Observations of field‐aligned currents in association with strong convection electric fields at subauroral latitudes

Abstract

An examination of regions of strong convection electric fields (E >50 mV/m) equatorward of the auroral zone has been made on the basis of data from the S3‐2 satellite in 1976. Only seven examples were found, which indicates a low occurrence rate even after accounting for the gaps in data coverage. While this phenomenon did not correlate with the magnitude of Kp or AE, it is always substorm related. The electric field and magnetic field data indicate that the electric field is generated by plasma sheet ions being driven closer to the earth than plasma sheet electrons by magnetospheric convection in the evening sector. The existence of a net field‐aligned current into the ionosphere through the region indicates the presence of latitudinal conductivity gradient. The depletions of ionospheric particles near regions of strong field‐aligned currents (≥1 µA/m²) into the ionosphere indicate that upward moving ionospheric electrons are carrying the current. The evacuation of the E region approximately 1 min after the onset of the electric field as suggested by Banks and Yasuhara (1978) is not supported by the data, but it may occur on a time scale of ∼30 min. If both the F region and E region are depleted in the strong convection region, the result may be a naturally occurring ‘hole’ in the ionosphere.