Data from ISEE were used in a small number of case studies to establish that ULF waves observed to be left handed in the spacecraft frame were in fact right handed and attempting to propagate away from the shock, parallel to the ion beams (Hoppe and Russell, 1983). This showed that, qualitatively, they had to be generated by the backstreaming ion beams through the right hand ion-ion beam instability. However, the properties of the waves were not used to compute the expected beam speed, although it was expected that the field aligned distributions were responsible for their generation. With Cluster, it is expected that quantitative tests of the wave particle interaction can be made.
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