Morphology of evening sector aurorae in λ557.7‐nm Doppler temperatures

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Abstract
An all‐sky scanning Fabry‐Pérot spectrometer was used to observe temperatures of auroral OI (557.7‐nm) emissions over Poker Flat, Alaska (65.12N, 147.43W). The sudden temporal and spatial changes in Doppler temperatures observed are likely owing to the emission height changing as a response to variations in the characteristic energy of the precipitating electron population. Three cases were analyzed: (1) A Doppler temperature drop (∼200 K) over the entire sky occurred immediately after an auroral brightening; the temperature remained lower after the auroral intensity had resumed its quiescent levels. (2) A local increase of Doppler temperature, colocated with a weak auroral arc, occurred 25 minutes before a westward propagating substorm onset. When the auroral luminosity suddenly increased the Doppler temperature had a sharp decrease. (3) The region inside a loop‐like auroral arc showed elevated Doppler temperature relative to that of the arc itself. Auroral fading prior to onset was accompanied by increased temperatures.