Change in the eleven-year modulation at the time of the June 8, 1969, Forbush decrease

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

doi:10.1029/ja077i025p04839

Cited by 25 publications

(16 citation statements)

References 9 publications

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“…This identity in both slope and magnitude between short term variations separated by one year is to be expected if a unique relationship exists but it would be unlikely to occur accidentally. The observations of Lockwood, Lezniak and Webber (1972), which refer to integral flux above 60 MeV per nucleon, do not display the inverse relationship emphasized here. However, the very weak dependence upon neutron rate exhibited by this flux between June 1969 and June 1971 is to be expected when a few low energy particles following a steep inverse relationship are mixed together with higher energy particles having a positive correlation.…”

Section: Introductionmentioning

confidence: 84%

Modulation of cosmic ray protons and helium nuclei near solar maximum

Rygg

O’Gallagher²,

Earl³

1974

J. Geophys. Res

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Balloon observations of proton and helium spectra in 1970, 1971 and 1972, which (1970)(1971)(1972).Computer generated spectra based on simple two parameter modulation models describe the basic features of the observations if one of the variable parameters is used to characterize the rigidity dependence of the diffusion coefficient. On the other hand, models which do not allow such a variation are not consistent with the observations.

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Section: Introductionmentioning

confidence: 84%

Modulation of cosmic ray protons and helium nuclei near solar maximum

Rygg

O’Gallagher²,

Earl³

1974

J. Geophys. Res

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“…1. Observation of a high depression of the cosmic-ray particles at low cut-off rigidities (<0.6 GV) during the recovery phase has been previously reported (e.g., Lockwood, 1971;Lockwood et al, 1972;Ifedili, 1973;Iucci et al, 1974;Ifedili, 1996b). However, no attempts have been made to identify the interplanetary conditions that caused the unusually long recovery of the FD that occurred at 1 AU on June 8, 1969.…”

Section: The Forbush Decreases and Interplanetary Disturbancesmentioning

confidence: 92%

“…(a) about July 25 at Kula (P c = 13.3 GV) as obtained from figure 1 of Lockwood et al (1972) (b) August 13 at Mt. Washington (P c = 1.24 GV) as in Fig.…”

Section: Dependence Of Length Of Recovery On Energymentioning

confidence: 99%

“…In order to understand this feature in the framework of the quasi-stationary model for the galactic cosmic ray modulation, some researchers needed to introduce abrupt change in either energy dependence of the modulation function (Lockwood et al, 1972) or distribution of solar activity on the solar disk (Iucci et al, 1974). This paper proposes an alternative and new idea to understand the unusually long recovery phase of the FD in terms of the recurring intensity depressions due to the long-lived corotating solar wind streams (CSWSs) superposed on the recovery phase of the FD.…”

Section: Introductionmentioning

confidence: 99%

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Forbush decrease of June 8, 1969: Causes of the unusually long recovery

Ifedili

2014

Earth Planet Sp

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The cosmic-ray decreases and interplanetary disturbances, that occurred at 1 AU during the period, June 8-July 21, 1969, have been investigated by using the cosmic-ray intensity data recorded with ground-based monitors at Mt. Washington and Deep River, as well as the Interplanetary Magnetic Field (magnitude and direction) and the Solar Wind Plasma bulk speed, density and temperature at 1 AU. We observed a two-step Forbush decrease on June 8-9, 1969, which was due to the structure within the shock and sheath preceding the interplanetary coronal mass ejection. We also observed two cosmic-ray depressions on June 16-20 and July 13-15, 1969, which were attributed to a long-lived corotating high-speed solar wind stream. The outward propagating interplanetary shock waves that occurred at about 0700 UT on June 16, 1969, and at about 1400 UT on July 13, 1969 and which were associated with the long-lived corotating high-speed solar wind stream, most probably swept away the galactic cosmic rays, causing the delay in the Forbush decrease recovery at 1 AU, and, hence, the unusually long recovery of the two-step Forbush decrease at 1 AU with onset on June 8, 1969. The additional depressions by the interplanetary shocks associated with the long-lived corotating high-speed solar wind streams which were superposed on the recovery phase of the Forbush decrease of June 8, 1969, were shown to be larger on the lower energy galactic cosmic-ray particles, and therefore the duration of the recovery phase would be much longer in the lower energy region, an expectation which is consistent with the observations.

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“…Low-energy (60 MeV/nucleon) cosmic ray protons and helium nuclei were measured on board the Imp 4 and Imp 5 satellites by Van Hollebeke et al [1972,1973], whereas the University of Chicago experiment on board the same satellites observed these particles in the 40-to 90-MeV/nucleon energy range [Garcia-Munoz et al, 1973]. Proton integral intensities around last solar maximum have been obtained by Lockwood et al [1972Lockwood et al [ , 1973 for energies above 60 MeV/nucleon and by Burger andSwanenburg [1973a, 1974] for energies above 400 MeV/nucleon. All these observations reveal the presence of a hysteresis effect in cosmic ray modulation, or, in other words, a time lag in the maximum of modulation between low-and high-energy cosmic ray particles (see the detailed discussion on the identity of hysteresis and time lag by Rygg et al [1974]).…”

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confidence: 99%

Long-term cosmic ray modulation in the period 1966-1972 and interplanetary magnetic fields

Winkler¹,

Bedijn²

1976

J. Geophys. Res.

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The changes in the energy spectra of cosmic ray electrons, protons, and α particles above roughly 50 MeV/nucleon, as observed during the period 1966–1972, have all been theoretically reproduced by numerical solutions of the steady state transport equation for cosmic rays in the solar system. These solutions have been obtained by smoothly varying the rigidity and radial dependence in a nonseparable model of the interplanetary diffusion coefficient, which is characterized by four parameters. The diffusion coefficient which is implied by these numerical solutions is then compared with the observed power spectra of interplanetary magnetic field fluctuations, validity of the quasi‐linear adiabatic theory being assumed. It appears that the changes occurring in the two observables, i.e., diffusion coefficient and magnetic power spectra, agree qualitatively surprisingly well. Uncertainties and simplifying assumptions implied in the theory and data do not permit comparison of the two observables in absolute magnitude with good accuracy, but it is shown that they are not in conflict. It is concluded that the nonseparable model used for the diffusion coefficient matches, within the limitations of theoretical and observational accuracy, the available data of cosmic ray modulation as well as of interplanetary magnetic field fluctuations.

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Change in the eleven-year modulation at the time of the June 8, 1969, Forbush decrease

Cited by 25 publications

References 9 publications

Modulation of cosmic ray protons and helium nuclei near solar maximum

Modulation of cosmic ray protons and helium nuclei near solar maximum

Forbush decrease of June 8, 1969: Causes of the unusually long recovery

Long-term cosmic ray modulation in the period 1966-1972 and interplanetary magnetic fields

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