Observations of upstream ions and low‐frequency waves on ISEE 3

We present three examples of correlated observations of 35‐ to 1600‐keV upstream ions and low‐frequency waves measured on ISEE 3, located between ∼76 and ∼200 R E from the earth's bow shock. The observations show that when no upstream waves are present, the particle anisotropies are beamlike, aligned along the magnetic field after transformation into the drift velocity reference frame. When waves are present, the pitch angle distributions are broadened, the amount of broadening being correlated with the amount of wave activity. These waves are transverse, circularly polarized, and have a period of ∼30 s. From our observations we conclude that during long‐lasting events an equilibrium is reached where the region between the spacecraft and the bow shock contains a significant amount of low‐frequency wave activity, together with significant pitch angle scattering. The amount of scattering decreases with upstream distance, ranging from strong scattering at the bow shock to weak scattering at ISEE 3.