We report observations of the H+, He+, and O+ polar wind ions in the polar cap (>80° invariant latitude, ILAT) above the collision‐dominated altitudes (>2000 km), from the suprathermal mass spectrometer (SMS) on EXOS D (Akebono). SMS regularly observes low‐energy (a few eV) upward ion flows in the high‐altitude polar cap, poleward of the auroral oval. The flows are typically characteristic of the polar wind, in that they are field‐aligned and cold (Ti < 104 °K), and the parallel (field‐aligned) velocities of the different ion species vary inversely with the respective ion masses. A statistical study of the altitude, invariant latitude, and magnetic local time distributions of the parallel velocities of the respective ion species is described, and preliminary estimates of ion temperatures and densities, uncorrected for perpendicular drifts and spacecraft potential effects, are also presented. For all three ion species, the parallel ion velocity increased with altitude. In the high‐latitude polar cap (>80° ILAT), the average H+ velocity reached 1 km/s near 2000 km, as did the He+ velocity near 3000 km and the O+ velocity near 6000 km. At Akebono apogee (10,000 km), the averaged H+, He+, and O+ velocities were near 12,7, and 4 km/s, respectively. Both the ion velocity and temperature distributions exhibited a day‐to‐night asymmetry, with higher average values on the dayside than on the nightside.

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In the high-altitude polar cap, the suprathermal ion mass spectrometer (SMS) on the EXOS D (Akebono) satellite frequently "observed" ion depletion zones (IDZ) in which the thermal-energy ion flux was below the detection limit of SMS, corresponding to thermal-energy ion densities less than 10 '2 cm ø. These IDZ are located primarily in the nightside region of the magnetosphere at invariant latitudes above 70' and at altitudes preferentially near apogee and between 8000 and 10,000 km (EXOS D apogee) but extending down to 3000 km. In contrast, outside the IDZ, the SMS regularly observed outflowing H +, He +, O +, and O ++ polar wind ions with energies typically less than 10 eV in the polar cap. Also, at sufficiently low altitudes below the IDZ the SMS instrument always observed W, He +, 0 +, and O ++ ions that were stationary in the Earth's corotating frame, i.e., ions observed in the spacecraft ram direction.

It is found that the occurrence and luminosity of diffuse auroras, including pulsating auroras, in the dawn sector show space-time variations synchronized with geomagnetic Pc5 pulsations. The activation region of aurora (not auroral structure) quasi-periodically propagates towards the northwest. The observed propagation velocities at the ionospheric level are about 1km/s northward and about 15km/s westward, respectively. These velocities are in good agreement with the phase velocities of Pc5 pulsations previously measured by radars and by ground networks of geomagnetic field observations. Oscillations in drifts of auroral patches generally in the east-west direction are found to be synchronized with the Pc5 pulsations. The observations suggest that the ground Pc5 pulsations do not necessarily reflect the HM wave structures in the magnetosphere, but the wave nature could be inferred from a close examination of the relationships between the ground magnetic pulsations and concurrent auroral dynamics.

Counterstreaming ions or ions traveling simultaneously both parallel and antiparallel to the magnetic field direction have been briefly noted in the literature but have not been studied previously in depth. We have studied over 60 counterstreaming ion (CSI) events observed on the ISEE 1 satellite. Often, both oxygen and hydrogen ions at a number of energy levels are Counterstreaming, but some events show only either oxygen or hydrogen ions at one or more energy levels involved. One particularly interesting event shows only counterstreaming oxygen ions with 417 eV energy; oxygen ions of lower energy (215 eV) and higher energy (630–17,000 eV) and all the hydrogen ions between 215 and 17,000 eV energy have lower fluxes and/or nearly isotropic pitch angle distributions. This event correlates well with wave activity in the 17‐ to 100‐Hz band and is also accompanied by 200‐eV downgoing and 400‐eV upgoing electrons. Details of this and some other CSI events are presented. The CSI events were found to occur at altitudes of about 2–8 RE on L shells of about 5–12 in the evening‐to‐morning sector from about 1700 to 0900 LT; the majority of the CSI events at altitudes between 2 and 5 RE and L values from 5 to 8 involve oxygen ions, while at higher altitudes from about 5 to 8 RE and higher L values from about 8 to 12 the majority involve hydrogen ions. Some features suggest wave‐particle interaction may be involved in some CSI events.