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.

We report observations of molecular upflowing ions in the high-altitude auroral ionosphere by the EXOS D (Akebono) suprathermal mass spectrometer (SMS). At Akebono altitude, the occurrence of molecular upflowing ions was rare and was often confined in latitudinal extent, in both the dayside and the nightside. In the dayside, molecular upflowing ions were observed up to about 85' A, inside and up to -10 ø poleward of the cleft. In the nightside, they were generally located at lower invariant latitudes (-60ø-75øA) and were observed both inside and equatorward of regions of energetic (1-10 keV) electron precipitation. The observed molecular ions appeared as a minor component of the upflowing ionospheric ion population, with a flux typically less than 5% but at times as high as 15% of the total. They were composed of comparable fluxes of NO* and N2* ions; at times, smaller fluxes of O2* were also observed. The observed NO*/N2* ratio ranged from 0.3 to 1.3; the observed O2*/N2* ratio was 0.1 or less. They were invariably accompanied by enhanced N* ion flux, the N*/O* ratio being 0.5-1.0. They were more intense (flux -10 s cm -2 s4), had higher density (-0.1-0.2 cm '3) and lower energy (-5 to -20 eV/q), and were more anisotropic and peaked near the upward field line direction, in the dayside than in the nightside. Data from about 440 Akebono passes in the 7-month period from November 1989 to May 1990 were surveyed for their occurrence. Molecular ions were found in 14 passes, i.e., 3% of the passes. In most but not all cases, the Kp index was 4 or higher at the time of their observation and in the preceding several hours, suggesting that they typically occur in periods of sustained auroral activity. These observations are compared with previous low-altitude observations and discussed in terms of the transit and recombination times of the observed molecular ions, the orders-of-magnitude enhancement in neutral molecular densities and the corresponding N*, N2* and NO* ion production above the F region in periods of prolonged auroral activity, and the moderate energization of the ions immediately after their production. 1. INTRODUCIION The auroral ionosphere is an important source of energetic ions in the magnetosphere (see, for example, recent reviews by Chappell [ 1988], Shelley [ 1986], and Yau and Lockwood [ 1988]). Ionospheric ion energization varies from a few electron volts in the polar wind [Nagai et al., 1984], to tens of electron volts in upwelling ions [Lockwood et al., 1985; Pollock et al., 1990] and upflowing polar cap ions [Shelley et al., 1982], to hundreds of electron volts in perpendicular ions and conics [Klumpar, 1979; Whalen et al., 1978; Yau et al., 1983], and to keV in auroral ion beams [Coffin et al., 1987]. In general, the mass distribution of accelerated ionospheric ions reflects the low-altitude source region composition with H* and O* dominating the distribution at high altitude [ Yau et al., 1985a, b; Coffin et al., 1988]. In the F region and topside polar ionosphere, extensive observations of th...

A statistical study is presented of the occurrence frequency distribution of upflowing ionospheric ions (UFI) in the high‐altitude (8000–23,000 km) auroral and polar cap ionosphere, using measurements from the energetic ion composition spectrometer aboard Dynamics Explorer 1. In this survey, distinction is made between UFI of different masses (H+ and O+), energies (0.01–1, 1–4, and 4–17 keV/e), and pitch angle characteristics (within 20° from , between 20° and 80° from , and transverse to ). The increased statistical accuracy of the data and the added dimensions in this study relative to earlier work at lower altitudes provide a more detailed picture of UFI events. Occurrence frequencies are determined for both H+ and O+ UFI at the different energies as a function of altitude, invariant latitude, magnetic local time, and magnetic activity (Kp index). It is shown that the occurrence frequency and intensity distribution of O+ UFI have a marked magnetic dependence, whereas the H+ UFI occurrence displays little variation with magnetic activity. The occurrence frequency of O+ conics decreases with altitude, in relation to that of H+ conics. Also, ≈90° H+ conics occur 2–3 times more frequently than O+. The invariant latitude‐local time distribution of the occurrence frequency for both H+ and O+ is auroral‐oval‐like in that the frequency peaks at a more equatorward latitude and has a broader latitudinal extent in the nightside than in the dayside. However, this association with the auroral oval is energy‐dependent, the oval for low‐energy UFI being distinctly more poleward than that for energetic UFI. The low‐energy O+ UFI occurrence is relatively uniform in local time; the H+ UFI occurrence frequency distribution shows a broad distribution peaking in the noon sector. Both the H+ and O+ conics distributions display a dawn‐dusk asymmetry in favor of the dusk sector. In the polar cap (poleward of the statistical auroral oval), the H+ and O+ ion outflows (≈2×1024 s−1 and 3×1024 s−1, respectively, at quiet times, and ≈3×1024 s−1 and 1×1025 s−1 at disturbed times) represent a significant ionospheric source to the magnetotail. The results of this study are shown to be consistent with previous, less detailed surveys of UFI at lower altitudes and provide a basis with which to examine possible acceleration mechanisms.

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During geomagnetically active times, the suprathermal mass spectrometer on the Akebono satellite frequently observes upflowing molecular ions (NO +, N2 +, 02 +) in the 2-3 Earth radii geocentric distance regions in the auroral zone. Molecular ions originating at ionospheric altitudes must acquire an energy of the order of 10 eV in order to overcome gravitation and reach altitudes greater than 2 Re. This energy must be acquired in a time short compared with the local dissociative recombination lifetime of the ions; the latter is of the order of minutes in the F region ionosphere (300-500 km altitude). Upflowing molecular ions thus provide a test particle probe into the mechanisms responsible for heavy ion escape from the ionosphere. In this paper we analyze the extensive complement of plasma, field, and wave data obtained on the Akebono satellite in a number of upflowing molecular ion events observed at high altitudes (5000 -10,000 km). We use these data to investigate the source of energization of the molecular ions at ionospheric altitudes. We show that Joule heating and ion resonance heating do not transfer enough energy or do not transfer it fast enough to account for the observed fluxes of upflowing molecular ions. We found that the observed field-aligned currents were too weak to support large-scale field-aligned current instabilities at ionospheric altitudes. The data suggest but in the absence of high-resolution wave measurements in the 300 to 500 km altitude range cannot ascertain the possibility that a significant fraction of escape energy is transferred to molecular ions in localized regiom from intense plasma waves near the lower hybrid frequency. We also compared the energization of molecular iota to that of the geophysiqally important O + ions in the 300 to 500 km altitude range, where the energy transfer to O" is believed to occur via small-scale plasma instabilities, ion resonance, and ion-neutral frictional heating. Direct observation of energy input to the ionosphere from all of these sources in combination with in situ measurements of the density and temperature of neutral and ionized oxygen in the 300 to 500 km range are required to determine the relative importance of these energy sources in providing O + with sufficient energy to escape the ionosphere. Introduction Twenty years after the discovery that significant fluxes of O + escape from the ionosphere [Shelley et al., 1972], there exists little or no quantitative information about the relative importance of the various physical processes responsible for the energization and extraction of O + and other heavy ions Paper number 94JA01738. from the Earth's ionosphere. (For a review of the pioneering work on ionospheric ion acceleration and escape, see Johnson [1983]). It is generally agreed that the high latitude auroral ionosphere interacts with the neutral atmosphere to damp plasma motions driven by the solar wind interaction with the magnetosphere. The energy imparted by the solar wind in these time and spatially variable interactions produ...