In this chapter, the following characteristics of waves and plasmas in ionosphere are discussed. (1) Plane waves. (2) Propagation in a dispersive medium. (3) Propagation in an anisotropic medium. (4) Wave packets. (5) Phase paths and packet paths. (6) Electromagnetic waves. (7) Plasma frequencies. (8) Gryrofrequencies. (9) The Debye length and (10) Motions of ions in crossed electric and magnetic fields.

This book chapter presents a discussion of magnetoionic theory in relation to radiowave propagation in the ionosphere. It begins with the Appleton formula, its properties, and approximations followed by radiowave polarization theory including ordinary-extraordinary wave coupling. Ray direction in a magnetoplasma is also discussed as well as effects of heavy ions. Finally, the chapter closes with the generalization of magnetoionic theory.

This chapter presents a discussion on the morphology of the ionosphere. It begins with the analysis of synoptic variations in the ionosphere together with the spatiotemporal variations of the critical frequency of its individual layers. Models for the ionospheric layers are also dealt with including the D region and the sporadic E and spread F layers. Finally, electron and ion temperature structures of the ionosphere are discussed.

This chapter deals with the effects of ionospheric propagation on a radio signal's amplitude and phase structure. Radio signal attenuation in terms of losses e.g. power loss and spatial losses are discussed together with ionospheric absorption and its temporal and spatial variations. Polarization matching and fading are also included. Radio signal frequency in relation to its phase is also given focus. Ionospheric drifts, traveling ionospheric disturbances, acoustic-gravity waves, and nonreciprocal phenomena are also discussed.

This chapter deals with the effects of different ionospheric disturbances on radio communication. These disturbances include solar disturbances, sudden ionospheric disturbances, ionospheric storms, polar cap absorption (PCA) events, traveling ionospheric disturbances (large scale), and associated disturbances in the geomagnetic field (solar flare effect, SFE), aurora, and magnetospheric substorms. High latitude radio communications is also discussed. Finally, ionospheric forecasting and its accuracy is presented.

The medium-frequency band (300-3000 kHz) is dominated by the amplitude modulation (AM) broadcast band (≈ 500-1700 kHz). This frequency band has an enormous economic, social, and political impact on everyday life and it is intensively used. Although the MF band is an important part of the radio spectrum, our knowledge of propagation in the band is rather poor because of (i) spectrum congestion, (ii) high absorption, (iii) the complicated role of the Earth's magnetic field, (iv) difficulty in separating deviative from nondeviative effects, (v) collisions, and (vi) the fact that, on the lower frequencies, the medium is not slowly varying. For efficient use of the MF band it is essential for users to share the same channel with minimum interference. Thus the estimation of the signal strength in distant regions is an important consideration in channel sharing with potentially interfering transmitters. This chapter deals with midfrequency radiowave propagation in the ionosphere including skywave signal propagation and midfrequency broadcasting.

The very-high-frequency range is defined as between 30 MHz and 300 MHz. The ionosphere can reflect radio signals on frequencies of > 50 MHz but over most of the VHF range the main effect of the ionosphere is to scatter radio energy by irregularities. Such irregularities exist in the D region (turbulence), in the E region (meteors and sporadic E), and in the F region, especially near the dip equator and in high latitudes (plasma instabilities). On lower frequencies (e.g. less than 50 MHz) propagation effects such as Faraday rotation, angular refraction, and time delay can be important. The value of Y(=f_H/f) is small (<0.05), and under most conditions the propagation is essentially quasi-longitudinal (e.g. on 60 MHz for θ ≲ 89.28° with f_H = 1.5 MHz) and the ray path is almost straight. The maximum electron densities in the ionosphere are rarely sufficient to reflect radio waves on frequencies much above 30 MHz except for relatively short periods (e.g. in the equatorial regions and in higher latitudes near the maximum of the sunspot cycle). For communications on the ground the main ionospheric mechanism is scattering by plasma irregularities. The chief irregularities in the ionosphere are: (i) turbulence in the D region; (ii) ionized trails due to the passage of meteors through the atmosphere; (iii) spread-F (field aligned); (iv) sporadic E; and (v) artificial irregularities. This chapter deals with very high frequency radiowave propagation in the ionosphere with particular focus on scattering phenomena including D-region scatter, meteorscatter, auroral scatter, and equatorial scatter. VHF propagation by ionospheric layers is also discussed.

This chapter presents problem exercises for ionospheric radiowave propagation theory.