Coalescence of recurrent streams of different sizes and amplitudes

Two corotating streams per solar rotation, separated by the heliospheric plasma sheet, were observed at 1 AU during 1974, and the streams recurred four times during the interval from day 145 to day 255. A single compound stream per solar rotation was observed at 5.5–6.0 AU during the corresponding interval from day 165 to day 275, indicating that the two recurrent streams observed at 1 AU coalesced between 1 AU and 6 AU. The average maximum speed of one of the recurrent streams was 805 km/s while that of the other recurrent stream was 705 km/s. The compound stream was not formed by the overtaking of the slow stream by the fast stream. Rather, it was probably formed by a process involving both filtering (due to the fact that the slow stream was 50% wider than the fast stream) and a geometrical effect.