GNGTS 2015 - Atti del 34° Convegno Nazionale

GNGTS 2015 S essione 2.1 13 distribution, the only direction that an electric field, magnetic field and radiation field can point to is radially outward from the centre of the sphere. However, in a radiation field the electric and magnetic fields must be transverse to the direction of motion, so this system also will not produce any radiation, or have a magnetic field. The electric field E , the charge density ρ , and the convective current density v are given by E = - ∇ϕ , 4π ρ = - ∇ 2 ϕ , v = (∂/∂t ∇ϕ )/ ∇ 2 ϕ , where ϕ (x,y,z,t) is the time variable electric potential in the region A of the space, see Fig. 2. Fig. 2 – Regions A and B where electric charges are accelerating and electric potential satisfy Laplace’s equation. These choices, together with H= 0 , automatically satisfyMaxwell’s equations and describe an electromagnetic source, in an arbitrary volume, which only produces a static electric field outside the source region. For a true charged cloud which radially oscillates, the charge distribution decrease gradually with distance, and therefore a net electric field exists at a certain distance; to which a very small variable magnetic field is associated. Being that CIEN stations are located near residential areas, where noise on magnetic detection is not very low, the possibility of revealing very low magnetic field variations is scarce. This model can explain why electric perturbations are not recorded by distant CIEN stations (Fidani, 2011b). Furthermore, to increase the possibility of detecting a magnetic component associated to the recorded ELF electric perturbations, the magnetic loops should be installed in the same positions as the electrodes. On the other hand, electric field oscillations were recorded by all 14 CIEN stations also before many rainfalls without evidencing seismic activity. It has been reported that rainfalls are often preceded by electric ions variations in the atmosphere (Takahashi, 1972). These observations suggest that electric oscillatory phenomena occur togetherwith air ions concentrationfluctuations and/or meteorological instabilities. Amodel for a spherically symmetric and dynamically stable structures has been proposed for the atmosphere by balancing electrostatic forces with air pressure (Tennakone, 2011). The possibility of forming stable spherically symmetric charge configurations in the atmosphere has been the subject of many past investigations, which have been conducted with the aim of better understanding unusual atmospheric phenomena, such as ball lightning (BL) and EQL (Singer, 1971; Tennakone, 2006). Thus, these charge configurations are potentially able to explain both observations of electric oscillations and luminosities in the atmosphere, with luminosities appearing when strong meteorological or seismic phenomena occur (Fidani and Martinelli, 2015). However, in the atmosphere they are subject to far transport by wind. Being so, this charged cloud model requires further investigation in order to determine if there are correlations between earthquakes and ELF perturbations, and between rainfalls and ELF perturbations. The genuine anomalies which preceded the studied earthquake cases will be therefore only a ratio of the total recorded ones, whereas the other anomalies are spurius and principally caused by meteorology. Probability of earthquake occurrence from anomalies with meteorological influence. The time dependent synthetic probabilities of earthquake occurrence on the basis of electric anomalies recorded by CIEN can be evaluated. The meteorological processes can generate spurius anomalies and, thus generate a noise factor. It can be quantified by introducing a reliability parameter r , which is defined by the ratio of the genuine anomaly numbers to the total ones. The conditional probability of an earthquake occurring between t and t + τ on the condition that no earthquake occurs during a period between 0 and t is (Maeda and Yoshida, 1990)