Double ion streams in the solar wind

Distinct interpenetrating ion streams have been identified in the solar wind for the first time. They are shown to be interplanetary in origin and to be associated with the filling in of regions of density rarefactions accompanying high-velocity streams. With few exceptions, the ion stream with the lower-energy density flux has higher energy. Furthermore, nonradial magnetic field directions seem to inhibit double ion streaming. It is tentatively suggested that the origin of solar wind double streaming is the breakup and merging of thin high-velocity filaments into regions of plasma rarefactions.