The overall configuration of the interplanetary magnetic field upstream of Saturn as revealed by Cassini observations

Abstract

The Cassini spacecraft approached Saturn during the declining phase of the solar cycle, at a time when the heliosphere was highly structured by compressions and rarefactions associated with corotating interaction regions (CIRs). We examine in detail the hourly averaged interplanetary magnetic field (IMF) data prior to Saturn Orbit Insertion and during one subsequent orbit of Cassini closer to solar minimum, where the spacecraft spent several months in the solar wind. We observe the effects of CIRs on IMF structure and show examples of where this structure is disturbed by the passage of strong coronal mass ejections and by solar cycle effects. We examine the field directions and find that in general, they correspond well to the predictions of the Parker model, but with several notable deviations, which we discuss.