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Solar Cycle Variations of Modulation Parameters of Galactic Cosmic-Rays in the Heliosphere
Citation
Munakata, K and Miyasaka, H and Sakurai, I and Yasue, S and Kato, C and Akahane, S and Koyama, M and Hall, DL and Fujii, Z and Fujimoto, K and Sakakibara, S and Humble, JE and Duldig, ML, Solar Cycle Variations of Modulation Parameters of Galactic Cosmic-Rays in the Heliosphere, Advances in Space Research, 29, (10) pp. 1527-1532. ISSN 0273-1177 (2002) [Refereed Article]
DOI: doi:10.1016/S0273-1177(02)00205-3
Abstract
Solar cycle variations of modulation parameters are derived from cosmic-ray anisotropy observed by a network of multidirectional muon telescopes. The network covers wide ranges of median rigidity of primary cosmic-rays and effective latitude of viewing. It was found that the radial density gradient varies with a good correlation with the solar activity, while the parallel mean-free-path of the cosmic-ray diffusion varies with an anti-correlation with the solar activity. These features are both in accord with the conventional modulation theory incorporating convection and diffusion processes. The correlation coefficients of yearly mean values of radial density gradient and parallel mean-free-path with the sunspot number were respectively 0.7 and 0.6. The bi-directional latitudinal gradient showed a clear 22-year solar magnetic cycle as predicted by the drift model for the cosmic-ray transport in the heliosphere. The unidirectional latitudinal gradient, on the other hand, showed no clear variation related to the 11-year solar activity or 22-year solar magnetic-cycles, but it remains positive after the late 80's implying a higher density of cosmic-rays in the southern hemisphere below the heliospheric current sheet. We also analyze temporal variations of modulation parameters derived from neutron monitor observations at ~10 GV. By comparing with those obtained from muon observations at 60 GV, we discuss the rigidity dependence of temporal variations of modulation parameters. © 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved.
Item Details
| Item Type: | Refereed Article |
|---|---|
| Research Division: | Physical Sciences |
| Research Group: | Astronomical and Space Sciences |
| Research Field: | Galactic Astronomy |
| Objective Division: | Expanding Knowledge |
| Objective Group: | Expanding Knowledge |
| Objective Field: | Expanding Knowledge in the Physical Sciences |
| UTAS Author: | Humble, JE (Dr John Humble) |
| ID Code: | 24012 |
| Year Published: | 2002 |
| Web of Science® Times Cited: | 3 |
| Deposited By: | Physics |
| Deposited On: | 2002-08-01 |
| Last Modified: | 2003-05-07 |
| Downloads: | 0 |
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