A survey of long-term interplanetary magnetic field variations

Interplanetary magnetic field data from 10 IMP, AIMP, and HEOS spacecraft were merged into a composite data set spanning 1963 to 1974. A consideration of the mutual consistency of the individual data sets reveals agreement typically to within 0.2 gamma. Composite data set analysis reveals: (1) whereas the yearly averaged magnitudes of all field vectors show virtually no solar cycle variation, the yearly averaged magnitudes of positive- and negative-polarity field vectors show separate solar cycle variations, consistent with variations in the average azimuthal angles of positive- and negative-polarity field vectors, (2) there is no heliolatitude dependence of long time average field magnitudes, (3) field vectors parallel to the earth-sun line are on the average 1 gamma less in magnitude than field vectors perpendicular to this line, and (4) the heliolatitude-dependent dominant polarity effect exhibits a complex sign reversal in the 1968 to 1971 period and a measure of symmetry in 1972 to 1974 not found in earlier data.