The Fluid Ionosphere

In this review paper, the equations of motion describing the fluid dynamics of the ionosphere are constructed step by step, so that any master or post-graduate student may get familiar with the general theory of the “traditional” approach to Ionospheric Physics, in which chemicals forming the Earth’s upper atmosphere are represented as fluids in mutual interaction. The hypotheses on which the smooth-field fluid representation is based are discussed in terms of microscopic dynamics of the gas particles; this discussion is oriented to prepare the reader for the post-fluid approaches to the physics of turbulence. The fluid-dynamical picture of the ionosphere is the most classical and conceptually simple one, and this makes it extremely widespread in terms of theoretical models and applications. The advantages and achievements of this theory are highlighted, its limits are discussed, and perspectives to go beyond it sketched.