Consequences of the Distribution of Galactic Cosmic-Ray Density in the Solar System

Subramanian, Ganesh; Sarabhai, V.

doi:10.1086/149266

Cited by 38 publications

(12 citation statements)

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“…However, the practical difficulties, caused by time variations of the cosmic ray intensity, instrumental drifts, and meteorological and environmental variations, are great. Consequently, the existence of the required density gradient which should manifest itself as an annual variation in the nucleonic intensity of about 1%, has not been confirmed (Subramanian, 1970).…”

Section: Semidiurnal Anisotropymentioning

confidence: 99%

“…Subramanian and Sarabhai (1967), ascribing this gradient to the distribution of Three cases of possible cosmic ray density distributions. Full galactic cosmic ray density is assumed for 0 = 90 ~ (Subramanian and Sarabhai, 1967).…”

Section: Semidiurnal Anisotropymentioning

confidence: 99%

“…For example, Subramanian and Sarabhai (1967) suggested that latitudinal gradients would produce a diurnal anisotropy with maximum amplitude at right angles to the mean spiral direction. A change in this gradient could cause day-to-day changes in the variational spectrum (cf.…”

Section: Transient Anisotropiesmentioning

confidence: 99%

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The cosmic ray solar diurnal anisotropy

Pomerantz

Duggal

1971

Space Sci Rev

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This paper reviews the present state of knowledge concerning the diurnal and semidiurnal variations in the galactic cosmic ray intensity. The analytical procedures that are required for extracting from the original data the desired information concerning the characteristics of the anisotropies outside the magnetosphere are described. These include corrections for atmospheric fluctuations, the determination of the amplitudes and phases of the daily variations, and their interpretation in terms of the free space anisotropies that give rise to them. The experimental results concerning the 24-h wave, including its long-term variations with periods of one and two solar cycles, and the characteristics of the total dmrnal anisotropy are then discussed. The semidmrnal amsotropy is considered next. Transient anisotropies which manifest themselves as day-to-day variations, recurrence tendencies, cosmic ray storms, and diurnal variation trains, and which can introduce appreciable changes in the spectral parameters, are also of interest. The evolution of theoretical models developed to account for the diurnal and semidiurnal anisotropies, and fluctuations thereof, are then discussed in the light of the experimental results. Finally, the general features that are now well established, and the nature of the remaining problems, are summarized.

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Section: Semidiurnal Anisotropymentioning

confidence: 99%

Section: Semidiurnal Anisotropymentioning

confidence: 99%

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The cosmic ray solar diurnal anisotropy

Pomerantz

Duggal

1971

Space Sci Rev

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“…The angular diameter θ of the gyro-orbit is related to the rigidity by the expression (Subramanian & Sarabhai 1967) …”

Section: Gradient Anisotropymentioning

confidence: 99%

Corotating Solar Wind Structures and Recurrent Trains of Enhanced Diurnal Variation in Galactic Cosmic Rays

Yeeram

Ruffolo

Sáiz

et al. 2014

ApJ

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Data from the Princess Sirindhorn Neutron Monitor at Doi Inthanon, Thailand, with a vertical cutoff rigidity of 16.8 GV, were utilized to determine the diurnal anisotropy (DA) of Galactic cosmic rays (GCRs) near Earth during solar minimum conditions between 2007 November and 2010 November. We identified trains of enhanced DA over several days, which often recur after a solar rotation period (∼27 days). By investigating solar coronal holes as identified from synoptic maps and solar wind parameters, we found that the intensity and anisotropy of cosmic rays are associated with the high-speed streams (HSSs) in the solar wind, which are in turn related to the structure and evolution of coronal holes. An enhanced DA was observed after the onset of some, but not all, HSSs. During time periods of recurrent trains, the DA was often enhanced or suppressed according to the sign of the interplanetary magnetic field B, which suggests a contribution from a mechanism involving a southward gradient in the GCR density, n, and a gradient anisotropy along B × ∇n. In one non-recurrent and one recurrent sequence, an HSS from an equatorial coronal hole was merged with that from a trailing mid-latitude extension of a polar coronal hole, and the slanted HSS structure in space with suppressed GCR density can account for the southward GCR gradient. We conclude that the gradient anisotropy is a source of temporary changes in the GCR DA under solar minimum conditions, and that the latitudinal GCR gradient can sometimes be explained by the coronal hole morphology.

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“…It is well established that the daily variation observed in local solar time has both diurnal (a pure sine wave with a period of 24 hours) and semidiurnal components. Subramanian and Sarabhai [1967] and Quenby and Lietti [1968] first attributed the semidiurnal component to a second-order anisotropy arising from a bidirectional latitudinal density gradient, in which cosmic ray density increases on both sides of the a higher population of particles exists. Analyzing the diurnal variations observed by neutron monitors and an ionization chamber over a time span exceeding 50 years, Bieber and Chen [1991] confirmed the existence of a bidirectional latitudinal density gradient which reversed with the solar magnetic polarity reversal at approximately every solar sunspot maximum period.…”

Section: Introductionmentioning

confidence: 99%

Solar semidiurnal anisotropy of galactic cosmic ray intensity observed by the two‐hemisphere network of surface‐level muon telescopes

Munakata¹,

Kitawada²,

Yasue³

et al. 1998

J. Geophys. Res.

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Abstract. Observations made by the two-hemisphere network of surface-level, multidirectional muon telescopes at Hobart (Tasmania, Australia) and Nagoya (Aichi, Japan) are used to examine the origin of the solar semidiurnal variation in cosmic ray intensity. The network allows us to precisely determine the asymmetry of the variation across both hemispheres. It is shown that the variation is consistent with the north-south (NS) symmetric distribution of cosmic ray intensity in space. The phase of the space harmonic vector responsible for the variation is consistent with both the second-order anisotropy expected from a bidirectional latitudinal density gradient (type I) and also one arising from pitch angle scattering (type II). The network also observed a purely NS antisymmetric, antisidereal diurnal variation with the maximum phases differing by 12 hours between the two hemispheres. This is consistent with an antisidereal diurnal variation arising from annual modulation of the solar diurnal variation produced by a second-order anisotropy. The phase of the space harmonic vector responsible for the antisidereal diurnal variation is consistent with the phases predicted from both type I and type II anisotropies. It is shown, however, that the ratio of the amplitude of the space harmonic vector of the antisidereal diurnal variation to that of the solar semidiurnal variations is consistent with the type II anisotropy but not with the type I anisotropy. This result implies that the solar semidiurnal variation and the antisidereal diurnal variation observed during the period 1992-1995 mainly arise from the type II anisotropy and cannot be explained solely as arising from the type I anisotropy. IntroductionGround-level cosmic ray detectors scan various directions in space as Earth rotates. The daily variation in their counting rates reflects the anisotropic intensity distribution of galactic cosmic rays in space. It is well established that the daily variation observed in local solar time has both diurnal (a pure sine wave with a period of 24 hours) and semidiurnal components.

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Consequences of the Distribution of Galactic Cosmic-Ray Density in the Solar System

Cited by 38 publications

References 0 publications

The cosmic ray solar diurnal anisotropy

The cosmic ray solar diurnal anisotropy

Corotating Solar Wind Structures and Recurrent Trains of Enhanced Diurnal Variation in Galactic Cosmic Rays

Solar semidiurnal anisotropy of galactic cosmic ray intensity observed by the two‐hemisphere network of surface‐level muon telescopes

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