This chapter deals with horizontally inhomogeneous ionosphere. First, we will show that the quasi-DC (direct current) approximation is appropriate for the description of ionospheric currents caused by FMS and Alfvén waves. Next, we will discuss how this approximation can be applied to an ionosphere containing irregularities of different scales. Then we will show several examples of global distributions of magnetic variations produced either by the fieldaligned currents of an incident Alfvén wave or by the electric field of an FMS-wave.
We have shown that FMS-wave is almost insensitive to the ionospheric conductivity. The transition region between the dayside and nightside ionosphere is one example of a strong horizontal gradient of electron concentration, it is therefore also an example of a strong horizontal anomaly of the conductivity. We have also shown that on the contrary, the dependency of transmission on ionospheric conductivity becomes an important factor for Alfvén waves. The behavior of the ground magnetic field at sunrise and sunset is then discussed and its dependence on the initial MHD-mode is examined.
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(2007). Inhomogeneous Ionosphere. In: Hydromagnetic Waves in the Magnetosphere and the Ionosphere. Astrophysics and Space Science Library, vol 353. Springer, Dordrecht. https://doi.org/10.1007/978-1-4020-6637-5_9
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DOI: https://doi.org/10.1007/978-1-4020-6637-5_9
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