File(s) not publicly available
Enhanced sidereal diurnal variation of galactic cosmic rays observed by the two-hemisphere network of surface level muon telescopes
journal contributionposted on 2023-05-16, 11:36 authored by Munakata, K, Kitawada, T, Yasue, S, Mori, S, Kato, C, Koyama, M, Akahane, S, Hall, DL, Fujii, Z, Fujimoto, K, John Humble, Fenton, AG, Fenton, KB, Marcus DuldigMarcus Duldig
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 Â± 0.008% at 60 GV and maximum at 6.9 Â± 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 Î¾NS = -Î»âŠ¥ GÎ¸ diffusion if both the cross-field mean-free-path Î»âŠ¥ and the southward directed unidirectional latitudinal density gradient GÎ¸ have large enough magnitudes. It is shown that the sector-dependent solar diurnal variations are also enhanced in the period, consistent with GÎ¸ being directed south of the ecliptic plane. Magnitudes of GÎ¸ and Î»âŠ¥ derived from the observations are discussed. Copyright 1999 by the American Geophysical Union.
Publication titleJournal of Geophysical Research
Department/SchoolSchool of Natural Sciences
PublisherAmerican Geophysical Union
Place of publicationWashington DC