The full adiabatic theory is used to describe wave propagation in a warm magnetoplasma for frequencies around the plasma frequency and the upper hybrid resonance frequency. By comparison with the microscopic theory for directions perpendicular and parallel to the static magnetic field, we can well define the range of validity of the full adiabatic theory, which can then be used for computation of the group velocity. The variation of this group velocity as a function of frequency for several directions of propagation is shown for models corresponding to the ionosphere and the far magnetosphere. Three factors deserve attention: (1) the upper hybrid resonance and its neighborhood can be rigorously studied for far magnetospheric conditions by using the full adiabatic theory; (2) the computed modes present a mixed electrostatic‐electromagnetic character; (3) The minima in group velocities for pseudoresonance frequencies progressively fill up as the temperature increases.

The envelope and the wave form of the resonance signals obtained by a rocket‐borne RF sounder experiment have been recorded on the ground. The processing of the data concerning the third harmonic of the electron gyrofrequency (3fH) has led to the conclusion that it results from two waves having slightly different frequencies (typically, 1 kHz); the amplitudes of these waves depend on the antenna orientation. Beating between the two waves causes a modulation of the signal amplitude similar to the modulation already observed with the topside sounders, which can be explained in the same way.

The waveforms and envelopes of resonance signals observed in the ionosphere at 2, 3, 4, and 5fH by rocket experiment are compared with the analytical results provided by a spatial ray‐tracing procedure which takes the gradient of Earth's magnetic field into account. An approximate calculation yields the algebraic expression of the wave damping from whence the decrease of the received signals is deduced versus time as well as their frequency variations.

A procedure for determining ray trajectories in warm magnetoplasmas is presented; it is based on mathematical treatments of the wave dispersion relation. This procedure is used to interpret topside resonance at the upper hybrid frequency as oblique echoes. The following results are obtained: when/e • 2/% two Doppler shifted echoes are received after reflection from above the emitting satellite; their frequencies are plotted as functions of time. The absence of such echoes is observed for/e • 2/%

The propagation of waves in a hot magnetoplasma near gyroharmonics is studied by means of analytical ray tracing. To get the parametric equations of the paths a dispersion relation is first obtained through the electrostatic hypothesis and some mathematical approximations. For this case, it is shown that, except near reflection, waves transmitted from an ionospheric sounder travel almost along the static magnetic field and that the gradient of the magnetic field may be responsible for their reflection back to the spacecraft antenna. In certain cases two distinct trajectories can simultaneously intersect the receiving antenna thus giving rise to beats which are sometimes observed experimentally. The theoretical formulas are applied to a 3fH resonance.