Solar Cycle 21 effects on the interplanetary magnetic field and related parameters at 0.7 and 1.0 AU

Abstract

Magnetometer data obtained over the course of the previous solar cycle by the Pioneer Venus orbiter (PVO) at ∼ 0.7 AU and IMP 8 at 1.0 AU are used to compare the long‐term behavior of the interplanetary magnetic field (IMF) at these two heliocentric distances. Similarities include an enhancement in the typical or median field magnitude during the declining phase of the solar cycle as compared to solar maximum or minimum, slight decreases in the Parker spiral angle from the declining phase through solar minimum, similar trends in the Alfvénic and magnetosonic Mach numbers, and the remarkably consistent sector structure noted previously. Differences include the temporal behavior of the high‐field tail of the field distribution, showing that high fields are most frequently observed during solar maximum at the Earth but during the declining phase of activity at Venus. This latter feature suggests that the perceived occurrence history of large fields from transient disturbances such as coronal mass ejections is a sensitive function of position within the heliosphere.