Abstract
Abstract. The conventional equations of ionospheric electrodynamics, highly succesful in modeling observed phenomena on sufficiently long time scales, can be derived rigorously from the complete plasma and Maxwell's equations, provided that appropriate limits and approximations are assumed. Under the assumption that a quasi-steady-state equilibrium (neglecting local dynamical terms and considering only slow time variations of external or aeronomic-process origin) exists, the conventional equations specify how the various quantities must be related numerically. Questions about how the quantities are related causally or how the stress equilibrium is established and on what time scales are not anwered by the conventional equations but require the complete plasma and Maxwell's equations, and these lead to a picture of the underlying physical processes that can be rather different from the commonly presented intuitive or ad hoc explanations. Particular instances include the nature of the ionospheric electric current, the relation between electric field and plasma bulk flow, and the interrelationships among various quantities of neutral-wind dynamo.
Highlights
The conventional treatment of ionospheric electrodynamics expounded in standard textbooks and tutorial publications (e.g. Matsushita, 1967; Rishbeth and Garriott, 1969; Bostrom, 1973; Kelley, 1989; Volland, 1996; Rishbeth, 1997; Richmond and Thayer, 2000; Heelis, 2004; Fuller-Rowell and Schrijver, 2009, and many others) has a dual aspect: the equations used to carry out calculations, and the verbal descriptions intended to explain physical processes represented by the equations
The purpose of this paper is to show that, when the complete plasma and Maxwell’s equations are applied, the conventional equations are obtained under appropriate well-defined approximations, but the more rigorous physical understanding of causal sequences and time variations may be different from, and sometimes inconsistent with, the conventional verbal descriptions
The conventional equations of ionospheric electrodynamics are obtained by neglecting all acceleration terms in the momentum equations and all time derivatives in Maxwell’s equations; only slow time variations are considered, e.g. from varying external influences, or from density or temperature profile changes due to aeronomic processes
Summary
The conventional treatment of ionospheric electrodynamics expounded in standard textbooks and tutorial publications (e.g. Matsushita, 1967; Rishbeth and Garriott, 1969; Bostrom, 1973; Kelley, 1989; Volland, 1996; Rishbeth, 1997; Richmond and Thayer, 2000; Heelis, 2004; Fuller-Rowell and Schrijver, 2009, and many others) has a dual aspect: the equations used to carry out calculations, and the verbal descriptions intended to explain physical processes represented by the equations. The purpose of this paper is to show that, when the complete plasma and Maxwell’s equations are applied, the conventional equations are obtained under appropriate well-defined approximations, but the more rigorous physical understanding of causal sequences and time variations may be different from, and sometimes inconsistent with, the conventional verbal descriptions. The conventional ionospheric equations may be accepted as valid under restricted conditions (it is no surprise that, despite their deficient treatment of plasma physics, they have proved adequate to explain the observations), but the detailed description of some underlying physical processes needs to be revised.
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