Average electron content gradients and nighttime electron fluxes in the mid-latitude ionosphere

Abstract

Observations of the total electron content (TEC) made at Lindau (52°N, 10°E) by means of low orbiting satellites during the period March 1970–December 1972 enabled evaluation of the meridional component of the TEC gradient over the station. The behaviour of this component is investigated in connection with the temporal TEC changes using the medians of both quantities. The gradient reflects well known seasonal changes in the ionosphere such as the semiannual anomaly around noon which leads to relatively strong TEC increases towards the south (up to 9 × 10 15 m −2 degree −1). For the time shortly after midnight, a second semiannual variation of the gradient shows up with enhanced southward TEC increases. Regular northward ionization increases are found near sunrise in summer. Average TEC increases or markedly reduced decreases during the night were obtained for almost every month during the observation period. This special phenomenon of the nighttime ionosphere is discussed with respect to maximum input fluxes of different kinds, which would be necessary to produce the observed effects. Under normal nighttime conditions, the TEC gradients can lead to changes in the ionization of up to 3 × 10 12 m −2 −1 due to horizontal plasma transport, when electric fields of reasonable strength (≈ 2 mV/m) are present.