R. H. Wand

Millstone Hill measurements on 26 February 1979 during the solar eclipse and formation of a midday F-region trough☆

On 26 February 1979, the Millstone Hill incoherent scatter radar was operated to observe the F-region over Canada along the path of the total eclipse of the sun. A continuous scanning mode was used with the radar elevation fixed at 4° and the azimuth swept continuously from 350° to 298°. Each scan required 20 min to complete and useful results were obtained at ranges up to 2992 km. The path of totality crossed the center of the region swept by the radar beam. The F-region electron density, ion temperature, electron temperature and ion line-of-sight drift were measured. Electric field components have been extracted from the radar line-of-sight component of the ion drift by assuming that the electric field may be represented by a quasi-static two-dimensional potential with the potential assumed constant along geomagnetic field lines. Electron density decreases were observed in association with the eclipse. At 300 km an ∼50% decrease occurred near the region of totality, but the variations were small above 450 km. However, apparently unrelated to the eclipse, very large electric fields developed in the region under view. Somewhat later a well defined trough formed north of Λ = 70°, whose equatorward edge is extremely sharp and appears to be approaching the radar with time. Large values of the electron and ion temperatures were observed in the trough and the trough formed where the drift was westwards and exceeded 1000 m s−1. It is suggested that the observed through may be due to an increase in the rate of the charge transfer reaction O+ + N2 → NO+ + N in the presence of a very large electric field impressed from the magnetosphere in association with a large magnetic disturbance.