Journal articles on the topic 'Geomagnetic variation'
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Sutcliffe, P. R. "The development of a regional geomagnetic daily variation model using neural networks." Annales Geophysicae 18, no. 1 (January 31, 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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Arifin, Lukman, and John Maspupu. "MODEL EMPIRIS HARI TENANG VARIASI MEDAN GEOMAGNET DI STASIUN GEOMAGNET TONDANO MANADO." JURNAL GEOLOGI KELAUTAN 12, no. 2 (February 16, 2016): 115. http://dx.doi.org/10.32693/jgk.12.2.2014.251.
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Penentuan model empiris hari tenang variasi medan geomagnet dikonstruksi berdasarkan data geomagnet dari stasiun geomagnet (SG) Badan Meteorologi Klimatologi dan Geofisika (BMKG) Tondano, Manado. Hari tenang variasi medan geomagnet dinyatakan sebagai fungsi dari keempat komponen atau variabel yang mempengaruhinya yaitu: aktivitas matahari SA (solar activity), hari dalam setahun DOY (date of year), usia bulan LA (lunar age) dan waktu lokal LT (local time). Dalam bentuk matematis ditulis sebagai, EMQD ( SA, DOY, LA, LT ) = f(SA). g(DOY). h(LA). m(LT). Model empiris yang didasarkan pada fungsi kecocokan ini terdiri dari 270 bentuk ekspresi matematik. Sedangkan bentuk-bentuk ekspresi matematik ini juga mencakup proses-proses non-linier yang tak dapat diabaikan dalam model empiris hari tenang variasi medan geomagnet tersebut. Model empiris ini dapat ditiru atau dikonstruksi kembali pada suatu selang waktu yang relatif panjang (misalnya satu siklus matahari), asalkan kondisi geomagnet selalu berada dalam keadaan tenang. Kontribusi dari model empiris hari tenang ini akan memberikan informasi tentang gangguan geomagnet yang ada di stasiun geomagnet Tondano (Nilai Gangguan geomagnet = Nilai variasi medan geomagnet yang terukur – Nilai model empiris hari tenang). Dengan demikian model ini akan memberikan informasi gangguan geomagnet untuk operasi survey geomagnet disekitar stasiun geomagnet Tondano, Manado.
Kata kunci : Model empiris, Hari tenang, Variasi medan geomagnet.
The determination an empirical model of the quiet daily geomagnetic field variation that is constructed based on geomagnetic data from Tondano, Manado station geomagnetic This quiet daily of geomagnetic field variation was described as a function of four variables that its influence, these are solar activity (SA), day of year (DOY), lunar age (LA) and local time (LT). In the mathematically writes: EMQD ( SA, DOY, LA, LT ) = f(SA). g(DOY). h(LA). m(LT). The empirical model based on this fitting function consist of 270 coefficients which included in expression form of mathematic. While, expression form of this mathematic also comprise nonlinear processes which can not minimized in the empirical model of the quiet daily geomagnetic field variation. This empirical model can be reconstructed on the time interval that is long relative (for example one solar cycle). Provided that, under geomagnetic quiet conditions. Contribution of this empirical model of the quiet daily variation is can give information about the existence of geomagnetic disturbance at Tondano (value of geomagnetic disturbance equal value of measurable geomagnetic field variation minus value of empirical model of the quiet daily variation). Thus, information about the existence of this geomagnetic disturbance very useful for necessity geomagnetic survey at Tondano, Manado geomagnetic station.
Keywords: Empirical model, the quiet daily variation, geomagnetic field variation.
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Maspupu, John, and Setyanto C. D. Pranoto. "MODEL PARSIAL HARI TENANG VARIASI MEDAN GEOMAGNET SEBAGAI FUNGSI HARI DALAM SETAHUN, USIA BULAN DAN WAKTU LOKAL DI STASION GEOMAGNET TONDANO." JURNAL GEOLOGI KELAUTAN 12, no. 1 (February 16, 2016): 43. http://dx.doi.org/10.32693/jgk.12.1.2014.245.
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Penentuan suatu model parsial hari tenang variasi medan geomagnet di stasion geomagnet Tondano merupakan fungsi Date of Year (DOY), Lunar Age (LA), dan Local Time (LT). Diperoleh tiga model parsial hari tenang variasi medan geomagnet yaitu = g(DOY), = h(LA), dan = m(LT). Kontribusi dari DOY terhadap hari tenang variasi medan geomagnet sangatlah kecil (sebesar 0,784.10-3 %). Kontribusi faktor fisis lainnya diduga berperan terhadap hari tenang variasi medan geomagnet . Informasi hasil analisis model parsial variasi hari tenang terhadap usia bulan menunjukkan adanya anomali di sekitar lokasi pengamatan. Model parsial hari tenang variasi medan geomagnet yang diperoleh akan membentuk model empiris dari hari tenang. Model empiris akan memberikan informasi gangguan geomagnet untuk kegiatan survei geofisika di perairan Sulawesi Utara.
Kata kunci : Model parsial, hari tenang, variasi medan geomagnet, DOY, LA, LT, Tondano.
Determination of partial model from quiet daily geomagnetic field variation ( ) at geomagnetic station in Tondano is a function of Day of Year (DOY), Lunar Age (LA) and Local Time (LT). It obtains three partial models of quiet daily geomagnetic field variation, those are = g(DOY), = h(LA), dan = m(LT). Contribution from DOY to the quiet daily geomagnetic field variation ( ) is very small (around 0,784.10-3 %). Another contribution of physical factor presumes to play role to quiet daily geomagnetic field ( ). Information of analysis result of quiet daily partial model to lunar age indicates anomaly occurrence around the observation location. Partial model of the obtained quite daily geomagnetic will form empirical model of quite day. This empirical model will provide any information about geomagnetic disturbance for geophysical survey in North Sulawesi Waters.
Keywords: Partial model, the quiet daily variation, geomagnetic field variation, DOY, LA, LT, Tondano.
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KUZNETSOV, V. V., V. V. PLOTKIN, I. I. NESTEROVA, and N. I. IZRAILEVA. "Universal Geomagnetic Variation." Journal of geomagnetism and geoelectricity 44, no. 7 (1992): 481–94. http://dx.doi.org/10.5636/jgg.44.481.
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Le Mouël, J. L., E. Blanter, and M. Shnirman. "The six-month line in geomagnetic long series." Annales Geophysicae 22, no. 3 (March 19, 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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Lyatsky, W., and A. M. Hamza. "Seasonal and diurnal variations of geomagnetic activity and their role in Space Weather forecast." Canadian Journal of Physics 79, no. 6 (June 1, 2001): 907–20. http://dx.doi.org/10.1139/p01-049.
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A possible test for different models explaining the seasonal variation in geomagnetic activity is the diurnal variation. We computed diurnal variations both in the occurrence of large AE (auroral electrojet) indices and in the AO index. (AO is the auroral electrojet index that provides a measure of the equivalent zonal current.) Both methods show a similar diurnal variation in geomagnetic activity with a deep minimum around (37) UT (universal time) in winter and a shallower minimum near 59 UT in equinoctial months. The observed UT variation is consistent with the results of other scientists, but it is different from that expected from the RussellMcPherron mechanism proposed to explain the seasonal variation. It is suggested that the possible cause for the diurnal and seasonal variations may be variations in nightside ionospheric conductivity. Recent experimental results show an important role for ionospheric conductivity in particle acceleration and geomagnetic disturbance generation. They also show that low ionospheric conductivity is favorable to the generation of auroral and geomagnetic activity. The conductivity in conjugate nightside auroral zones (where substorm generation takes place) is minimum at equinoxes, when both auroral zones are in darkness. The low ionospheric conductivity at equinoxes may be a possible cause for the seasonal variation in the geomagnetic activity with maxima in equinoctial months. The diurnal variation in geomagnetic activity can be produced by the UT variation in the nightside ionospheric conductivity, which in winter and at equinoxes has a maximum around 45 UT that may lead to a minimum in geomagnetic activity at this time. We calculated the correlation patterns for the AE index versus solar-wind parameters inside and outside the (27) UT sector related to the minimum in geomagnetic activity. The correlation patterns appear different in these two sectors indeed, which is well consistent with the UT variation in geomagnetic activity. It also shows that it is possible to improve significantly the reliability of the Space Weather forecast by taking into account the dependence of geomagnetic activity not only on solar-wind parameters but also on UT and season. Our test shows that a simple account for the dependence of geomagnetic activity on UT can improve the reliability of the Space Weather forecast by at least 50% in the 27 UT sector in winter and equinoctial months. PACS No.: 91.25Le
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Trichtchenko, L., and D. H. Boteler. "Modelling of geomagnetic induction in pipelines." Annales Geophysicae 20, no. 7 (July 31, 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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Xiao, Sheng Hong, Zhi Wu Cai, Yan Min Xie, and Shao Feng Bian. "Navigation and Positioning by Using the Insufficient Geomagnetic Components." Advanced Materials Research 569 (September 2012): 707–11. http://dx.doi.org/10.4028/www.scientific.net/amr.569.707.
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Geomagnetic field information of the vehicle contains abundant positional information, so the positional information can be derived from the geomagnetic observational value. Firstly, base on the analysis of geomagnetic maps of southeast China, the least square algorithm is used for modeling the local geomagnetism on WMM2010(world magnetic model)database. Then, the optimal positional model can be derived. The simulation has been done, from the simulation results we can see that the mean- squared error of the model in latitude and longitude are about 0.7062 sea mile and 1.8735 sea mile respectively. At last, according to the shortcoming of geomagnetic course system such as costing more time and money in calibration error, the partial geomagnetic field model is applied on correcting the compass variation. The analysis of simulation result indicates that the accuracy has been significantly improved.
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Marques de Souza Franco, Adriane, Rajkumar Hajra, Ezequiel Echer, and Mauricio José Alves Bolzan. "Seasonal features of geomagnetic activity: a study on the solar activity dependence." Annales Geophysicae 39, no. 5 (October 18, 2021): 929–43. http://dx.doi.org/10.5194/angeo-39-929-2021.
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Abstract. Seasonal features of geomagnetic activity and their solar-wind–interplanetary drivers are studied using more than five solar cycles of geomagnetic activity and solar wind observations. This study involves a total of 1296 geomagnetic storms of varying intensity identified using the Dst index from January 1963 to December 2019, a total of 75 863 substorms identified from the SuperMAG AL/SML index from January 1976 to December 2019 and a total of 145 high-intensity long-duration continuous auroral electrojet (AE) activity (HILDCAA) events identified using the AE index from January 1975 to December 2017. The occurrence rates of the substorms and geomagnetic storms, including moderate (-50nT≥Dst>-100nT) and intense (-100nT≥Dst>-250nT) storms, exhibit a significant semi-annual variation (periodicity ∼6 months), while the super storms (Dst≤-250 nT) and HILDCAAs do not exhibit any clear seasonal feature. The geomagnetic activity indices Dst and ap exhibit a semi-annual variation, while AE exhibits an annual variation (periodicity ∼1 year). The annual and semi-annual variations are attributed to the annual variation of the solar wind speed Vsw and the semi-annual variation of the coupling function VBs (where V = Vsw, and Bs is the southward component of the interplanetary magnetic field), respectively. We present a detailed analysis of the annual and semi-annual variations and their dependencies on the solar activity cycles separated as the odd, even, weak and strong solar cycles.
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Mandrikova, Oksana, Anastasia Rodomanskay, and 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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Krylov, Viacheslav V. "Influence of Geomagnetic Disturbances at Different Times of Day on Locomotor Activity in Zebrafish (Danio Rerio)." Clocks & Sleep 3, no. 4 (November 29, 2021): 624–32. http://dx.doi.org/10.3390/clockssleep3040045.
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The influence of magnetic fields and natural geomagnetic storms on biological circadian rhythms are actively studied. This study reveals an impact of local natural perturbations in the geomagnetic field that occurred at different times of the day on circadian patterns of locomotor activity of zebrafish. A decrease in zebrafish swimming speed was observed during the geomagnetic disturbances before or after the fluctuations of diurnal geomagnetic variation. However, if the geomagnetic perturbations coincided with the fluctuations of diurnal geomagnetic variation, the decrease in zebrafish swimming speed was insignificant. This result suggests that the biological effects of geomagnetic disturbances may depend on synchronization with the diurnal geomagnetic variation. It implies that the previously published correlations between geomagnetic activity and medical or biological parameters could result from a disruption in circadian biorhythms.
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Mikhailov, A. V. "Ionospheric F1 layer long-term trends and the geomagnetic control concept." Annales Geophysicae 26, no. 12 (November 28, 2008): 3793–803. http://dx.doi.org/10.5194/angeo-26-3793-2008.
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Abstract. A previous approach to the ionospheric long-term trend analysis has been applied to the foF1 observations from Slough and Rome in order to investigate a possible relationship between the foF1 and the long-term variation of geomagnetic activity. A 40-year period, starting in 1962, has been used for the analysis. According to the results obtained earlier for F2 and E-region trends, geomagnetic control of the long-term variation has also been revealed for the foF1. Thus, it is now possible to speak about the geomagnetic control of the ionospheric trends in the whole ionosphere. This is not surprising as the Earth's ionosphere is a single entity that is strongly controlled, either directly or indirectly, by the magnetic field. As with the F2-region, this geomagnetic control is provided via neutral composition and temperature changes. A very long-term (centennial) increase in geomagnetic activity in the 20th century is seen in the long-term foF1 variations as well. After its removal, the residual foF1 trends are very small and insignificant. In principal, this means that the observed foF1 long-term variations have a natural origin and can be attributed to solar and geomagnetic activity long-term variations. However, the situation in the thermosphere has been changing since 1997 and available foF2 observations at the two stations reveal information about the "break down" of the geomagnetic control in the F2-region. Possible reasons of these changes are discussed.
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Peddie, Norman W. "International Geomagnetic Reference Field Revision 1985." GEOPHYSICS 51, no. 4 (April 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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L. Clúa de Gonzalez, Alicia, Virginia M. Silbergleit, Walter D. Gonzalez, and Bruce T. Tsurutani. "Annual variation of geomagnetic activity." Journal of Atmospheric and Solar-Terrestrial Physics 63, no. 4 (March 2001): 367–74. http://dx.doi.org/10.1016/s1364-6826(00)00190-5.
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Kataja, Eero. "Daily variation of geomagnetic activity." Deutsche Hydrographische Zeitschrift 41, no. 3-6 (May 1988): 217–26. http://dx.doi.org/10.1007/bf02225931.
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Yoshida, Shigeo, and Yozo Hamano. "Geomagnetic decadal variations caused by length-of-day variation." Physics of the Earth and Planetary Interiors 91, no. 1-3 (September 1995): 117–29. http://dx.doi.org/10.1016/0031-9201(95)03038-x.
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Lin, Jyh-Woei. "Geomagnetic Storm Related to Disturbance Storm Time Indices." European Journal of Environment and Earth Sciences 2, no. 6 (November 5, 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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Lepidi, Stefania, Lili Cafarella, Patrizia Francia, Andrea Piancatelli, Manuela Pietrolungo, Lucia Santarelli, and Stefano Urbini. "A study of geomagnetic field variations along the 80° S geomagnetic parallel." Annales Geophysicae 35, no. 1 (January 24, 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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Mandrikova, Oksana V., Igor S. Solovyev, Sergey Y. Khomutov, Vladimir V. Geppener, Dmitry M. Klionskiy, and Mikhail I. Bogachev. "Multiscale variation model and activity level estimation algorithm of the Earth's magnetic field based on wavelet packets." Annales Geophysicae 36, no. 5 (September 19, 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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Makarov, Georgy. "GEOMETRIC FACTOR IN SEASONAL VARIATIONS OF DAILY AVERAGE VALUES OF THE GEOMAGNETIC INDEX Dst." Solar-Terrestrial Physics 6, no. 4 (December 22, 2020): 50–56. http://dx.doi.org/10.12737/stp-64202008.
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The work uses data on the geomagnetic index Dst for the period 1966–2015. Under quiet conditions, the occurrence of seasonal variations of the daily average Dst index depends on geometric factors of the interaction between the solar wind and the magnetosphere; and under disturbed conditions, on the development of a partial ring current in the magnetosphere. At large negative values of the Dst index, there is no seasonal variation in it. The imperfection of the network of Dst stations is assumed to lead to the formation of annual variation in Dst. The formation of a semiannual variation is associated with the movement of the plasma sheet relative to the plane of the geomagnetic equator during the annual rotation of Earth around the Sun. Based on the data on semiannual variations in the number of days n(Dst), the critical daily average value of the geomagnetic index Dst is determined, starting from which we can speak of disturbed days: Dst≤–24 nT.
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Makarov, Georgy. "GEOMETRIC FACTOR IN SEASONAL VARIATIONS OF DAILY AVERAGE VALUES OF THE GEOMAGNETIC INDEX Dst." Solnechno-Zemnaya Fizika 6, no. 4 (December 22, 2020): 59–66. http://dx.doi.org/10.12737/szf-64202008.
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The work uses data on the geomagnetic index Dst for the period 1966–2015. Under quiet conditions, the occurrence of seasonal variations of the daily average Dst index depends on geometric factors of the interaction between the solar wind and the magnetosphere; and under disturbed conditions, on the development of a partial ring current in the magnetosphere. At large negative values of the Dst index, there is no seasonal variation in it. The imperfection of the network of Dst stations is assumed to lead to the formation of annual variation in Dst. The formation of a semiannual variation is associated with the movement of the plasma sheet relative to the plane of the geomagnetic equator during the annual rotation of Earth around the Sun. Based on the data on semiannual variations in the number of days n(Dst), the critical daily average value of the geomagnetic index Dst is determined, starting from which we can speak of disturbed days: Dst≤–24 nT.
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Li, Chen, Li Zhian, and Zhou Zhengfeng. "Rapid Variation of LOD and Solar Flares." Symposium - International Astronomical Union 156 (1993): 317–21. http://dx.doi.org/10.1017/s0074180900173413.
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The sequence of LOD in the period from 1988 to 1991 (which was published in Bulletin B by IERS) is analyzed. Using the method of multiple filter, all the periodic terms are removed. Therefore, the rapid and outstanding variations of LOD that greater than 0.1ms in May, 1989 and Jan., 1990 are shown in the residual series. Because of many bursts of solar flares in the period of Mar.8 to 16 and Nov.7 to 17, there are geomagnetic storms in Mar. and Nov.1989. The strong geomagnetic variation probably induces the rapid variation of LOD.
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Akpaneno, Aniefiok, Matthew Joshua, and K. R. Ekundayo. "THE STUDY OF LONGITUDINAL AND LATITUDINAL VARIATION OF EQUATORIAL ELECTROJET SIGNATURE AT STATIONS WITHIN THE 96°MM AND 210°MM AFRICAN AND ASIAN SECTORS RESPECTIVELY UNDER QUIET CONDITIONS." FUDMA JOURNAL OF SCIENCES 5, no. 2 (July 15, 2021): 511–32. http://dx.doi.org/10.33003/fjs-2021-0502-662.
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Solar quiet current (S_q) and Equatorial Electrojet (EEJ) are two current systems which are produced by electric current in the ionosphere. The enhancement of the horizontal magnetic field is the EEJ. This research is needed for monitoring equatorial geomagnetic current which causes atmospheric instabilities and affects high frequency and satellite communication. This study presents the longitudinal and latitudinal variation of equatorial electrojet signature at stations within the 96°mm and 210°mm African and Asian sectors respectively during quiet condition. Data from eleven observatories were used for this study. The objectives was to determine the longitudinal and latitudinal geomagnetic field variations during solar quiet conditions, Investigate monthly variation and diurnal transient seasonal variation; Measure the strength of the EEJ at stations within the same longitudinal sectors and find out the factors responsible for the longitudinal and latitudinal variation of EEJ. Horizontal (H) component of geomagnetic field for the year 2008 from Magnetic Data Acquisition System (MAGDAS) network were used for the study. The International Quiet Days (IQDs) were used to identify quiet days. Daily baseline values for each of the geomagnetic element H were obtained. The monthly average of the diurnal variation was found. The seasonal variation of dH was found. Results showed that: The longitudinal and latitudinal variation in the dH differs in magnitude from one station to another within the same longitude due to the difference in the influence of the EEJ on them.
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Lockwood, Mike, Mathew J. Owens, Luke A. Barnard, Carl Haines, Chris J. Scott, Kathryn A. McWilliams, and John C. Coxon. "Semi-annual, annual and Universal Time variations in the magnetosphere and in geomagnetic activity: 1. Geomagnetic data." Journal of Space Weather and Space Climate 10 (2020): 23. http://dx.doi.org/10.1051/swsc/2020023.
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We study the semi-annual variation in geomagnetic activity, as detected in the geomagnetic indices am, aaH, AL, Dst and the four aσ indices derived for 6-hour MLT sectors (around noon, dawn, dusk and midnight). For each we compare the amplitude of the semi-annual variation, as a fraction of the overall mean, to that of the corresponding variation in power input to the magnetosphere, Pα, estimated from interplanetary observations. We demonstrate that the semi-annual variation is amplified in the geomagnetic data compared to that in Pα, by a factor that is different for each index. The largest amplification is for the Dst index (factor ~ 10) and the smallest is for the aσ index for the noon MLT sector (aσ-noon, factor ≈ 1.1). By sorting the data by the prevailing polarity of the Y-component (dawn-dusk) of the Interplanetary Magnetic Field (IMF) in the Geocentric Solar Equatorial (GSEQ) reference frame, we demonstrate that the Russell-McPherron (R-M) effect, in which a small southward IMF component in GSEQ is converted into geoeffective field by Earth’s dipole tilt, is a key factor for the semi-annual variations in both Pα and geomagnetic indices. However, the variability in the southward component in the IMF in the GSEQ frame causes more variability in power input to the magnetosphere Pα than does the R-M effect, by a factor of more than two. We show that for increasingly large geomagnetic disturbances, Pα delivered by events of large southward field in GSEQ (known to often be associated with coronal mass ejections) becomes the dominant driver and the R-M effect declines in importance and often acts to reduce geoeffectiveness for the most southward IMF in GSEQ: the semi-annual variation in large storms therefore suggests either preconditioning of the magnetosphere by average conditions or an additional effect at the equinoxes. We confirm that the very large R-M effect in the Dst index is because of a large effect at small and moderate activity levels and not in large storms. We discuss the implications of the observed “equinoctial” time-of-year (F) – Universal Time (UT) pattern of geomagnetic response, the waveform and phase of the semi-annual variations, the differences between the responses at the June and December solstices and the ratio of the amplitudes of the March and September equinox peaks. We also confirm that the UT variation in geomagnetic activity is a genuine global response. Later papers will analyse the origins and implications of the effects described.
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Lockwood, Mike, Kathryn A. McWilliams, Mathew J. Owens, Luke A. Barnard, Clare E. Watt, Chris J. Scott, Allan R. Macneil, and John C. Coxon. "Semi-annual, annual and Universal Time variations in the magnetosphere and in geomagnetic activity: 2. Response to solar wind power input and relationships with solar wind dynamic pressure and magnetospheric flux transport." Journal of Space Weather and Space Climate 10 (2020): 30. http://dx.doi.org/10.1051/swsc/2020033.
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This is the second in a series of papers that investigate the semi-annual, annual and Universal Time (UT) variations in the magnetosphere. We present a varied collection of empirical results that can be used to constrain theories and modelling of these variations. An initial study of two years’ data on transpolar voltage shows that there is a semi-annual variation in magnetospheric flux circulation; however, it is not as large in amplitude as that in geomagnetic activity, consistent with the latter showing a non-linear (quadratic) variation with transpolar voltage. We find that during the persistent minimum of the UT variation in geomagnetic activity, between about 2 and 10 UT, there is also a persistent decrease in observed transpolar voltage, which may be, in part, caused by a decrease in reconnection voltage in the nightside cross-tail current sheet. We study the response of geomagnetic activity to estimated power input into the magnetosphere using interplanetary data from 1995 onwards, an interval for which the data are relatively free of data gaps. We find no consistent variation in the response delay with time-of-year F and, using the optimum lag, we show that the patterns of variation in F-year spectrograms are very similar for geomagnetic activity and power input into the magnetosphere, both for average values and for the occurrence of large events. The Russell–McPherron (R–M) mechanism is shown to be the central driver of this behaviour. However, the (R–M) effect on power input into the magnetosphere is small and there is a non-linear amplification of the semi-annual variation in the geomagnetic response, such that a very small asymmetry in power input into the magnetosphere Pα between the “favourable” and “unfavourable” polarities of the IMF BY component generates a greatly amplified geomagnetic response. The analysis strongly indicates that this amplification is associated with solar wind dynamic pressure and its role in squeezing the near-Earth tail and so modulating the storage and release of energy extracted from the solar wind. In this paper, we show that the equinoctial pattern is found in the residuals of fits of Pα to the am index and that the amplitude of these equinoctial patterns in the am fit residuals increases linearly with solar wind dynamic pressure. Similarly, the UT variation in am is also found in these fit residuals and also increases in amplitude with solar wind dynamic pressure.
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Bhattacharyya, A., and B. Mitra. "Changes in cosmic ray cut-off rigidities due to secular variations of the geomagnetic field." Annales Geophysicae 15, no. 6 (June 30, 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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Akpaneno, Aniefiok, and 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, no. 1 (July 14, 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., and 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, no. 2 (July 16, 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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Kuznetsov, V. V., V. V. Plotkin, I. I. Nesterova, and M. S. Pozdeeva. "Geomagnetic Control of Universal Variation foF2." Journal of geomagnetism and geoelectricity 47, no. 3 (1995): 237–52. http://dx.doi.org/10.5636/jgg.47.237.
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Thaku, N. K., M. V. Mahashabde, B. R. Arora, B. P. Singh, B. J. Srivastava, and S. N. Prasad. "Geomagnetic variation anomalies in peninsular India." Geophysical Journal International 86, no. 3 (September 1, 1986): 839–54. http://dx.doi.org/10.1111/j.1365-246x.1986.tb00663.x.
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Korte, M., and C. G. Constable. "Centennial to millennial geomagnetic secular variation." Geophysical Journal International 167, no. 1 (October 2006): 43–52. http://dx.doi.org/10.1111/j.1365-246x.2006.03088.x.
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Malin, S. R. C., and D. E. Winch. "Annual variation of the geomagnetic field." Geophysical Journal International 124, no. 1 (January 1996): 170–74. http://dx.doi.org/10.1111/j.1365-246x.1996.tb06361.x.
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Gillet, N., V. Lesur, and N. Olsen. "Geomagnetic Core Field Secular Variation Models." Space Science Reviews 155, no. 1-4 (December 15, 2009): 129–45. http://dx.doi.org/10.1007/s11214-009-9586-6.
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Wang, Xiao Mao. "Study on Variation Rate Characters of Mid-to-Low Latitude Area Geomagnetic Field during Geomagnetic Storms." Applied Mechanics and Materials 448-453 (October 2013): 2125–31. http://dx.doi.org/10.4028/www.scientific.net/amm.448-453.2125.
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Geomagnetic field changes acutely during geomagnetic storms. According to Faraday's law of electromagnetic induction, the change of the geomagnetic field produces geomagnetically induced current (GIC) in power grid, which directly damages the power equipment and threatens safe operation of power grid. The more dramatically geomagnetic field changes, the bigger geomagnetically induced current in power grid becomes, and thus, the greater harm it brings to power grid. In this paper, based on the H and D components of recent geomagnetic storm data measured by several mid-to-low latitude geomagnetic observatories, the variation law of the amplitude of north-south and east-west geomagnetic component change rate (dX/dt and dY/dt) pulse with geomagnetic latitude was analyzed when geomagnetic field changed very severely. Finally, the possibilities of power grid in different direction affected by GIC with the change of latitude were discussed. The analysis results will contribute to the evaluation, measurement and control of GIC in Chinese current and future power grid.
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De Michelis, P., R. Tozzi, and A. Meloni. "On the terms of geomagnetic daily variation in Antarctica." Annales Geophysicae 27, no. 6 (June 22, 2009): 2483–90. http://dx.doi.org/10.5194/angeo-27-2483-2009.
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Abstract. The target of this work is to investigate the nature of magnetic perturbations produced by ionospheric and magnetospheric currents as recorded at high-latitude geomagnetic stations. In particular, we investigate the effects of these currents on geomagnetic data recorded in Antarctica. To this purpose we apply a mathematical method, known as Natural Orthogonal Composition, to analyze the magnetic field disturbances along the three geomagnetic field components (X, Y and Z) recorded at Mario Zucchelli Station (IAGA code TNB; geographic coordinates: 74.7° S, 164.1° E) from 1995 to 1998. Using this type of analysis, we characterize the dominant modes of the geomagnetic field daily variability through a set of empirical orthogonal functions (EOFs). While such mathematically independent EOFs do not necessarily represent physically independent modes of variability, we find that some of them are actually related to well known current patterns located at high latitudes.
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Viljanen, A., A. Pulkkinen, O. Amm, R. Pirjola, and T. Korja. "Fast computation of the geoelectric field using the method of elementary current systems and planar Earth models." Annales Geophysicae 22, no. 1 (January 1, 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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Bellanger, E., V. G. Kossobokov, and J. L. Le Mouël. "Predictability of geomagnetic series." Annales Geophysicae 21, no. 5 (May 31, 2003): 1101–9. http://dx.doi.org/10.5194/angeo-21-1101-2003.
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Abstract. The aim of this paper is to lead a practical, rational and rigorous approach concerning what can be done, based on the knowledge of magnetic series, in the field of prediction of the extreme geomagnetic events. We compare the magnetic vector differential at different locations computed with different resolutions, from an entire day to minutes. We study the classical correlations and the simplest possible prediction scheme to conclude a high level of predictability of the magnetic vector variation. The results obtained are far from a random guessing: the error diagrams are either comparable with earthquake prediction studies or out-perform them when the minute sampling is used in accounting for hourly magnetic vector variation. We demonstrate how the magnetic extreme events can be predicted from the hourly value of the magnetic variation with a lead time of several hours. We compute the 2-D empirical distribution of consecutive values of the magnetic vector variation for the estimation of conditional probabilities of different types. The achieved results encourage further development of the approach to prediction of the extreme geomagnetic events.Key words. Ionosphere (modeling and forecasting) – Magnetospheric physics (storms and substorms)
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Elias, A. G., B. S. Zossi, A. R. Gutierrez Falcon, E. S. Comedi, and 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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Vorobev, Andrei, Vyacheslav Pilipenko, Gulnara Vorobeva, and Olga Khristodulo. "Development and application of problem-oriented digital twins for magnetic observatories and variation stations." Information and Control Systems, no. 2 (April 29, 2021): 60–71. http://dx.doi.org/10.31799/1684-8853-2021-2-60-71.
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Introduction: Magnetic stations are one of the main tools for observing the geomagnetic field. However, gaps and anomalies in time series of geomagnetic data, which often exceed 30% of the number of recorded values, negatively affect the effectiveness of the implemented approach and complicate the application of mathematical tools which require that the information signal is continuous. Besides, the missing values add extra uncertainty in computer simulation of dynamic spatial distribution of geomagnetic variations and related parameters. Purpose: To develop a methodology for improving the efficiency of technical means for observing the geomagnetic field. Method: Creation of problem-oriented digital twins of magnetic stations, and their integration into the collection and preprocessing of geomagnetic data, in order to simulate the functioning of their physical prototypes with a certain accuracy. Results: Using Kilpisjärvi magnetic station (Finland) as an example, it is shown that the use of digital twins, whose information environment is made up of geomagnetic data from adjacent stations, can provide the opportunity for reconstruction (retrospective forecast) of geomagnetic variation parameters with a mean square error in the auroral zone of up to 11.5 nT. The integration of problem-oriented digital twins of magnetic stations into the processes of collecting and registering geomagnetic data can provide automatic identification and replacement of missing and abnormal values, increasing, due to the redundancy effect, the fault tolerance of the magnetic station as a data source object. For example, the digital twin of Kilpisjärvi station recovers 99.55% of annual information, and 86.73% of it has an error not exceeding 12 nT. Discussion: Due to the spatial anisotropy of geomagnetic field parameters, the error at the digital twin output will be different in each specific case, depending on the geographic location of the magnetic station, as well as on the number of the surrounding magnetic stations and the distance to them. However, this problem can be minimized by integrating geomagnetic data from satellites into the information environment of the digital twin. Practical relevance: The proposed methodology provides the opportunity for automated diagnostics of time series of geomagnetic data for outliers and anomalies, as well as restoration of missing values and identification of small-scale disturbances.
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Pietrolungo, M., S. Lepidi, L. Cafarella, L. Santarelli, and D. Di Mauro. "Daily variation at three Antarctic geomagnetic observatories within the polar cap." Annales Geophysicae 26, no. 8 (August 4, 2008): 2179–90. http://dx.doi.org/10.5194/angeo-26-2179-2008.
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Abstract. In this work we present a statistical analysis of the diurnal variation as observed at three Antarctic observatories located at different positions within the polar cap during the year 2006. Data used for the analysis are from the Italian geomagnetic observatory at Mario Zucchelli Station (formerly Terra Nova Bay, geographic latitude 74.7° S, corrected geomagnetic latitude 80.0° S), from the French-Italian observatory at Concordia Station (75.1° S, 88.9° S) and from the French observatory at Dumont D'Urville (66.7° S, 80.4° S), which are located in pairs at the same geographic and corrected geomagnetic latitude; such a position allows to distinguish whether the geographic or the geomagnetic reference system is better suitable to describe the observed phenomena at so high latitudes. The peculiarities of the daily variation as observed during this year and its relation with the observatory location and magnetospheric and interplanetary conditions were analysed. Data were also studied taking into account different Lloyd seasons. The results indicate that the 24-h variation is quite persistent, but its amplitude strongly depends on season and global geomagnetic activity: indeed, it almost vanishes during local winter for quiet geomagnetic conditions; this reduction is more evident at the stations closer to the geographic pole, where the solar radiation reduction during winter is more dramatic. The Interplanetary Magnetic Field orientation has been found to be important in that the north-south and the east-west components control the amplitude and the diurnal pattern of the variation, respectively.
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Carlos, Reyes, Ayesta Gárate, and Navarro Reyes. "Solar flares and variation of local geomagnetic field: Measurements by the Huancayo Observatory over 2001-2010." Serbian Astronomical Journal, no. 194 (2017): 87–99. http://dx.doi.org/10.2298/saj160424002c.
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We study the local variation of the geomagnetic field measured by the Huancayo Geomagnetic Observatory, Peru, during 2001-2010. Initially, we sought to relate the SFI values, stored daily in the NOAA's National Geophysical Data Center, with the corresponding geomagnetic index; however, no relation was observed. Nonetheless, subsequently, a comparison between the monthly geomagnetic-activity index and the monthly SFI average allowed observing a temporal correlation between these average indices. This correlation shows that the effect of the solar flares does not simultaneously appear on the corresponding magnetic indices. To investigate this, we selected the most intense X-class flares; then, we checked the magnetic field disturbances observed in the Huancayo Geomagnetic Observatory magnetograms. We found some disturbances of the local geomagnetic field in the second and third day after the corresponding solar flare; however, the disturbance strength of the local geomagnetic field is not correlated with the X-class of the solar flare. Finally, there are some disturbances of the local geomagnetic field that are simultaneous with the X-class solar flares and they show a correlation with the total flux of the solar flare.
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Wu, Wei Li. "Minimum Amplitude of Geomagnetic Disturbance in Electrical Power System Leading to 500kV transformer DC Bias." Advanced Materials Research 676 (March 2013): 251–54. http://dx.doi.org/10.4028/www.scientific.net/amr.676.251.
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This article analysis the relationship between geomagentically induced currents(GIC) in electrical power system flowing through 500kV transformer neutral point in Ling’Ao power grid and the geomagnetic data observed at Guangzhou geomagnetic observatory during 2004/11 -2006/12. It is found that correlation coefficient between GIC and magnetic field component variation may be greater than that of time derivative of the geomagnetic field, which are all less than -0.5. According to the relation, The minimum amplitude of geomagnetic component variation is 7.08(nT/min) in term of transformer of single or three phase five columns while is about27.47(nT/min) when the type is three phase three columns.
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Otsuka, Kuniaki, Germaine Cornelissen, Andi Weydahl, Denis Gubin, Larry A. Beaty, and Masatoshi Murase. "Rules of Heliogeomagnetics Diversely Coordinating Biological Rhythms and Promoting Human Health." Applied Sciences 13, no. 2 (January 10, 2023): 951. http://dx.doi.org/10.3390/app13020951.
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This investigation reviews how geomagnetic activity affects the circadian variation in blood pressure (BP) and heart rate (HR) and their variabilities of clinically healthy individuals. A small study in Alta, Norway (latitude of 70.0° N), serves to illustrate the methodology used to outline rules of procedure in exploring heliogeomagnetic effects on human physiology. Volunteers in the Alta study were monitored for at least 2 days between 18 March 2002 and 9 January 2005. Estimates of the circadian characteristics of BP and HR by cosinor and the Maximum Entropy Method (MEM) indicate an increase in the circadian amplitude of systolic (S) BP on geomagnetic-disturbance days compared to quiet days (p = 0.0236). Geomagnetic stimulation was found to be circadian-phase dependent, with stimulation in the evening inducing a 49.2% increase in the circadian amplitude of SBP (p = 0.0003), not observed in relation to stimulation in the morning. In two participants monitored for 7 days, the circadian amplitude of SBP decreased by 23.4% on an extremely disturbed day but increased by 50.3% on moderately disturbed days (p = 0.0044), suggesting a biphasic (hormetic) reaction of the circadian SBP rhythm to geomagnetics. These results indicate a possible role of geomagnetic fluctuations in modulating the circadian system.
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Campbell-Brown, M. D. "Solar cycle variation in radar meteor rates." Monthly Notices of the Royal Astronomical Society 485, no. 3 (March 8, 2019): 4446–53. http://dx.doi.org/10.1093/mnras/stz697.
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ABSTRACT 16 yr of meteor radar data from the Canadian Meteor Orbit Radar (CMOR) were used to investigate the link between observed meteor rates and both solar and geomagnetic activity. Meteor rates were corrected for transmitter power and receiver noise, and seasonal effects were removed. A strong negative correlation is seen between solar activity, as measured with the 10.7 cm flux, and observed meteor rates. This lends support to the idea that heating in the atmosphere at times of elevated solar activity changes the scale height and therefore the length and maximum brightness of meteors; a larger scale height near solar maximum leads to longer, fainter meteors and therefore lower rates. A weaker negative correlation was observed with geomagnetic activity as measured with the K index; this correlation was still present when solar activity effects were removed. Meteor activity at solar maximum is as much as 30 per cent lower than at solar minimum, strictly due to observing biases; geomagnetic activity usually affects meteor rates by less than 10 per cent.
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Obiekezie, T. N., S. C. Obiadazie, and G. A. Agbo. "Day-to-Day Variability of H and Z Components of the Geomagnetic Field at the African Longitudes." ISRN Geophysics 2013 (August 29, 2013): 1–7. http://dx.doi.org/10.1155/2013/909258.
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The Day-to-day variability of the geomagnetic field elements at the African longitudes has been studied for the year 1987 using geomagnetic data obtained from four different African observatories. The analysis was carried out on solar quiet days using hourly values of the Horizontal, , and vertical, , geomagnetic field values. The results of this study confirm that Sq is a very changeable phenomenon, with a strong day-to-day variation. This day-to-day variation is seen to be superimposed on magnetic disturbances of a magnetospheric origin.
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Zheng, Hui, Hubiao Wang, Lin Wu, Hua Chai, and Yong Wang. "Simulation Research on Gravity-Geomagnetism Combined Aided Underwater Navigation." Journal of Navigation 66, no. 1 (July 30, 2012): 83–98. http://dx.doi.org/10.1017/s0373463312000343.
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Gravity Aided Navigation (GravAN) and Geomagnetism Aided Navigation (GeomAN) are two methods for correcting Inertial Navigation System (INS) errors of Autonomous Underwater Vehicles (AUVs) without compromising the AUV mission. One requirement for applying these methods is the relatively large field feature variations along the navigation trajectory. But in some regions with small gravity or geomagnetic variation, it is very difficult to achieve a reliable result solely by GravAN or GeomAN. If these two methods were combined, gravity and geomagnetism information could be complementary and the aided navigation ability could potentially be improved, especially in those regions when neither method is valid. Based on that concept, a Gravity and Geomagnetism Combined Aided Navigation (GGCAN) method is consequently proposed in this paper as a possible solution. The Gravity Anomaly Grid (GAG2) and Earth Geomagnetic Anomaly Grid (EMAG2) are utilized as the background databases, and then a Multiple Model Adaptive Estimation (MMAE) is adopted to obtain an optimal estimated navigation position. Furthermore, an Optimal Weight Allocation Principle (OWAP) is introduced to the combined GravAN and GeomAN methods, together with a weighted average. In simulation, two special regions in the Western Pacific Ocean were chosen to test the proposed method. The results show that GGCAN can improve the position success rate and reduce the error, compared to GravAN or GeomAN. Results indicate that the GGCAN method proposed in this study is able to improve the accuracy and reliability of an aided navigation system.
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RAO, DRK, and RK BANSAL. "Secular variation of Geomagnetic Elements at Alibag-." MAUSAM 20, no. 2 (April 30, 2022): 141–44. http://dx.doi.org/10.54302/mausam.v20i2.5443.
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Attempts are made to represent secular variations of geomagnetic elements (H. Z and D) of Alibag by fitting polynomials of third order to the observed annual mean values for the years 1905-65. The coefficients of the fitted curve account for more than 99 percent of the total variation in case of H and D and 98 per cent in case of z. The coefficients are compared with those computed by Moos, Pramanik and Pramanik and Ganguli for the same station. A probable change of position or intensity or both of the focus of the H-field in the region is inferred from the change in trend of H and D curves about the year 1964. The residual H,Z and D curves did not show any parallelism with solar activity as judged from sunspot numbers. H and Z residuals nearly indicated a periodicity of 3 solar cycles whereas D showed a periodicity of 2 solar cycles.
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Friederich, F., M. Sinnhuber, B. Funke, T. von Clarmann, and J. Orphal. "Local impact of solar variation on NO<sub>2</sub> in the lower mesosphere and upper stratosphere from 2007 to 2012." Atmospheric Chemistry and Physics 14, no. 8 (April 23, 2014): 4055–64. http://dx.doi.org/10.5194/acp-14-4055-2014.
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Abstract. MIPAS/ENVISAT data of nighttime NO2 volume mixing ratios (VMR) from 2007 until 2012 between 40 km and 62 km altitude are compared with the geomagnetic Ap index and solar Lyman-α radiation. The local impact of variations in geomagnetic activity and solar radiation on the VMR of NO2 in the lower mesosphere and upper stratosphere in the Northern Hemisphere is investigated by means of superposed epoch analysis. Observations in the Northern Hemisphere show a clear 27-day period of the NO2 VMR. This is positively correlated with the geomagnetic Ap index at 60–70° N geomagnetic latitude but also partially correlated with the solar Lyman-α radiation. However, the dependency of NO2 VMR on geomagnetic activity can be distinguished from the impact of solar radiation. This indicates a direct response of NOx (NO + NO2) to geomagnetic activity, probably due to precipitating particles. The response is detected in the range between 46 km and 52 km altitude. The NO2 VMR epoch maxima due to geomagnetic activity is altitude-dependent and can reach up to 0.4 ppb, leading to mean production rates of 0.029 ppb (Ap d)−1. Observations in the Southern Hemisphere do not have the same significance due to a worse sampling of geomagnetic storm occurances. Variabilities due to solar variation occur at the same altitudes at 60–70° S geomagnetic latitude but cannot be analyzed as in the Northern Hemisphere. This is the first study showing the direct impact of electron precipitation on NOx at those altitudes in the spring/summer/autumn hemisphere.
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Bhardwaj, S. K., and G. K. Rangarajan. "Geomagnetic Secular Variation at the Indian Observatories." Journal of geomagnetism and geoelectricity 49, no. 9 (1997): 1131–44. http://dx.doi.org/10.5636/jgg.49.1131.
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Russell, C. T. "The universal time variation of geomagnetic activity." Geophysical Research Letters 16, no. 6 (June 1989): 555–58. http://dx.doi.org/10.1029/gl016i006p00555.
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