Simultaneous observations of neutral winds and electric fields at spaced locations in the dawn auroral oval

On March 21, 1987, a chemical release experiment was carried out in the dawn sector of the auroral oval and polar cap to measure E and F region neutral winds. The Sondre Stromfjord, Greenland, incoherent scatter radar provided electric field and electron density measurements for 14 hours prior to the experiment and 6 hours after. F region wind measurements were available from the University of Michigan Fabry-Perot interferometer throughout the night of March 20–21. The 30-hour period prior to the launch was quiet, except for minor substorms, and the y component of the IMF was away from the Sun corresponding to positive By. The results show that F region neutral flow was in the direction expected with a By>0 plasma convection pattern if the Lorentz forcing was dominant. The gradients in the flow were found to have comparable contributions from the divergence and vorticity. The E region winds showed a complicated spiral structure in which the tip of the wind vector traced out an anticyclonic spiral with increasing height. However, the direction of rotation reversed over a small height range near 110-km altitude. An unusual feature of the observations was the wind magnitude of over 100 m/s near 105–110 km. The observed E region wind profiles have been compared with the tidal structure expected from Forbes' (1982a, b) tidal mode model. The observations can be reconciled with the theory to some extent if a 4–5 hour phase difference is invoked. However, the observed divergence and vorticity in the flow are 4 to 13 times larger than the theory predicts. The latter indicates that higher-order modes than those treated by Forbes, and possibly generated by the diurnal and semidiurnal periodicities in the magnetospheric forcing, may contribute significantly to the high-latitude thermospheric flow.