The role of drift on the diurnal anisotropy and on temporal changes in the energy spectra of the 11-year variation for galactic cosmic rays

Abstract

Neutron monitor and interplanetary magnetic field data have been used to study features of the role of drift effect in the temporal changes of the diurnal anisotropy and of the energy spectrum of the 11-year variation of galactic cosmic rays. In order to strictly separate the sectors of the interplanetary magnetic field and its influence on the anisotropy of galactic cosmic rays four solar minima periods (1965, 1976, 1987 and 1997) have been considered. An attempt to separate drift effects in the diurnal anisotropy of galactic cosmic rays, first, due to the gradient and curvature of the regular interplanetary magnetic field, and second, due to the heliospheric neutral sheet has been made. The global survey methods has been used to calculate the components of the three dimensional diurnal anisotropy of galactic cosmic rays based on neutron monitors data. It is shown that there are significant differences between the diurnal anisotropy of galactic cosmic rays found in the reliably established various sectors (duration of each sectors is ≥ 4 days) of the interplanetary magnetic field. The interplanetary magnetic field sector structure effect in the diurnal anisotropy of galactic cosmic rays is assumed to be connected to the heliospheric neutral sheet drift, while 22-year variation of the diurnal anisotropy of galactic cosmic rays is assumed to be connected to drift due to the gradient and curvature of the regular interplanetary magnetic field for different qa > 0 and qA<0 solar magnetic cycles. It is shown that the role of drift in the temporal changes of the energy spectrum of the 11-year variation of GCR is insignificant in both of the qA > 0 and the qA<0 solar magnetic cycles. The temporal changes of the exponent index of the 11-year variation of GCR generally is connected with the various character of the diffusion in interplanetary space for minima and maxima epochs of solar activity.