Auroral zone thermospheric dynamics: 2. Individual nights

Ground‐based Fabry‐Perot spectrometer measurements of the O I 15867 K (630.0 nm; 1 K = 1 cm−1) emission line were obtained from College, Alaska, during the winters of 1981 to 1983. Averages of the temperatures and winds, derived from these measurements, show a general flow driven by ion drag due to magnetospheric convection. This hypothesis was supported by results from a global thermospheric circulation model. Individual nights, however, show differences from the average flow pattern. During the recovery phase of an auroral substorm, when the westward electrojet is over the observing site, the equatorward meridional wind decreases in magnitude. The zonal wind is generally westward in the evening and eastward in the morning. However, the crossover from westward to eastward flow is a function of the location of the substorm onset and the arrival of the westward electrojet over College. Zenith winds can be very large (200 m/s) and show no systematic pattern, perhaps due to a superposition of wave modes from the auroral zone source region. An example of a night with little auroral activity highlights the effects of magnetospheric convection and the auroral electrojet on the normal auroral zone wind pattern. Temperature measurements occasionally show large enhancements, usually associated with type‐A red aurora.