Abstract
Abstract. A complete theory of low-frequency MHD oscillations of the Earth's weakly ionized ionosphere is formulated. Peculiarities of excitation and propagation of electromagnetic acoustic-gravity, MHD and planetary waves are considered in the Earth's ionosphere. The general dispersion equation is derived for the magneto-acoustic, magneto-gravity and electromagnetic planetary waves in the ionospheric E- and F-regions. The action of the geomagnetic field on the propagation of acoustic-gravity waves is elucidated. The nature of the existence of the comparatively new large-scale electromagnetic planetary branches is emphasized.
Highlights
In the present review, both new and known branches of electromagnetic oscillations of the Earth’s weakly ionized upper atmosphere are considered; the Earth’s magnetic field ionospheric E- and F-layers consisting of electrons, ions and neutral particles
In the first class of waves belong the acoustic, inertio-gravitational and MHD (Alfven and magnetoacoustic) waves, while the second class of waves contains planetary Rossby waves and magnetogradient waves, which are caused by the latitudinal inhomogeneity of both the angu
The density ρ and pressure P are described by two scalar equations: the continuity equation and the energy equation for polytropic processes
Summary
Both new and known branches of electromagnetic oscillations of the Earth’s weakly ionized upper atmosphere (ionosphere) are considered; the Earth’s magnetic field ionospheric E- and F-layers consisting of electrons, ions and neutral particles. For the synoptic processes (two weeks and more), it may be considered that the atmosphere always is in the quasi-static and quasi-geostrophic states As it was shown (Monin and Obukhov, 1958; Yaglom, 1953), when observing these conditions four frequencies of acoustic-gravity waves (AGW) fall out from the dispersion equation and only the frequency of planetary Rossby waves remains. With phase velocity depending on the orientation of the wave vector k with respect to the geomagnetic field H 0, are generated due to the tension of the geomagnetic lines of force and, as it will be shown below, can be very slow (10÷50 m s−1) and long-period (1÷2 days), when the wave vector k is almost transversal to H 0 and fast, when vectors k and H 0 are parallel It follows that the traditional method of wave filtration used in the troposphere does not work under the ionospheric conditions.
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