Geometry and radial width of interaction regions

Abstract

We study the characteristics of a combined set of in-ecliptic observations of Interaction Regions (IRs) detected by 5 spacecraft that traveled to Jupiter at different phases of the solar cycle: Pioneer 10 and 11 (descending phase cycle 20); Voyager 1 and 2 (ascending phase cycle 21); and Ulysses (post-maximum phase cycle 22). The fast streams associated with IRs detected by the Voyager spacecraft were slower than the fast streams of the Pioneers and Ulysses. In about half of all the IRs the slow solar wind had a higher dynamic pressure than the fast wind. These variations in the ratios of dynamic pressure were present at all phases of the cycle. The inferred geometry of IRs and the tilt angle of the heliospheric current sheet agree qualitatively with predictions of heliocentric evolution of the 3-D model by Pizzo. The IRs detected by the Pioneer spacecraft tended to thinner than the IRs detected by the Voyager spacecraft and Ulysses.