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Earth’S Crust International Symposium ECLIPSE 99, 13th-15th Aug., 1999, Istanbul -Published in Ast. Soc. Pacific Conf. Series Vol. 205, pp:208-215. (2000) Monitoring of the telluric currents origined by atmospheric events in Boyali, northwestern Turkey ILYAS CAGLAR and CIHANGIR ERYILDIZ Istanbul Technical University, Faculty of Mines, Istanbul, Türkiye. Email:[email protected] Abstract Telluric currents have a number of origins caused by naturel events such as activities electrochemistry, atmospheric electricity, ionospheric conditions, solar activity and geomagnetism. Telluric currents circulate continuously in the upper regions of the earth’s crust. Between 21 and 27 Boyali Black Sea August 1991, ground based observations of the telluric currents weremade at Boyali, Kastamonu Trache (northwestern Turkey). During the continuous monitoring, the telluric (origined by Pc geomagnetic NAFZ pulsations) and the other currents are simultaneously recorded on a paper. It is readily apparent that Tarakli the persistent variations and the micropulsations have different patterns caused by high atmospheric Anatolia electricity due to local lightnings, and by geomagnetic field of the Earth. The additional examples Introduction The alternating electromagnetic field of the earth that has a regional nature and is intimately related to the phenomena on the sun and in the ionosphere (Fig. 1 and Fig. 2). It is long since they therefore are Aegean Sea known to be closely related to terrestrial and extra-terrestrial phenomena. The electromagnetic field apparently arises as a result of current systems set up mechanically in the ionosphere. These Figure 4. The regional location of the telluric monitoring site electromagnetic waves are noted at the earth’s surface as variations in the geomagnetic field and the telluric current field. The electric part of such a field is known as the telluric current field. They are associated with the general electromagnetic character of the earth as with solar activity (Rooney, DRIFT (ELECTRODE POLARIZATION) Figure 5. The possible general shape of a 1.0 telurogram showing various effects.(after N-S Kunetz, 1965: Principles of 0.5 dipoles telluric prospecting,Compagnie E-W Generale de Géophysique-Paris) 0 T I Earth 1 T T W T Differences of potential (mV) Differences 0.5 E T T Sun :Pure telluric or earth currents I :Industrial stray currents E:Atmospheric electricity I W :Wind effect 0 Figure 1. The Sun plays a very important role in causing the various changes in the electromagnetic field in the Earth. Analysis of the Telurograms and conclusions Sometimes electric (interference) fields appear having frequencies similar to those of telluric current field which distort the phenomenon (Fig. 6). Typical sources of these interference are: Industrial Interference-- In recording sites near industrial cities or electric railways, industrial currents cause sudden irregular changes which can be easily recognized on the telurograms (Fig. 6b). Inductive Interference-- If the measurements are made near telephone or electric transmission lines, interference signals at 5 to 50 cyc/sec are induced in the measuring circuits. Noise due to the wind-- In windy Earth weather, interference with amplitude from 0.2 to 0.4 mV, and with periods from 1.5 to 2 sec are introduced in telurogram. These voltages are due to the electromotive forces induced by the magnetic field or the earth in wind-blown wires. Figure 2 Micropulsations of 0.2 second to a 25.8.1991 10 hour period are also caused Boyali 9.40 by interaction between the solar 10.40 wind and magnetosphere. Micropulsations origined by Solar Winds In Fig. 3 the amplitude spectrum of the short-period variation in the geomagnetic field indicating the peaks is shown. Micropulsations of 0.2 second to 10 hour period are also caused by ineraction between the solar wind and the magnetosphere. Here Pc1=0.2-5 sec, Pc2=5-10 sec, Pc3=10-45 sec, Pc5=150- Atmospheric electricity 600 sec and Pc6>600 sec. A typical spectrum of diurnal (or daily) variation is shown in Fig. 3. The full scale:20mV diurnal variation is believed to be caused by the intercation of the conducting ionospheric layers of the upper atmosphere with the main magnetic field. This is mainly produced by two large loops in the ionosphere at about 100 km height on the side of the Earth which faces the Sun. A 27 day period and its harmonics which may be related to tides caused by Moon’s arbital motion. The solar activity and magnetic storms caused by anormal variations of the micropulsations generally affect telephone, b 12.00 satellite and radio communications (Table 1). 11.00 Telluric or earth currents 1 hour 1 day Drift (electrode polarization) Pc5 & cultural noise 100 27 days 1 year 10 Pc4 26.8.1991 Pc3 Boyali Pc2 full scale:20mV 1 Pc1 Figure 6. Some records of Telurograms from Boyali. 0.1 ELF Electro-tellurogram Magnetic field (nT) 0.01 -8 -6 -4 a 10 10 10 10-2 101 102 atmospheric electricity Frequency (Hz) Figure 3. The amplitude spectrum of the geomagnetic fields. Pc1, etc., refer to micropulsations. (redrawn from Serson (1973), Phys. Earth Planet Int., 7, 313. Tarakli 14.08.1992 Frequency: 0.1-2Hz Magnetogram After Davies, K., 1982: KDP Text notes. b Electro-tellurogram Customer day or night type or activity effects producing effect Civillan satellite communication night magnetic storms solar radio emissions Communication (VHF) day Tarakli 14.08.1992 Commercial aviation-polar cap day&night PCA, magnetic storms Frequency:0.1-0.5Hz Magnetogram Commercial aviation navigation(VLF) day&night PCA, magnetic storms c Electro-tellurogram Electric power companies day&night magnetic storms Long line telephone communication day&night magnetic storms Frequency:0.01-0.125Hz High altitude polar flights, day&night solar proton events radiation hazards Civilian HF communication day&night X-ray emission, U.V. local emission, magnetic atmospheric Tarakli 14.08.1992 electricity Magnetogram Geophysical exploration day magnetic storms Scientific satellite studies day&night Optical solar flares, Figure 7. Electro-tellurograms and magnetograms recorded at Tarakli site. magnetic storms Solar constant measurements X-ray emission, U.V. day&night 15 emission, solar proton spectrums of the telluric The electro-tellurograms and magnetograms simultaneously events and magnetic fields recorded at Tarakli site using magnetotelluric system are Scientific rocket studies, Optical solar flares, 12 shown in Fig. 7. These records show that telluric field magnetosphere, ionosphere, day&night solar features, variations origined by Pc geomagnetic pulsations are upper atmosphere, sun magnetic storms 9 roughly periodic with an average period of a few dozen International community All seconds and amplitude about several tens millivolts. Some day&night field distortions due to atmospheric electricity are indicated Scientific ground studies Optical solar flare, 6 day&night in the records. These records are obtained for different IMS, sun, interplanetary magnetic storms Amplitude frequency bands that are related to the types of Pc magnetosphere, ionosphere, upper solar proton emission, 3 micropulsations. The spectral analysis results of the record atmosphere, stratosphere, troposphere, day&night X-ray emission, U.V. in Fig. 7c is shown in Fig. 8. From this figure it can easily seismological/geomagnetic emission, solar features 0 visible that the electro-telluric and magnetic field variations are generally in coherent over the frequency range 0.01- Table 1. Users of ionospheric forecasts 0 0.04 0.08 0.12 Frequency 0.125 Hz. This pattern indicates a good induction in the earth’s crust origined by external electromagnetic field. Based on the ionospheric observations at Istanbul (Turkey) in 1968, electromagnetic radiowaves 12 distorted by solar activity are investigated (Agopyan, 1995: N.Canitez symposium, April 12-14, Istanbul). F-region within ionosphere is mostly affected by magnetic storms which caused by large and sudden increases in the energy density of the solar wind. 9 Telluric monitoring at Boyali (northwestern Anatolia) 6 Acknowledgments: Between 21 and 27 August 1991, ground based observations of the telluric currents were made at The work in this paper is partly suppoted by Boyali, Kastamonu. The Boyali area is located at 41.3N, 34.15E (Fig. 4) on the region of Cangal Istanbul Teknik Üniversitesi Arastirma Fonu grant ITU- metaophiolite geological units. The micropulsations (i.e. telluric currents caused by them), measuring 3 Amplitude*0.01 727 and by TUBITAK-YDABCAG-433/G. system is located in a quiet place approximately 10 km, out of the town of Tasköprü, Kastamonu.The station is located on the area, with the lowest noise level. A telluric monitoring station using an electric dipole of 100 m length with north-south direction is constructed in the area. Two grounded 0 0.04 electrodes, Cu-CuSO4 non-polarizing type, are used for the electric dipole. During the continuous 0 0.08 0.12 Figure 8. Fourier spectrum of the electro-tellurogram and monitoring, the telluric and other currents are simultaneously recorde on a paper, by a strip chart- Frequency magnetogram in Fig. 7c. recorder. The already various pattern of the telluric records (telurograms) are shown in Fig. 5..
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