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By observing the ionospheric F region simultaneously in multiple beams with the middle and upper atmosphere radar, we have been able to track the passage of gravity waves and measure their propagation characteristics. Here we develop a climatology of wave propagation based on the observation of 58 daytime experiments conducted during 1986–1994. The thermosphere seems to be continuously swept by waves detectable by an incoherent scatter radar. These waves generally come for hours on end from a consistent or slowly varying direction, which can be any direction on a given day. Statistically, the waves show a moderate preference for southward travel, with this preference being reduced or shifted to southeastward travel during disturbed times. On average, the horizontal phase trace speed remains near 240 m/s for all periods inspected (40–130 min). This speed matches the behavior expected for lossless waves with 150–200 km vertical wavelength. We find small variability in this relation for different times of day, seasons, solar and magnetic conditions, and directions of wave travel, though waves on disturbed days seem to travel moderately faster on solar minimum mornings.
Oliver et al. (Wed,) studied this question.