Topside plasma frequency resonance below the cyclotron frequency

The behavior of the resonance at the plasma frequency, when that frequency is less than the electron cyclotron frequency, is quite different from the previous investigations where the plasma frequency is larger. Ray paths are again found that will return energy to a moving topside sounder over a range of frequencies and corresponding delay times. Only one type of ray path is found, however, and its reflection takes place in the less dense region above. Furthermore, there is a maximum delay time above which no paths are possible, so that the observation of the ‘ringing’ should be limited to a short range of delay times.