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Enhanced sidereal diurnal variation of galactic cosmic rays observed by the two-hemisphere network of surface level muon telescopes
Citation
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]
Abstract
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 and Space Sciences |
| Research Field: | High Energy Astrophysics; 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 |
| Downloads: | 0 |
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