The Pioneer 10, 11, and Voyager 2 spacecraft are well suited for exploring spatial gradients in the distant solar wind. Between 1984 and 1986 Pioneer 11 and Voyager 2 were located at nearly the same heliocentric distance (≂20 AU) and longitude but were widely separated in latitude; Pioneer 11 was at a heliographic latitude of ≥15¿ while Voyager 2 was near the solar equator. Pioneer 10 was located near the solar equator but at a considerably greater heliocentric distance (≂40 AU). IMP observations at 1 AU provide an inner heliosphere baseline.

Prior to mid-1985, Pioneer 11 and Voyager 2 observed nearly identical solar wind structures. The characteristics and arrival times of these structures were similar at both spacecraft.

After day 150 and 1985 this situation changed dramatically. The velocity structure at Voyager 2 became flatter. The velocities seen at Voyager 2 also fell with respect to Pioneer 11; the difference in velocities observed by the two spacecraft grew to 200 km s-1 by late 1986. In late 1985 Pioneer 10 observed a change in the solar wind similar to that observed at Voyager 2. These changes in the solar wind at low latitudes may be related to a change which occurred in the coronal hole structure in early 1985.