Observations of interplanetary scintillation on about 900 sources made with the 3.6 hectare array at Cambridge have been used to map, and to track, 96 heliospheric transients during August 1978–September 1979. This sample included most of the interplanetary shocks recorded by near-Earth spacecraft in the same period.

Some corotating interaction regions were observed but the most frequent disturbances were “erupting streams” in which spherical shells of enhanced density were driven by the birth of high-speed solar wind streams which persisted for several days. Although these transients were of the type traditionally associated with solar flares or disappearing filaments they were not caused by such processes. Back-projection to the Sun indicated that the sources were always associated with coronal holes. It is concluded that the sources of the most energetic interplanetary transients are mid-latitude coronal holes which, near solar maximum, produce sporadic high-speed streams lasting several days, in contrast to the more stable flows typical of the declining phase of the solar cycle.