We have studied the vertical bulk ion drift data recorded by the DE 2 satellite between 200 and 1000km altitudes. For this data set we have found that field‐aligned ion flows between 100ms−1 and 3km s−1 are a common occurrence in the high‐latitude F region. The flows are predominantly upward near the cusp region and throughout the auroral zone. Strong downward flows of somewhat smaller magnitude are also recorded but mostly over the polar cap. These statements are true for all drift speeds in excess of 50ms−1 and for all altitudes and magnetic activity levels sampled. The morphology of low‐altitude upward flowing ions agrees well with the morphology of outflowing ions, ion beams, and ion conics observed at much higher altitudes, but the low‐altitude fluxes are often considerably greater. This suggests that a large fraction of the upflowing ions actually returns to the ionosphere, to be observed as large downward ion fluxes. We propose that upflowing ion events are generated by sudden large changes in the ion temperature below the neutral exobase, where ion frictional heating dominates the ion energy balance. The sudden changes in temperature occur when the horizontal velocity of a convecting field tube increases rapidly in regions like the cusp.

Ample evidence supports the significance of the high‐latitude ionospheric contribution to magnetospheric plasma. Assuming flux conservation along a flux tube, the upward field‐aligned ion flows observed in the magnetosphere require high‐latitude ionospheric field‐aligned ion upflows of the order of 108 to 109 cm−2 s−1. Since radar and satellite observations of high‐latitude F region flows at times exceed this flux requirement by an order of magnitude, the thermal ionospheric upflows are not simply the ionospheric response to a magnetospheric flux requirement. Several ionospheric ion upflow mechanisms have been proposed, but simulations based on fluid theory do not reproduce all the observed features of ionospheric ion upflows. Certain asymmetries in the statistical morphology of high‐latitude F region ion upflows suggest that the ion upflows may be generated by ion‐neutral frictional heating. We developed a single‐component (O+), time‐dependent gyro‐kinetic model of the high‐latitude F region response to frictional heating in which the neutral exobase is a discontinuous boundary between fully collisional and collisionless plasmas. The concept of a discontinuous neutral exobase and the assumption of a constant and uniform polarization electric field reduce the ion guiding center motion in the frame of a convecting flux tube to simple one‐dimensional ballistic trajectories. We thus are able to analytically calculate a time and height‐dependent ion velocity distribution function, from which we can compute the ion density, parallel velocity, parallel and perpendicular temperature, and parallel flux. Using our model, we simulated the response of a convecting flux tube between 500 km and 2500 km to various frictional heating inputs; the results were both qualitatively and quantitatively different from fluid model results, which may indicate an inadequacy of the fluid theory approach. The gyro‐kinetic frictional heating model responses to the various simulations were qualitatively similar: (1) initial perturbations of all the modeled parameters propagated rapidly up the flux tube, (2) transient values of the ion parallel velocity, temperature, and flux exceeded 3 km s−1, 2 × 104 K, and 109 cm−2 s−1. respectively, (3) a second transient regime developed wherein the parallel temperature drops to very low values (a few hundred Kelvins), and (4) well after heating ceased, large parallel temperatures and large downward parallel velocities and fluxes developed as the flux tube slowly returned to diffusive equilibrium. The ion velocity distributions during the simulation are often non‐Maxwellian and are sometimes composed of two distinct ion populations.

Eraruination of the ion drift vel•i•v•or measured on the DE 2 spacecraft reveals the sign ificance of ionospheric flows both perpendicular and parallel to the magnetic field at high latitudes. During periods of southward ditched interplanetary magnetic field the familiar two-cell convection pattern perpendicular to the magnetic field is associated with field-aligned motion predominantly upward in the dayside auroral zone and cusp, and predominantly downward in the polar cap. Frictional heating by convection through the neutral gas and heating by energetic particle precipitation are believed to be responsible for the bulk of the upward flow with downward flows resulting from subsequent cooling of the plasma. Some of the upward flowing plasma is apparently given escape energy at altitudes above about 800 kin. The average flow of ions across the entire high-latitude region at 400 km is outward and comparable to the energetic ion outflow observed at much higher altitudes by DE 1.