Excitation of vortices using linear and nonlinear magnetostatic waves

It is shown that stationary vortex structures can be excited in a ferrite film. This is the first proposal for creating vortex structures in the important cm and mm wavelength ranges. It is shown that both linear and nonlinear structures can be excited using a three-beam interaction created with circular antennae. These give rise to a special phase distribution created by linear and nonlinear mixing. An interesting set of three clockwise rotating vortices joined by one counter-rotating one presents itself in the linear regime: a scenario that is only qualitatively changed by the onset of nonlinearity. It is pointed out that control of the vortex structure, through parametric coupling, based upon a microwave resonator, is possible and that there are many interesting possibilities for applications.Comment: 28 pages, 13 figure

Excitation of planetary electromagnetic waves in the inhomogeneous ionosphere

In this paper we develop a new method for the analysis of excitation and propagation of planetary electromagnetic waves (PEMW) in the ionosphere of the Earth. The nonlinear system of equations for PEMW, valid for any height, from D to F regions, including intermediate altitudes between D and E and between E and F regions, is derived. In particular, we have found the system of nonlinear one-fluid MHD equations in the β-plane approximation valid for the ionospheric F region (Aburjania et al., 2003a, 2005). The series expansion in a "small" (relative to the local geomagnetic field) non-stationary magnetic field has been applied only at the last step of the derivation of the equations. The small mechanical vertical displacement of the media is taken into account. We have shown that obtained equations can be reduced to the well-known system with Larichev–Reznik vortex solution in the equatorial region (see e.g. Aburjania et al., 2002). The excitation of planetary electromagnetic waves by different initial perturbations has been investigated numerically. Some means for the PEMW detection and data processing are discussed

Penetration of the electric and magnetic field components of Schumann resonances into the ionosphere

International audienceA penetration of electric and magnetic fields of the first global electromagnetic ELF resonance into the ionosphere in the cavity Earth-ionosphere is investigated numerically. It is shown that a penetration height for magnetic components is 2?3 times greater than for electric components and it depends essentially on the value of the geomagnetic field and its orientation with respect to the normal to the Earth's surface. A penetration height for the electric field is about 50÷70 km, and for the magnetic field it is 120÷240 km. An influence of variations of the conductivity of the ionosphere at the daytime and nighttime and under different solar activity on a penetration of the fields of the first Schumann resonance has been investigated. Keywords. Electromagnetics (Guided waves) ? Ionosphere (Ionosphere-atmosphere interactions; Wave propagation

Spectrum of the seismic-electromagnetic and acoustic waves caused by seismic and volcano activity

International audienceModeling of the spectrum of the seismo-electromagnetic and acoustic waves, caused by seismic and volcanic activity, has been done. This spectrum includes the Electromagnetic Emission (EME, due to fracturing piezoelectrics in rocks) and the Acoustic Emission (AE, caused by the excitation and the nonlinear passage of acoustic waves through the Earth's crust, the atmosphere, and the ionosphere). The investigated mechanism of the EME uses the model of fracturing and the crack motion. For its analysis, we consider a piezoelectric crystal under mechanical stresses, which cause the uniform crack motion, and, consequently, in the vicinity of the moving crack also cause non-stationary polarization currents. A possible spectrum of EME has been estimated. The underground fractures produce Very Low (VLF) and Extremely Low Frequency (ELF) acoustic waves, while the acoustic waves at higher frequencies present high losses and, on the Earth's surface, they are quite small and are not registered. The VLF acoustic wave is subject to nonlinearity under passage through the lithosphere that leads to the generation of higher harmonics and also frequency down-conversion, namely, increasing the ELF acoustic component on the Earth's surface. In turn, a nonlinear propagation of ELF acoustic wave in the atmosphere and the ionosphere leads to emerging the ultra low frequency (ULF) acousto-gravity waves in the ionosphere and possible local excitation of plasma waves

Volcano Popocatepetl, Mexico: ULF geomagnetic anomalies observed at Tlamacas station during March?July, 2005

International audienceIn this paper the first results of ULF (Ultra Low Frequency) geomagnetic anomalies observed at Tlamacas station (Long. 261.37, Lat. 19.07) located at 4 km near the volcano Popocatepetl (active volcano, Long. 261.37, Lat. 19.02) for the period March?July, 2005 and their analysis are presented. The geomagnetic data were collected with a 3-axial fluxgate magnetometer designed at UCLA (University of California, Los Angeles, 1 Hz sampling rate frequency, GPS). Our analysis reveals some anomalies which are suspected to be generated by local volcanic origin: the EM background in the vicinity of the volcano is significantly noisier than in other reference stations; the sporadic strong noise-like geomagnetic activity observed in the H-component; locally generated geomagnetic pulsations (without preferred polarization) are detected only at Tlamacas station

Interpretation of the microwave non-thermal radiation of the Moon during impact events

The results of recent observations of the non-thermal electromagnetic (EM) emission at wavelengths of 2.5cm, 13cm, and 21cm are summarized. After strong impacts of meteorites or spacecrafts (Lunar Prospector) with the Moon's surface, the radio emissions in various frequency ranges were recorded. The most distinctive phenomenon is the appearance of quasi-periodic oscillations with amplitudes of 3–10K during several hours. The mechanism concerning the EM emission from a propagating crack within a piezoactive dielectric medium is considered. The impact may cause the global acoustic oscillations of the Moon. These oscillations lead to the crackening of the Moon's surface. The propagation of a crack within a piezoactive medium is accompanied by the excitation of an alternative current source. It is revealed that the source of the EM emission is the effective transient magnetization that appears in the case of a moving crack in piezoelectrics. The moving crack creates additional non-stationary local mechanical stresses around the apex of the crack, which generate the non-stationary electromagnetic field. For the cracks with a length of 0.1–1µm, the maximum of the EM emission may be in the 1–10GHz range

Electromagnetic emission from magnetite plate cracking under seismic processes

International audienceElectromagnetic emission generated by cracking of a magnetite plate is theoretically investigated. The non-stationary mechanical stresses, produced by moving the tip of a crack and a wave of mechanical unloading in the plate are considered as the sources of the radiation. It is demonstrated that the radiation is produced by the appearance of a non-stationary magnetic moment in the plate

Geomagnetic anomalies observed at volcano Popocatepetl, Mexico

International audienceResults of the ULF geomagnetic monitoring of the volcano Popocatepetl (Mexico) and their analysis are summarized and presented for the period 2003?2006. Our analysis reveals some anomalies which are considered to be of local volcanic origin: the EM background in the vicinity of the volcano was found to be significantly noisier than at other reference stations; sporadic strong noise-like geomagnetic activity was observed in the H-component; some geomagnetic pulsations were observed only at the Tlamacas station (located at 4 km near the volcano). The results are discussed in terms of a physical mechanism involving the presence of a second magmatic chamber within the volcano and, finally, further perspective directions to study volcanic geodynamical processes besides the traditional ones are given

Model of the propagation of very low-frequency beams in the Earth–ionosphere waveguide: principles of the tensor impedance method in multi-layered gyrotropic waveguides

The modeling of very low-frequency (VLF) electromagnetic (EM) beam propagation in the Earth–ionosphere waveguide (WGEI) is considered. A new tensor impedance method for modeling the propagation of electromagnetic beams in a multi-layered and inhomogeneous waveguide is presented. The waveguide is assumed to possess the gyrotropy and inhomogeneity with a thick cover layer placed above the waveguide. The influence of geomagnetic field inclination and carrier beam frequency on the characteristics of the polarization transformation in the Earth–ionosphere waveguide is determined. The new method for modeling the propagation of electromagnetic beams allows us to study the (i) propagation of the very low-frequency modes in the Earth–ionosphere waveguide and, in perspective, their excitation by the typical Earth–ionosphere waveguide sources, such as radio wave transmitters and lightning discharges, and (ii) leakage of Earth–ionosphere waveguide waves into the upper ionosphere and magnetosphere. The proposed approach can be applied to the variety of problems related to the analysis of the propagation of electromagnetic waves in layered gyrotropic and anisotropic active media in a wide frequency range, e.g., from the Earth–ionosphere waveguide to the optical waveband, for artificial signal propagation such as metamaterial microwave or optical waveguides