Second spherical harmonics of the cosmic ray angular distribution

In order to clarify the nature of the semidiurnal variation of the cosmic ray intensity the second spherical harmonics of the three dimensional cosmic ray anisotropy have been derived considering the second moments of the statistical Boltzmann equation. Utilizing the results both the density gradient model and the pitch angle distribution theory are discussed. In the presence of a considerable sunward streaming the second harmonic of the cosmic ray angular distribution turns out to be of pitch angle type. Further it is suggested that the semidiurnal variation is produced, in an indirect way, by the 0.3% sunward streaming observed recently in the 1-5 GeV range. (Sz.Z.)