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[1] We present observations by the Suprathermal Mass Spectrometer (SMS) on Akebono (EXOS-D) of ion outflow in the energy range from <1 to $70 eV. These observations cover a unique region of phase space and present an opportunity to ''tie together'' observations from disparate satellites. outflow rates in this range exhibit a strong correlation with the solar wind kinetic pressure, the solar wind electric field, and the variability in the interplanetary magnetic field (IMF) in the hour preceding. While these factors are also associated with increased geomagnetic activity (Kp), a separate, Kp-independent effect is also found, showing a correlation of ion outflow with solar wind density and an anticorrelation with solar wind velocity.

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were used to determine the mass composition, magnitude, magnetic activity dependence, long-term variations, and topology (MLT-invariant latitude distribution) of energetic (0.01-17 keV/el) terrestrial outflow. The September 1981 to May 1984 period coincided with the declining phase of the current solar cycle (cycle 21), when the monthly average of the solar radio flux at 10.7 cm, Fxo.v, decreased from a high of 222 ( x 10 -22 W m -2 Hz-X) in September 1981 to a low of 93 in November 1983. At both magnetically quiet and active times, the O* outflow rate exhibited long-term variations which correlated with the declining solar radio flux. Overall, the O* outflow rate in the 1981-1982 period was a factor of 2 larger than the 1983-1984 rate. Any corresponding variation in the H* outflow rate, if present, was much smaller and not statistically significant. At solar maximum (in 1981-1982), the total ion outflow rate (H f and O f) was 1.5 x 1026 ions s-• at active times (3 < Kp < 5) and 5 x 1025 ions s -• at quiet times (Kp < 2). The active time flow was predominantly O f; the Of/H f ratio was 3. At quiet times, H f and O f flows were comparable, and the ratio was 0.9. In 1983-1984, a period of reduced solar activity, the total ion outflow rate was 1.0 x 10 26 ions s -x at active times and 4 x 1025 ions s-• at quiet times. The O f/H f ratio was 1.1 and 0.6, respectively. In both H f and O f, the outflow was dominated by < 1-keV ions. Ions of 1-17 keV/el constituted less than 10% of the total ion outflow. The O f ion outflow rate increased exponentially with the Kp index, the rate at very disturbed times (Kp > 6) being a factor of 30 larger than the quiet time (Kp = 0) value. The increase in the H f outflow rate with Kp was more modest, the disturbed time (Kp > 6) rate being a factor of 5 larger than the quiet time value. At quiet times (Kp = 0-2), 10-20% of H f and 20-25% of O f ion outflow occurs above 80 ø invariant. At active times (Kp = 3-5), 20-30% of H f and 30-35% of O f outflows occur above 76 ø invariant. Defining the polar cap as the latitude region above 80 ø invariant at low Kp and above 76 ø invariant at high Kp, the ratio of polar cap to auroral ion outflow is 0.2-0.3 at quiet times and 0.4-0.5 at active times. In other words, the polar cap ion outflow is smaller than, but nevertheless nonnegligible compared with, the auroral ion outflow, particularly at active times. For both H f and O f, the distributions of upward ion fluxes peak near 78 ø invariant in the noon sector. The averaged quiet time H f upward flux at the peak invariant latitude, normalized to 1000-km altitude, is 2-3 x 108 cm -2 s-•. The corresponding quiet time O f upward flux is --• 2 x 108 cm -2 s -• at solar maximum and increases to --• 5 x 108 cm -2 s -• at active times (Kp = 3-5). In the night side the upward ion flux peaks at lower latitude. At quiet times the peak flux in the midnight sector is a factor of 3-5 smaller than the peak flux in the noon sector. At active times it is a factor of 2 smaller. Over 95% of the quiet time (energet...

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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A statistical analysis is presented of the long-term variations of upflowing ionospheric ion (UFI) occurrence morphology in the high-altitude (8000-23,300 km) auroral and polar cap ionosphere, using data from the Dynamics Explorer 1 Energetic Ion Composition Spectrometer from 1981 to 1984. The study is based on over 100,000 data samples, each consisting of pitch angle distributions of H + and O + intensities at 0.01-1, 1-4, and 4-17 keV/e. The data samples were grouped into 91-day intervals (seasons). Within each interval they were sorted into altitude, invariant latitude, magnetic local time, and magnetic activity (Kp index) bins, and the occurrence frequency and intensity characteristics of H + and O + UFI in the respective bins were determined. The September 1981 to May 1984 period coincides with the declining phase of solar cycle 21, when the solar radio flux at 10.7 cm, Fxo.7, decreased from a high of 222 ( x 10 -22 W m -2 Hz -x) in September 1981 to a low of 93 in November 1983. The observed occurrence frequency, intensity, and angular characteristics of O + UFI exhibited marked variations which correlate with variations in the solar radio flux (and which envelop those of magnetic activity and seasonal origins). In contrast, the H + UFI morphology did not display any observable long-term variations. At both quiet (Kp _< 2 +) and active times (3-<_ Kp _< 5 +) the solar maximum O + data displayed (1) a factor of 2-3 increase in the occurrence frequency of intense UFI; (2) a similar increase in the occurrence frequency of transversely accelerated ions above 8000 km; and (3) an increase in conic abundance (fraction of ion conics in UFI). Together, items (1) and (3) imply about a twofold increase of energetic O + outflow to the magnetosphere at solar maximum; items (2) and (3) indicate an upward shift inthe perpendicular ion acceleration region. The correlation of O + UFI abundance and occurrence with variations of the solar radio flux, in the absence of magnetic and other geophysical variations, suggests solar activity variations related to the solar flux to be the causative factor in the long-term variations in observed UFI morphology. Seasonal variations in UFI occurrence were present in O + and absent in H +. The O + frequencies in the summer periods were found to be significantly higher than the values in winter periods of comparable solar activity. The observed solar activity and seasonal variations are interpreted in terms of increased ionospheric and atmospheric scale heights at solar maximum and summer solstice, which effectively shift the O +-H charge exchange altitude upward and facilitate O + injection to higher altitudes. The observed variations are compared with solar cycle variations in the ring current density, and their magnetospheric implications are discussed.