Abstract. We report observations of a direct ionospheric plasma outflow response to the incidence of an interplanetary shock and associated coronal mass ejection (CME) upon

[1] Earth's high-latitude outflow of H + and O + ions has been examined with the Toroidal Imaging Mass-Angle Spectrograph instrument on the Polar satellite in the 15-eV to 33-keV energy range over an almost 3-year period near solar minimum (1996)(1997)(1998). This outflow is compared with solar wind plasma and interplanetary magnetic field (IMF) data from the Wind spacecraft, the latter having been time shifted to the subsolar magnetopause and averaged for 15 min prior to each sampling of Earth's magnetic fieldaligned ion flow densities. When the flow data are arranged according to the polarity of the IMF B z (in GSM coordinates) and limited to times with B z > 3 nT or B z < À3 nT, the total rate of ion outflow is seen to be significantly enhanced with negative B z , typically by factors of 2.5-3 for the O + and 1.5-2 for the H + , more than previously reported from similar but less extensive comparisons. With either IMF B z polarity the rate of ion outflow is well correlated with the solar wind energy flow density, especially well with the density of kinetic energy flow. The rate of ion outflow within the instrument's energy range is a strong function of the Polar satellite altitude, increasing almost threefold from perigee (R $ 2 R E ) toward apogee (R $ 4-9 R E ) for O + ions, i.e., up to 10 26 ions s À1 or more per hemisphere. The apogee enhancement may be still larger for the H + , but it is obscured by mantle flow of cusp origin solar H + . Ion mean energy also increases with altitude, leading to about a twentyfold increase in the O + energy flow rate from Polar perigee to apogee altitude, reaching values of 20 GW or more per hemisphere. While the perigee outflow of H + has little or no seasonal modulation, in terms of ions s À1 the O + outflow rates at both altitudes do increase during local summer and so does the rate of cusp origin H + flow near apogee. The latter rate, in fact, has very similar seasonal modulation as the O + rates, suggesting that it has a significant influence on the O + outflow.

The Dynamics Explorer (DE) pair of spacecraft provide a unique opportunity to search for the presence of electric fields aligned parallel to magnetic field lines by sampling, nearly simultaneously, the velocity‐space distribution functions of ions and electrons at two points on auroral field lines: DE 1 at high altitudes (9000–15,000 km in this study) and DE 2 at low altitudes (400–800 km). Three independent techniques are used to infer the auroral electrostatic potential difference from the particle distributions: (1) the energy of the precipitating electrons at DE 2 (compared to that at DE 1), (2) the energy of the upgoing ions at DE 1, and (3) the widening of the loss cone for electrons at DE 1. The three estimates are in general agreement, confirming the long‐standing, but not fully accepted, hypothesis that parallel electrostatic fields of 1–10 kV potential drop at 1–2 RE altitude are an important source for auroral particle acceleration. The upflowing ion distribution typically can be characterized by a sharp peak and a falloff at high energies of the form exp‐{(E‐Epeak)/Eo}, with Epeak being the peak energy and Eo the characteristic energy. This is the functional dependence one expects if a Maxwellian of thermal energy Eo is accelerated upward by a parallel electric field with eΦ=Epeak. The fact that the peak energies and not the flow velocities of the various ion species are in agreement also lends strong credence to the parallel electric field hypothesis. The acceleration mechanism cannot be a simple parallel electric field, however, for two reasons: first, the characteristic energy Eo is considerably larger than the ionospheric thermal energy (Eo is typically hundreds of electron volts and 20–30% of Epeak), and second, the energy Epeak is typically 30–50% smaller than that inferred by the two other independent techniques. The distribution does appear to be consistent with an ionospheric source, heated within (or above) the acceleration region, since the ion average energy is comparable to eΦ. The average energies of O+ and He+ are comparable to, but typically somewhat larger than, that of H+, indicating that a two‐stream instability may be the heating mechanism. Electron heating is also detected within the auroral acceleration region, with gains in characteristic energies of 10–15% of eΦ. From the high‐altitude electron measurements, we can determine a minimum potential distribution as a function of altitude in order to overcome the mirror force. We find that in one case at least 9M V of the 2300‐V potential drop must occur above 7000 km, and at least 960 V above 2000 km.

Abstract. We present observations of the magnitude and variability of escaping suprathermal ions in the energy per charge range of 15 eV/e to 33 keV/e. The data were obtained from the Toroidal Imaging Mass-Angle Spectrograph (TIMAS) on the Polar spacecraft from April 1996 to September 1998 over the Earth's southern Polar cap during solar minimum conditions. The net outflow rates of ionospheric ions derived from this data set are significantly different from those inferred from analysis of similar data obtained at higher altitudes from the Dynamics Explorer (DE) 1 satellite. The data present a clear picture of the seasonal variation of ion outflow as a function of solar illumination (i.e., season). We conclude that the differences between the present results and previous DE 1 estimates of the magnitude of escaping suprathermal ions can be explained by energization of the H + component of the Polar wind above the 6000-8000 km altitude region, where the Polar data were acquired. We also note that seasonal variations in He + outflow presented here are not as large as those reported previously.

[1] We report hemispheric average fluxes and energies of outflowing energetic (0.015 < E/q < 33 keV) H + , O + , and He + ions in dynamic boundary-related coordinates, from observations obtained by the Polar/TIMAS instrument near 6000 km altitude in the southern hemisphere during quiet geomagnetic intervals at solar minimum. We discuss our observations in terms of known energization and transport processes. We find that only a small fraction of energetic ions escape from the ionosphere directly into the polar cap and at quiet times the characteristic energies of escaping H + are between 30 and 300 eV in the cusp region and between 30 eV and 1.2 keV in the midnight sector. For O + we conclude the characteristic energy in the cusp is $100 eV and between 150 and 600 eV in the midnight sector. Our data suggest that the relative energization and acceleration of O + is significantly different in the noon quadrant. The observations and analysis presented here also suggest that O + has activity dependent transport paths from the ionosphere to the ring current that have not previously been identified.