High amplitude anisotropic wave train events in the cosmic ray intensity during 1981-90

Abstract

The high amplitude anisotropic wave train events (HAEs) in cosmic ray (CR) intensity have been investigated during the period 1981-90 using the neutron monitoring data for different latitudes. In all, 21 HAEs have been studies. It has been observed that the phase of the diurnal anisotropy remains in the same co-rotational direction for majority of the events. On the other hand, the phase of the diurnal anisotropy changes to later hours in some of the events. Further, the amplitude of the semi-diurnal anisotropy for HAEs remains statistically the same, but the phase of the semi-diurnal anisotropy has been found to shift to later hours for all events. Furthermore, the HAEs occur dominantly during the declining phase of the solar activity. The geomagnetic activity index (Ap) has been observe to remain low during the period of each HAE. The possible sources to cause the enhanced daily variation have been proposed to occur on the backside of the sun.