ULF electromagnetic turbulence in the high‐latitude topside ionosphere

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Abstract
Results obtained by the Aureol 3 satellite on electromagnetic waves in the ELF range in the high‐latitude topside ionosphere show the existence of a new type of turbulence. This turbulence is observed on both the electric and magnetic wave components and appears as bursts of 0.1 s to a few seconds typical duration in the polar cusp and auroral zone, associated with field‐aligned currents and low energy electron precipitations. The two possible interpretations of these observations, either in terms of a filamentary structure of the field‐aligned currents or of Alfven waves are discussed. For either of these models the observed values of the parallel component of the electric field are much larger than those predicted by classical models of the electrodynamics of the lower ionosphere. These results are compared with recent observations and might indicate the existence of acceleration mechanisms at low altitudes.