Streaming of galactic cosmic rays in the interplanetary magnetic field

Hashim, A.; Bercovitch, M.; Steljes, J. F.

doi:10.1007/bf00145475

Cited by 10 publications

(1 citation statement)

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“…The FD event consists of mainly main phase and recovery phase. Hereinafter, we use the term of main phase for the decreasing part in the GCR intensity time profile [ Hashim et al , 1972]. The main phase of a sudden decrease occurs in less than a half day, and the phase of recovery lasts several days.…”

Section: Introductionmentioning

confidence: 99%

Globally nonsimultaneous Forbush decrease events and their implications

Kim

2008

J. Geophys. Res.

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[1] Forbush decrease (FD) events are supposed to happen simultaneously over the globe of the Earth. However, there have been several reports on nonsimultaneous FD events. We investigate for the first time the properties of nonsimultaneous FD events and the solar wind conditions causing such events in detail in order to determine what solar wind conditions lead to global simultaneity of FD events. We examined the hourly data of the Oulu Neutron Monitor (NM) station from 1998 to 2002. We have selected 49 FD events that have greater than 3.5% intensity reductions. Global simultaneity was determined by comparing the time profiles of these FD events with those recorded by other NM stations at Inuvik and Magadan. These three NM stations are located at close magnetic latitude (cutoff rigidity) but fairly evenly spaced in longitudes. The solar wind parameters driving FD event main phase are studied. Most FD event onsets (37 out of 49) are observed simultaneously by each NM station in universal time (UT) regardless of the location of the station, whereas some other FD events are not simultaneously detected but are at similar local times (LT). The stronger FD events tend to be simultaneous events, but the weaker FD events are nonsimultaneous. The simultaneous FD events are caused by the solar wind of higher speed and stronger IMF, whereas the nonsimultaneous events are driven by relatively lower speed and weaker IMF solar wind. The nonsimultaneous FD event may occur only if the main phase of the FD is superposed in phase with the declining phase of diurnal variation. Our interpretation is that the simultaneous FD events might occur when the high-speed strong magnetic barrier (interplanetary shock sheath and magnetic cloud) overtakes the Earth, whereas the nonsimultaneous FD events may occur only when the slow-moving weak magnetic barrier passes by on the duskside of the Earth. The global simultaneity of FD events depends on speed and IMF strength of solar wind overtaking Earth's magnetosphere and its propagation direction. This model of FD simultaneity can be tested by the STEREO mission.

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Section: Introductionmentioning

confidence: 99%

Globally nonsimultaneous Forbush decrease events and their implications

Kim

2008

J. Geophys. Res.

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Measurement of the solar diurnal anisotropy of the cosmic-ray albedo neutron flux

Ifedili

1982

Sol Phys

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The solar diurnal anisotropy of the cosmic-ray albedo neutron flux has been measured by a neutron detector on board the OGO-6 satellite. On the average the diurnal amplitudes and phases of the cosmic ray albedo neutron flux (_<10 MeV) were respectively 0.18 (+0.02)% and 15(+1) hr LT though there were substantial fluctuations of a few days duration which did not depend on the solar sector structure polarity and a 27-day periodicity in the diurnal amplitudes which was associated with the Sun's rotation.

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