Unusually low amplitude anisotropic wave train events in cosmic ray intensity

Abstract

The exceptionally low amplitude anisotropic wave train events (LAEs) have been investigated using the neutron monitoring cosmic ray intensity data during the period 1981-90. It has been observed that for majority of the LAEs, the phase of the diurnal anisotropy remains in the corotational direction. However, for some of the LAEs, the shift in the phase of the diurnal anisotropy has been observed to early hours. Further, the LAEs have been observed to be dominant during the period of minimum solar activity. The interplanetary magnetic field (IMF) and solar wind plasma (SWP) parameters and also different features at solar disc have been investigated. The results indicate that the LAEs are the consequence of the accumulated effect of the multiple probable sources acting in such a way that the amplitude remains low continuously for the successive days and phase in the corotational direction; or the amplitude remains low regularly for the number of days, but the phase shifts to earlier hours.