Solar cycle variations of cosmic ray intensity and large-scale structure of the heliosphere

Agrawal, SantP.

doi:10.1007/bf00194622

Cited by 13 publications

(6 citation statements)

References 3 publications

(4 reference statements)

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“…In 1974, the year of high speed solar wind streams (HSSWS), a remarkable change in the variation of cosmic rays is observed. These results are consistent with the results reported before (Agrawal 1983;Shrivastava 1990;Agrawal et al 1993;EL-Borie 1995;EL-Borie et al 1995). Fig.…”

supporting

confidence: 96%

Diurnal variations of cosmic rays during a solar magnetic cycle

1996

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We have used data from five neutron monitor stations with primary rigidity (Rm) ranging from 16 GeV to 33 GeV to study the diurnal variations of cosmic rays over the period: 1965-1986 covering one 22-year solar magnetic cycle. The heliosphere interplanetary magnetic field (IMF) and plasma hourly measurements taken near Earth orbit, by a variety of spacecraft, are also used to compare with the results of solar diurnal variation. The local time of maximum of solar diurnal variations displays a %year cycle due to the solar polar magnetic field polarities. In general, the annual mean of solar diurnal amplitudes, magnitude of IMF and plasma parameters are found to show separate solar cycle variations. Moreover, during the declining period of the twenty and twenty-one solar cycles, large solar diurnal amplitudes are observed which associated with high values of solar wind speed, plasma temperature and interplanetary magnetic field magnitude B3.

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confidence: 96%

Diurnal variations of cosmic rays during a solar magnetic cycle

1996

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“…An idea of the phase of diurnal anisotropy begins from the previous studies (Forbush, 1967(Forbush, , 1969(Forbush, , 1981Duggal, Forbush, andPomerantz, 1970a, 1970b;Agrawal, 1983). That is, the intensity of high-energy particles is controlled by the diffusion effect due to the magnitude of IMF.…”

Section: Discussionmentioning

confidence: 97%

“…We analyzed the hourly GCR intensity data archived at the Huancayo (Haleakala), Rome and Oulu NM stations, and examined the latitudinal effect (cut-off rigidity effect) mentioned by Agrawal (1983) on the phase. We used the data from the Huancayo NM station for the period of 1953 -1991 and the data for the period of 1992 -2006 from the Haleakala NM station as the replacement of the Huancayo NM station.…”

Section: Methods and Datamentioning

confidence: 99%

“…Thus, the interpretation of the mechanism in the diurnal variation is still a matter of debate (Bieber, Evenson, and Matthaeus, 1987;Potgieter and Burger, 1990). Agrawal (1983) suggested that the effective parameters determining the diurnal anisotropy are the rigidity of particles (the energy-dependent phase shift) and B × ∇n p (IMF varying with the sunspot cycle and particle density gradient associated with the reversal of the solar poloidal field). The previous studies on the diurnal variation are concentrated on the mechanism and anisotropy of the diurnal variations.…”

Section: Introductionmentioning

confidence: 99%

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Modulation Cycles of Galactic Cosmic Ray Diurnal Anisotropy Variation

Bieber

2010

Sol Phys

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The diurnal variation of the galactic cosmic ray (GCR) count rates measured by a ground-based neutron monitor (NM) station represents an anisotropic flow of GCR at 1 AU. The variation of the local time of GCR maximum intensity (we call the phase) is thought in general to have a period of two sunspot cycles (22 years). However, other interpretations are also possible. In order to determine the cyclic behavior of GCR anisotropic variation more precisely, we have carried out a statistical study on the diurnal variation of the phase. We examined 54-year data of Huancayo (Haleakala), 40-year data from Rome, and 43-year data from Oulu NM stations using the 'pile-up' method and the F -test. We found that the phase variation has two components: of 22-year and 11-year cycles. All NM stations show mainly the 22-year phase variation controlled by the drift effect due to solar polar magnetic field reversal, regardless of their latitudinal location (cut-off rigidity). However, the lower the NM station latitude is (the higher the cut-off rigidity is), the higher is the contribution from the 11-year phase variation controlled by the diffusion effect due to the change in strength of the interplanetary magnetic fields associated with the sunspot cycle.

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“…In other words, they assumed a common rigidity spectrum for two ecliptic components, parallel and perpendicular to the IMF. Bieber & Chen (1991) (hereafter referred as Paper II), on the other hand, also reported that the magnitude of the observed phase variation in A > 0 solar minimum increases with GCR rigidity (Agrawal 1983). This rigidity dependent feature of the observed phase variation cannot be reproduced properly, as long as the rigidity spectrum common for two ecliptic components is assumed.…”

Section: Introductionmentioning

confidence: 99%

Long-Term Variation of the Solar Diurnal Anisotropy of Galactic Cosmic Rays Observed With the Nagoya Multi-Directional Muon Detector

Munakata

Kozai

Kato

et al. 2014

ApJ

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We analyze the three dimensional anisotropy of the galactic cosmic ray (GCR) intensities observed independently with a muon detector (MD) at Nagoya in Japan and neutron monitors over four solar activity cycles. We clearly see the phase of the free-space diurnal anisotropy shifting toward earlier hours around solar activity minima in A > 0 epochs, due to the reduced anisotropy component parallel to the mean magnetic field. This component is consistent with a rigidity independent spectrum, while the perpendicular anisotropy component increases with GCR rigidity. We suggest that this harder spectrum of the perpendicular component is due to contribution from the drift streaming. We find that the bidirectional latitudinal density gradient is positive in A > 0 epoch, while it is negative in A < 0 epoch, in accord with the drift model prediction. The radial density gradient of GCRs, on the other hand, varies with ∼11-year cycle with maxima (minima) in solar maximum (minimum) periods, but we find no significant difference between the radial gradients in A > 0 and A < 0 epochs.The corresponding parallel mean free path is larger in A < 0 than in A > 0.We also find, however, that parallel mean free path (radial gradient) appears to persistently increase (decreasing) in the last three cycles of weakening solar activity. We suggest that simple differences between these parameters in A > 0 and A < 0 epochs are seriously biased by these long-term trends.

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Solar cycle variations of cosmic ray intensity and large-scale structure of the heliosphere

Cited by 13 publications

References 3 publications

Diurnal variations of cosmic rays during a solar magnetic cycle

Diurnal variations of cosmic rays during a solar magnetic cycle

Modulation Cycles of Galactic Cosmic Ray Diurnal Anisotropy Variation

Long-Term Variation of the Solar Diurnal Anisotropy of Galactic Cosmic Rays Observed With the Nagoya Multi-Directional Muon Detector

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