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|Title:||Solar cycle dependence of low amplitude anisotropic wave train events|
|Authors:||Mishra, Rajesh K|
Mishra, Rekha Agarwal
|Keywords:||Cosmic ray;Solar cycle;Sunspot;Anisotropy|
|Abstract:||A large number of low amplitude anisotropic wave train events (LAEs) of cosmic ray diurnal anisotropy have been studied during 1980-1994 as a function of solar activity represented by sunspot numbers using the hourly neutron monitor data of Deep River station. The amplitude as well as direction of the diurnal anisotropy is well correlated with solar cycle during low amplitude days. The time of maximum for all days lies along 1650 hrs LT direction and is mostly caused by depression of cosmic ray intensity along garden hose direction or the increase of the intensity along anti-garden hose direction similar to that of high amplitude events. However, the direction of anisotropy for LAEs shows a preferential direction along ~1250 hrs LT direction and this may be attributed to the increase in diffusion of particles perpendicular to interplanetary magnetic field lines. The shift of time of maximum along ~1250 hrs LT direction for LAEs may be attributed to the increase in diffusion of particles perpendicular to interplanetary field lines. However, the shift of time of maximum for LAEs along 1550 hrs LT direction is mainly caused by corotation of cosmic ray particles along with solar system magnetic fields similar to that of normal diurnal variation. The occurrence of LAEs is solar activity dependent. It may be concluded that interplanetary turbulences responsible for cosmic ray modulation effects do not reach the Earth during solar minimum and maximum, which results in the dominance of LAEs during these periods. The increase in diurnal amplitude of LAEs during solar minimum and maximum is contributed by the additional flow of cosmic ray particles due to corotating streams.|
|Appears in Collections:||IJRSP Vol.37(5) [October 2008]|
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