A study of the diurnal variation in the thermosphere as derived by satellite drag

An analysis was performed on 29,574 densities derived from the drag of 10 satellites to determine simultaneously the parameters of the solar-activity effect in the thermosphere on the one hand, and the amplitude and shape of the diurnal-variation curve on the other. This paper reports on the study of the diurnal variation only. Although a considerable amount of smoothing is inherent in the drag method, it seemed useful to see whether any change could be detected in the shape of the diurnal-variation curve with height, latitude and solar activity. None was detected; the curve remains remarkably stable, symmetric, with a maximum at 14 hr 20 min L.S.T. and a minimum at 2 hr 20 min L.S.T. A systematic variation of the temperature range with height is observed when static models are used to derive it.