Decades of Diurnal Anisotropy: Unravelling the Time of Maximum of Diurnal Anisotropy

Abstract

The diurnal anisotropy in cosmic ray intensity has been the subject of continuous observation and study over the past seven decades. This phenomenon is characterised by diurnal variations in the direction of arrival of cosmic rays and plays an important role in the spatial distribution and propagation mechanism of these high-energy particles. The time of maximum of diurnal anisotropy, which is a key parameter in understanding the fundamental process, has displayed variations that have been attracting researchers for years. This study used 60 years of neutron monitor data to analyse the phase diurnal anisotropy of the cosmic ray flux. The data were collected from the Inuvik and Moscow neutron monitor stations and analysed using the Fourier analysis method. The dataset spanned six decades and was used to identify anisotropic patterns. The results showed that the phase of diurnal variability changed slightly between the A>0 and A<0 polarity epochs, indicating a shift in the anisotropy of the cosmic ray flux arriving at the Earth. During 2019-20, the phase of diurnal anisotropy shifted towards the early hours. This study aimed to better understand these temporal variations.