F region parameters can change by relatively large amounts over short periods of time (fraction of an hour) under so-called “undisturbed” conditions. There is evidence that these changes are due to propagating acoustic gravity waves. While the periods of these variations and other local parameters (Doppler velocity and angle of arrival) can be measured with a high-resolution digital ionosonde, other quantities like wavelength or magnitude and direction of the propagation velocity cannot be observed. The Clarke Lake radio astronomical antenna array which can be operated in the HF band allows tracking the motion of medium scale (100–500 km) disturbances by observation of the changes in the apparent position of radio stars. Some first data samples were recorded and analyzed (R. L. Higgins and B. McManus, private communication, 1987).
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