Influence of solar heliospheric parameters on cosmic rays anisotropy

Abstract

In the present work the cosmic ray data of three different neutron monitoring stations, Deep River, Inuvik, and Tokyo, located at different geomagnetic cutoff rigidities and altitudes have been harmonically analyzed for the period 1980-95 for a comparative study of diurnal semi-diurnal and tri-diurnal anisotropies in cosmic ray intensity in connection with the change in interplanetary magnetic field Bz component and solar wind velocity on 60 quietest days. It is observed that the amplitudes of all the three harmonics increase during the period 1982-84 at all the stations during the high speed solar wind stream epoch and remain low during the declining phase of the stream. The amplitudes of the three harmonics have no obvious characteristics associated with the time variation of magnitude of the Bz component. The phases of all the three harmonics have no time variation characteristics associated with solar wind velocity and Bz. Key words: cosmic rays: anisotropy: interplanetary magnetic field: solar poloidal magnetic field 1. Introduction Cosmic ray (CR) intensity exhibits a daily variation composed of a prominent diurnal component and also a semidiurnal component of lesser amplitude. The diurnal, semi-diurnal as well as the tri-diurnal variation play an important role in constructing the whole picture of the modulation mechanism of the cosmic ray intensity in interplanetary space. The CR variations observed near the Earth are an integral result of numerous solar and heliospheric phenomena, so any parameter alone cannot determine the behavior of CR. Ballif et al. [1] correlated Kp and Ap with the mean fluctuations in amplitude of the interplanetary magnetic field (IMF), which in turn is related to the diffusive component of convectiondiffusion theory. Ap is also found to be related to solar wind velocity, V, which is related to the convective component of convection-diffusion theory. Days on which the transient magnetic variations are regular and smooth are said to be magnetically quiet or calm or Q days. These are the days with low values of Ap and Kp. According to solar geophysical data (SGD) the five quietest