Midlatitude measurements of the ionospheric electric field during the ALADDIN programme

Three measurements of ionospheric electric field were made during the 24-h ALADDIN rocket program at Wallops Island on June 29-30, 1974. The first of these used a double probe instrument, flown at 1500 Local Solar Time, and the second and third measurements were made by barium cloud releases at evening and morning twilight. These three electric field vectors have been compared with the predictions of a number of models of electric field due to the dynamo effects of various atmospheric tides, and also of a possible magnetospheric origin. On the assumption that the measurements were made at a location equatorward of the afternoon convergence and poleward of the morning divergence in the electric field patterns related to the Sq current system, Stening's (1973) model of the diurnal variation of the electric field induced by the (1, -2) tidal model at the time of the summer solstice correctly predicts the directions of the observed electric field. Forbes and Lindzen's (1976, 1977) model, incorporating the three major propagating tidal modes as well as the evanescent (1, -2) mode, also bears an acceptable relationship to the ALADDIN electric field directions. The ALADDIN E-field magnitudes are comparable with those obtained by ground-based observations from Millstone Hill and from Saint Santin but are about half of Stening's model values, and three times those of Forbes and Lindzen. Saint Santin E-field directions, at the same latitude but 75 deg difference in longitude, are distinctly different from ALADDIN, implying that longitudinal differences are significant.