Equatorial electrojet at African longitudes: first results from magnetic measurements

Abstract. In the framework of the French participation in the International Equatorial Electrojet Year (IEEY), ten magnetotelluric stations were installed between November 1992 and November 1994 along a 1200-km-long meridian profile, between Lamto (latitude 6.2°N, Côte d'Ivoire) to the south and Tombouctou (latitude 16.7°N, Mali) to the north. These stations measured digitally the three components of the magnetic field and the two components of the telluric electric field, and operated over a period of 20 months. The magnetic data is used to study the features of the equatorial electrojet (EEJ) in West African longitude. The measurement of the telluric electric field variations will be presented elsewhere. Hourly mean values are used to study the morphological structure of the regular diurnal variation SR of the three components (H, D, and Z) of the earth magnetic field and to characterize the EEJ during magnetically quiet days. The occurrences of the counter-electrojet (CEJ) are set forth, emphasizing its seasonal variability. Assumed to be a current ribbon, the EEJ main parameters (the position of its center, its width, and the amplitude of its current density at the center) are determined. A preliminary analysis of the time variations of these parameters is presented over period of 20 months (from January 1993 to August 1994). Results are compared with those obtained during previous experiments of the same kind.

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Deciphering archeological contexts from the magnetic map: Determination of daub distribution and mass of Chalcolithic house remains

The Holocene ◽

10.1177/0959683619857238 ◽

2019 ◽

Vol 29 (10) ◽

pp. 1637-1652 ◽

Cited By ~ 1

Author(s):

Natalie Pickartz ◽

Robert Hofmann ◽

Stefan Dreibrodt ◽

Knut Rassmann ◽

Liudmyla Shatilo ◽

...

Keyword(s):

Magnetic Field ◽

Magnetic Measurements ◽

Magnetic Data ◽

Forest Steppe ◽

Distribution Maps ◽

Depth Functions ◽

The North ◽

Holistic Understanding

The unique size and development of prehistoric megasites of the north Pontic Cucuteni-Tripolye Chalcolithic groups (4100–3600 BCE) challenge modern archeology and paleoecology. The extremely large number of houses (approximately 3000, mostly burned) necessitates the development of multidisciplinary technologies to gain a holistic understanding of such sites. In this contribution, we introduce a novel geophysical methodology and a detailed analysis of magnetic data – including evolved modeling techniques – to provide critical information about the setup of findings, enabling a thorough understanding of the settlement dynamics, apart from invasive excavation techniques. The case study is based on data from magnetic field maps and distribution maps of the daub and pottery find categories. This information is used to infer magnetic models for each find category to numerically calculate their magnetic fields for comparison with the archeological data. The comparison quantifies the sensitivity of the magnetic measurements with respect to the distribution of the different find categories. Next, via inversion computation, the characteristic depth functions of soil magnetization are used to generate maps of magnetization from the measured magnetic field maps. To validate the inverted soil magnetization maps, the magnetic excavation models are used, providing an interpretational frame for the application to magnetic anomalies outside excavated areas. This joint magnetic and archeological methodology allows estimating the find density and testing hypotheses about the burning processes of the houses. In this paper, we show internal patterns of burned houses, comparable to archeological house models, and their calculated masses as examples of the methodology. An application of the new approach to complete megasites has the potential to enable a better understanding of the settlement structure and its evolution, improve the quality of population estimations, and thus calculate the human impact on the forest steppe environment and address questions of resilience and carrying capacity.

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Earth magnetic field effects on Swarm electric field instrument

Planetary and Space Science ◽

10.1016/j.pss.2012.10.004 ◽

2012 ◽

Vol 73 (1) ◽

pp. 145-150 ◽

Cited By ~ 4

Author(s):

S. Rehman ◽

J. Burchill ◽

A. Eriksson ◽

R. Marchand

Keyword(s):

Magnetic Field ◽

Electric Field ◽

Magnetic Field Effects ◽

Field Effects ◽

Earth Magnetic Field ◽

Electric Field Instrument

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TELLURIC SOUNDING—A MAGNETOTELLURIC METHOD WITHOUT MAGNETIC MEASUREMENTS

Geophysics ◽

10.1190/1.1439731 ◽

1966 ◽

Vol 31 (1) ◽

pp. 185-191 ◽

Cited By ~ 9

Author(s):

S. H. Yungul

Keyword(s):

Magnetic Field ◽

Electric Field ◽

Magnetic Measurements ◽

Sedimentary Basins ◽

Base Station ◽

Primary Objective ◽

Field Station ◽

Field Operation ◽

Resistivity Log ◽

The Magnetic Field

The basic theory and objectives of telluric sounding (TS) are about the same as those of the well‐known method of magnetotelluric sounding (MTS) (Cagniard, 1953). Both methods make use of the natural electromagnetic phenomena known as geomagnetic micropulsations to obtain crude “resistivity logs” from the surface down to great depths, without drilling, if the subsurface has mild structures, low dips, and lateral continuity in the electrical resistivity. Let the x-y plane of the Cartesian coordinates represent the surface of the earth. With MTS, the field operation consists of simultaneously recording the time variations of an arbitrary x component of the electric field, [Formula: see text], called a tellurogram, and that of the y component of the magnetic field, [Formula: see text], called a magnetogram, both at the same point where the downward information is desired. The main difficulty is in the measurement of the magnetic field variations with sufficient accuracy. The measurement of the electric field variations is very simple and expeditious. TS bypasses this difficulty, because it does not require the measurement of the magnetic field. With TS, the field operation requires two electric field recording units. One of these units remains at a “base station” where the subsurface is known from a well log, while the second unit is placed at a “field station” where one wishes to explore the subsurface. Thus, for each sounding, one obtains two simultaneous tellurograms. These are Fourier analyzed. The ratios of the electric field amplitudes as a function of frequency, combined with the resistivity log at the base station, furnish the MTS‐type data at the field station that are interpreted in the usual manner to yield a crude resistivity log at the field station. The primary objective of TS is the exploration of sedimentary basins. It may be preferable to MTS in certain cases and vice versa; it is not meant to replace MTS. The theoretical basis and the procedures of TS are discussed in this paper.

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Ultra-lightweight integrated unmanned aerial systems for a wide range of geophysical magnetic exploration: a single system for high-precision archaeological surveys to rugged topography geological acquisitions

10.5194/egusphere-egu21-7290 ◽

2021 ◽

Author(s):

Jeanne Mercier de Lépinay ◽

Tristan Fréville ◽

Baptiste Kiemes ◽

Luis Miguel Sanabria ◽

Bruno Gavazzi ◽

...

Keyword(s):

Magnetic Field ◽

High Resolution ◽

High Precision ◽

Adaptive Systems ◽

Magnetic Measurements ◽

Magnetic Sensor ◽

Magnetic Data ◽

Industrial Sectors ◽

Wide Range ◽

The Magnetic Field

Magnetic mapping is commonly used in the academic and industrial sectors for a wide variety of objectives. To comply with a broad range of survey designs, the use of unmanned aerial vehicles (UAVs) has become frequent over the recent years. The majority of existing systems involves a magnetic acquisition equipment and its carrier (an UAV in this context) with no -or very few- connections between the two systems. Terremys is conceiving and optimizing UAVs specifically adapted for geophysical magnetic acquisitions together with the appropriate processing tools, and performs magnetic surveying in challenging environments. Terremys&#8217; &#8220;Q6&#8221; system weights 2.5 kg in air, including UAV & instrumentation, and allows 30 min swarm or individual flights.Rotary-wing UAVs are found to be the most adaptive systems for a wide range of contexts and constraints (extensive range of flights heights even with steep slopes). They offer more flight flexibility than fixed-wing aircrafts. One of the major problems in the use of rotary-wings UAVs for magnetic mapping is the magnetic field generated by the aircraft itself on the measurements. Towing the magnetic sensor 2 to 5 m under the aircraft reduces data positioning accuracy and decreases the performances of the UAV, which can be critical for high-resolution surveys. To overcome these problems, a deployable 1 m long boom&#160;is rigidly attached to the UAV. The UAV magnetic signal can be divided between 1-the magnetic field of the whole equipment and 2-a low to high frequency magnetic field mostly originating from the motors. The magnetization of the system is the principal source of magnetic noise. It is modelled and corrected by calibration-compensation processes permitted by the use of three-component fluxgate magnetometers. The time-varying noise depends on the motors rotational speed and is minimized by optimizing the UAV components and characteristics along with the boom&#8217;s length.The final set-up is able to acquire magnetic data with a precision of 1 to 5 nT at any height from 1 to 150 m above ground level. The high-precision magnetic measurements are coupled with a centimetric RTK navigation system to allow for high-resolution surveying. The quality of the obtained data is similar to that obtained with ground or aerial surveys with conventional carriers and matches industrial standards. Moreover, Terremys&#8217; systems merge in real-time data from all the aircraft instruments in order to integrate magnetic measurements, positioning information and all the UAV&#8217;s flight data (full telemetry) into a unique synchronized data file. This opens up many possibilities in terms of QA/QC, data processing and facilitates on-field workflows.Case studies with diverse designs, flight altitudes and targets are presented to investigate the acquisition performances for different applications, as distinct as network positioning, archaeological prospecting or geological mapping.The full integration of the magnetic sensor to the drone opens the possibility for implementation additional sensors to the system. The adjoining of other magnetic sensors would allow multi-sensors surveying and increases daily productivity. Diverse geophysical sensors can also be added, such as thermal/infrared cameras, spectrometers, radar/SAR.

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An analytical representation of the geomagnetic field in Canada for 1975. Part II: The secular change

Canadian Journal of Earth Sciences ◽

10.1139/e78-024 ◽

1978 ◽

Vol 15 (2) ◽

pp. 237-244 ◽

Cited By ~ 5

Author(s):

E. Dawson ◽

L. R. Newitt

Keyword(s):

Magnetic Field ◽

Secular Change ◽

Main Magnetic Field ◽

Annual Change ◽

Mean Values ◽

The North ◽

Magnetic Inclination ◽

Polynomial Extrapolation ◽

Annual Means ◽

The Magnetic Field

Annual mean values of the north (X), east (Y) and vertical (Z) components of the magnetic field from 20 observatories in Canada and adjacent countries for the period 1955–1976 are used to test secular change derived from cubic time terms in a polynomial model. This model was used to derive the main magnetic field charts of Canada for 1975. The rms deviation in the secular change for 1975 (annual change) is a disappointing 16 nT. Graphs of observed and computed annual means show that this fit will worsen with time, especially in Y and Z. For these reasons the annual change contours on the above-mentioned charts were derived by conventional graphical methods. Graphs of the magnetic declination (D), the horizontal intensity (H) and Z were drawn for 20 observatories and 157 Canadian and American repeat stations. Values were extrapolated to 1975 and contoured. A comparison of graphical and polynomial methods show that this simple graphical extrapolation is more sensitive to small significant secular changes than a polynomial extrapolation. We show annual change charts in X, Y and Z constructed by this method.The movement of centres of intense secular change, called isoporic foci, in X, Y and Z, are examined to determine their influence on the secular change pattern in Canada. These indicate that Y and D will continue to decrease, while X and H will continue to increase over most of the country. The total intensity (F), the magnetic inclination (I), and Z will all decrease rapidly in southern Canada.

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The characteristics of field-aligned currents associated with equatorial plasma bubbles as observed by the CHAMP satellite

Annales Geophysicae ◽

10.5194/angeo-27-2685-2009 ◽

2009 ◽

Vol 27 (7) ◽

pp. 2685-2697 ◽

Cited By ~ 25

Author(s):

J. Park ◽

H. Lühr ◽

C. Stolle ◽

M. Rother ◽

K. W. Min ◽

...

Keyword(s):

Magnetic Field ◽

Electric Field ◽

Field Measurements ◽

Current Strength ◽

Meridional Plane ◽

Champ Satellite ◽

Poynting Flux ◽

Plasma Bubbles ◽

Equatorial Plasma Bubbles ◽

Earth Magnetic Field

Abstract. Field-aligned currents (FACs) generate magnetic deflections perpendicular to the ambient Earth magnetic field. We investigate the characteristics of FACs associated with equatorial plasma bubbles (EPBs) as deduced from magnetic field measurements by the CHAMP satellite. Meridional magnetic deflections inside EPBs show a clear hemispheric anti-symmetry for events observed before 21:00 LT: inward in the Northern Hemisphere and outward in the Southern Hemisphere. When an eastward electric field is assumed the magnetic signature signifies a Poynting flux directed downward along the magnetic field lines. This means that FACs are driven by a high-altitude equatorial source. Such a scheme cannot be drawn as strictly from our observations after 22:00 LT, possibly because of a westward turning of the electric field inside EPBs and/or a decay of EPBs later at night. The perpendicular magnetic deflection is tilted by 40° from the magnetic meridional plane in westward direction, which implies that the depleted volume of EPBs, as well as the FAC structure, is tilted westward by 40° above the magnetic equator. The peak-to-peak amplitude of the FAC density is found to range typically between 0.1–0.5 μA/m2. The field-aligned sheet current density and the diamagnetic current strength show no correlation.

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Some problems with old magnetic data processing

E3S Web of Conferences ◽

10.1051/e3sconf/202019602029 ◽

2020 ◽

Vol 196 ◽

pp. 02029

Author(s):

Sergey Y. Khomutov ◽

Manjula Lingala

Keyword(s):

Magnetic Field ◽

Scientific Community ◽

Magnetic Measurements ◽

Field Vector ◽

Digital Data ◽

Magnetic Data ◽

Total Field ◽

Analog To Digital ◽

The Past ◽

Lack Of Information

Continues magnetic measurements at the IKIR FEB RAS obser-vatories Magadan (MGD), Paratunka (PET), Yuzhno-Sakhalinsk (YSS), Cape Schmidt (CPS) and Khabarovsk (KHB) and CSIR-NGRI observatories Hyder-abad (HYB) and Choutuppal (CPL) have been started almost since their formation. A significant part of the results obtained is presented in the WDC and INTERMAGNET databases. However, a large amount of raw data remains un-processed and unavailable for using by scientific community. In the past few years, institutes has been making efforts to process and reprocess old magnetic data. Digital images of analog magnetograms of the Observatory Paratunka since 1967 were obtained and the possibility of their use for calculation hourly and minute values of magnetic field elements was evaluated. Old digital data that was available during the conversion from analog to digital magnetometers is processed. The main problem of processing or re-processing archived data is the lack of information (metadata) about the measurement conditions. First of all, these are the results of absolute observations, which are necessary to obtain the values of the elements of the total field vector. In this paper, some technologies are proposed that allow to use the data obtained during processing of analog magnetograms to adjust the digital magnetometers records. A signif-icant problem is the lack or inaccuracy of information about the temperature conditions in the variation pavilion, about magnetometers or support equipment maintenance or about works in and near the pavilions. As we accumulate the experience during the processing of old magnetic data, a “catalog” of noise and its typical images is formed. This makes it more reliable and efficient to identify and remove this noise from records.

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A new shipboard three‐component magnetometer

Geophysics ◽

10.1190/1.1442054 ◽

1986 ◽

Vol 51 (10) ◽

pp. 1992-1998 ◽

Cited By ~ 68

Author(s):

Nobuhiro Isezaki

Keyword(s):

Magnetic Field ◽

Magnetic Moments ◽

Vertical Component ◽

The North ◽

Intensity Measurements ◽

Compensation Device ◽

The Fourier Transform ◽

North And South ◽

The Magnetic Field ◽

Three Components

The three components of the geomagnetic field were measured at sea by STCM (Shipboard Three Component Magnetometer) with a relative accuracy of 50 ± 25 nT. The STCM was controlled by a microcomputer, and the three geomagnetic components were calculated by reducing the magnetic field due to the ship’s remanent and induced magnetic moments, the only assumption being that the magnetic field is linearly related to the magnetic moments. Although STCM has no particular magnetic compensation device, it can be set at any place on board of any kind of ship. In the KH82-5 cruise, the three component measurements were conducted along latitude 42 °N north of the Mendocino fracture zone where there are well‐defined magnetic anomaly lineations trending north and south. STCM measured the north component anomalies with very small amplitudes compared to the east and downward component anomalies, which shows that lineations trend north and south. The three measured component anomalies are almost identical to the anomalies calculated from the well‐established time scale; thus, STCM measures the three components correctly. The vector geomagnetic measurements are more useful for analysis of marine geomagnetic anomalies than are the total‐intensity measurements. The DELPWAKASHIO 84/1 cruises provide good examples for examination of the linearity of magnetic anomalies on a single track by using the Fourier transform of the horizontal and vertical component anomalies.

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Induction effects of geomagnetic disturbances in the geo-electric field variations at low latitudes

Annales Geophysicae ◽

10.5194/angeo-35-39-2017 ◽

2017 ◽

Vol 35 (1) ◽

pp. 39-51 ◽

Cited By ~ 4

Author(s):

Vafi Doumbia ◽

Kouadio Boka ◽

Nguessan Kouassi ◽

Oswald Didier Franck Grodji ◽

Christine Amory-Mazaudier ◽

...

Keyword(s):

Solar Flare ◽

Electric Field ◽

West Africa ◽

Geomagnetic Storm ◽

Geomagnetic Field ◽

Equatorial Electrojet ◽

Geomagnetic Disturbances ◽

The North ◽

Low Latitudes ◽

Dip Equator

Abstract. In this study we examined the influences of geomagnetic activity on the Earth surface electric field variations at low latitudes. During the International Equatorial Electrojet Year (IEEY) various experiments were performed along 5° W in West Africa from 1992 to 1995. Among other instruments, 10 stations equipped with magnetometers and telluric electric field lines operated along a meridian chain across the geomagnetic dip equator from November 1992 to December 1994. In the present work, the induced effects of space-weather-related geomagnetic disturbances in the equatorial electrojet (EEJ) influence area in West Africa were examined. For that purpose, variations in the north–south (Ex) and east–west (Ey) components of telluric electric field were analyzed, along with that of the three components (H, D and Z) of the geomagnetic field during the geomagnetic storm of 17 February 1993 and the solar flare observed on 4 April 1993. The most important induction effects during these events are associated with brisk impulses like storm sudden commencement (ssc) and solar flare effect (sfe) in the geomagnetic field variations. For the moderate geomagnetic storm that occurred on 17 February 1993, with a minimum Dst index of −110 nT, the geo-electric field responses to the impulse around 11:00 LT at LAM are Ex =  520 mV km−1 and Ey =  400 mV km−1. The geo-electric field responses to the sfe that occurred around 14:30 LT on 4 April 1993 are clearly observed at different stations as well. At LAM the crest-to-crest amplitude of the geo-electric field components associated with the sfe are Ex =  550 mV km−1 and Ey =  340 mV km−1. Note that the sfe impact on the geo-electric field variations decreases with the increasing distance of the stations from the subsolar point, which is located at about 5.13° N on 4 April. This trend does not reflect the sfe increasing amplitude near the dip equator due the high Cowling conductivity in the EEJ belt.

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Anomaly in the earth magnetic field at north provinces of Najaf city

Iraqi Journal of Physics (IJP) ◽

10.30723/ijp.v12i23.331 ◽

2019 ◽

Vol 12 (23) ◽

pp. 1-5

Author(s):

Arif S. Baron

Keyword(s):

Magnetic Field ◽

Numerical Simulation ◽

Spherical Harmonic ◽

Kriging Method ◽

Rich Region ◽

The North ◽

The Earth ◽

Earth Magnetic Field ◽

Magnetic Model ◽

East Component

This paper investigated in the numerical simulation model to calculate the Earth magnetic field components at north provinces of Najaf city (Longitude 44.316 o -44.3592o E and Latitude 32.0508o - 32.0256o N). The components of the Earth magnetic field (total intensity (F), horizontal intensity (H), declination (D), inclination (I), the north component(X), the east component(Y), and Down component(Z)) were found by using spherical harmonic world magnetic model (WMM2010). A great deal of anomaly has been discovered in all components of the Earth magnetic field at the selected region (Long. 44.345o-44.335o E, Lat.32.042o-32.032o N) using Kriging method. This anomaly can be attributed either to oil rich region or cracking in the Earth crust.

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