Data from an oblique‐incidence time‐delay measurement experiment over an 1150‐km east–west path between Sterling, Virginia, and St. Louis, Missouri, are used to examine the accuracy of the transmission‐curve method of determining oblique‐incidence ionosphere characteristics from vertical‐incidence soundings. The experiment employed a pulsed sweep‐frequency ionosphere recorder at each of the endpoints and another at the midpoint of the great‐circle path. A small but consistent difference between the maximum usable frequencies (MUF) observed at the endpoint stations and the MUF determined from the vertical‐incidence soundings was found. Seasonal trends of this difference are presented. The results of the analysis indicate that the average error of the transmission‐curve‐derived MUF varies between zero and 5 per cent too low, depending on time of day and season. Random variations result in a spread of about 10 per cent between the upper and lower decile errors.
In the last few years experiments were reported which demonstrated propagation of electromagnetic waves through an overdense magnetoplasma, i.e., a plasma whose plasma frequency is greater than the frequency of the probing wave. The interpretation of the experimental results was based on the ``whistler mode.'' The ``whistler mode'' appears in the infinite plane wave solutions of Maxwell's equations for an infinite homogeneous magnetoplasma. In a laboratory plasma, the effects of the boundaries of the plasma may play an important role in determining the propagation properties of the waves. These effects are examined and the analysis shows that the waves may, under certain circumstances, exhibit sufficiently different qualitative and quantitative characteristics to seriously limit the applicability of the infinite medium theory to bounded plasmas. To illustrate this point, the properties of waves propagating in a dense, homogeneous, cylindrical plasma bounded by a conducting wall are examined and compared with the properties of the wave predicted from infinite plane wave theory.
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