Three-dimensional cosmic ray anisotropy in interplanetary space. III. Origin of cosmic ray solar semi-diurnal variation

Journal Article · Thu Jun 01 04:00:00 EDT 1972 · Rep. Ionosphere Space Res. Jap., v. 26, no. 1-2, pp. 1-30

OSTI ID:4368408

Nagashima, K; Ueno, H; Fujimoto, K; Fujii, Z; Kondo, I

Annual modulation of cosmic-ray daily variation, observed by ion- chambers at Cheltenhan and Christchurch, were studied in order to determaine the anisotropy responsible for the solar semi-diurnal variation of cosmic rays. So far, two hypotheses have beenproposed for the explanation of the anisotropy. One is called the density gradient hypothesis which assumes the existence of cosmic- ray density gradient in the direction perpendicular to the ecliptic plane as a result of diffusion process. The other is called the pitch-angle distribution hypothesis which assumes a specific form of cosmic-ray pitch-angle distribution against the interplanetary magnetic line of force as a result of a particle's spiral motion along the direction. Although cosmic-ray space distributions, predicted from these hypotheses, are different from one another, they each produce semi-diurnal variation similar to the other's. Therefore, they cannot be discriminated from each other by observing simply the semi-diurnal variation. In order to determine the origin of the semi-diurnal variation, it is required to observe a special'' diurnal variation, characterizing these anisotropies. Different from the usual'' diurnal variation, the special'' variation shows a strange behavior that, in spite of its finite daily amplitude, its yearly average becomes very small or zero as a result of its annual modulation due to the Earth's revolution around the Sun. Because of this nature, it is necessary to observe the annual modulations of the special'' diurnal variation for the determaination of the origin. The present analysis of the annual modulation will give some decisive evidence which will lend support to the pitch-angle distribution hypothesis. (auth)

• Research Organization: Nagoya Univ., Japan
• NSA Number: NSA-29-013347
• OSTI ID: 4368408
• Journal Information: Rep. Ionosphere Space Res. Jap., v. 26, no. 1-2, pp. 1-30, Journal Name: Rep. Ionosphere Space Res. Jap., v. 26, no. 1-2, pp. 1-30; ISSN RISRA
• Country of Publication: Japan
• Language: English

Related Subjects

*COSMIC RADIATION-- DAILY VARIATIONS
*INTERPLANETARY SPACE-- ANISOTROPY
DIFFUSION
LEGENDRE POLYNOMIALS
MAGNETIC FIELDS
MODULATION
N56100* --Physics (Astrophysics & Cosmology)--Cosmic Radiation
N56400 --Physics (Astrophysics & Cosmology)--Solar Phenomena
SOLAR ATMOSPHERE
SPATIAL DISTRIBUTION
TEMPERATURE DEPENDENCE
THREE-DIMENSIONAL CALCULATIONS
VECTORS