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Enhanced sidereal diurnal variation of galactic cosmic rays observed by the two-hemisphere network of surface level muon telescopes


Munakata, K and Kitawada, T and Yasue, S and Mori, S and Kato, C and Koyama, M and Akahane, S and Hall, DL and Fujii, Z and Fujimoto, K and Humble, JE and Fenton, AG and Fenton, KB and Duldig, ML, Enhanced sidereal diurnal variation of galactic cosmic rays observed by the two-hemisphere network of surface level muon telescopes, Journal of Geophysical Research, 104, (A2) pp. 2511-2519. ISSN 0148-0227 (1999) [Refereed Article]

DOI: doi:10.1029/1998JA900057


Significant enhancements of the cosmic ray sidereal diurnal variation were observed during the period 1992-1995 by the two-hemisphere network of surface-level multidirectional muon telescopes at Hobart (Tasmania, Australia) and Nagoya (Aichi, Japan). The telescopes cover the primary cosmic ray rigidity range of 50-120 GV. Since the enhancement is less prominent in the higher rigidity range (150-550 GV) covered by the shallow underground observations at Misato and Sakashita, it is concluded that the enhancement was caused by significant solar modulation in the lower energy region. Observed sidereal diurnal variations, corrected for spurious variations by a procedure proposed by Nagashima, give a space harmonic vector with amplitude of 0.104 ± 0.008% at 60 GV and maximum at 6.9 ± 0.3 hour local sidereal time. The time of maximum is consistent with northward streaming of cosmic rays perpendicular to the ecliptic plane. Such a north-south anisotropy is expected from cross-field ξNS = -λ⊥ Gθ diffusion if both the cross-field mean-free-path λ⊥ and the southward directed unidirectional latitudinal density gradient Gθ have large enough magnitudes. It is shown that the sector-dependent solar diurnal variations are also enhanced in the period, consistent with Gθ being directed south of the ecliptic plane. Magnitudes of Gθ and λ⊥ derived from the observations are discussed. Copyright 1999 by the American Geophysical Union.

Item Details

Item Type:Refereed Article
Research Division:Physical Sciences
Research Group:Astronomical sciences
Research Field:High energy astrophysics and galactic cosmic rays
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the physical sciences
UTAS Author:Humble, JE (Dr John Humble)
UTAS Author:Fenton, AG (Dr Geoff Fenton)
UTAS Author:Fenton, KB (Dr Peter Fenton)
UTAS Author:Duldig, ML (Dr Marc Duldig)
ID Code:16079
Year Published:1999
Web of Science® Times Cited:4
Deposited By:Physics
Deposited On:1999-08-01
Last Modified:2000-05-20

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