Two intense Forbush decreases of solar activity cycle 22 |
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Authors: | HS Ahluwalia RC Ygbuhay ML Duldig |
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Institution: | 1. University of New Mexico, Department of Physics & Astronomy, MSC07 4220, 800 Yale Blvd NE, Albuquerque, NM 87131-1156, USA;2. Australian Antarctic Division, 203 Channel Highway, Kingston, Tasmania, 7050, Australia |
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Abstract: | We study two intense Forbush decreases that occurred during two adjacent SOLTIP (Solar connection of Transient Interplanetary Processes) intervals; namely SOLTIP 1 (22–27 March 1991) and SOLTIP 2 (1–17 June 1991); galactic cosmic ray intensity at the depth of the second Forbush decrease was the lowest ever recorded since continuous monitoring by Climax neutron monitor began in 1951 (58% below the solar minimum value of 1954), indicating extreme conditions in the heliosphere that prevented galactic cosmic rays from reaching the Earth. These decreases were seen propagating in outer heliosphere by the deep space missions Voyagers 1, 2 and Pioneer 10, 11, with suitable time delays. We analyze hourly, pressure corrected, neutron monitor data from the global sites in both hemispheres, and muon telescopes located underground; they respond to 10–300 GV range of the galactic cosmic ray spectrum. This circumstance provides us an ideal opportunity to study the rigidity dependence of the amplitudes of the two Forbush decreases. In both cases the amplitude is found to be a power law in rigidity, with negative exponents. |
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Keywords: | Forbush decrease Cycle 22 Galactic cosmic rays |
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