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Publication Details
AFRICAN RESEARCH NEXUS
SHINING A SPOTLIGHT ON AFRICAN RESEARCH
earth and planetary sciences
Drift effects and the cosmic ray density gradient in a solar rotation period: First observation with the Global Muon Detector Network (GMDN)
Astrophysical Journal, Volume 681, No. 1, Year 2008
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Description
We present for the first time hourly variations of the spatial density gradient of 50 GeV cosmic rays within a sample solar rotation period in 2006. By inversely solving the diffusive flux equation, including the drift, we deduce the gradient from the anisotropy that is derived from the observation made by the Global Muon Detector Network (GMDN). The anisotropy obtained by applying a new analysis method to the GMDN data is precise and free from atmospheric temperature effects on the muon count rate recorded by ground-based detectors. We find the derived north-south gradient perpendicular to the ecliptic plane is oriented toward the heliospheric current sheet (HCS; i.e., southward in the toward sector of the interplanetary magnetic field [IMF] and northward in the away sector). The orientation of the gradient component parallel to the ecliptic plane remains similar in both sectors, with an enhancement of its magnitude seen after the Earth crosses the HCS. These temporal features are interpreted in terms of a local maximum of the cosmic ray density at the HCS. This is consistent with the prediction of the drift model for the A < 0 epoch. By comparing the observed gradient with the numerical prediction of a simple drift model, we conclude that particle drifts in the large-scale magnetic field play an important role in organizing the density gradient, at least in the present A < 0 epoch. We also found that corotating interaction regions did not have such a notable effect. Observations with the GMDN provide us with a new tool for investigating cosmic-ray transport in the IMF. © 2008. The American Astronomical Society. All rights reserved.
Authors & Co-Authors
Okazaki, Yasushi
Japan, Sendai
Tohoku University
Fushishita, A.
Japan, Matsumoto
Shinshu University
Narumi, T.
Japan, Matsumoto
Shinshu University
Kato, Chihiro
Japan, Matsumoto
Shinshu University
Yasue, S.
Japan, Matsumoto
Shinshu University
Kuwabara, Takao
United States, Newark
The Bartol Research Institute
Bieber, John William
United States, Newark
The Bartol Research Institute
Evenson, Paul Arthur
United States, Newark
The Bartol Research Institute
Rockenbach, M.
Brazil, Sao Jose Dos Campos
Instituto Nacional de Pesquisas Espaciais
Dal Lago, Alisson
Brazil, Sao Jose Dos Campos
Instituto Nacional de Pesquisas Espaciais
Schuch, Nelson Jorge
Brazil, Sao Jose Dos Campos
Instituto Nacional de Pesquisas Espaciais
Fujii, Z.
Japan, Nagoya
Nagoya University
Duldig, Marcus Leslie
Australia, Hobart
Australian Antarctic Division
Humble, John E.
Australia, Hobart
University of Tasmania
Sabbah, Ismail S.
Kuwait, Kuwait City
Kuwait University
Egypt, Alexandria
Faculty of Science
Kóta, József
United States, Tucson
The University of Arizona
Munakata, Kazuoki
Japan, Matsumoto
Shinshu University
Statistics
Citations: 48
Authors: 17
Affiliations: 10
Identifiers
Doi:
10.1086/588277
ISSN:
0004637X
e-ISSN:
15384357