Traveling ionospheric disturbances originating in the auroral oval during polar substorms

A study of large-scale traveling ionospheric disturbances has been carried out by investigating the signatures they leave in columnar electron content records. Columnar content was obtained at a number of widely spaced stations by measuring the Faraday rotation angle of a signal from a geostationary satellite. The results of observations from February 1967 to November 1968 are presented. A simple model relating variations in electron concentration produced by the passage of atmospheric gravity waves to changes in columnar content is developed. Using this model the observed fluctuations in columnar content are shown to be consistent with the effects expected to be produced by neutral atmospheric waves. Virtually all fluctuations studied occurred during magnetically disturbed periods with a tendency for more frequent occurrence near the middle of magnetic storms. A good correlation between the relative amplitudes of the disturbances, defined as the rms amplitude of the perturbations in electron content divided by the unperturbed content, and Kp is shown to exist. The disturbances exhibit a diurnal variation in speed and direction of travel. The speed variation is not completely explained. The average variation in direction of travel is consistent with a source located near dipole latitude 78°N and 1900 geomagnetic time. It is suggested that the disturbances originate in the auroral oval during polar substorms.