Investigating tensor anisotropy of cosmic rays during large-scale solar wind disturbances

Abstract

The observable anisotropy of cosmic rays has first been decomposed into zonal harmonics and components of vector and tensor anisotropy. We examine Forbush decreases in cosmic rays that occurred in November 2001 and November 2004. It is shown that at the beginning of a Forbush decrease an antisunward convective current of cosmic rays predominates; and during the recovery phase, a sunward diffusive current of particles along the interplanetary magnetic field dominates. During the phase of intensity drop, short-time decreases in the second zonal harmonic take place. These decreases occur with abrupt changes of the interplanetary magnetic field intensity and solar wind speed. During the passage of large-scale solar wind disturbances, the tensor anisotropy behaves in a complicated way. To explain its behavior, a further detailed investigation is required. spherical harmonics of the angular CR-distribution are obtained using the global survey method. In each case, the average number of stations is equal to 32. The analysis shows that the temporal change of the isotropic component is caused by a magnetic mirror. For the first time, the zonal harmonics are reliably distinguished, and the existence of the antisymmetric diurnal CR-variation in a low energy range, which is oriented along IMF, is recognized. We compare our results with those obtained earlier.

Keywords

• cosmic rays
• tensor anisotropy
• Forbush decrease
• coronal mass ejection