Top PDF Electric field measurements on Cluster: comparing the double-probe and electron drift techniques

Electric field measurements on Cluster: comparing the double-probe and electron drift techniques

Electric field measurements on Cluster: comparing the double-probe and electron drift techniques

Each technique has its own merits and weaknesses. Dou- ble probe instruments have relative advantages in terms of conceptual simplicity, regular and essentially unlimited sam- pling frequency, the possibility to measure rapidly vary- ing fields at arbitrarily high amplitudes, and an operational principle independent of the magnetic field. On the other hand, as the measurement principle depends on the electro- static coupling of the probe to the plasma surrounding it, the technique is sensitive to perturbations from the space- craft or the wire booms supporting the probes. Though there are many ways to reduce such perturbations, including de- sign symmetry, biasing of probes and bootstrapping of ad- jacent boom elements, their possible influence always con- stitutes an uncertainty which only comparison to other mea- surements can eliminate. In contrast, electron drift instru- ments are quite insensitive to the details of the spacecraft environment, as the keV energy typical for electrons emit- ted by EDI is much higher than any potentials arising on a well-designed scientifc spacecraft (normally less than 50 V). In the weak magnetic fields typical for Cluster, the emit- ted electrons also spend most of their time in an orbit far away from the spacecraft, further diminishing any influence of the spacecraft-plasma interaction. In addition, the elec- tron drift technique does not depend on spacecraft orienta- tion, while double probe instruments at best can have shorter booms along the spin axis and are often confined to mea- surements in the spin plane. A strength of the EDI technique is that the measurement relies upon simple geometry; thus, when beam tracking is successful the absolute measurement is relatively reliable and does not require calibration or offset correction. However, as the electron drift method relies on observing electrons returned to the spacecraft by the ambient magnetic and electric fields, the magnetic field has to be suf- ficiently strong for the emitted beam not to disperse too much for detection. Rapid variations in the magnetic or electric field will also complicate the beam tracking, so the method works best in regions where the field variations are less rapid than the tracking bandwidth (∼100 Hz), and the angular step-
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Centrifugal acceleration in the magnetotail lobes

Centrifugal acceleration in the magnetotail lobes

Several populations of different species and different en- ergy are thus of interest to understand both planetary atmo- spheric loss due to solar wind interaction and magnetospheric dynamics. One particularly difficult population to measure is the cold proton plasma in the lobes. These protons may have a significant flux while still not enough energy to be observ- able by particle spectrometers, due to the significant positive potential of a sunlit spacecraft in a tenuous plasma. This observational difficulty has been overcome by a recently in- troduced technique described by Engwall et al. (2006a). In brief the method uses the fact that for suitable conditions an enhanced wake is formed around the positively charged spacecraft. The wake disturbs the electric field measure- ments by the Cluster double probe experiment (Gustafsson et al., 2001). By comparing the electric field measurement signature of the wake with a model, the flow velocity can be determined. The wake does not disturb the electron drift in- strument EDI (Paschmann et al., 2001), which can be used to determine the perpendicular (E × B) plasma flow, mak- ing a decomposition of the plasma flow into its parallel and perpendicular parts possible. The density can be estimated from the spacecraft potential, so that the field-aligned flux of plasma can be determined. By applying this new method En- gwall et al. (2009b) could show that cold proton fluxes dom- inates in the distant lobes, out to 19 R E geocentric distance.
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The Electron Drift Instrument on Cluster: overview of first results

The Electron Drift Instrument on Cluster: overview of first results

In this paper we have presented three polar passes that demonstrate that EDI is able to make precise drift velocity measurements under a wide range of conditions, which in- clude the low and variable magnetic and electric fields in the magnetosheath . Drift velocities as low as 1 km s −1 are observed, corresponding to electric fields of 0.1 mV m −1 . An outstanding feature in these observations is the quasi- periodic electric field rotationsobserved on 5 March 2001 over the polar cap on the dayside at 81 ◦ invariant latitude. A key advantage of the EDI technique is that the beam probes the ambient electric field at a distance of some kilometers from the spacecraft, and therefore essentially outside the lat- ter’s influence. Furthermore, the analysis is essentially ge- ometric in nature and thus the accuracy can be quite high. And last but not least, EDI always measures the entire drift velocity, and thus the total transverse electric field, includ- ing any component along the spacecraft spin axis, while the double-probe instrument on Cluster (EFW) measures only in the spin-plane. On the other hand, EDI beam tracking will be disrupted in very low magnetic fields, large fluxes of ambi- ent electrons, and by very rapid changes in magnetic and/or electric fields. Thus EDI and EFW complement each other nicely. Comparisons with EFW are turning out to be very promising, as the remarkable agreement in the example pre- sented in this paper demonstrates. Comparisons with the per- pendicular component of the plasma bulk velocity measured by the CIS instrument have also started.
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Rev. Bras. Geof.  vol.25 suppl.2

Rev. Bras. Geof. vol.25 suppl.2

A conventional Langmuir Probe, operating in the saturation ion current mode was launched on board the rocket to measure the ion number density, which is the same as the electron number density in a quasi-neutral ionospheric plasma. When operating in the saturation electron or ion current mode the electron (ion) number density is proportional to the measured current and can be easily estimated by normalizing with some absolute measure- ment of the electron density like that from a Plasma Frequency Probe or from a ground based Digisonde. It is now well esta- blished that the electron number density estimated from the me- asured saturation ion current is more reliable than that estimated from the saturation electron current (Brace, 1998). Electron num- ber density estimated from the electron saturation current collec- ted by a probe is seen to be approximately 20 percent more than that estimated from the ion saturation current, and sometimes an empirically derived normalization factor is applied to the electron density based on the ratio of the electron density to ion density measured in regions of higher density where the ion density can be measured accurately (Brace, 1998). However, the accuracy of electron density measurements made by a conventional LP is limited by several factors like, the plasma sheath effect, the ef- fect of the vehicle floating potential, contamination of the probe surface, secondary electron and photo emission from the sensor surface etc (see Muralikrishna & Abdu, 1991).
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SPECTRAL FEATURES OF E- AND F-REGION PLASMA IRREGULARITIES AS OBSERVED BY ROCKET-BORNE ELECTRON DENSITY PROBES FROM BRAZIL

SPECTRAL FEATURES OF E- AND F-REGION PLASMA IRREGULARITIES AS OBSERVED BY ROCKET-BORNE ELECTRON DENSITY PROBES FROM BRAZIL

The plasma density profiles estimated from the three experi- ments agree reasonably well with each other, especially when one considers the general profile and the large-scale variations in it. A close look at the electron density height profiles clearly shows the existence of a wide spectrum of scale sizes in the plasma irre- gularities. All the upleg height profiles clearly show the presence of irregularities associated with what is known as the phenome- non of high altitude Spread-F. The presence of medium amplitude plasma bubbles in the high altitude region can be seen in all the upleg profiles while the profiles from the LP and PFP experiments give an idea of the distribution of the small-scale irregularities in this height region. An important feature observed in all the profi- les is the continuous presence of plasma irregularities of a large range of vertical scale sizes in the altitude range of 340 km to 817 km. Plasma bubbles with dimensions of a few kilometres to several tens of kilometres along the rocket trajectory are obser- ved in the height region of 350 km to 550 km during the upleg of the rocket. The electron number density varied considerably in these spatial structures, for example a decrease by a factor of 2.6 in a vertical extension of 1 km near the altitude of 497 km. Near 535 km altitude the electron density increased by a factor of 1.8 within a height range of 2.7 km. Density structures of ver- tical scale sizes in the range of hundreds of meters also were observed superposed on the large-scale structures. During the rocket upleg two height regions of intense irregularities were ob- served, one between 366 and 480 km and the other between 684 and 812 km. The LP and PFP experiments have sufficient height resolution to study the amplitude fluctuations in the small-scale plasma irregularities down to a few meters, while the HFC expe- riment has a height resolution with typical values of about 100 m near the altitude of 300 km. The Langmuir Probe (LP) could make measurements of irregularities of vertical scale sizes more than 8 m in these height ranges, while the Plasma Frequency Probe, could make measurements of irregularities of vertical scale sizes as small as 0.5 m. For all the three experiments the height re- solution improves with height due to the decrease in the rocket velocity.
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PHASE GRADIENT METHOD OF MAGNETIC FIELD MEASUREMENTS IN ELECTRIC VEHICLES

PHASE GRADIENT METHOD OF MAGNETIC FIELD MEASUREMENTS IN ELECTRIC VEHICLES

Magnetic Fields Encountered in Electric Transport: Rail Systems, Trolleybus and Cars // Proceedings of the 22th International Conference on Electromagnetic Compatiability «EMC Europe 2[r]

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Global manifestations of a substorm onset observed by a multi-satellite and ground station network

Global manifestations of a substorm onset observed by a multi-satellite and ground station network

different substorm trigger mechanisms. The main causes for these controversies are probably the limitation in observa- tions. During the last several decades, great progress has been achieved in observational techniques. The Cluster quar- tet, along with Double Star set up an excellent constellation for exploring the geospace. The latter two satellites, compris- ing TC-1 and TC-2, are part of the first scientific mission in China to study the Earth’s magnetosphere (Liu et al., 2005). As a special feature, the magnetic local time of the Double Star coincides at apogee with that of the Cluster spacecraft. In a dedicated study Nakamura et al. (2005) used simultane- ous observations of Cluster and Double Star to investigate the processes in the magnetotail associated with a dipolarization. By using a multi-point analysis technique they have deter- mined that the propagation of the dipolarization was mainly dawnward. However, detailed ionospheric signatures related to this propagation of the disturbance are not included.
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Multi-spacecraft observation of plasma dipolarization/injection in the inner magnetosphere

Multi-spacecraft observation of plasma dipolarization/injection in the inner magnetosphere

A sequence of auroral images observed by IMAGE/WIC in the Southern Hemisphere is presented in Fig. 4. The back- ground level has been removed, as the auroras were rather faint and the image was visibly affected by direct solar ra- diation. The bright “oval” visible at ∼70 ◦ CGLat in the dusk-midnight sector is actually only the poleward part of the auroral oval. According to the DMSP F14 flyby at 03:25–03:29 UT in the near-midnight sector, the poleward and equatorward boundaries were located at ∼71.5 and 63 ◦ CGLat, 23:00–24:00 h MLT. Two poleward boundary inten- sifications, marked “S1” and “S2”, were detected at 03:18 and 03:22 UT. The intensification “S1” showed distinct fea- tures of an auroral tongue propagating equatorward. The au- roral tongue was most clear and intense at 03:20 UT, but its traces can be seen on the next 3 frames until 03:24 UT at around 22.5 h MLT. The second spot “S2” was weaker and patchy, close to the background level. Its remnants can be discerned until 03:30 UT at a somewhat later MLT (∼23.5). Also, this auroral feature propagated equatorward. Both in- tensifications (although rather faint in the equatorward part) resemble auroral streamers in the shape and behavior and may be associated with the electron injections “i1” and “i2”, which were observed 3–4 min after the initiation of poleward intensification at more dawnward location (Fig. 5).
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The Impact of the Expansion of the Bolsa Familia Program on the Time Allocation of Youths And Their Parents Lia Chitolina Miguel Nathan Foguel Naercio Menezes-Filho

The Impact of the Expansion of the Bolsa Familia Program on the Time Allocation of Youths And Their Parents Lia Chitolina Miguel Nathan Foguel Naercio Menezes-Filho

As the multinomial model is non-linear, the marginal effect of the treatment in a DID model is not the marginal impact of the interaction between time and treatment, but the difference of the cross-differences, as described by Puhani (2012). The results of Table 7 (in terms of marginal effects) show that the BVJ has a significant effect on the probability studying and working at the same time, but not on the other outcome variables. The estimated marginal effects mean that the probability of a youngster studying and working increases by 4.2 percentage points with the BVJ, compared with a baseline of 30% in the control group in 2006. The estimated coefficients for the categories ‘studying only’ and ‘working only’ were negative but not statistically significant. It seems, therefore, that treated adolescents do not quit their jobs to study because of the program, but do both activities at the same time. This raises questions about the long run impacts of the program, since the quality of the night classes is notoriously low in Brazil.
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First results of electric field and density observations by Cluster EFW based on initial months of operation

First results of electric field and density observations by Cluster EFW based on initial months of operation

plasma sheet ion with a characteristic energy of 4 keV. To proceed with phase velocity estimates, we have to look in more detail at separate magnetopause crossings. In Fig. 14, we zoom into one outbound magnetopause cross- ing at about 15:02:10 UT. The top panel shows that most of the change in the satellite potential occurs within a time pe- riod of less than a second. The spatial scale is shown in the middle panel. It is obtained by estimating the velocity of the magnetopause along its normal direction, which in this case, is 107 km/s, from the times at which −V sc at all 4 spacecraft pass the 15 V level. The assumption is made that the magnetopause on the scale of satellite separation is flat and moves with a constant velocity. We can see that most of the satellite potential change is within a distance of less than 100 km. This is comparable to the gyroradius of 100 eV magnetosheath protons, which is about 70 km. In the bot- tom panel, we show the electric field data around the mag- netopause crossing in the reference frame moving with the magnetopause (without V × B correction). The electric field has been calculated assuming that its component parallel to B is zero. One can see the large electric fields inside the magne- tosphere which have both tangential and normal components with respect to the magnetopause. During this crossing, the field becomes small approximately 100 km before the mag-
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Bol. Ciênc. Geod.  vol.19 número4

Bol. Ciênc. Geod. vol.19 número4

7.2 m CE95 using 354 CPs (Table 1). Regarding the presence of systematic errors, the distribution of error vectors for theses subsets (Figures 5c and 5d) suggest that while in imagery collected from 2008 onwards error vectors are randomly distributed, in imagery collected before 2008 a horizontal offset towards northwest may be present. Therefore, since the horizontal accuracy of pre-2008 imagery in GE is significantly lower than that of imagery collected during and after 2008 (tested at the 1% level of significance using t-test) and larger horizontal errors occur in pre- 2008 imagery (Table 2), the results suggest that, possibly as a result of the “Ground Truth” program, imagery added after 2008 to GE has a better horizontal positional accuracy than imagery added before 2008.
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Auroral E-region electron density height profile modificationby electric field driven vertical plasma transport:some evidence in EISCAT CP-1 data statistics

Auroral E-region electron density height profile modificationby electric field driven vertical plasma transport:some evidence in EISCAT CP-1 data statistics

We finish by addressing some critical points of the VPT theory itself; some of them were already mentioned by Hu- uskonen et al. (1984). The authors of paper H estimated the lifetime of the ions assuming a value of the effective recom- bination coefficient of α=2×10 −13 m 3 s −1 . In 1992, Nygr´en et al. (1992) published a report on a novel EISCAT measure- ment of α, using the decay of the electron density after peri- ods of short-lived (∼4 s) auroral precipitation bursts. Their measurement (for a review on earlier works, see Nygr´en et al., 1992 and references therein) was at this time the most precise measurement in the height range from 85 to 115 km. Re-analysis of the same data by Ulich et al. 2000 yielded an even higher precision by allowing a time dependent α during the precipitation events and the process of electron density decay. This approach was made possible by the use of the Sodankyl¨a Ion Chemistry model of Turunen et al. (1996). Now, if we use this most recent value of α=4×10 −13 m 3 s −1
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Electric field measurements in a NLC/PMSE region during the MASS/ECOMA campaign

Electric field measurements in a NLC/PMSE region during the MASS/ECOMA campaign

Though there are models for NLC and PMSE formation which largely agree with ground-based observations (L¨ubken et al., 2008; Rapp and L¨ubken, 2004; Rapp and Thomas, 2006), there are less data available for the comparison of in situ measurements to appropriate models. There are few di- rect observations of turbulence and its effects on the elec- trical structure of NLC (L¨ubken et al., 2002). The electron density fluctuations that reflect radar should create measur- able electric field fluctuations (Lie-Svendsen et al., 2003a,b; Robertson, 2007). Reduced conductivity due to electron scavenging by large aerosols can create large DC electric fields within NLC (Holzworth and Goldberg, 2004). Addi- tionally, large voltage fluctuations were seen in the aft probes of both DROPPS rocket flights. Holzworth et al. (2001) and Sternovsky et al. (2004) showed that this was due to the probes rotating into and out of the rocket wake. A handful of rocket campaigns have flown electric field sensors to inves- tigate these phenomena (Goldberg et al., 1993; Zadorozhny et al., 1993; Holzworth et al., 2001; Pfaff et al., 2001; Blix et al., 2003; Strelnikov et al., 2006), but the data has, thusfar, been too variable to draw generally applicable conclusions.
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The influence of the arc plasma treatment on the structure and microhardness C120U carbon tool steel

The influence of the arc plasma treatment on the structure and microhardness C120U carbon tool steel

Carbon steel C120U grade is largely used on the tools for cutting, for dies and knives, for stamping and drawing tools, hobs, thread rolling tools and in many other applications due to her typical properties - high hardness, good toughness and compressive strength. The surface of the steel can be modified by using surface engineering's techniques. Remelting of the surface layer by the source of concentrated energy is promising technique to improve properties of the materials [1-6]. Laser or electron beam use to melting of the surface of tool steels aims to obtain a modified layer with increased microhardness and abrasion resistance [7,8]. The surface remelted layer has usually a finer and more homogenous structure than its original base material. The remelting with the arc plasma (TIG- tungsten inert gas or GTAW - gas tungsten arc welding) used as an economical and easily
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On the structure of field-aligned currents in the mid-altitude cusp

On the structure of field-aligned currents in the mid-altitude cusp

We study two mid-altitude northern cusp crossings (29 Au- gust 2002 and 10 September 2002) by the Cluster spacecraft, concentrating on the spacecraft for which ion, electron and magnetic data are available with clear signatures of field- aligned currents. We study the cusp data of sc-1 for 29 Au- gust 2002 and sc-4 for 10 September 2002. In the rest of the paper, we refer to these events as: event A for sc-1 (29 Au- gust 2002) and event B for sc-4 (10 September 2002). The two data sets are plotted in the same format in Figs. 2 and 3, with, from top to bottom, CIS ion spectrogram in the di- rection parallel (downward) to the magnetic field (panels a), PEACE electron spectrogram in the parallel and anti-parallel directions (panels b, c), electron and ion field-aligned cur- rents at the resolution of the particle distributions (panels d). Panels (e) show the components perpendicular and parallel to the local magnetic field of the FGM magnetic perturba- tions. The perpendicular component of the perturbation is di- rectly associated with the field-aligned currents and the par- allel component is a measure of the diamagnetic effect due to particle injection. The next two panels display the results of the variance analysis of the perpendicular magnetic pertur- bation. The polarisation angle (panel f), defining the direc- tion of the eigenvector associated with the largest eigenvalue, is now measured from the magnetic east, providing in addi- tion a physically meaningful direction of the current sheet. Panel (g) shows the variance ratio between the two largest eigenvalues. Finally, the total particle and magnetic field- aligned currents are shown on panels (h). The FACs deduced from magnetic data are calculated over 5 points (∼20 s) with v sheet = 0 only, and are not defined where the angle between
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A fully probe corrected near-field far-field transformation technique employing plane-wave synthesis

A fully probe corrected near-field far-field transformation technique employing plane-wave synthesis

Abstract. The far-field behavior of an antenna under test (AUT) can be obtained by exciting the AUT with a plane wave. In a measurement, it is sufficient if the plane wave is artificially generated in the vicinity of the AUT. This can be achieved by using a virtual antenna array formed by a probe antenna which is sequentially sampling the radiating near- field of the AUT at different positions. For this purpose, an optimal filter for the virtual antenna array is computed in a preprocessing step. Applying this filter to the near-field mea- surements, the far-field of the AUT is obtained according to the propagation direction and polarization of the synthesized plane wave. This means that the near-field far-field transfor- mation (NFFFT) is achieved simply by filtering the near-field measurement data. Taking the radiation characteristic of the probe antenna into account during the synthesis process, its influence on the NFFFT is compensated.
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Braz. J. Phys.  vol.36 número2A

Braz. J. Phys. vol.36 número2A

In Eq. (3) and Eq. (4) the first term on the right describes the rate of change of the energy of the phonons due to inter- action with the electrons. More precisely they account for the gain of the energy transferred to then from the hot carriers and then the sum of contributions J E LO and J E AC is equal to the

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A two-fluid model describing the finite-collisionality, stationary Alfvén wave in anisotropic plasma

A two-fluid model describing the finite-collisionality, stationary Alfvén wave in anisotropic plasma

phenomenon in that the first case involves a fluctuating, trav- eling pattern and the second case involves a non-fluctuating, non-traveling pattern. In contrast to the dispersive Alfv´en wave, the inclusion of the interaction between dc cross-field plasma flow and an initial dc field-aligned current provides a dc free energy source to support the non-fluctuating, non- traveling StA pattern in the absence of a structured driver. To summarize, whereas one approach is to choose either the wave frame or the lab frame (in which a Doppler shift is in- troduced), we treat the problem in a single frame of reference (the lab frame) within which the wave phase velocity is zero. Whereas the seminal paper for dispersive Alfv´en waves is Goertz and Boswell (1979), the seminal papers for station- ary Alfv´en waves are Mallinckrodt and Carlson (1978) and Maltsev et al. (1977). The term “stationary Alfv´en wave” was introduced by Maltsev et al. (1977) to describe a sta- tionary electromagnetic structure resulting from plasma con- vection past a conducting strip. The application of the term was broadened by Mallinckrodt and Carlson (1978) to in- clude structuring from a moving field source in a magnetized plasma. The term “Alfv´en wing” is used to describe a sta- tionary wave resulting from moving conductors, for exam- ple in the case of Io orbiting within Jupiter’s magnetosphere (Chust et al., 2005) or as a result of a conducting tether orbit- ing with a spacecraft (Sallago and Platzeck, 2004). In these cases, the structure of the stationary wave is imposed by the source, although Chust et al. (2005) argue that additional fil- amentation can result. In contrast to previous descriptions of Alfven wings, the nonlinear two-fluid model described here and by Knudsen (1996) includes the effects of electron iner- tia, leading to a self-consistent StA wave that restructures a large-scale current sheet into a new electromagnetic equilib- rium, and does not require a structured source. Also, as with its time-varying counterpart – the dispersive Alfven wave – the StA wave develops a significant parallel electric field as a result of finite electron mass and plasma temperature.
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Structure of X5CrNi18-10 and S355NL Steels after Remelting with the Electric Arc

Structure of X5CrNi18-10 and S355NL Steels after Remelting with the Electric Arc

The tested steels have wide application as a construction material, meeting particular conditions of loading during exploitation. Steel S355NL is often used in building constructions and machine construction, operating, among others areas in mining, drilling and motor industry. Steel X5CrNi18-10 according to the standard PN-EN 10088, is ranked as resistant to corrosion. It is used in many industrial branches such as in food and chemical industry, in devices used in medicine or households. The type is widely used due to its chemical capacity in contact with many types of chemical compounds.
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Hybrid Adaptive Filter development for the minimisation of transient fluctuations superimposed on electrotelluric field recordings mainly by magnetic storms

Hybrid Adaptive Filter development for the minimisation of transient fluctuations superimposed on electrotelluric field recordings mainly by magnetic storms

The recovery of EEP signals has long puzzled the scien- tific community but very few approaches have shown promis- ing results (Hadjioannou and Vallianatos, 1993; Rovithakis and Vallianatos, 2000; Konstantaras et al., 2006b). The method of “the subtraction of the telluric inductive compo- nent from electric field recordings” (Hadjioannou and Val- lianatos, 1993) developed in the early 1990s has the dis- advantage of the assumption that the existence of preseis- mic magnetic fields does not influence the estimated induced electrical components. In an effort to ignore the impedance tensor, a method incorporating neural networks has been de- veloped (Rovithakis and Vallianatos, 2000), where the neural network is trained to predict the Earth’s electric field. Thus, any electrotelluric anomaly due to a seismoelectric source is enhanced on the prediction error signal, measured as the dif- ference of the recorded and the predicted electric field signal, as it is an “external” signal added on and not a genuine part of the electric field. However the effectiveness of the method relies on the assumption that at the time of their occurrence EEPs are not accompanied by any significant magnetotelluric anomalies.
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