Recent incoherent scatter electron density measurements made with 0.9-km-altitude resolution Barker-coded pulses are combined with the Jacchia neutral atmosphere model to generate nighttime electrical conductivities for the lower ionosphere at Arecibo. Electron density profiles and derived conductivities are presented for nights characterized by low and high magnetic activity. A model for nighttime electron densities incorporating 17 nights of data is presented along with the computed electrical conductivities. The features of the model include: (1) a sharply defined lower boundary at 85 km, (2) a layer between 85 and 120 km having an average density of 2 × 10³ cm−3 and showing a weak symmetry about solar midnight due to the ionizing effect of scattered solar ultraviolet radiation, (3) a valley of low electron density above 120 km that is progressively filled in with ionization as magnetic activity increases, and (4) electron density enhancements in the upper E region occurring 4 hours after local midnight as a result of downward transport of plasma from the F region. Height-integrated conductivities calculated from the model and the two nights of observations are also given.
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Rowe et al. (1973) studied this question.
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