High amplitude anisotropic wave trains in cosmic rays

Abstract

In the present study the occurrence of an unusual class of high amplitude anisotropic wave trains in the cosmic ray neutron intensity, which is distinctly different from the average diurnal variation as well as from other recognized types of high amplitude anisotropic wave trains are noted and the directional distribution in the interplanetary space determined. The major objective of this paper is to study the first three harmonics of high amplitude anisotropic wave trains of cosmic ray intensity over the period 1981–1994 for Deep River Neutron Monitoring station. The significant characteristics of these events are that the high amplitude wave trains show a maximum intensity of diurnal component in a direction earlier than 1800 h/co-rotational direction. It is noticed that these events are weakly dependent on high-speed solar wind streams or by the sources on the Sun responsible for producing these streams such as polar coronal holes. However, the possibility of occurrence of these events during high-speed solar wind streams cannot be denied. The occurrence of high amplitude events is dominant for positive polarity of B z . Majority of the HAEs have occurred when D st-index remains negative and A p-index remains ⩽ 18 nT . All the three harmonics of HAEs except the amplitude of second harmonic do not show any significant correlation associated with D st and A p-index. The corotating streams produce significant deviations in cosmic ray intensity as well as in solar wind speed during high amplitude anisotropic wave train events.