Using the maximum entropy method (MEM), the cosmic-ray power spectral density in the frequency range 3 x 10-9-2 • 10-Hz has been estimated for the period 1947-1990. Cosmic-ray intensity data were integrated from the ion chamber at Huancayo and the neutron monitor at Deep River, following the method of Nagashima and Morishita (1980). The estimated spectrum shows power-law dependence (f-1.62), with several peaks superimposed. Periodicities of the different peaks are identified and related to solar activity phenomena; most of them were reported in the past. Once the ll-yr variation is eliminated, the most prominent feature in the spectrum is a variation, not reported before, with a period of L68 yr (604.8 d). This peak is correlated with fluctuations of similar periodicities found in the southern coronal hole area and in large active regions. The importance that this variation may have to elucidate the solar magnetic flux emergence and the activity cycle is discussed.

No abstract

Abstract.The geomagnetic observatory of Juriquilla Mexico, located at longitude -100.45 • and latitude 20.70 • , and 1946 m a.s.l., has been operational since June 2004 compiling geomagnetic field measurements with a three component fluxgate magnetometer. In this paper, the results of the analysis of these measurements in relation to important seismic activity in the period of 2007 to 2009 are presented. For this purpose, we used superposed epochs of Discrete Wavelet Transform of filtered signals for the three components of the geomagnetic field during relative seismic calm, and it was compared with seismic events of magnitudes greater than M s > 5.5, which have occurred in Mexico. The analysed epochs consisted of 18 h of observations for a dataset corresponding to 18 different earthquakes (EQs). The time series were processed for a period of 9 h prior to and 9 h after each seismic event. This data processing was compared with the same number of observations during a seismic calm. The proposed methodology proved to be an efficient tool to detect signals associated with seismic activity, especially when the seismic events occur in a distance (D) from the observatory to the EQ, such that the ratio D/ρ < 1.8 where ρ is the earthquake radius preparation zone. The methodology presented herein shows important anomalies in the Ultra Low Frequency Range (ULF; 0.005-1 Hz), primarily for 0.25 to 0.5 Hz. Furthermore, the time variance (σ 2 ) increases prior to, during and after the seismic event in relation to the coefficient D1 obtained, principally in the Bx (N-S) and By (E-W) geomagnetic components. Therefore, this paper proposes and develops a new methodology to extract the abnormal signals of the geomagnetic anomalies related to different stages of the EQs.

Part of Special Issue "Precursory phenomena, seismic hazard evaluation and seismo-tectonic electromagnetic effects" Abstract. Results of the ULF electromagnetic emission during the Izu, 2000 earthquake (EQ) swarm and Miyake volcano eruptions during the summer period of 2000 are presented and analyzed. The analysis of the obtained data has been performed in 3 main directions: traditional statistical analysis, i.e. analysis of time dynamics of spectral density, polarization ratios and their derivatives, Principal Component Analysis, and Fractal Analysis. The statistical characteristics were studied at different frequency sub-bands in a frequency range 10 −3 -0.3 Hz. These methods of data processing are described and the obtained results are illustrated and discussed. Some peculiarities of the obtained results such as the rise of the second principal component and the rise of the fractal index can be interpreted as possible shorttime precursors.

Abstract. Electromagnetic 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.

No abstract

Ultra low frequency (ULF) acoustic waves, propagating in the ionosphere, may produce a decrease of the ionospheric density of the F-layer. In turn, decreasing the density of the ionospheric plasma results in the increase of the transparency of the ionosphere for cosmic radio waves. In this paper, simulations of nonlinear frequency down-conversion of extremely low frequency (ELF) acoustic waves into ULF acoustic waves are presented. The propagation of excited ULF waves within the non-isothermal ionosphere is simulated, and the increase of the transparency of the ionospheric F-layer for cosmic radio waves due to plasma density modulation is also considered. We argue that this phenomenon takes place jointly with an increase of the transparency caused by the periodic structure of extremely low frequency (ELF) acoustic waves in the E-layer of the ionosphere. Both phenomena have previously been confirmed experimentally.

No abstract