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 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
Author:	Humble, JE (Dr John Humble)
Author:	Fenton, AG (Dr Geoff Fenton)
Author:	Fenton, KB (Dr Peter Fenton)
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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