak, J. A.; Webber, W. R.

doi:10.1029/ja076i007p01605

Cited by 66 publications

(30 citation statements)

References 27 publications

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“…Its magnitude, however, is smaller than many previous choices for K, but is chosen so that the maximum of the modulated intensity spectrum for protons at 1 AU occurs at -400 MeV, in agreement with spectra observed near solar maximum (e.g. Lezniak and Webber, 1971). …”

Section: An Illustrative Numerical Solutionmentioning

confidence: 75%

Solar modulation of galactic cosmic rays: 3. Implications of the Compton-Getting Coefficient

Fisk

Forman²,

Axford

1973

J. Geophys. Res.

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It is useful to express spectra of modulated galactic cosmic rays in terms of the Compton‐Getting coefficient C. This parameter can reveal the energy range over which the force field approximation is valid and the range where convection effects dominate over those of diffusion. A value of C near zero over an extended low‐energy range (according to recent observations this is the situation for protons) implies that the radial gradient at low energies cannot be large. This small gradient may imply, in turn, that the diffusion coefficient increases beyond 1 AU less rapidly than if it were proportional to heliocentric radial distance and/or that there is essentially no scattering for a sizeable distance from the sun to earth. The behavior of C with rigidity (or energy) is discussed in terms of the omnidirectional distribution function ƒ0. Contours of constant ƒ0 in the heliocentric distance versus rigidity plane are useful for illustrating the mean rigidity loss experienced by cosmic rays in the interplanetary medium.

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Section: An Illustrative Numerical Solutionmentioning

confidence: 75%

Solar modulation of galactic cosmic rays: 3. Implications of the Compton-Getting Coefficient

Fisk

Forman²,

Axford

1973

J. Geophys. Res.

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“…Secondly, observations of Webber (1967) and Lezniak and Webber (1971) have shown a splitting in the fractional modulation between protons and helium nuclei at low rigidities, with a greater modulation for protons than helium.…”

Section: Past Tests Of Theorymentioning

confidence: 99%

“…(This will also be discussed below.) Thus, although shown by Lezniak and Webber (1971) to account for the splitting in the modulation of protons and helium nuclei for the years 1965 and 1968. They employed a diffusion coefficient increasing exponentially with radius and a magnitude approximately equal that of Fisk (1971).…”

Section: Past Tests Of Theorymentioning

confidence: 99%

Modulation of low-energy cosmic rays

Sari¹

1975

J. Geophys. Res.

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Recent theories have related the diffusion of cosmic rays in the solar wind to the power spectrum of interplanetary magnetic field fluctuations. In this study the power spectrum‐diffusion coefficient relation for low‐energy protons (T < 80 MeV) is tested directly, and the relative contribution to the scattering from directional discontinuities in the magnetic field is examined. Modulation parameters Vw/Krr, the solar wind speed divided by the radial diffusion coefficient, are calculated from Pioneer 6 magnetic field and solar wind data and are compared with simultaneous Imp 3 observations of the 20‐ to 80‐MeV proton flux. Daily variations in the 40‐ to 80‐MeV proton flux are found to respond to changes in Vw/Krr, as is predicted by a perturbation solution of the Fokker‐Planck equation once the contribution from directional discontinuities in the magnetic field is subtracted from the diffusion coefficients. This finding is interpreted to imply that a large percentage of the identified discontinuities are basically tangential. A lack of correlation between the 20‐ to 40‐MeV flux and the parameter changes is interpreted as being due to either the invalidity of the theory at lower energies or the presence of a continuous flux of high‐energy solar protons. A well‐defined time lag between changes in the 60‐ to 80‐MeV proton flux and corresponding changes in Vw/Krr is observed during a period when the interplanetary magnetic field is predominantly radial and the Imp 3‐sun‐Pioneer 6 angle is greater than 10°. This lag is consistent with the interpretation of little or no cross‐field diffusion or a perpendicular diffusion coefficient less than 3 × 1019 cm²/s.

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“…Figure 2, adapted from Smart and Shea (1985) shows changes in the energy spectrum of cosmic rays from solar maximum to solar minimum. Almost all of the modulation is below 2 to 5 GeV, and the modulation about a factor of 2 near 1 GeV (see also Lezniak and Webber (1971)). The modulation of the energy spectrum is due to the lower energy cosmic rays, with smaller gyroradii in the solar wind magnetic fields, being more affected by the magnetic irregularities of CMEs.…”

Section: Solar Wind Modulation Of the Global Electric Circuitmentioning

confidence: 99%

Solar Wind Modulation of the Global Electric Circuit and Apparent Effects on Cloud Microphysics, Latent Heat Release, and Tropospheric Dynamics.

Tinslev

1996

J. geomagn. geoelec

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The solar wind modulation of the energy distribution and flux of galactic cosmic rays causes 1 l year cycles in the latitude distribution of air-earth current density in the global electric circuit. Similar changes occur with solar activity on the day to day time scale. At least 3 independent data sets correlate changes in tropospheric winds and vorticity with measured and modelled changes in air-earth current density in the troposphere. These are (1) the decadal oscillations in winter in the North Atlantic region, with period averaging I I ± 2 years over the last 120 years, and which appear to have been phase locked to the solar cycle except for a period of generally low solar activity prior to 1925; (2) the decrease in 500 mbar Vorticity Area Index (VAI) in winter at times of Forbush decreases of cosmic ray flux; and (3) decreases of 500 mbar VAI in winter at times of solar wind magnetic sector boundary passages, when volcanic aerosols from Agung and El Chicon were in the global stratosphere, together with solar wind sector modulated relativistic electron precipitation. One possible physical mechanism connecting changes in air-earth current density with changes in tropospheric dynamics is via the accumulation of electrostatic charge at cloud tops affecting the microphysics of ice nucleation and precipitation, with consequences for latent heat release and the intensification of winter cyclones.

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Solar modulation of cosmic ray protons, helium nuclei, and electrons: A comparison of experiment with theory

Cited by 66 publications

References 27 publications

Solar modulation of galactic cosmic rays: 3. Implications of the Compton-Getting Coefficient

Solar modulation of galactic cosmic rays: 3. Implications of the Compton-Getting Coefficient

Modulation of low-energy cosmic rays

Solar Wind Modulation of the Global Electric Circuit and Apparent Effects on Cloud Microphysics, Latent Heat Release, and Tropospheric Dynamics.

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