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We present in detail the algorithm of the electrostatic–quasi-stationary–electromagnetic/MHD approximations and equivalent external sources (EQUEMES method) to develop the quasi-stationary–electromagnetic models of seismo-ionospheric coupling. The penetration of the electromagnetic feld created by near-Earth alternative currents of ULF range was simulated by solving equations for the horizontal electric feld components Ex, Ey of the second order with respect to the vertical coordinate z. This system of two second-order equations is derived from the system of Maxwell equations. The penetration of rather strong horizontal electric feld [of order of (1–10) mV/m] to the ionospheric E and F layers has been modeled. The corresponding variations in the electron concentration in the E and lower F layers of the ionosphere reach a value of order of (1–10)%. Farther increase in these variations can be connected with the related synergetic processes. A possibility of the efective initiation of electron concentration perturbations in the unstable near-equatorial plasma in the F layer of the ionosphere by the packet of atmospheric gravity waves radiated by the near-ground source is illustrated. A good correspondence of the results obtained on the basis of this model to the data of satellite observations is shown.
In the previous paper the electric field Einside, inside a conductive path (and along its axis), having a conductivity s appreciably larger than that of the host medium, s', was studied in the static approximation, for the case of a current dipole source parallel to the path. Here, the same problem is studied but for a source perpendicular to the path. The following two types of paths we considered: (i) a cylindrical channel of radius R and infinite length, and (ii) a layer of width w and infinite extent. If D denotes the distance of the source from the path, and d the distance of the measuring site from the source, we find that the electric field Einside at remote sites (e.g., d/R or d/w of the order of 10(2)) varies as 1/D for the case of a source neighboring to the conductive cylinder, while it is almost independent of D (and w) for the case of a layer. In the case of the cylinder, the values of the ratio Einside/Ehost at (d/R)crit (see the previous paper); significantly exceed (e.g., by one order of magnitude for usual conductivity ratios between 200/1 and 4000/1, but for appreciably small values of D/R, e.g., D/R=2) the corresponding values when the dipole is parallel to the path. The general case, when the dipole source forms a certain angle with its neighboring highly conductive path terminating inside the host medium, is also investigated. The following four points emerge as far as the electric field Eoutside measured inside the more resistive medium but close to an edge is concerned. First, its direction is regulated from the angle between the emitting dipole and the direction of the (elongated) conductive path (as well as from the distance of the source). Second, its amplitude is usually larger than that of Ehost by a factor of around s/s', but there arc also some cases of over-amplification, i.e., the value of Eoutside/Ehost significantly exceeds the conductivity ratio s/s': such an over-amplification may even occur in cases of conductive paths that are not connected. Third, its amplitude versus the distance from the edge varies only slowly, i.e., [Eoutside] 1/r(t) where t is around (but smaller than) unity. Fourth, for a circularly polarized EM plane wave incident on the surf ace of a conductive half-space (containing a highly conductive path close to the interface), the direction of the electric field variations, measured on the surface but close to the end of the path, is generally different from the direction of Eoutside arising from a dipole source which forms a certain angle with its neighboring conductive path. Finally, the above points are applied to the case of the low frequency electric signals that are detected before earthquakes; this results in a natural explanation of the procedure that is followed to determine the parameters of an impending earthquake from the components of the precursory electric signal.
The frequency dependence of the electric field produced by an electric current dipole lying inside or very close to a highly conductive cylinder (s), of infinite length and radius R, embedded in a significantly less conductive medium (s') is investigated. The study is extended to the case when the dipole is located inside or very close to a highly conductive layer (s), of infinite extent and width w, embedded in a significantly less conductive medium (s'). At large distances d from the source and for appreciably low frequencies, i.e., f<fc or f >f0, the electric field is attenuated with a skin depth significantly smaller than deltaout having as a lower limit the skin depth deltain for a full volume of conductivity s. The properties of the recordings, at remote distances, from a current dipole source emitting an exponentially decaying signal of unit initial amplitude and a relaxation time constant t is also studied. The source is located either inside a full volume of conductivity s' or inside a conductive half-space at a depth h (<< d). In the case of homogeneous medium s', a certain relaxation time t0 = žs'd(2)/4 exists due to the diffusion dynamics, leading to the following conclusions. If t << t0 the recordings have an enlarged duration of around t0 and an amplitude orders of magnitude smaller than that corresponding to the static case. If t > t0 the recordings have a duration almost equal to that of the emitted signal, and arrive after a time of around t0, and their amplitude approaches that of the static case. In the case of the current source located within a conductive half-space, the signal recorded at remote observation sites on the interface, arrives in two parts. The first part (which "diffuses" from the source to the interface and then propagates as a surface wave) has a duration significantly smaller than the second part ("solely diffusing" through the conductive medium). The study is extended to the case of a series of signals emitted at equal time-intervals. The application of the above to the earth explain the absence of co-fracture signals but do indicate, that the precursory Seismic Electric Signals reach detectable values at certain sites on the earth's surface.
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