Auroral Zone Thermospheric Dynamics Using Fabry-Perot Interferometric Measurements Of The Neutral Oxygen 15867K Emission (Solar Maximum, Electrojets, Temperature)

Abstract

Forty-four nights of thermospheric neutral wind and temperature measurements were obtained from College, Alaska (65(DEGREES) invariant latitude) during solar maximum using a ground-based Fabry-Perot interferometer. When averaged by increasing geomagnetic activity, the wind exhibits two main features. First, the general flow pattern, poleward and westward in the evening, changing to southward and eastward in the morning, persists with increasing activity. The flow velocity increases and the change in direction occurs earlier in magnetic local time as the geomagnetic activity increases. Second, as the activity increases, the meridional wind pattern shifts equatorward with the auroral oval. Consequently, the low geomagnetic activity average wind pattern in the north is similar to the moderate activity average pattern in the south. The average thermospheric temperature is governed by the geomagnetic activity and by the previous day's 10.7cm solar flux. The increase in temperature with solar flux is about the same as with auroral activity ((DBLTURN) 225(DEGREES)K). The dynamical behavior on individual nights highlights the importance of local auroral substorms, which can cause large deviations from both global models and the observed averages. Coupling between the E and F regions is inferred by comparing the bulk motion of the optical aurora and the observed wind. Westward-drifting auroral forms accompany the westward evening zonal wind. The arrival of the westward electroject heralds the change from westward to eastward zonal flow, with time delays from less than fifteen minutes to over two hours. Increasing electrojet strength results in higher zonal wind speeds. Around magnetic midnight, as the aurora moves east, the equatorward meridional wind decreases in velocity. Vertical winds are commonly observed and can be quite large and variable, particularly during pulsating aurora. Type-A red aurorae are associated with large (>300(DEGREES)K) temperature increases, consistent with atmospheric heating due to precipitating electrons.