Cosmic ray solar semidiurnal anisotropy .2. Heliospheric relationships of anisotropy parameters

We have used the corrected experimental semidiurnal variation observations described at length in Paper 1, to compute the amplitude and direction of semidiurnal anisotropy in free space for the period 1965 to 1992. The time interval covers several epochs of solar activity maxima, minima, and polar field reversals. We find that the amplitude of anisotropy fluctuates between 0.05% and 0.10%, except for the period 1971 to 1977 when it acquires a value as large as 0.25% at high primary rigidities (R(m) > 16 GV). The physical cause of this anomalous behavior is not identified yet. The asymptotic time stays close to 0300 LT, independent of the primary rigidity (R). This direction is perpendicular to the nominal direction of interplanetary magnetic field (IMF) at Earth's orbit. The polarity of IMF has no effect on the semidiurnal anisotropy parameters. The physical significance of our results is discussed in the contest of the theoretical ideas available in the literature. The contributions from the symmetric transverse gradients to semidiurnal anisotropy appear to be minimal, but those from pitch angle scattering may be appreciable.