Drift and absorption measurements in the lower ionosphere and their interpretation using spectral analysis

Phase angle differences of quasi-periodic coherent disturbances of a quantity measured at three points in a stochastic medium can be interpreted as a result of travelling-line or plane-wave disturbances. Drift and absorption measurements in the lower ionosphere have been discussed in this way in the recent literature. It has been found that drift velocities occasionally and absorption disturbances always indicate dispersion in the plane of observation. It is shown that a medium with 'frozen' structures moving with a constant velocity can result in apparent frequency-dependent velocities. Ensembles of plane surfaces of travelling disturbances can be applied to construct a new type of model for simulating moving fading patterns of radio waves as used for drift observations.