Journal articles: 'Geomagnetic variations'

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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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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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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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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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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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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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Bochníček, J., P. Hejda, V. Bucha, and J. Pýcha. "Possible geomagnetic activity effects on weather." Annales Geophysicae 17, no. 7 (July 31, 1999): 925–32. http://dx.doi.org/10.1007/s00585-999-0925-4.

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Abstract. Tropospheric temperature and pressure fields on the Northern Hemisphere in the winter periods 1952-1996 were investigated. Composite maps of those fields, created for the high and low geomagnetic activity and individual quasi-biennial oscillation (QBO), phases show clear differences not only between different levels of geomagnetic activity, but also between the two phases of QBO. Special attention was given to the behaviour of the lower troposphere in January and February 1982.Key words. Geomagnetism and paleomagnetism (time variations · diurnal to regular). Meteorology and atmospheric dynamics (general circulation; middle atmosphere dynamics)

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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, 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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Воробьев, Андрей, Andrey Vorobev, Вячеслав Пилипенко, Vyacheslav Pilipenko, Ярослав Сахаров, Yaroslav Sakharov, Василий Селиванов, and Vasiliy Selivanov. "Statistical relationships between variations of the geomagnetic field, auroral electrojet, and geomagnetically induced currents." Solar-Terrestrial Physics 5, no. 1 (March 22, 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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Spivak, A. A., and S. A. Riabova. "Geomagnetic Variations during Strong Earthquakes." Izvestiya, Physics of the Solid Earth 55, no. 6 (November 2019): 811–20. http://dx.doi.org/10.1134/s1069351319060077.

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Sheremet’eva, O. V., and S. E. Smirnov. "Tidal components of geomagnetic variations." Geomagnetism and Aeronomy 47, no. 5 (October 2007): 588–97. http://dx.doi.org/10.1134/s0016793207050076.

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Adushkin, V. V., A. A. Spivak, S. A. Ryabova, and V. A. Kharlamov. "Tidal effects in geomagnetic variations." Doklady Earth Sciences 474, no. 1 (May 2017): 579–82. http://dx.doi.org/10.1134/s1028334x17050105.

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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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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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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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Kurazhkovskii, A. Yu, N. A. Kurazhkovskaya, and B. I. Klain. "Spectrum of Quaziperiodic Variations in Paleomagnetic Activity in the Phanerozoic." Russian Geology and Geophysics 63, no. 11 (November 1, 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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Kilifarska, Natalya, Antonia Mokreva, and Tsvetelina Velichkova. "North Atlantic Oscillation and Variations of Geomagnetic Field." Proceedings of the Bulgarian Academy of Sciences 75, no. 11 (November 30, 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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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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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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SUKHAREV, A., M. ORLYUK, M. RYABOV, L. SOBITNIAK, V. BEZRUKOVS, S. PANISHKO, and 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 (July 1, 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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Караханян, Ашхен, Ashhen Karakhanyan, Сергей Молодых, and Sergey Molodykh. "Spatial distribution of temperature during geomagnetic disturbances." Solar-Terrestrial Physics 4, no. 4 (December 21, 2018): 59–62. http://dx.doi.org/10.12737/stp-44201808.

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We propose an index of efficiency of the solar activity effect on the tropospheric temperature, which takes into account the spatial irregularity of the response to this effect. As a proxy of solar activity we take the PC index of geomagnetic activity, designed to monitor the geomagnetic field at high latitudes. Using NCEP/NCAR reanalysis data, we carry out a comparative analysis of variations in the proposed index and lower-troposphere temperature variations during geomagnetic disturbances. We identify the presence of a high degree of correlation between the temperature in the 925–700 hPa layer and the proposed index of solar activity effect. The spatio-temporal analysis of the index and temperature variations shows that the index of effi-ciency of the solar activity effect describes well both the value and the sign of the observed variations in the spa-tial distribution of the lower-troposphere temperature as compared to the frequently used index of geomagnetic activity.

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Li, Zheng, Meng Sun, Jingyuan Li, Kedeng Zhang, Hua Zhang, Xiaojun Xu, and Xinhua Zhao. "Significant Variations of Thermospheric Nitric Oxide Cooling during the Minor Geomagnetic Storm on 6 May 2015." Universe 8, no. 4 (April 12, 2022): 236. http://dx.doi.org/10.3390/universe8040236.

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Using observations by the SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) instrument on board the TIMED (Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics) satellite and simulations by the TIEGCM (Thermosphere-Ionosphere-Electrodynamics General Circulation Model), we investigate the daytime variations of thermospheric nitric oxide (NO) cooling during the geomagnetic storm on 6 May 2015. The geomagnetic storm was minor, as the minimum Dst was −28 nT, the maximum Kp was 5+ and the maximum AE was 1259 nT. However, significant enhancements of peak NO cooling rate and prominent decreases in the peak NO cooling altitude were observed from high latitudes to low latitudes in both hemispheres on the dayside by the SABER instrument. The model simulations underestimate the response of peak NO cooling and have no significant variation of the altitude of peak NO cooling rate on the dayside during this minor geomagnetic storm. By investigating the temporal and latitudinal variations of vertical NO cooling profiles inferred from SABER data, we suggest that the horizontal equatorward winds caused by the minor geomagnetic storm were unexpectedly strong and thus play an important role in inducing these significant daytime NO cooling variations.

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Spivak, A. A., and S. A. Riabova. "Geomagnetic effect of earthquakes." Доклады Академии наук 488, no. 2 (September 24, 2019): 197–201. http://dx.doi.org/10.31857/s0869-56524882197-201.

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Based on the results of instrumental observations carried out at a number of mid-latitude observatories of the INTERMAGNET network and at the Mikhnevo Geophysical Observatory of Institute of Geosphere Dynamics of Russian Academy of Sciences, it is shown that strong earthquakes are accompanied by increased variations of Earth’s magnetic field. In this case, the short-period stage (period ~ 0.5-0.8 min) and long-period stage (period ~ 5-20 min) of increased geomagnetic variations are clearly distinguished. The maximum amplitude of induced geomagnetic variations is 1.5-2 nT and 2- 4 nT, respectively, for short-period and long-period variations. A similar in morphology and almost synchronous nature of the induced geomagnetic disturbances at the observatories located at significantly different distances from the earthquake source is noted.

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28

Glassmeier, K. H., J. Vogt, A. Stadelmann, and S. Buchert. "Concerning long-term geomagnetic variations and space climatology." Annales Geophysicae 22, no. 10 (November 3, 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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29

Mikhailov, A. V., and B. A. de la Morena. "Long-term trends of <i>f</i>oE and geomagnetic activity variations." Annales Geophysicae 21, no. 3 (March 31, 2003): 751–60. http://dx.doi.org/10.5194/angeo-21-751-2003.

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Abstract. A relationship between foE trends and geomagnetic activity long-term variations has been revealed for the first time. By analogy with earlier obtained results on the foF2 trends it is possible to speak about the geomagnetic control of the foE long-term trends as well. Periods of increasing geomagnetic activity correspond to negative foE trends, while these trends are positive for the decreasing phase of geomagnetic activity. This "natural" relationship breaks down around 1970 (on some stations later) when pronounced positive foE trends have appeared on most of the stations considered. The dependence of foE trends on geomagnetic activity can be related with nitric oxide variations at the E-layer heights. The positive foE trends that appeared after the "break down" effect may also be explained by the [NO] decrease which is not related to geomagnetic activity variations. But negative trends or irregular foE variations on some stations for the same time period require some different mechanism. Chemical pollution of the lower thermosphere due to the anthropogenic activity may be responsible for such abnormal foE behavior after the end of the 1960s.Key words. Ionosphere (ionosphere-atmosphere interactions; ionospheric disturbances)

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30

Karinen, A., K. Mursula, Th Ulich, and J. Manninen. "Does the magnetosphere behave differently on weekends?" Annales Geophysicae 20, no. 8 (August 31, 2002): 1137–42. http://dx.doi.org/10.5194/angeo-20-1137-2002.

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Abstract. Global geomagnetic activity has been suggested to be enhanced during weekends above the weekly average after 1930. Before the 1930s, weekends and weekdays were found to be equally active. This so-called "weekend effect" was suggested to be due to power line harmonic radiation (PLHR) in the VLF range emitted by electric power lines. Since the consumption of electric power is different on weekends and weekdays, leading to different PLHR intensities, this could possibly cause the "weekend effect" in global geomagnetic activity. In the present paper, we reanalyse the suggested "week-end effect" in global geomagnetic activity using the 69-year planetary geomagnetic Ap index and the 131-year antipodal aa index. We conclude that there is no statistically significant "weekend effect" during the interval covered by these geo-magnetic activity indices. Although global geomagnetic activity is slightly enhanced on weekends from the 1930s to the 1980s, the more recent data show rather a relative decrease in global geomagnetic activity on weekends, contrary to the expected increase in the "weekend effect", due to increasing power consumption. Moreover, the weekly distribution is fairly similar in solar wind speed and global geomagnetic activity during the last 35 years, further supporting the view that the "weekend effect" is only a statistical fluctuation.Key words. Geomagnetism and paleomagnetism (time variations, diurnal to secular) – Magnetospheric physics (planetary magnetospheres; storms and substorms)

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31

Rotanova, N. M., T. N. Bondar, and E. V. Kovalevskaya. "Wavelet analysis of secular geomagnetic variations." Russian Journal of Earth Sciences 5, no. 5 (December 2, 2003): 375–83. http://dx.doi.org/10.2205/2003es000138.

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Sridharan, Muthusamy, and Ayyathurai M. S. Ramasamy. "Gabriel graph of geomagnetic Sq variations." Acta Geophysica 58, no. 6 (March 1, 2010): 973–87. http://dx.doi.org/10.2478/s11600-010-0004-y.

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33

Winch, D. E. "Solar and Lunar Daily Geomagnetic Variations." Exploration Geophysics 24, no. 2 (June 1993): 147–50. http://dx.doi.org/10.1071/eg993147.

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34

Korte, Monika, and 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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35

Kohsiek, A., M. Kiefer, C. E. Meek, and A. H. Manson. "Fluctuations in tides and geomagnetic variations." Geophysical Research Letters 25, no. 6 (March 15, 1998): 889–92. http://dx.doi.org/10.1029/98gl00384.

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36

Gao, Yufen. "Geomagnetic daily variations around Huanghai earthquake." Acta Seismologica Sinica 5, no. 1 (February 1992): 127–31. http://dx.doi.org/10.1007/bf02650909.

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37

Olsen, N. "Magnetospheric contributions to geomagnetic daily variations." Annales Geophysicae 14, no. 5 (May 31, 1996): 538–44. http://dx.doi.org/10.1007/s00585-996-0538-0.

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Abstract. The contribution of magnetospheric current systems to geomagnetic daily variations is analyzed by means of a spherical harmonic analysis (SHA) using elementary models as well as the Tsyganenko model of the magnetosphere. It is discovered that the magnetospheric contribution to some SHA coefficients is much higher than the known average value of about 20%, especially when considering non-local time terms and solstitial conditions.

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38

Minorsky, Peter V. "Do geomagnetic variations affect plant function?" Journal of Atmospheric and Solar-Terrestrial Physics 69, no. 14 (October 2007): 1770–74. http://dx.doi.org/10.1016/j.jastp.2006.12.004.

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39

Chamalaun, Francois, and Charles Barton. "Comprehensive Mapping of Australia's Geomagnetic Variations." Eos, Transactions American Geophysical Union 71, no. 51 (1990): 1867. http://dx.doi.org/10.1029/90eo00376.

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40

Ogunade, S. O. "Solar-terrestrial relations and geomagnetic variations." Earth, Moon, and Planets 70, no. 1-3 (1995): 163–71. http://dx.doi.org/10.1007/bf00619460.

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41

Reshetnyak, M. Yu. "Latitudinal Variations of the Geomagnetic Field." Izvestiya, Physics of the Solid Earth 59, no. 2 (April 2023): 115–19. http://dx.doi.org/10.1134/s1069351323020106.

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42

Липко, Юрий, Yuriy Lipko, Александр Пашинин, Aleksandr Pashinin, Равиль Рахматулин, Ravil Rakhmatulin, Виталий Хахинов, and Vitaliy Khakhinov. "Geomagnetic effects caused by rocket exhaust jets." Solnechno-Zemnaya Fizika 2, no. 3 (September 17, 2016): 33–40. http://dx.doi.org/10.12737/19634.

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In the space experiment Radar–Progress, we have made 33 series of measurements of geomagnetic variations during ignitions of engines of Progress cargo spacecraft in low Earth orbit. We used magneto-measuring complexes, installed at observatories of the Institute of Solar-Terrestrial Physics of Siberian Branch of the Russian Academy of Sciences, and magnetotelluric equipment of a mobile complex. We assumed that engine running can cause geomagnetic disturbances in flux tubes crossed by the spacecraft. When analyzing experimental data, we took into account space weather factors: solar wind parameters, total daily mid-latitude geomagnetic activity index Kр, geomagnetic auroral electrojet index AE, global geomagnetic activity. The empirical data we obtained indicate that 18 of the 33 series showed geomagnetic variations in various time ranges.

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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, no. 1 (March 1991): 1–6. http://dx.doi.org/10.1007/bf01625053.

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44

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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45

Kovaltsov, G. A., and I. G. Usoskin. "Regional cosmic ray induced ionization and geomagnetic field changes." Advances in Geosciences 13 (August 13, 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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Altadill, D. "On the 18-day quasi-periodic oscillation in the ionosphere." Annales Geophysicae 14, no. 7 (July 31, 1996): 716–24. http://dx.doi.org/10.1007/s00585-996-0716-0.

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Abstract. The presence and persistence of an 18-day quasi-periodic oscillation in the ionospheric electron density variations were studied. The data of lower ionosphere (radio-wave absorption at equivalent frequency near 1 MHz), middle and upper ionosphere (critical frequencies f0E and f0F2) for the period 1970–1990 have been used in the analysis. Also, solar and geomagnetic activity data (the sunspot numbers Rz and solar radio flux F10.7 cm, and aN index respectively) were used to compare the time variations of the ionospheric with the solar and geomagnetic activity data. Periodogram, complex demodulation, auto- and cross-correlation analysis have been used. It was found that 18-day quasi-periodic oscillation exists and persists in the temporal variations of the ionospheric parameters under study with high level of correlation and mean period of 18–19 days. The time variation of the amplitude of the 18-day quasi-periodic oscillation in the ionosphere seems to be modulated by the long-term solar cycle variations. Such oscillations exist in some solar and geomagnetic parameters and in the planetary wave activity of the middle atmosphere. The high similarities in the amplitude modulation, long-term amplitude variation, period range between the oscillation of investigated parameters and the global activity of oscillation suggests a possible solar influence on the 18-day quasi-periodic oscillation in the ionosphere.

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Sokol-Kutylovskii, O. L. "The measurement of a weak alternating magnetic field in unshielded space." Metrologiya, no. 1 (May 31, 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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48

Kocharov, G. E., A. V. Blinov, A. N. Konstantinov, and V. A. Levchenko. "Temporal 10Be and 14C Variations: A Tool for Paleomagnetic Research." Radiocarbon 31, no. 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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Воробьев, Андрей, Andrey Vorobev, Вячеслав Пилипенко, Vyacheslav Pilipenko, Ярослав Сахаров, Yaroslav Sakharov, Василий Селиванов, and Vasiliy Selivanov. "Statistical relationships between variations of the geomagnetic field, auroral electrojet, and geomagnetically induced currents." Solnechno-Zemnaya Fizika 5, no. 1 (March 22, 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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Mihai, Andrei, Victorin-Emilian Toader, Iren-Adelina Moldovan, and Mircea Radulian. "Exploring the Relationship between Geomagnetic Variations and Seismic Energy Release in Proximity to the Vrancea Seismic Zone." Atmosphere 14, no. 6 (June 10, 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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Journal articles on the topic 'Geomagnetic variations'

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