Abstract
VHF coherent scatter radar observations of an auroral substorm over Alaska are analyzed in the context of multibeam incoherent scatter plasma density and drifts data and green‐line all‐sky optical imagery. Coherent scatter arises from Farley Buneman waves which are excited in theEregion whenever the convection electric field is greater than about 20 mV/m. Aperture synthesis radar imaging and other aspects of the methodology facilitate the precise spatial registration of the coherent scatter with coincident optical and incoherent scatter radar measurements. Discrete auroral arcs were found to separate diffuse regions of coherent backscatter and, sometimes, to align with the boundaries of those regions. At other times, auroral arcs and torches lined up adjacent to discrete, structured regions or radar backscatter. Drastic variations in the Doppler shifts of the coherent scatter from one side of the auroral forms to the other suggest the presence of field‐aligned currents. An empirical formula based on previous studies but adapted to account approximately for the effects of wave turning was used to estimate the convection electric field from the moments of the coherent scatter Doppler spectra. Line‐of‐sightF region plasma drift measurements from the Poker Flat Incoherent Scatter Radar (PFISR) were found to be in reasonable agreement with these convection field estimates. Reasons why the empirical formulas may be expected to hold are discussed.
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