Long-term variation of cosmic ray anisotropy during high amplitude days

Abstract

In the present study the occurrence of a large number high amplitude event (HAE) of cosmic ray diurnal anisotropy during 1981-1994 has been examined as a function of solar activity using the hourly neutron monitor data of Deep River station. The diurnal time of maximum for both HAE as well as for all days is found to shift significantly towards an earlier time as compared to the co-rotational/azimuthal direction since the year 1991 onward. It is found that diurnal amplitude significantly deviates and reaches its maximum, and phase remains in the co-rotational direction during the years close to solar activity maximum for HAE. The occurrence of HAE is dominant in the declining phase of solar activity. The amplitude as well as phase of the cosmic ray diurnal anisotropy during HAEs is well correlated with the sunspot numbers.