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Open Access

Coexistence of cosmic-ray sidereal anisotropies originating in galactic space and at the heliomagnetospheric nose and tail boundaries, observed with muon detectors in the energy region of 60100 GeV

Earth, Planets and Space200658:BF03352648

Received: 30 March 2005

Accepted: 24 June 2006

Published: 25 December 2006


The coexistence of two kinds of cosmic-ray sidereal anisotropy was found by observations with underground muon telescopes in the energy region (> 200 GeV) in 1995: one is the galactic anisotropy with a deficit flux in the direction with right ascension α G = 12 hr and declination δ G = 20°. The other is the excess flux from the heliomagnetospheric tail direction (α T 6 hr) and would be produced on the heliotail boundary where it is considered that the interaction between the galactic and solar magnetic fields could produce the cosmic-ray acceleration. On the other hand, another anisotropy of helioboundary origin from the helionose direction (α 18 hr), being accompanied by the heliotail-in anisotropy, was found through the observations with neutron monitors in the low energy region (20 GeV) in 2005. These observations, however, lack information in the mid-energy region (20200 GeV). In order to bridge the absence of information, the cosmic-ray sidereal daily variations in the energy regions (60100 GeV) have been derived from the observations with muon telescopes and ion chambers on the ground in the period 1936–2003. It is shown that all the three anisotropies coexist in this energy region and are subject to their respective solar modulations. On the basis of these modulations, the characteristics of the anisotropies are determined through intercomparison with the observations in the high and low energy regions.

Key words

Cosmic-ray sidereal anisotropyheliomagnetosphere (HMS)boundary of HMSpolarity of HMSsolar modulation