Articles de revues : « Geomagnetic field variations »

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Sutcliffe, P. R. « The development of a regional geomagnetic daily variation model using neural networks ». Annales Geophysicae 18, n^o 1 (31 janvier 2000) : 120–28. http://dx.doi.org/10.1007/s00585-000-0120-0.

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Abstract. Global and regional geomagnetic field models give the components of the geomagnetic field as functions of position and epoch; most utilise a polynomial or Fourier series to map the input variables to the geomagnetic field values. The only temporal variation generally catered for in these models is the long term secular variation. However, there is an increasing need amongst certain users for models able to provide shorter term temporal variations, such as the geomagnetic daily variation. In this study, for the first time, artificial neural networks (ANNs) are utilised to develop a geomagnetic daily variation model. The model developed is for the southern African region; however, the method used could be applied to any other region or even globally. Besides local time and latitude, input variables considered in the daily variation model are season, sunspot number, and degree of geomagnetic activity. The ANN modelling of the geomagnetic daily variation is found to give results very similar to those obtained by the synthesis of harmonic coefficients which have been computed by the more traditional harmonic analysis of the daily variation.Key words. Geomagnetism and paleomagnetism (time variations; diurnal to secular) · Ionosphere (modelling and forecasting)

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Peddie, Norman W. « International Geomagnetic Reference Field Revision 1985 ». GEOPHYSICS 51, n^o 4 (avril 1986) : 1020–23. http://dx.doi.org/10.1190/1.1442144.

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IAGA Division I, Working Group 1 deals with the topic “Analysis of the Main Field and Secular Variations.” One of the more important functions of the working group is the periodic revision of the International Geomagnetic Reference Field (IGRF). The thirteen members of the working group have professional interests covering a broad spectrum of geomagnetic science, including the theory and practice of geomagnetic analysis and modeling, the theory of the origin of the magnetic fields of the Earth and other bodies, the theory of geomagnetic secular variation, the application of field models in magnetic survey data processing, and geomagnetic charting.

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Воробьев, Андрей, Andrey Vorobev, Вячеслав Пилипенко, Vyacheslav Pilipenko, Ярослав Сахаров, Yaroslav Sakharov, Василий Селиванов et Vasiliy Selivanov. « Statistical relationships between variations of the geomagnetic field, auroral electrojet, and geomagnetically induced currents ». Solar-Terrestrial Physics 5, n^o 1 (22 mars 2019) : 35–42. http://dx.doi.org/10.12737/stp-51201905.

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Using observations from the IMAGE magnetic observatories and the station for recording geomagnetically induced currents (GIC) in the electric transmission line in 2015, we examine relationships between geomagnetic field and GIC variations. The GIC intensity is highly correlated (R>0.7) with the field variability |dB/dt| and closely correlated with variations in the time derivatives of X and Y components. Daily variations in the mean geomagnetic field variability |dB/dt| and GIC intensity have a wide night maximum, associated with the electrojet, and a wide morning maximum, presumably caused by intense Pc5–Pi3 geomagnetic pulsations. We have constructed a regression linear model to estimate GIC from the time derivative of the geomagnetic field and AE index. Statistical distributions of the probability density of the AE index, geomagnetic field derivative, and GIC correspond to the log-normal law. The constructed distributions are used to evaluate the probabilities of extreme values of GIC and |dB/dt|.

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Trichtchenko, L., et D. H. Boteler. « Modelling of geomagnetic induction in pipelines ». Annales Geophysicae 20, n^o 7 (31 juillet 2002) : 1063–72. http://dx.doi.org/10.5194/angeo-20-1063-2002.

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Abstract. Geomagnetic field variations induce telluric currents in pipelines, which modify the electrochemical conditions at the pipe/soil interface, possibly contributing to corrosion of the pipeline steel. Modelling of geomagnetic induction in pipelines can be accomplished by combining several techniques. Starting with geomagnetic field data, the geoelectric fields in the absence of the pipeline were calculated using the surface impedance derived from a layered-Earth conductivity model. The influence of the pipeline on the electric fields was then examined using an infinitely long cylinder (ILC) model. Pipe-to-soil potentials produced by the electric field induced in the pipeline were calculated using a distributed source transmission line (DSTL) model. The geomagnetic induction process is frequency dependent; therefore, the calculations are best performed in the frequency domain, using a Fourier transform to go from the original time domain magnetic data, and an inverse Fourier transform at the end of the process, to obtain the pipe-to-soil potential variation in the time domain. Examples of the model calculations are presented and compared to observations made on a long pipeline in the auroral zone.Key words. Geomagnetism and paleomagnetism (geo-magnetic induction)

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Kilifarska, Natalya, Antonia Mokreva et Tsvetelina Velichkova. « North Atlantic Oscillation and Variations of Geomagnetic Field ». Proceedings of the Bulgarian Academy of Sciences 75, n^o 11 (30 novembre 2022) : 1628–37. http://dx.doi.org/10.7546/crabs.2022.11.10.

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The North Atlantic Oscillation is one of the most influential climatic modes in the Northern Hemisphere. However, the mechanism(s) standing behind its wide spectra of variations is still unknown despite its numerous investigations. This paper presents evidence for a synchronization between secular variations of geomagnetic field intensity and NAO long-term variability. Analysis of the connectivity between geomagnetic secular variations and the sea-level pressure – point by point, in a grid with resolution 10 [deg] in latitude and longitude – reveals that the strength of their relation is unevenly distributed over the Northern Hemisphere. Based on the machine learning analysis over the period 1900–2019, we found that there are two centres of significant geomagnetic-pressure relations – the weaker of them is placed slightly north of Iceland, and the stronger one is in a close proximity to Azores islands. The suggested mechanism for geomagnetic influence on the near surface climatic conditions includes the geomagnetic modulation of energetic particles precipitating in Earth's atmosphere, and their impact on the lower stratospheric ozone. The analysis of ozone-pressure relation shows, in addition, reasonable similarities with the spatial patterns of geomagnetic-pressure relations.

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Korte, Monika, et Raimund Muscheler. « Centennial to millennial geomagnetic field variations ». Journal of Space Weather and Space Climate 2 (2012) : A08. http://dx.doi.org/10.1051/swsc/2012006.

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Reshetnyak, M. Yu. « Latitudinal Variations of the Geomagnetic Field ». Izvestiya, Physics of the Solid Earth 59, n^o 2 (avril 2023) : 115–19. http://dx.doi.org/10.1134/s1069351323020106.

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Lepidi, Stefania, Lili Cafarella, Patrizia Francia, Andrea Piancatelli, Manuela Pietrolungo, Lucia Santarelli et Stefano Urbini. « A study of geomagnetic field variations along the 80° S geomagnetic parallel ». Annales Geophysicae 35, n^o 1 (24 janvier 2017) : 139–46. http://dx.doi.org/10.5194/angeo-35-139-2017.

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Abstract. The availability of measurements of the geomagnetic field variations in Antarctica at three sites along the 80° S geomagnetic parallel, separated by approximately 1 h in magnetic local time, allows us to study the longitudinal dependence of the observed variations. In particular, using 1 min data from Mario Zucchelli Station, Scott Base and Talos Dome, a temporary installation during 2007–2008 Antarctic campaign, we investigated the diurnal variation and the low-frequency fluctuations (approximately in the Pc5 range, ∼ 1–7 mHz). We found that the daily variation is clearly ordered by local time, suggesting a predominant effect of the polar extension of midlatitude ionospheric currents. On the other hand, the pulsation power is dependent on magnetic local time maximizing around magnetic local noon, when the stations are closer to the polar cusp, while the highest coherence between pairs of stations is observed in the magnetic local nighttime sector. The wave propagation direction observed during selected events, one around local magnetic noon and the other around local magnetic midnight, is consistent with a solar-wind-driven source in the daytime and with substorm-associated processes in the nighttime.

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Akpaneno, Aniefiok, et O. N. Abdulahi. « INVESTIGATING THE VARIATIONS OF HORIZONTAL (H) AND VERTICAL (Z) COMPONENTS OF THE GEOMAGNETIC FIELD AT SOME EQUATORIAL ELECTROJET STATIONS ». FUDMA JOURNAL OF SCIENCES 5, n^o 1 (14 juillet 2021) : 539–57. http://dx.doi.org/10.33003/fjs-2021-0501-661.

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This research is monitoring equatorial geomagnetic current which causes atmospheric instabilities and affects high frequency and satellite communication. It presents the variations of Horizontal (H) and vertical (Z) component of the geomagnetic field at some Equatorial Electrojet (EEJ) Stations during quiet days. Data from five (5) observatories along the magnetic equator were used for the study. Daily baseline values for each of the geomagnetic element 𝐻 and Z were obtained. The monthly average of the diurnal variation and the seasonal variations were found. Results showed that the variations of the geomagnetic element of both H and Z differ in magnitudes from one stations to another along the geomagnetic Equator due to the differences of their geomagnetic latitude. The Amplitude curves for Z) are seen to be conspicuously opposite to that of H), and there is absence of CEJ in Z- Component but present in H- Components. The values during the pre-sunrise hours are low compare to daytime hours. Minimum variations of dH was observed during June solstice and maximum variations was observed during Equinox season. This study shows that daily variations of (H) and (Z) occur in all the stations. The enhancement in H is as a result of EEJ current.

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Akpaneno, Aniefiok F., et O. N. Abdullahi. « INVESTIGATING THE VARIATIONS OF HORIZONTAL (H) AND VERTICAL (Z) COMPONENTS OF THE GEOMAGNETIC FIELD AT SOME EQUATORIAL ELECTROJET STATIONS ». FUDMA JOURNAL OF SCIENCES 5, n^o 2 (16 juillet 2021) : 531–48. http://dx.doi.org/10.33003/fjs-2021-0502-667.

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This research is monitoring equatorial geomagnetic current which causes atmospheric instabilities and affects high frequency and satellite communication. It presents the variations of Horizontal (H) and vertical (Z) component of the geomagnetic field at some Equatorial Electrojet (EEJ) Stations during quiet days. Data from five (5) observatories along the magnetic equator were used for the study. Daily baseline values for each of the geomagnetic element 𝐻 and Z were obtained. The monthly average of the diurnal variation and the seasonal variations were found. Results showed that the variations of the geomagnetic element of both H and Z differ in magnitudes from one stations to another along the geomagnetic Equator due to the differences of their geomagnetic latitude. The Amplitude curves for Z) are seen to be conspicuously opposite to that of H), and there is absence of CEJ in Z- Component but present in H- Components. The values during the pre-sunrise hours are low compare to daytime hours. Minimum variations of dH was observed during June solstice and maximum variations was observed during Equinox season. This study shows that daily variations of (H) and (Z) occur in all the stations. The enhancement in H is as a result of EEJ current

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Sokol-Kutylovskii, O. L. « The measurement of a weak alternating magnetic field in unshielded space ». Metrologiya, n^o 1 (31 mai 2021) : 46–59. http://dx.doi.org/10.32446/0132-4713.2021-1-46-59.

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In connection with attempts to use various types of sensors for measuring weak magnetic fields in geophysics, magnetobiology, and medicine in an unshielded space, the problem of comparing the results of these measurements arose. The issues of measuring a weak alternating magnetic field by various magnetic induction sensors in an unshielded space in the absence of obvious geomagnetic variations are considered. It is shown that the amplitude of natural geomagnetic noise in a quiet geomagnetic field in the absence of geomagnetic variations has a random character; therefore, gradient methods for measuring a weak alternating magnetic field are limited from below by the level of natural geomagnetic noise. The influence of the size of sensors of a weak alternating magnetic field on the results of measurements of broadband random geomagnetic noise is noted.

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Elias, A. G., B. S. Zossi, A. R. Gutierrez Falcon, E. S. Comedi et B. F. de Haro Barbas. « LONG-TERM TRENDS IN COSMIC RAYS AND GEOMAGNETIC FIELD SECULAR VARIATIONS ». PHYSICS OF AURORAL PHENOMENA 44 (2021) : 79–80. http://dx.doi.org/10.51981/2588-0039.2021.44.018.

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Cosmic rays are modulated by solar and geomagnetic activity. In addition, the flux that arrives to the Earth is sensitive to the inner geomagnetic field through its effect on the geomagnetic cutoff rigidity, Rc. This field has been decaying globally at a rate of ~5% per century from at least 1840. However, due to its configuration and non-uniform trend around the globe, its secular variation during the last decades has induced negative and positive Rc trends depending on location. In the present work, the database from the World Data Center for Cosmic Rays (WDCCR) is used to analyze long-term trend variations linked to geomagnetic secular variations. This database includes more than 100 stations covering, some of them, almost seven decades since the 1950’s. Those stations spanning more than 20 years of data are selected for the present study in order to adequately filter solar activity effects.

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Lin, Jyh-Woei. « Geomagnetic Storm Related to Disturbance Storm Time Indices ». European Journal of Environment and Earth Sciences 2, n^o 6 (5 novembre 2021) : 1–3. http://dx.doi.org/10.24018/ejgeo.2021.2.6.199.

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The magnitude of the Disturbance Storm Time (Dst) index varied in relation to the extremely small negative integer that indicated a large geomagnetic storm. The large sharpened variants of negative Dst indices could describe the detailed features of a geomagnetic storm. the Dst index was estimated using an algorithm through time and frequency-domain band-stop filtering to remove the solar-quiet variation and the mutual coupling effects between the Earth’s rotation, the Moon’s orbit, and the Earth’s orbit around the Sun. A good geomagnetic model that could describe the true variations in the geomagnetic field when undergoing diverse space weather, and one that could even predict variations in the geomagnetic field with a high accuracy. A suitable temporal resolution for the Dst index was per hour.

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Mandrikova, Oksana, Anastasia Rodomanskay et Alexander Zaitsev. « Analysis of geomagnetic disturbances dynamics during increased solar activity and magnetic storms (according to the measurements of INTERMAGNET station network) ». E3S Web of Conferences 127 (2019) : 02003. http://dx.doi.org/10.1051/e3sconf/201912702003.

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We present and describe an automated method for analysis of magnetic data and for detection of geomagnetic disturbances based on wavelet transformation. The parameters of the computational algorithms allow us to estimate the characteristics of non-uniformly scaled peculiar properties in the variations of geomagnetic field that arise during increasing geomagnetic activity. The analysis of geomagnetic data before and during magnetic storms was carried out on the basis of the method according to ground station network. Periods of increasing geomagnetic activity, which precede and accompany magnetic storms, are highlighted. The dynamic of geomagnetic field variation in the auroral zone is considered in detail.

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Kovaltsov, G. A., et I. G. Usoskin. « Regional cosmic ray induced ionization and geomagnetic field changes ». Advances in Geosciences 13 (13 août 2007) : 31–35. http://dx.doi.org/10.5194/adgeo-13-31-2007.

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Abstract. Cosmic ray induced ionization (CRII) is an important factor of outer space influences on atmospheric properties. Variations of CRII are caused by two different processes – solar activity variations, which modulate the cosmic ray flux in interplanetary space, and changes of the geomagnetic field, which affects the cosmic ray access to Earth. Migration of the geomagnetic dipole axis may greatly alter CRII in some regions on a time scale of centuries and longer. Here we present a study of CRII regional effects of the geomagnetic field changes during the last millennium for two regions: Europe and the Far East. We show that regional effects of the migration of the geomagnetic dipole axis may overcome global changes due to solar activity variations.

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Glassmeier, K. H., J. Vogt, A. Stadelmann et S. Buchert. « Concerning long-term geomagnetic variations and space climatology ». Annales Geophysicae 22, n^o 10 (3 novembre 2004) : 3669–77. http://dx.doi.org/10.5194/angeo-22-3669-2004.

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Abstract. During geomagnetic polarity transitions the surface magnetic field of the Earth decays to about 25% and less of its present value. This implies a shrinking of the terrestrial magnetosphere and posses the question of whether magnetospheric magnetic field variations scale in the same manner. Furthermore, the geomagnetic main field also controls the magnetospheric magnetic field and space weather conditions. Long-term geomagnetic variations are thus intimately related to space climate. We critically assess existing scaling relations and derive new ones for various magnetospheric parameters. For example, we find that ring current perturbations do not increase with decreasing dipole moment. And we derive a scaling relation for the polar electrojet contribution, indicating a weak increase with increasing internal field. From this we infer that the ratio between external and internal field contributions may be weakly enhanced during polarity transitions. Our scaling relations also provide more insight on the importance of the internal geomagnetic field contribution for space climate.

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Rokityansky, I. I., et A. V. Tereshyn. « Spectra of the geomagnetic field diurnal variations ». Geofizicheskiy Zhurnal 41, n^o 5 (15 novembre 2019) : 105–14. http://dx.doi.org/10.24028/gzh.0203-3100.v41i5.2019.183633.

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Sumaruk, P. V., et T. P. Sumaruk. « Solar activity and geomagnetic field secular variations ». Kosmìčna nauka ì tehnologìâ 16, n^o 2 (30 mars 2010) : 5–11. http://dx.doi.org/10.15407/knit2010.02.005.

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ROLPH, T. C., et J. SHAW. « Variations of the Geomagnetic Field in Sicily ». Journal of geomagnetism and geoelectricity 38, n^o 12 (1986) : 1269–77. http://dx.doi.org/10.5636/jgg.38.1269.

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Glukhikh, I. I., V. I. Utkin, Yu G. Astrakhantsev, N. A. Beloglazova et V. P. Starovoitov. « Variations of the geomagnetic field in boreholes ». Doklady Earth Sciences 415, n^o 2 (août 2007) : 935–39. http://dx.doi.org/10.1134/s1028334x07060244.

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Fournier, A., C. Eymin et T. Alboussière. « A case for variational geomagnetic data assimilation : insights from a one-dimensional, nonlinear, and sparsely observed MHD system ». Nonlinear Processes in Geophysics 14, n^o 2 (25 avril 2007) : 163–80. http://dx.doi.org/10.5194/npg-14-163-2007.

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Abstract. Secular variations of the geomagnetic field have been measured with a continuously improving accuracy during the last few hundred years, culminating nowadays with satellite data. It is however well known that the dynamics of the magnetic field is linked to that of the velocity field in the core and any attempt to model secular variations will involve a coupled dynamical system for magnetic field and core velocity. Unfortunately, there is no direct observation of the velocity. Independently of the exact nature of the above-mentioned coupled system – some version being currently under construction – the question is debated in this paper whether good knowledge of the magnetic field can be translated into good knowledge of core dynamics. Furthermore, what will be the impact of the most recent and precise geomagnetic data on our knowledge of the geomagnetic field of the past and future? These questions are cast into the language of variational data assimilation, while the dynamical system considered in this paper consists in a set of two oversimplified one-dimensional equations for magnetic and velocity fields. This toy model retains important features inherited from the induction and Navier-Stokes equations: non-linear magnetic and momentum terms are present and its linear response to small disturbances contains Alfvén waves. It is concluded that variational data assimilation is indeed appropriate in principle, even though the velocity field remains hidden at all times; it allows us to recover the entire evolution of both fields from partial and irregularly distributed information on the magnetic field. This work constitutes a first step on the way toward the reassimilation of historical geomagnetic data and geomagnetic forecast.

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Kurazhkovskii, A. Yu, N. A. Kurazhkovskaya et B. I. Klain. « Spectrum of Quaziperiodic Variations in Paleomagnetic Activity in the Phanerozoic ». Russian Geology and Geophysics 63, n^o 11 (1 novembre 2022) : 1261–69. http://dx.doi.org/10.2113/rgg20214403.

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Abstract —Detection of common quasiperiodicities in the paleointensity behavior and lengths of polarity intervals of the Earth’s magnetic field was carried out. The paleointensity data were analyzed in the 170 Ma–present day interval. Behavior of the lengths of geomagnetic polarity intervals was investigated within the interval spanning the entire Phanerozoic (540 Ma–present age). It was found that the spectrum of the main paleointensity variations and polarity interval lengths is discrete and includes quasiperiodic variations with characteristic times of 15, 8, 5, and 3 Ma. The characteristic times of these quasiperiodic variations in the geomagnetic field at the beginning and end of the Phanerozoic differed not more than 10%. The spectral density of quasiperiodic changes in the geomagnetic field changed cyclically over geological time. The connection between the behavior of the amplitudes of paleointensity variations, the lengths of geomagnetic polarity intervals, and their spectral density is shown. The spectral density of quasiperiodic paleointensity variations (geomagnetic activity) was relatively high in the 150–40 Ma interval (Cretaceous–early Paleogene). At this time, the amplitudes of paleointensity variations and the lengths of geomagnetic polarity intervals increased. Within the intervals spanning 170–150 Ma and 30 Ma–present age, the quasiperiodic variations of paleointensity were barely expressed against its background noise variations, while the amplitudes of paleointensity variations and the lengths of polarity intervals were decreasing. Alternations of the time intervals in which paleointensity variations acquired either a quasiperiodic or noise character took place during the evolution of the geomagnetic field.

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Lepidi, S., L. Cafarella, P. Francia, A. Meloni, P. Palangio et J. J. Schott. « Low frequency geomagnetic field variations at Dome C (Antarctica) ». Annales Geophysicae 21, n^o 4 (30 avril 2003) : 923–32. http://dx.doi.org/10.5194/angeo-21-923-2003.

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Abstract. We conduct an analysis of the geomagnetic field variations recorded at the new Antarctic station Dome C, located very close to the geomagnetic pole, which has been operating for approximately one month during the 1999–2000 campaign. We also perform a comparison with simultaneous measurements at the Italian Antarctic station Terra Nova Bay, in order to investigate the spatial extension of the phenomena observed at very high latitude. Our results show that between the two stations the daily variation is similar and the fluctuations with f ~ 1 mHz are coherent, provided that in both cases the comparison is made between geographically oriented components, suggesting that ionospheric currents related to the geographic position, more than field-aligned currents, are responsible for the lowest frequency variations; conversely, higher frequency (Pc5) fluctuations are substantially decoupled between the two stations. We also found that at Dome C the fluctuation power in the 0.55–6.7 mHz frequency band is well related with the solar wind speed during the whole day and that at Terra Nova Bay the correlation is also high, except around local geomagnetic noon, when the station approaches the polar cusp. These results indicate that the solar wind speed control of the geomagnetic field fluctuation power is very strict in the polar cap and less important close to the polar cusp.Key words. Magnetospheric physics (MHD waves and instabilities; Polar cap phenomena; Solar wind-magnetosphere interactions)

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Bolzan, Maurício J. A., Clezio M. Denardini et Alexandre Tardelli. « Comparison of <i>H</i> ; component geomagnetic field time series obtained at different sites over South America ». Annales Geophysicae 36, n^o 3 (26 juin 2018) : 937–43. http://dx.doi.org/10.5194/angeo-36-937-2018.

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Abstract. The geomagnetic field in the Brazilian sector is influenced by the South American Magnetic Anomaly (SAMA) that causes a decrease in the magnitude of the local geomagnetic field when compared to other regions in the world. Thus, the magnetometer network and data set of space weather over Brazil led by Embrace are important tools for promoting the understanding of geomagnetic fields over Brazil. In this sense, in this work we used the H component of geomagnetic fields obtained at different sites in South America in order to compare results from the phase coherence obtained from wavelet transform (WT). Results from comparison between Cachoeira Paulista (CXP) and Eusébio (EUS), and Cachoeira Paulista and São Luis (SLZ), indicated that there exist some phenomena that occur simultaneously in both locations, putting them in the same phase coherence. However, there are other phenomena putting both locations in a strong phase difference as observed between CXP and Rio Grande, Argentina (RGA). This study was done for a specific moderate geomagnetic storm that occurred in March 2003. The results are explained in terms of nonlinear interaction between physical phenomena acting in distinct geographic locations and at different times and scales. Keywords. Geomagnetism and paleomagnetism (time variations – diurnal to secular)

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Mandrikova, Oksana V., Igor S. Solovyev, Sergey Y. Khomutov, Vladimir V. Geppener, Dmitry M. Klionskiy et Mikhail I. Bogachev. « Multiscale variation model and activity level estimation algorithm of the Earth's magnetic field based on wavelet packets ». Annales Geophysicae 36, n^o 5 (19 septembre 2018) : 1207–25. http://dx.doi.org/10.5194/angeo-36-1207-2018.

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Abstract. We suggest a wavelet-based multiscale mathematical model of geomagnetic field variations. The model is particularly capable of reflecting the characteristic variation and local perturbations in the geomagnetic field during the periods of increased geomagnetic activity. Based on the model, we have designed numerical algorithms to identify the characteristic variation component as well as other components that represent different geomagnetic field activity. The substantial advantage of the designed algorithms is their fully automatic performance without any manual control. The algorithms are also suited for estimating and monitoring the activity level of the geomagnetic field at different magnetic observatories without any specific adjustment to their particular locations. The suggested approach has high temporal resolution reaching 1 min. This allows us to study the dynamics and spatiotemporal distribution of geomagnetic perturbations using data from ground-based observatories. Moreover, the suggested approach is particularly capable of discovering weak perturbations in the geomagnetic field, likely linked to the nonstationary impact of the solar wind plasma on the magnetosphere. The algorithms have been validated using the experimental data collected at the IKIR FEB RAS observatory network. Keywords. Magnetospheric physics (storms and substorms)

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Rastogi, R. G. « Geomagnetic field variations at low latitudes and ionospheric electric fields ». Journal of Atmospheric and Terrestrial Physics 55, n^o 10 (août 1993) : 1375–81. http://dx.doi.org/10.1016/0021-9169(93)90105-8.

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SUKHAREV, A., M. ORLYUK, M. RYABOV, L. SOBITNIAK, V. BEZRUKOVS, S. PANISHKO et A. ROMENETS. « Results of comparison of fast variations of geomagnetic field and ionospheric scintillations of 3C 144 radio source in the area of Odessa geomagnetic anomaly ». Astronomical and Astrophysical Transactions, Volume 33, Numéro 1 (1 juillet 2022) : 67–88. http://dx.doi.org/10.17184/eac.6481.

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From November 2017 to May 2019 at the Astronomical Observatory of Odessa I.I. Mechnikov National University, the variational component of the geomagnetic field was monitored to study short-periodic geomagnetic variations in the central part of the Odessa regional magnetic anomaly. The measurements were carried out using a LEMI-008 precision fluxgate magnetometer with a sampling rate of 1 Hz. The aim of this work is to compare the manifestation of short-periodic geomagnetic oscillations (which in some cases coincided with periods of geomagnetic pulsations) and ionospheric scintillations of the 3C 144 radio source (Taurus A) according to the data of URAN-4 low-frequency phased antenna array at frequencies of 20 and 25 MHz. The data obtained were processed on a daily basis using the method of continuous wavelet transform, as well as band-pass filtering based on Fourier transform, to select individual frequency bands containing irregular and quasi-harmonic variations in the geomagnetic field and radio flux density. The analysis of results of the observations, during geomagnetic disturbances, storms and in calm conditions, is carried out. The data from long-term monitoring of variational component of the geomagnetic field in the most interesting, central part of the Odessa magnetic anomaly, where such studies have not been conducted before, have been obtained. Observations of various manifestations of ionospheric scintillations were carried out both during magnetic storms and during a calm geomagnetic field. It is shown that during storms, main scintillation time scale of the 3C 144 radio source is 1–3 minutes. Ionospheric scintillations occasionally show a quasiperiodic structure.

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Воробьев, Андрей, Andrey Vorobev, Вячеслав Пилипенко, Vyacheslav Pilipenko, Ярослав Сахаров, Yaroslav Sakharov, Василий Селиванов et Vasiliy Selivanov. « Statistical relationships between variations of the geomagnetic field, auroral electrojet, and geomagnetically induced currents ». Solnechno-Zemnaya Fizika 5, n^o 1 (22 mars 2019) : 48–58. http://dx.doi.org/10.12737/szf-51201905.

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Using observations from the IMAGE magnetic observatories and the station for recording geomagnetically induced currents (GIC) in the electric transmission line in 2015, we examine relationships between geomagnetic field and GIC variations. The GIC intensity is highly correlated (R>0.7) with the field variability |dB/dt| and closely correlated with variations in the time derivatives of X and Y components. Daily variations in the mean geomagnetic field variability |dB/dt| and GIC intensity have a wide night maximum, associated with the electrojet, and a wide morning maximum, presumably caused by intense Pc5–Pi3 geomagnetic pulsations. We have constructed a regression linear model to estimate GIC from the time derivative of the geomagnetic field and AE index. Statistical distributions of the probability density of the AE index, geomagnetic field derivative, and GIC correspond to the log-normal law. The constructed distributions are used to evaluate the probabilities of extreme values of GIC and |dB/dt|.

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Nechasova, I. E., et O. V. Pilipenko. « Archaeomagnetic studies at Schmidt institute of physics of the earth, Russian Academy of Sciences : history and main results ». Физика Земли, n^o 2 (6 avril 2019) : 123–36. http://dx.doi.org/10.31857/s0002-333720192123-136.

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The archaeomagnetic studies carried out at the Schmidt Institute of Physics of the Earth of the Russian Academy of Sciences (IPE RAS) provided an important contribution to the international studies of the main magnetic field of the Earth for the past few thousand years. Extensive data on the intensity of geomagnetic field in the past 8000 years were obtained. Four most representative and long time series of the data have been constructed for Eurasia for the Iberian Peninsula, the Caucasus, Central Asia, and Siberia. Unique studies having no analogues in international research have been carried out into rapid variations in the geomagnetic field intensity with characteristic times starting from several tens of years. Based on the analysis of the international data on the ancient geomagnetic field, the spectrum of the variations in the geomagnetic field intensity with the periods ranging from decades to millennia was established and the characteristics ofthe variations whose superposition can describe the pattern of the changes of the geomagnetic field intensity were determined. It was found out that variations with different characteristic times have a differently directed drift, and the “main oscillation” with a characteristic time of 8000 years has an eastern drift.

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Le Mouël, J. L., E. Blanter et M. Shnirman. « The six-month line in geomagnetic long series ». Annales Geophysicae 22, n^o 3 (19 mars 2004) : 985–92. http://dx.doi.org/10.5194/angeo-22-985-2004.

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Abstract. Daily means of the horizontal components X (north) and Y (east) of the geomagnetic field are available in the form of long series (several tens of years). Nine observatories are used in the present study, whose series are among the longest. The amplitudes of the 6-month and 1-year periodic variations are estimated using a simple but original technique. A remarkably clear result emerges from the complexity of the geomagnetic data: the amplitude of the 6-month line presents, in all observatories, the same large variation (by a factor of 1.7) over the 1920–1990 time span, regular and quasi-sinusoidal. Nothing comparable comes out for the annual line. The 6-month line results from the modulation by an astronomical mechanism of a magnetospheric system of currents. As this latter mechanism is time invariant, the intensity of the system of currents itself must present the large variation observed on the 6-months variation amplitude. This variation presents some similarities with the one displayed by recent curves of reconstructed solar irradiance or the "Earth's temperature". Finally, the same analysis is applied to the aa magnetic index.Key words. Geomagnetism and paleomagnetism (time variations, diurnal to secular). Magnetospheric physics (current systems; polar cap phenomena)

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Chernogor, L. F., M. Yu Golub, Y. Luo, A. M. Tsymbal et M. B. Shevelev. « Variations in the geomagnetic field that accompanied the 10 June 2021 solar eclipse ». 34, n^o 34 (30 juin 2021) : 55–69. http://dx.doi.org/10.26565/2311-0872-2021-34-07.

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Urgency. At present, the existence of the geomagnetic effect of solar eclipses (SEs) is in question. The data presented in the literature are contradictory. Some researchers assert that the amplitude of the north-south component of the main geomagnetic field increases, while others that it decreases. The third group of researchers notes that this amplitude does not change at all, but instead the amplitude of the west-east component shows variations. In some cases, observations confirm the mechanism for the geomagnetic effect caused by disturbances in the Sq current system, while in other cases observations contradict with the mechanism. The difficulties that are encountered in observing the SE geomagnetic effect are caused by the fact that the magnetic field is subjected to the influence of many energy sources. The magnitude of the geomagnetic effect depends not only on the magnitude (phase) of the solar eclipse but also on the state of space weather, geographic coordinates of data acquisition, local time, season, etc. Therefore, the study of the geomagnetic effect from each new solar eclipse remains an urgent problem. The main feature of the 10 June 2021 Solar eclipse is its annularity. The maximum magnitude did not exceed 0.943, and the eclipse obscuration 89%. The aim of this work is to present the results of analysis of variations in the geomagnetic field that were recorded by the INTERMAGNET during the 10 June 2021 SE. Methods and Methodology. To analyze the effects in the main Earth’s magnetic field, the INTERMAGNET data have been utilized. The data have been analyzed from 15 magnetic observatories located between 77.47°-N and 48.17°-N latitude where the maximum phase varied from 0.943 to 0.124. The analysis was performed with 1-min temporal resolution providing a 0.1-nT resolution. To determine spectral content of the quasi-periodic variations, the systems spectral analysis has been used, which combines mutually complementary the short-time Fourier transform, the wavelet transform employing the Morlet wavelet as a basis function, and the Fourier transform in a sliding window with a width adjusted to be equal to a fixed number of harmonic periods. Results. An aperiodic geomagnetic effect of a solar eclipse has been detected and explained; it consists in a decrease by not greater than 30 nT in the level of the north-south component. The effect is explained by a variation in the ionospheric current density in the west-east direction as a result of a decrease in the electron density during the eclipse. A quasi-periodic geomagnetic effect of a solar eclipse has been revealed; it is explained by the generation of atmospheric gravity waves. The wave acts to modulate the ionospheric electric current, as well as to drag the electrons inducing additional quasi-periodic ionospheric current with a period equal to the wave period. The amplitude of the quasi-periodic variations was observed to be a few nanoteslas. The systems spectral analysis provided more precise values of periods of quasi-periodic variations in the geomagnetic field accompanying the solar eclipse, approximately 20 min and 35 min. Conclusions. The aperiodic and quasi-periodic geomagnetic effects are caused by the disturbance (generation) of the ionospheric current.

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Bhattacharyya, A., et B. Mitra. « Changes in cosmic ray cut-off rigidities due to secular variations of the geomagnetic field ». Annales Geophysicae 15, n^o 6 (30 juin 1997) : 734–39. http://dx.doi.org/10.1007/s00585-997-0734-6.

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Abstract. An analytical expression is derived for the cutoff rigidity of cosmic rays arriving at a point in an arbitrary direction, when the main geomagnetic field is approximated by that of an eccentric dipole. This expression is used to determine changes in geomagnetic cutoffs due to secular variation of the geomagnetic field since 1835. Effects of westward drift of the quadrupole field and decrease in the effective dipole moment are seen in the isorigidity contours. On account of the immense computer time required to determine the cutoff rigidities more accurately using the particle trajectory tracing technique, the present formulation may be useful in estimating the transmission factor of the geomagnetic field in cosmic ray studies, modulation of cosmogenic isotope production by geomagnetic secular variation, and the contribution of geomagnetic field variation to long term changes in climate through cosmic ray related modulation of the current flow in the global electric circuit.

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Mihai, Andrei, Victorin-Emilian Toader, Iren-Adelina Moldovan et Mircea Radulian. « Exploring the Relationship between Geomagnetic Variations and Seismic Energy Release in Proximity to the Vrancea Seismic Zone ». Atmosphere 14, n^o 6 (10 juin 2023) : 1005. http://dx.doi.org/10.3390/atmos14061005.

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Understanding the seismo–ionospheric coupling mechanism requires a quiet geomagnetic condition, as this represents an ideal situation to detect abnormal variations in the geomagnetic field. In reality, continuous interactions between solar wind and Earth’s magnetosphere create many fluctuations in the geomagnetic field that are more related to sun–magnetosphere interactions than to seismotectonic causes. A triaxial magnetometer was installed at the Muntele Rosu Observatory near the Vrancea seismic zone in 1996 to measure the local magnetic field. Since 2002, the data have become more consistent, allowing for the representation of long time series. Since then, variations have been observed on the eastern component (By) of the magnetic field, which sometimes overlaps with significant earthquakes. Previous studies have shown that high decreases in amplitude recorded on the By component of the magnetic field measured at Muntele Rosu have been accompanied by higher seismicity, while small decreases have been accompanied by lower seismic energy release. This research analyzes the geomagnetic data collected between September 2002 and May 2008 from two geomagnetic observatories, one located in the proximity of the Vrancea seismic zone and another one situated 120 km away. For each geomagnetic anomaly identified, the daily seismic energy released was plotted logarithmically, along with seismicity and Kp indices. Additionally, the daily seismic energy released was also plotted logarithmically for all earthquakes with Mw ≥3. To identify variations in the By component, datasets recorded at Muntele Rosu (MLR) were compared with those recorded at Surlari National Geomagnetic Observatory (SUA), to discriminate between global magnetic variations associated with solar activity and possible seismo–electromagnetic variations. The standard deviation (SDBy) was calculated for each anomaly recorded on the By component of the magnetic field and compared with the cumulative seismic energy release. To determine if this type of variation was present in other components of the magnetic field, the following ratios were calculated for all data recorded at Muntele Rosu: Bz/Bx, Bz/By, and Bz/BH. The size of the anomalies resulting from the standard deviation measured on the By component (SDBy) partially validates the relationship between the size of the anomalies and the seismic energy release during the anomaly. The relationship between the released seismic energy and the anomaly magnitude is vaguely respected, but these variations seem to follow two patterns. One pattern is described by smooth decreases, and the other pattern involves decreases where the By component varies significantly over short periods, generating decreases/increases in steps. It was noticed that seismic activity is greater for the second pattern. Additionally, using standard deviation measured on the magnetic field represents a great tool to discriminate external magnetic field variations from local, possibly seismo–magnetic variations.

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Střeštík, Jaroslav. « Long-term variations in geomagnetic and solar activities and secular variations of the geomagnetic field components ». Studia Geophysica & ; Geodætica 35, n^o 1 (mars 1991) : 1–6. http://dx.doi.org/10.1007/bf01625053.

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Sizova, L. Z. « The field-aligned currents effect on equatorial geomagnetic field variations ». Advances in Space Research 30, n^o 10 (novembre 2002) : 2247–52. http://dx.doi.org/10.1016/s0273-1177(02)80236-8.

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Elemo, Enoch Oluwaseun, et Akeem Babatunde Rabiu. « Magnetospheric and Ionospheric Sources of Geomagnetic Field Variations ». OALib 01, n^o 09 (2014) : 1–8. http://dx.doi.org/10.4236/oalib.1101035.

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Di Chiara, Anita, Emilio Herrero-Bervera et Evdokia Tema. « Geomagnetic field variations in the past : an introduction ». Geological Society, London, Special Publications 497, n^o 1 (2020) : 1–8. http://dx.doi.org/10.1144/sp497-2020-78.

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Bondar, T. N., V. P. Golovkov et S. V. Yakovleva. « Regional features of the geomagnetic field secular variations ». Geomagnetism and Aeronomy 48, n^o 4 (27 juillet 2008) : 529–35. http://dx.doi.org/10.1134/s0016793208040142.

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Gee, Jeffrey S., Steven C. Cande, Dennis V. Kent, Richard Partner et Kate Heckman. « Mapping Geomagnetic Field Variations with Unmanned Airborne Vehicles ». Eos, Transactions American Geophysical Union 89, n^o 19 (6 mai 2008) : 178–79. http://dx.doi.org/10.1029/2008eo190002.

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Kurazhkovskii, A. Yu, N. A. Kurazhkovskaya, B. I. Klain et V. Yu Bragin. « Variations of the geomagnetic field during the Cretaceous ». Russian Geology and Geophysics 53, n^o 7 (juillet 2012) : 712–19. http://dx.doi.org/10.1016/j.rgg.2012.05.010.

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Banerjee, M., M. K. Singh, Nagendra P. Singh et T. Lal. « MEM Analysis of Geomagnetic Field Variations Over Narssarssuaq ». Pure and Applied Geophysics 150, n^o 2 (1 octobre 1997) : 329–40. http://dx.doi.org/10.1007/s000240050079.

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Vokhmyanin, M. V., et D. I. Ponyavin. « Inferring interplanetary magnetic field polarities from geomagnetic variations ». Journal of Geophysical Research : Space Physics 117, A6 (juin 2012) : n/a. http://dx.doi.org/10.1029/2011ja017060.

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Burlatskaya, S. P., S. F. Burlatsky, A. F. Burlatsky et S. A. Didenko. « Types of variations in the geomagnetic field spectrum ». Izvestiya, Physics of the Solid Earth 42, n^o 3 (mars 2006) : 207–24. http://dx.doi.org/10.1134/s1069351306030049.

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WEI, Zi-Gang, et Wen-Yao XU. « Drifts and Intensity Variations of the Geomagnetic Field ». Chinese Journal of Geophysics 44, n^o 4 (juillet 2001) : 496–505. http://dx.doi.org/10.1002/cjg2.167.

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Viljanen, A., H. Nevanlinna, K. Pajunpää et A. Pulkkinen. « Time derivative of the horizontal geomagnetic field as an activity indicator ». Annales Geophysicae 19, n^o 9 (30 septembre 2001) : 1107–18. http://dx.doi.org/10.5194/angeo-19-1107-2001.

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Abstract. Geomagnetically induced currents (GICs) in technological conductor systems are a manifestation of the ground effects of space weather. Large GICs are always associated with large values of the time derivative of the geomagnetic field, and especially with its horizontal component (dH/dt). By using the IMAGE magnetometer data from northern Europe from 1982 to 2001, we show that large dH/dt’s (exceeding 1 nT/s) primarily occur during events governed by westward ionospheric currents. However, the directional distributions of dH/dt are much more scattered than those of the simultaneous baseline subtracted horizontal variation field vector ΔH. A pronounced difference between ΔH and dH/dt takes place at about 02–06 MLT in the auroral region when dH/dt prefers an east-west orientation, whereas ΔH points to the south. The occurrence of large dH/dt has two daily maxima, one around the local magnetic midnight, and another in the morning. There is a single maximum around the midnight only at the southernmost IMAGE stations. An identical feature is observed when large GICs are considered. The yearly number of large dH/dt values in the auroral region follows quite closely the aa index, but a clear variation from year-to-year is observed in the directional distributions. The scattering of dH/dt distributions is smaller during descending phases of the sunspot cycle. Seasonal variations are also seen, especially in winter dH/dt is more concentrated to the north-south direction than at other times. The results manifest the importance of small-scale structures of ionospheric currents when GICs are considered. The distribution patterns of dH/dt cannot be explained by any simple sheet-type model of (westward) ionospheric currents, but rapidly changing north-south currents and field-aligned currents must play an important role.Key words. Geomagnetism and paleomagnetism (geomagnetic induction; rapid time variations) - Ionosphere (ionospheric disturbances)

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Viljanen, A., A. Pulkkinen, O. Amm, R. Pirjola et T. Korja. « Fast computation of the geoelectric field using the method of elementary current systems and planar Earth models ». Annales Geophysicae 22, n^o 1 (1 janvier 2004) : 101–13. http://dx.doi.org/10.5194/angeo-22-101-2004.

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Abstract. The method of spherical elementary current systems provides an accurate modelling of the horizontal component of the geomagnetic variation field. The interpolated magnetic field is used as input to calculate the horizontal geoelectric field. We use planar layered (1-D) models of the Earth's conductivity, and assume that the electric field is related to the local magnetic field by the plane wave surface impedance. There are locations in which the conductivity structure can be approximated by a 1-D model, as demonstrated with the measurements of the Baltic Electromagnetic Array Research project. To calculate geomagnetically induced currents (GIC), we need the spatially integrated electric field typically in a length scale of 100km. We show that then the spatial variation of the electric field can be neglected if we use the measured or interpolated magnetic field at the site of interest. In other words, even the simple plane wave model is fairly accurate for GIC purposes. Investigating GIC in the Finnish high-voltage power system and in the natural gas pipeline, we find a good agreement between modelled and measured values, with relative errors less than 30% for large GIC values. Key words. Geomagnetism and paleomagnetism (geomagnetic induction; rapid time variations) – Ionosphere (electric field and currents)

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Belinskaya, Anastasiya, Aleksandr Kovalev, Nikolay Semakov et Sofiya Belinskaya. « Variations of ionospheric and geomagnetic field parameters during the June 18, 2013 Bachat earthquake ». Solar-Terrestrial Physics 7, n^o 1 (29 mars 2021) : 78–84. http://dx.doi.org/10.12737/stp-71202110.

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The paper presents the results of a study of variations in ionospheric parameters and local magnetic constant before, during, and after the Vachat earthquake, which occurred on June 18, 2013 at 23:02 UT (June 19, 2013 at 06:02 LT) with a magnitude 5.3–5.6 and epicenter coordinates 54.29 ° N, 86.17 ° E. We have used data from IPGG SB RAS and TSU ionospheric stations and INTERMAGNET geomagnetic observatories. We have established that in the period preceding the earthquake there was a rather sharp increase in the magnetic moment, and in the subsequent period there was an equally sharp decrease in the magnetic moment. It is noted that the analysis of the daily average values of the local magnetic constant is the most promising for searching for geomagnetic precursors of earthquakes. We have found a low strong sporadic layer Es for two days before the event, the like of which was not observed for 15 days before and 15 days after the event. In addition, on the days preceding the shock, the background values of the F2-layer critical frequency were larger by more than 20% at the local pre-event hours. On the second day after the earthquake, there appeared a night-time region of low values (about 14%), which persisted until the morning of the third day.

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Falayi, E. O., O. O. Ogundile, J. O. Adepitan et A. A. Okusanya. « Solar quiet variation of the horizontal and vertical components of geomagnetic field using wavelet analysis ». Canadian Journal of Physics 97, n^o 4 (avril 2019) : 450–60. http://dx.doi.org/10.1139/cjp-2018-0034.

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The solar quiet (Sq) variations of horizontal and vertical (SqH and SqZ) components of the geomagnetic field obtained from both the Northern Hemisphere and Southern Hemisphere of the International Real-Time Magnetic Observatory Network (INTERMAGNET) during solar maximum year 2001 were investigated. The results show enlargement of the SqH component of the geomagnetic field during the daytime, attributed to equatorial electrojet (EEJ) current closer to the geomagnetic equator at the electrojet stations (BNG and MBO), which are produced from large eastward flow of the current. It was observed that SqZ is positive at the southward and negative at the northward hemispheres. SqZ is amplified at HER and HBK around the daytime. Wavelet power spectrum based approach was employed to analyse the SqH, SqZ, and rate of induction (SqZ/SqH) time series in a sequence of time scaling from January to December. The higher energy of SqH and SqZ of the wavelet coefficients is noticeable at high frequency. The monthly variation rate of induction (SqZ/SqH) analyses during the Sq variations are associated with the influence of equatorwards penetration of electric fields from the field-aligned current, Earth conductivity, effect of the ocean, and ionospheric conductivity.

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Kocharov, G. E., A. V. Blinov, A. N. Konstantinov et V. A. Levchenko. « Temporal 10Be and 14C Variations : A Tool for Paleomagnetic Research ». Radiocarbon 31, n^o 2 (1989) : 163–68. http://dx.doi.org/10.1017/s0033822200044829.

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Temporal variations of cosmogenic radionuclide atmospheric concentrations can be caused by such global phenomena as solar activity and geomagnetic field changes as well as atmospheric circulation processes. These causes can be distinguished by the comparison of several isotope records corresponding to the same time period. We discuss a possibility for reconstructing the geomagnetic moment during the last 30,000 years from the comparison of 10Be and 14C concentrations in terrestrial archives. The results agree with conventional paleomagnetic data and promise to enrich our knowledge of geomagnetic field variations and reversals.

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Sumaruk, T. P. « GEODYNAMICS ». GEODYNAMICS 1(10)2011, n^o 1(10) (28 juin 2011) : 116–20. http://dx.doi.org/10.23939/jgd2011.01.116.

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In the paper the dynamic of solar activity and connected to it the geomagnetic field variations and its ecological disturbance on Ukrainis territory is analyzed. It is shown that solar activity concerning to the cycles with 100–200 years periods is in the state of transition to decreasing. Interconnection of the quasibiennial variations of solar and geomagnetic activities is studied. It is shown that ecological disturbance of geomagnetic field on Ukrainis the Ukrainis territory do not exceed of the quota.

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