TwinSat team meeting ISTC, London, August 01 - 05, 2011 Scattering of the VHF transmitter signals by electric discharges in the lower atmosphere and using scattered waves for seismicity monitoring in the TwinSat experiments V.M. Sorokin1, A.K. Yaschenko1 and V.M. Chmyrev2 1Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation, Russian Academy of Sciences (IZMIRAN), 142190 Troitsk, Moscow region, Russian Federation 2Schmidt Institute of Physics of the Earth (IPE), Russian Academy of Sciences, 10, B. Gruzinskaya Str., 123995 Moscow, Russian Federation This report presents the theory of VHF electromagnetic wave scattering by electrical discharges in the lower atmosphere. Discharges arise in turbulent atmosphere at strong DC electric field connected with growing seismic activity. Obtained results show that the onboard registration of direct and scattered VHF transmitter signals can be used as additional tool for detection of earthquake precursors by TwinSat .
This theory is based on the model of atmosphere – ionosphere electrodynamic coupling. According to this model DC electric field is generated by seismic related Electro Motive Force (EMF) in the lower atmosphere. Inclusion of EMF into the atmosphere – ionosphere electric circuit leads to DC electric field growth up to 10 mV/m in the lower ionosphere. [Sorokin et al., 2001; 2005; 2007; Sorokin and Chmyrev 2010] 1. Earth surface 2. Conductive layer of the ionosphere 3. External electric current in the lower atmosphere 4. Conductivity electric current in the atmosphere – ionosphere circuit 5. DC electric field in the ionosphere 6. Field - aligned electric current 7. Charged aerosols injected into the atmosphere by soil gases Electric field in the ionosphere
The ionization-recombination processes Equilibrium values of ion number densities are determined by the recombination process and the adhesion to aerosols in the atmosphere. The light single-charged ions and the heavy ions are produced as a result of light ions adhesion to aerosols in the atmosphere near the Earth’s surface. [Sorokin et al., 2007] EMF electric current and charge densities:
Spatial distribution of external current, atmospheric conductivity, aerosols and DC electric field in the convective atmosphere is described by the self-consistent set of nonlinear equations [Sorokin et al., 2007]:
Input parameters of model are the atmosphere turbulence and convection, atmosphere radioactivity and aerosols density near the ground. A source of ionization defines the conductivity in the near ground atmospheric layer Radioactive elements such as radon, radium, thorium, actinium and their decay products enter the atmosphere together with soil gas. [Sorokin et al., 2001; Sorokin et al., 2007] The vertical distribution of ion production rate is a result of atmospheric absorption of gamma radiation and alpha particles from the decay of radioactive elements being constituents of the atmospheric radioactivity. Curves 1,2 and 3 correspond to different levels of atmospheric radioactivity growing from 1 to 3.
An examples of large magnitude DC electric field distribution in the lower atmosphere normalized to the breakdown electric field [Sorokin et al., 2011] At definite conditions the seismic related DC electric field can reach the breakdown value in some region of the atmosphere (marked out by red in the figure below).
Fluctuations of the atmosphere density and DC electric field reaching the breakdown value in turbulent vortices cause the formation of random electrical discharges in the disturbed region
Existence of seismic related electrical discharges has been confirmed by over horizon observation of VHF electromagnetic radiation (Vallianatos and Nomicos, 1998). An explanation of the phenomena was presented in [Sorokin et al., 2011]
Electric field scattered by the discharge conducting channel Coordinates used for the calculation Hertz potential of scattered radiation Discharge is the vertical segment of conducting channel. The current density is formed as a result of charge polarization by incident electric field in the conducting channels.
Frequency spectrum of electromagnetic radiation scattered by the conducting channels of random electric discharges Green function: Power spectrum of the electromagnetic waves scattered by random discharges during the time interval T:
Calculation of scattered VHF radiation has been performed for the following parameters:
Electric field of scattered VHF radiation depends on horizontal distance at different altitudes
Spatial distribution of the electric field of scattered VHF radiation
Magnetic field of scattered VHF radiation depends on horizontal distance at different altitudes
Spatial distribution of the magnetic field of scattered VHF radiation
Experimental results Kushida & Kushida (1998, 2002) introduced an empirical earthquake prediction method based on monitoring anomalous VHF-band radio waves transmitted from an FM radio station beyond the line of sight. Sakai el al. (2001) showed that anomalous propagation of VHF-band radio waves emitted from a broadcasting station in Sendai City were related to earthquakes with magnitude greater than 5 that occurred in the area between Sendai and the Tateyama observatory in Chiba Prefecture. Fukumoto et al. (2002) confirmed that the anomalous propagation events were the result of scattering of VHF-band radio waves immediately prior to earthquakes, by documenting reception at an observatory that was beyond the line of sight of transmission location. Pilipenko et al. (2001) showed that the received intensities of scattered waves were stronger when the antenna was at a shallower angle, which implied that the scattering body was in the middle atmosphere rather than in the ionosphere. Fujiwara et al. (2004) also reached the same conclusion using a more rigorous method, and recorded no scattered waves when antennae were oriented vertically. Hayakawa et al. (2007) described a generation mechanism of atmospheric disturbances resulting from changes in geochemical quantities associated with earthquakes and VHF radio wave refraction. Yonaiguchi el al. (2007) discussed that the effect of long-range VHF wave propagation is usually due to meteorological radio ducting. Moriya et al., (2010) have observed the anomalous VHF-band radio-wave propagation beyond the line of sight prior to earthquakes. Radio waves transmitted from a given FM radio station are considered to be scattered, such that they could be received by an observation station beyond the line of sight.
Locations of four broadcasting stations with identical transmitting frequencies (83.8 MHz; output power in parentheses) and five observing stations. The cross indicates the hypocenter of the southern Rumoi sub-prefecture earthquake, M = 6.1, of 2004 December 14.
Scattered FM radio waves documented al ERM prior to the southern Rumoi sub-prefecture earthquake, M, =6.1. Blue traces (third channel) record a temporal change in the electric field at 83.8 MHz, which probably originated from the Haboro FM station rather than from HOO [Moriya et al., 2010].
Example of electric field strength variation caused by a sporadic E layer and recorded at ERM on 2004 June 18. EQ echoes from the HOO FM station are evident between 18:00 and 20:00 at ERM. The total duration of the echoes and the quiet period were analyzed for earthquakes that occurred beneath the Hidaka Mountains, using the data emitted from the HOO FM station and received at the only —30 km distant ERM observatory . The 1000-2000 m high Hidaka Mountains in between prevent the direct propagation between these sites. Such short-distance data are useful for reducing the uncertainty in identifying which earthquake is associated with the EQ echo and for obtaining highly reliable data [Moriya et al., 2010].
Scheme of registration of VHF signals on the satellite. 1. Transmitter, 2. Receiver, 3. Satellite, 4. Direct signal, 5. Scattered signal, 6. Electric discharges.
VHF observations onboard the satellite could be an effective tool for detection and locating the seismically modified atmospheric regions of anomalously strong (breakdown) DC electric field. It could be reached through simultaneous registration of broad band VHF radiation from the ‘discharge’ region and electromagnetic waves from the ground VHF transmitters, both direct and scattered signals. Using of the direction finding technique with highly sensitive onboard VHF receivers could allow to locate the source of emission and scattering in the atmosphere and therefore to make applicable an additional type of the precursor signals in space. Principally this task can be realized through installation of a pair of magnetic loop antennas and appropriate electric antenna on the micro satellite platform.
Conclusion. Pre-earthquake DC electric field reaching the breakdown value initiates numerous chaotic electrical discharges and related phenomena in the lower atmosphere Chaotic electrical discharges. Heating of atmosphere in the discharge region and the generation of outgoing long wave (8-12 μm) radiation. Broadband electromagnetic VHF emission observable on the ground and in space. Airglow in visible range of wavelengths. Refraction and scattering of VHF radio waves in the troposphere providing the reception of VHF transmitter signals by over-horizon ground-based receivers and by satellites. Growth of ozone concentration in the disturbed region.
Atmosphere Above Japan Heated Rapidly Before M9 Earthquake (http://www Atmosphere Above Japan Heated Rapidly Before M9 Earthquake (http://www.technologyreview.com/blog/arxiv/26773/) Infrared emissions above the epicenter increased dramatically in the days before the earthquake in Japan (D. Ouzounov et al., 2011)