Cosmic-ray diurnal anisotropy, 1936-1988 - Implications for drift and modulation theories

Journal Article · Wed May 01 04:00:00 EDT 1991 · Astrophysical Journal; (United States)

DOI:https://doi.org/10.1086/169976· OSTI ID:5589303

Bieber, J W; Chen, Jiasheng ^[1]

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1. Bartol Research Institute, Newark, DE (USA)

Data from five neutron monitor stations and one ionization-chamber station are employed to determine the variation of the cosmic-ray diurnal anisotropy over a time span exceeding 50 years. The amplitude of the diurnal anisotropy varies with a period of one sunspot cycle, while the phase varies with a period of two sunspot cycles. Using minimum-variance analysis, it is shown that the principal axis of variation of the anisotropy is nearly aligned with the mean magnetic field, in agreement with earlier conclusions of Forbush. These results provide new information on the long-term variation of cosmic-ray gradients. Taking nominal values for the parallel and perpendicular diffusion coefficients, it is found that the value of the radial gradient during epochs of negative solar magnetic polarity is persistently larger than during positive polarity epochs, while the bidirectional latitude gradient reverses sign with the solar magnetic polarity reversal. The behavior of both gradients favors the drift theory during solar minimum periods. 70 refs.

• OSTI ID: 5589303
• Journal Information: Astrophysical Journal; (United States), Journal Name: Astrophysical Journal; (United States) Vol. 372; ISSN ASJOA; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

640101* -- Astrophysics & Cosmology-- Cosmic Radiation
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ANISOTROPY
BARYONS
COSMIC RADIATION
DAILY VARIATIONS
ELEMENTARY PARTICLES
FERMIONS
GEOMAGNETIC FIELD
HADRONS
INTERPLANETARY MAGNETIC FIELDS
IONIZING RADIATIONS
MAGNETIC FIELDS
NEUTRONS
NUCLEONS
RADIATIONS
SOLAR ACTIVITY
SOLAR RADIATION
SOLAR WIND
STELLAR RADIATION
VARIATIONS