Artykuły w czasopismach: „Geomagnetic signatures”

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Zerbo, Jean-Louis, Frédéric Ouattara, Christine Amory Mazaudier, Jean-Pierre Legrand i John D. Richardson. "Solar Activity, Solar Wind and Geomagnetic Signatures". Atmospheric and Climate Sciences 03, nr 04 (2013): 610–17. http://dx.doi.org/10.4236/acs.2013.34063.

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Sutcliffe, P. R. "Modelling the Ionospheric Signatures of Geomagnetic Pulsations." Journal of geomagnetism and geoelectricity 46, nr 11 (1994): 1011–27. http://dx.doi.org/10.5636/jgg.46.1011.

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Kullen, A., S. Ohtani i T. Karlsson. "Geomagnetic signatures of auroral substorms preceded by pseudobreakups". Journal of Geophysical Research: Space Physics 114, A4 (kwiecień 2009): n/a. http://dx.doi.org/10.1029/2008ja013712.

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Masci, F. "On the multi-fractal characteristics of the ULF geomagnetic field before the 1993 Guam earthquake". Natural Hazards and Earth System Sciences 13, nr 1 (29.01.2013): 187–91. http://dx.doi.org/10.5194/nhess-13-187-2013.

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Abstract. Ida et al. (2005) document significant changes in the multi-fractal parameters of the ULF geomagnetic field H component starting about one month before the 1993 Guam earthquake. According to the authors, these multi-fractal signatures can be considered as precursory signals of the Guam earthquake. As a consequence, they conclude that the multi-fractal analysis may have an important role in the development of short-term earthquake prediction capabilities. Since this and other similar reports have motivated the idea that earthquake prediction based on electromagnetic precursory signals may one day become a routine technique, the presumed precursors need to be validated through independent datasets. In this review the seismogenic origin of the multi-fractal magnetic signatures documented by Ida et al. (2005) before the 8 August 1993 Guam earthquake is seriously put into question. By means of the geomagnetic ΣKp index, it is demonstrated that these multi-fractal parameter changes are normal signals induced by the variation of the global geomagnetic activity level.

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Alex, S., S. Mukherjee i G. S. Lakhina. "Geomagnetic signatures during the intense geomagnetic storms of 29 October and 20 November 2003". Journal of Atmospheric and Solar-Terrestrial Physics 68, nr 7 (kwiecień 2006): 769–80. http://dx.doi.org/10.1016/j.jastp.2006.01.003.

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Olawepo, A. O., i J. O. Adeniyi. "Signatures of strong geomagnetic storms in the equatorial latitude". Advances in Space Research 53, nr 7 (kwiecień 2014): 1047–57. http://dx.doi.org/10.1016/j.asr.2014.01.012.

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Lam, H. L., D. H. Boteler i L. Trichtchenko. "Case studies of space weather events from their launching on the Sun to their impacts on power systems on the Earth". Annales Geophysicae 20, nr 7 (31.07.2002): 1073–79. http://dx.doi.org/10.5194/angeo-20-1073-2002.

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Abstract. Active geomagnetic conditions on 12–13, 15–16, and 22–23 September 1999 resulted in geomagnetically induced currents (GIC) measurable in power systems in Canada and the United States. Different solar origins for these three events gave rise to dissimilar interplanetary signatures. We used these events to present three case studies, each tracing an entire space weather episode from its inception on the Sun, propagation through the interplanetary medium, manifestation on the ground as intense magnetic and electric fluctuations, and its eventual impact on technological systems.Key words. Geomagnetism and paleomagnetism (rapid time variations) – Interplanetary physics (interplanetary magnetic fields) – Solar physics, astrophysics, and astronomy (flares and mass ejections)

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Rawat, R., S. Alex i G. S. Lakhina. "Low-latitude geomagnetic signatures during major solar energetic particle events of solar cycle-23". Annales Geophysicae 24, nr 12 (21.12.2006): 3569–83. http://dx.doi.org/10.5194/angeo-24-3569-2006.

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Abstract. The frequency of occurrence of disruptive transient processes in the Sun is enhanced during the high solar activity periods. Solar cycle-23 evidenced major geomagnetic storm events and intense solar energetic particle (SEP) events. The SEP events are the energetic outbursts as a result of acceleration of heliospheric particles by solar flares and coronal mass ejections (CMEs). The present work focuses on the geomagnetic variations at equatorial and low-latitude stations during the four major SEP events of 14 July 2000, 8 November 2000, 24 September 2001 and 4 November 2001. These events have been reported to be of discernible magnitude following intense X-ray flares and halo coronal mass ejections. Low-latitude geomagnetic records evidenced an intense main phase development subsequent to the shock impact on the Earth's magnetosphere. Satellite observations show proton-flux enhancements associated with solar flares for all events. Correlation analysis is also carried out to bring out the correspondence between the polar cap magnetic field perturbations, AE index and the variations of low-latitude magnetic field. The results presented in the current study elucidate the varying storm development processes, and the geomagnetic field response to the plasma and interplanetary magnetic field conditions for the energetic events. An important inference drawn from the current study is the close correspondence between the persistence of a high level of proton flux after the shock in some events and the ensuing intense magnetic storm. Another interesting result is the role of the pre-shock southward IMF Bz duration in generating a strong main phase.

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Martin, Jr., R. F., R. Fricke i T. W. Speiser. "Modeled Particle Signatures of Magnetic Structures in the Geomagnetic Tail". Journal of geomagnetism and geoelectricity 48, nr 5 (1996): 809–19. http://dx.doi.org/10.5636/jgg.48.809.

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Masci, Fabrizio. "On claimed ULF seismogenic fractal signatures in the geomagnetic field". Journal of Geophysical Research: Space Physics 115, A10 (październik 2010): n/a. http://dx.doi.org/10.1029/2010ja015311.

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Pryse, S. E., A. M. Smith, I. K. Walker i L. Kersley. "Multi-instrument study of footprints of magnetopause reconnection in the summer ionosphere". Annales Geophysicae 18, nr 9 (30.09.2000): 1118–27. http://dx.doi.org/10.1007/s00585-000-1118-3.

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Abstract. Results are presented from a multi-instrument investigation of the signatures of equatorial reconnection in the summer, sunlit ionosphere. Well-established ion dispersion signatures measured during three DMSP satellite passes were used to identify footprints in ionospheric observations made by radio tomography, and both the EISCAT ESR and mainland radars. Under the prevalent conditions of southward IMF with the Bz component increasing in magnitude, the reconnection footprint was seen to move equatorward through the ESR field-of-view. The most striking signature was in the electron temperatures of the F2 region measured by the EISCAT mainland radar that revealed significantly enhanced temperatures with a steep equatorward edge, in general agreement with the leading edge of the ion dispersion. It is suggested that this sharp transition in the electron temperature may be an indicator of the boundary, mapping from the reconnection site, between closed geomagnetic field lines and those opened along which magnetosheath ions precipitate.Key words: Ionosphere (ionosphere-magnetosphere interactions; particle precipitation; plasma temperature and density)

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Masci, F. "Brief communication "On the recent reaffirmation of ULF magnetic earthquakes precursors"". Natural Hazards and Earth System Sciences 11, nr 8 (12.08.2011): 2193–98. http://dx.doi.org/10.5194/nhess-11-2193-2011.

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Abstract. Hayakawa et al. (2009) and Hayakawa (2011) have recently reviewed some "anomalous" ULF signatures in the geomagnetic field which previous publications have claimed to be earthquake precursors. The motivation of this review is "to offer a further support to the definite presence of those anomalies". Here, these ULF precursors are reviewed once again. This brief communication shows that the reviewed anomalies do not "increase the credibility on the presence of electromagnetic phenomena associated with an earthquake" since these anomalous signals are actually caused by normal geomagnetic activity. Furthermore, some of these ULF precursors have just been rebutted by previous publications.

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Syed Zafar, S. N. A., Roslan Umar, N. H. Sabri, M. H. Jusoh, A. Yoshikawa, S. Abe i T. Uozumi. "A statistical analysis of the relationship between Pc4 and Pc5 ULF waves, solar winds and geomagnetic storms for predicting earthquake precursor signatures in low latitude regions". IOP Conference Series: Earth and Environmental Science 880, nr 1 (1.10.2021): 012010. http://dx.doi.org/10.1088/1755-1315/880/1/012010.

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Abstract Short-term earthquake forecasting is impossible due to the seismometer’s limited sensitivity in detecting the generation of micro-fractures prior to an earthquake. Therefore, there is a strong desire for a non-seismological approach, and one of the most established methods is geomagnetic disturbance observation. Previous research shows that disturbances in the ground geomagnetic field serves as a potential precursor for earthquake studies. It was discovered that electromagnetic waves (EM) in the Ultra-Low Frequency (ULF) range are a promising tool for studying the seismomagnetic effect of earthquake precursors. This study used a multiple regression approach to analyse the preliminary study on the relationship between Pc4 (6.7-22 mHz) and Pc5 (1.7-6.7 mHz) ULF magnetic pulsations, solar wind parameters and geomagnetic indices for predicting earthquake precursor signatures in low latitude regions. The ground geomagnetic field was collected from Davao station (7.00° N, 125.40° E), in the Philippines, which experiences nearby earthquake events (Magnitude <5.0, depth <100 km and epicentre distance from magnetometer station <100 km). The Pc5 ULF waves show the highest variance with four solar wind parameters, namely SWS, SWP, IMF-Bz, SIE and geomagnetic indices (SYM/H) prior to an earthquake event based on the regression model value of R2 = 0.1510. Furthermore, the IMF-Bz, SWS, SWP, SWE, and SYM/H were found to be significantly correlated with Pc5 ULF geomagnetic pulsation. This Pc5 ULF magnetic pulsation behaviour in solar winds and geomagnetic storms establishes the possibility of using Pc5 to predict earthquakes.

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Srivastava, Nandita, Zavkiddin Mirtoshev i Wageesh Mishra. "Geomagnetic Consequences of Interacting CMEs of June 13-14, 2012". Proceedings of the International Astronomical Union 13, S335 (lipiec 2017): 65–68. http://dx.doi.org/10.1017/s1743921317010857.

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AbstractWe have studied the consequences of interacting coronal mass ejections (CMEs) of June 13-14, 2012 which were directed towards Earth and caused a moderate geomagnetic storm with Dst index ~ −86 nT. We analysed the in-situ observations of the solar wind plasma and magnetic field parameters obtained from the OMNI database for these CMEs. The in-situ observations show that the interacting CMEs arrive at Earth with the strongest (~ 150 nT) Sudden Storm Commencement (SSC) of the solar cycle 24. We compared these interacting CMEs to a similar interaction event which occurred during November 9-10, 2012. This occurred in the same phase of the solar cycle 24 but resulted in an intense geomagnetic storm (Dst ~ −108 nT), as reported by Mishra et al. (2015). Our analysis shows that in the June event, the interaction led to a merged structure at 1 AU while in the case of November 2012 event, the interacted CMEs arrived as two distinct structures at 1 AU. The geomagnetic signatures of the two cases reveal that both resulted in a single step geomagnetic storm.

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Kelley, M. C., F. Garcia, J. Makela, T. Fan, E. Mak, C. Sia i D. Alcocer. "Highly structured tropical airglow and TEC signatures during strong geomagnetic activity". Geophysical Research Letters 27, nr 4 (15.02.2000): 465–68. http://dx.doi.org/10.1029/1999gl900598.

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Dmitriev, A. V., i H. C. Yeh. "Geomagnetic signatures of sudden ionospheric disturbances during extreme solar radiation events". Journal of Atmospheric and Solar-Terrestrial Physics 70, nr 15 (grudzień 2008): 1971–84. http://dx.doi.org/10.1016/j.jastp.2008.05.008.

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Sutcliffe, P. R., i M. J. Jarvis. "The phase relationships of the ionospheric signatures of Pc1 geomagnetic pulsations". Journal of Atmospheric and Terrestrial Physics 58, nr 15 (listopad 1996): 1783–92. http://dx.doi.org/10.1016/0021-9169(95)00183-2.

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Seppälä, A., H. Lu, M. A. Clilverd i C. J. Rodger. "Geomagnetic activity signatures in wintertime stratosphere wind, temperature, and wave response". Journal of Geophysical Research: Atmospheres 118, nr 5 (12.03.2013): 2169–83. http://dx.doi.org/10.1002/jgrd.50236.

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Masci, F. "Comment on "Ultra Low Frequency (ULF) European multi station magnetic field analysis before and during the 2009 earthquake at L'Aquila regarding regional geotechnical information" by Prattes et al. (2011)". Natural Hazards and Earth System Sciences 12, nr 5 (25.05.2012): 1717–19. http://dx.doi.org/10.5194/nhess-12-1717-2012.

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Abstract. Prattes et al. (2011) report ULF magnetic anomalous signals claiming them to be possibly precursor of the 6 April 2009 MW = 6.3 L'Aquila earthquake. This comment casts doubts on the possibility that the observed magnetic signatures could have a seismogenic origin by showing that these pre-earthquake signals are actually part of normal global geomagnetic activity.

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Masci, F., i J. N. Thomas. "Review Article: On the relation between the seismic activity and the Hurst exponent of the geomagnetic field at the time of the 2000 Izu swarm". Natural Hazards and Earth System Sciences 13, nr 9 (6.09.2013): 2189–94. http://dx.doi.org/10.5194/nhess-13-2189-2013.

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Abstract. Many papers document the observation of earthquake-related precursory signatures in geomagnetic field data. However, the significance of these findings is ambiguous because the authors did not adequately take into account that these signals could have been generated by other sources, and the seismogenic origin of these signals have not been validated by comparison with independent datasets. Thus, they are not reliable examples of magnetic disturbances induced by the seismic activity. Hayakawa et al. (2004) claim that at the time of the 2000 Izu swarm the Hurst exponent of the Ultra-Low-Frequency (ULF: 0.001–10 Hz) band of the geomagnetic field varied in accord with the energy released by the seismicity. The present paper demonstrates that the behaviour of the Hurst exponent was insufficiently investigated and also misinterpreted by the authors. We clearly show that during the Izu swarm the changes of the Hurst exponent were strongly related to the level of global geomagnetic activity and not to the increase of the local seismic activity.

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Masci, F., i J. N. Thomas. "Review "On the relation between the seismic activity and the Hurst exponent of the geomagnetic field at the time of the 2000 Izu swarm"". Natural Hazards and Earth System Sciences Discussions 1, nr 2 (26.03.2013): 681–91. http://dx.doi.org/10.5194/nhessd-1-681-2013.

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Abstract. Many papers document the observation of earthquake-related precursory signatures in geomagnetic field data. However, the significance of these findings is ambiguous because the authors did not adequately take into account that these signals could have been generated by other sources, and the seismogenic origin of these signals have not been validated by comparison with independent datasets. Thus, they are not reliable examples of magnetic disturbances induced by the seismic activity. Hayakawa et al. (2004) claim that at the time of the 2000 Izu swarm the Hurst exponent of the Ultra-Low-Frequency (ULF: 0.001–10 Hz) band of the geomagnetic field varied in accord with the energy released by the seismicity. The present paper demonstrates that the behaviour of the Hurst exponent was insufficiently investigated and also misinterpreted by the authors. We clearly show that during the Izu swarm the changes of the Hurst exponent were strongly related to the level of global geomagnetic activity and not to the increase of the local seismic activity.

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Kleimenova, N. G., O. V. Kozyreva, K. Kauristie, J. Manninen i A. Ranta. "Case studies on the dynamics of Pi3 geomagnetic and riometer pulsations during auroral activations". Annales Geophysicae 20, nr 2 (28.02.2002): 151–59. http://dx.doi.org/10.5194/angeo-20-151-2002.

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Abstract. A sequence of three subsequent auroral activations (at 18:10, 19:48 and 20:00 UT) on 9 February 1997 is analysed. The brightenings of optical auroras were collocated with latitudinally localized bursts of pulsating riometer absorption and Pi3 geomagnetic pulsations. In two of the cases, the strongest westward directed electrojet currents and the footpoint of the upward directed field-aligned currents related to the auroral brightening were observed in the same region as the largest amplitude of the pulsations and their polarization changed. In the third case, field-aligned current signatures were present, but not so pronounced that their accurate location could not be defined. In all cases, the spectra of geomagnetic and absorption pulsations were similar. Based on ground-based observations alone, it is difficult to say whether the energetic particle precipitation (riometer absorption) was modulated by the geomagnetic pulsations or whether the geomagnetic pulsations were caused by varying ionospheric currents controlled by the precipitating particle intensity. However, the localized nature of both pulsations of the two different phenomena and their tight coupling with each other seem to support the latter option.Key words. Ionosphere (Particle precipitation) – Magnetospheric physics (auroral phenomena; MHD waves and instabilities)

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Sharma, Rahul, Nandita Srivastava i D. Chakrabarty. "Role of filament plasma remnants in ICMEs leading to geomagnetic storms". Proceedings of the International Astronomical Union 8, S300 (czerwiec 2013): 493–94. http://dx.doi.org/10.1017/s1743921313011708.

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AbstractWe studied three interplanetary coronal mass ejections associated with solar eruptive filaments. Filament plasma remnants embedded in these structures were identified using plasma, magnetic and compositional signatures. These features when impacted the Earth's terrestrial magnetosphere - ionosphere system, resulted in geomagnetic storms. During the main phase of associated storms, along with high density plasma structures, polarity reversals in the Y-component (dawn-to-dusk) of the interplanetary electric field seem to trigger major auroral substorms with concomitant changes in the polar ionospheric electric field. Here, we examine the cases where plasma dynamics and magnetic structuring in the presence of the prompt penetration of the electric field into the equatorial ionosphere affected the space weather while highlighting the complex geomagnetic storm-substorm relationship.

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Wright, Andrew N., i W. Allan. "Simulations of Alfvén waves in the geomagnetic tail and their auroral signatures". Journal of Geophysical Research: Space Physics 113, A2 (luty 2008): n/a. http://dx.doi.org/10.1029/2007ja012464.

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Slavin, J. A., D. N. Baker, J. D. Craven, R. C. Elphic, D. H. Fairfield, L. A. Frank, A. B. Galvin i in. "CDAW 8 observations of plasmoid signatures in the geomagnetic tail: An assessment". Journal of Geophysical Research 94, A11 (1989): 15153. http://dx.doi.org/10.1029/ja094ia11p15153.

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Hall, C. M. "Complexity signatures in the geomagnetic H component recorded by the Tromsø magnetometer (70° N, 19° E) over the last ¼ century". Nonlinear Processes in Geophysics Discussions 1, nr 1 (13.05.2014): 895–915. http://dx.doi.org/10.5194/npgd-1-895-2014.

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Abstract. Solar disturbances, depending on the orientation of the interplanetary magnetic field, typically result in perturbations of the geomagnetic field as observed by magnetometers on the ground. Here, the geomagnetic field's horizontal component, as measured by the ground-based observatory-standard magnetometer at Tromsø (70° N, 19° E) is examined for signatures of complexity. 25 year-long 10 s resolution datasets are analysed, but for fluctuations with timescales less than 1 day. Quantile-quantile (Q-Q) plots are employed first, revealing the fluctuations are better represented by Cauchy rather than Gaussian distributions. Thereafter, both spectral density and detrended fluctuation analysis methods are used to estimate values of the generalized Hurst exponent, α. The results are then compared with independent findings. Inspection and comparison of the spectral and detrended fluctuation analyses reveals that timescales between 1 h and 1 d are characterized by fractional Brownian motion with a generalized Hurst exponent of ~1.4 whereas including timescales as short as 1 min suggests fractional Brownian motion with a generalized Hurst exponent of ~1.6. This is consistent with changes in the position of the auroral electrojet that can be considered rapid during the course of an evening, whereas from minute-to-minute the electrojet moves more persistently in geomagnetic latitude.

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Rastogi, R. G. "Signatures of storm sudden commencements in geomagnetic H, Y and Z fields at Indian observatories during 1958−1992". Annales Geophysicae 17, nr 11 (30.11.1999): 1426–38. http://dx.doi.org/10.1007/s00585-999-1426-1.

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Abstract. The work describes an intensive study of storm sudden commencement (SSC) impulses in horizontal (H), eastward (Y) and vertical (Z) fields at four Indian geomagnetic observatories between 1958–1992. The midday maximum of ΔH has been shown to exist even at the low-latitude station Alibag which is outside the equatorial electrojet belt, suggesting that SSC is associated with an eastward electric field at equatorial and low latitudes. The impulses in Y field are shown to be linearly and inversely related to ΔH at Annamalainagar and Alibag. The average SC disturbance vector is shown to be about 10–20°W of the geomagnetic meridian. The local time variation of the angle is more westerly during dusk hours in summer and around dawn in the winter months. This clearly suggests an effect of the orientation of shock front plane of the solar plasma with respect to the geomagnetic meridian. The ΔZ at SSC have a positive impulse as in ΔH. The ratio of ΔZ/ΔH are abnormally large exceeding 1.0 in most of the cases at Trivandrum. The latitudinal variation of ΔZ shows a tendency towards a minimum over the equator during the nighttime hours. These effects are explained as (1) resulting from the electromagnetic induction effects due to the equatorial electrojet current in the subsurface conducting layers between India and Sri Lanka, due to channelling of ocean currents through the Palk Strait and (2) due to the concentration of induced currents over extended latitude zones towards the conducting graben between India and Sri Lanka just south of Trivandrum.Key words. Interplanetary physics (interplanetary shocks) · Ionosphere (equatorial ionosphere) · Magnetospheric physics (storms and substorms)

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Kasatkina, E. A., O. I. Shumilov, M. J. Rycroft, F. Marcz i A. V. Frank-Kamenetsky. "Atmospheric electric field anomalies associated with solar flare/coronal mass ejection events and solar energetic charged particle "Ground Level Events"". Atmospheric Chemistry and Physics Discussions 9, nr 5 (20.10.2009): 21941–58. http://dx.doi.org/10.5194/acpd-9-21941-2009.

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Abstract. We discuss the fair weather atmospheric electric field signatures of three major solar energetic charged particle events which occurred in on 15 April 2001, 18 April and 4 November, and their causative solar flares/coronal mass ejections (SF/CMEs). Only the 15 April 2001 shows clear evidence for Ez variation associated to SF/CME events and the other two events may support this hypothesis as well although for them the meteorological data were not available. All three events seem to be associated with relativistic solar protons (i.e. protons with energies >450 MeV) of the Ground Level Event (GLE) type. The study presents data on variations of the vertical component of the atmospheric electric field (Ez) measured at the auroral station Apatity (geomagnetic latitude: 63.8°, the polar cap station Vostok (geomagnetic latitude: −89.3°) and the middle latitude stations Voyeikovo (geomagnetic latitude: 56.1°) and Nagycenk (geomagnetic latitude: 47.2°). A significant disturbance in the atmospheric electric field is sometimes observed close to the time of the causative solar flare; the beginning of the electric field perturbation at Apatity is detected one or two hours before the flare onset and the GLE onset. Atmospheric electric field records at Vostok and Voyeikovo show a similar disturbance at the same time for the 15 April 2001 event. Some mechanisms responsible for the electric field perturbations are considered.

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Cao, Jin-Bin, Chunxiao Yan, Malcolm Dunlop, Henri Reme, Iannis Dandouras, Tielong Zhang, Dongmei Yang i in. "Geomagnetic signatures of current wedge produced by fast flows in a plasma sheet". Journal of Geophysical Research: Space Physics 115, A8 (sierpień 2010): n/a. http://dx.doi.org/10.1029/2009ja014891.

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Francia, Patrizia, Mauro Regi i Marcello De Lauretis. "Signatures of the ULF geomagnetic activity in the surface air temperature in Antarctica". Journal of Geophysical Research: Space Physics 120, nr 4 (kwiecień 2015): 2452–59. http://dx.doi.org/10.1002/2015ja021011.

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Currie, J. L., i C. L. Waters. "On the use of geomagnetic indices and ULF waves for earthquake precursor signatures". Journal of Geophysical Research: Space Physics 119, nr 2 (luty 2014): 992–1003. http://dx.doi.org/10.1002/2013ja019530.

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Gotoh, K., M. Hayakawa i N. Smirnova. "Fractal analysis of the ULF geomagnetic data obtained at Izu Peninsula, Japan in relation to the nearby earthquake swarm of June–August 2000". Natural Hazards and Earth System Sciences 3, nr 3/4 (31.08.2003): 229–36. http://dx.doi.org/10.5194/nhess-3-229-2003.

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Abstract. In our recent papers we applied fractal methods to extract the earthquake precursory signatures from scaling characteristics of the ULF geomagnetic data, obtained in a seismic active region of Guam Island during the large earthquake of 8 August 1993. We found specific dynamics of their fractal characteristics (spectral exponents and fractal dimensions) before the earthquake: appearance of the flicker-noise signatures and increase of the time series fractal dimension. Here we analyze ULF geomagnetic data obtained in a seismic active region of Izu Peninsula, Japan during a swarm of the strong nearby earthquakes of June–August 2000 and compare the results obtained in both regions. We apply the same methodology of data processing using the FFT procedure, Higuchi method and Burlaga-Klein approach to calculate the spectral exponents and fractal dimensions of the ULF time series. We found the common features and specific peculiarities in the behavior of fractal characteristics of the ULF time series before Izu and Guam earthquakes. As a common feature, we obtained the same increase of the ULF time series fractal dimension before the earthquakes, and as specific peculiarity – this increase appears to be sharp for Izu earthquake in comparison with gradual increase of the ULF time series fractal dimension for Guam earthquake. The results obtained in both regions are discussed on the basis of the SOC (self-organized criticality) concept taking into account the differences in the depths of the earthquake focuses. On the basis of the peculiarities revealed, we advance methodology for extraction of the earthquake precursory signatures. As an adjacent step, we suggest the combined analysis of the ULF time series in the parametric space polarization ratio – fractal dimension. We reason also upon the advantage of the multifractal approach with respect to the mono-fractal analysis for study of the earthquake preparation dynamics.

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He, Fei, Yong Wei i Weixing Wan. "Equatorial aurora: the aurora-like airglow in the negative magnetic anomaly". National Science Review 7, nr 10 (24.04.2020): 1606–15. http://dx.doi.org/10.1093/nsr/nwaa083.

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Abstract The most fantastic optical phenomena in the Earth's upper atmosphere are the auroras. They are highly informative indicators of solar activity, geomagnetic activity, upper atmospheric structures and dynamics, and magnetospheric energetic particles. An area where the geomagnetic field differs significantly from the expected symmetric dipole, such as at the South Atlantic Anomaly, where the magnetic field intensity is low, gives rise to stronger precipitation of energetic particles into the upper atmosphere. Impact excitation and the subsequent airglow emissions exhibit aurora-like dynamic signatures. Nomenclatures of nonpolar aurora or equatorial auroras are similar to those used with the polar auroras owing to their similar excitation mechanisms. This paper provides an overview of the knowledge and the challenges concerning auroral activity at the South Atlantic Anomaly, or more generally, at the negative magnetic anomaly. We emphasize systematic investigation of the equatorial auroras to reveal the temporal and spatial evolution of the magnetic anomaly and the behaviour of energetic particles in near-Earth space.

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Dudeney, J. R., K. B. Baker, P. H. Stoker i A. D. M. Walker. "The Southern Hemisphere Auroral Radar Experiment (SHARE)". Antarctic Science 6, nr 1 (marzec 1994): 123–24. http://dx.doi.org/10.1017/s0954102094000155.

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The near Earth space environment (known as Geospace) is dominated by the interaction between the solar wind and the geomagnetic field, which creates the magnetosphere. Considerable energy flows from the solar wind into the magnetosphere and ends up in the Earth's upper atmosphere (the thermosphere and ionosphere). The coupling of the geomagnetic field with that of the solar wind (known as the interplanetary magnetic field, or IMF) produces a variety of electro-dynamic responses with signatures such as electric fields and currents in the polar ionospheres. These produce, inter alia, motion of the ionospheric plasma (at altitudes between 100 and 1000kms) which can be monitored from the ground using radar techniques. Analysis of such plasma motion provides a very powerful means of investigating the nature of the interactions taking place at the boundaries between the magnetosphere and the solar wind. To do this effectively requires simultaneous measurements over as large an area (in latitude and longitude) as possible.

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Wright, D. M., T. K. Yeoman i T. B. Jones. "ULF wave occurrence statistics in a high-latitude HF Doppler sounder". Annales Geophysicae 17, nr 6 (30.06.1999): 749–58. http://dx.doi.org/10.1007/s00585-999-0749-2.

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Abstract. Ultra low frequency (ULF) wave activity in the high-latitude ionosphere has been observed by a high frequency (HF) Doppler sounder located at Tromsø, Norway (69.7°N, 19.2°E geographic coordinates). A statistical study of the occurrence of these waves has been undertaken from data collected between 1979 and 1984. The diurnal, seasonal, solar cycle and geomagnetic activity variations in occurrence have been investigated. The findings demonstrate that the ability of the sounder to detect ULF wave signatures maximises at the equinoxes and that there is a peak in occurrence in the morning sector. The occurrence rate is fairly insensitive to changes associated with the solar cycle but increases with the level of geomagnetic activity. As a result, it has been possible to characterise the way in which prevailing ionospheric and magnetospheric conditions affect such observations of ULF waves.Key words. Ionosphere (auroral ionosphere; ionosphere -magnetosphere interactions) · Magnetospheric physics (MHD waves and instabilities)

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36

Watanabe, Y., G. Cornélissen, F. Halberg, K. Otsuka i S. I. Ohkawa. "Associations by signatures and coherences between the human circulation and helio- and geomagnetic activity". Biomedicine & Pharmacotherapy 55 (listopad 2000): s76—s83. http://dx.doi.org/10.1016/s0753-3322(01)90008-3.

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Olsen, Nils, i Claudia Stolle. "Magnetic Signatures of Ionospheric and Magnetospheric Current Systems During Geomagnetic Quiet Conditions—An Overview". Space Science Reviews 206, nr 1-4 (27.09.2016): 5–25. http://dx.doi.org/10.1007/s11214-016-0279-7.

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Alperovich, L., V. Zheludev i M. Hayakawa. "Application of a wavelet technique for the detection of earthquake signatures in the geomagnetic field". Natural Hazards and Earth System Sciences 1, nr 1/2 (30.06.2001): 75–81. http://dx.doi.org/10.5194/nhess-1-75-2001.

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Abstract. We developed an algorithm especially adapted to single-station wavelet detection of geomagnetic events, which precede or accompany the earthquakes. The detection problem in this situation is complicated by a great variability of earthquakes and accompanied phenomena, which aggravates finding characteristic features of the events. Therefore we chose to search for the characteristic features of both "disturbed" intervals (containing earthquakes) and "quiet" recordings. In this paper we propose an algorithm for solving the problem of detecting the presence of signals produced by an earthquake via analysis of its signature against the existing database of magnetic signals. To achieve this purpose, we construct the magnetic signature of certain earthquakes using the distribution of the energies among blocks, which consist of wavelet packet coefficients.

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39

Dea, Jack Y., William Van Bise, Elizabeth A. Rauscher i Wolfgang-M. Boerner. "Observations of ELF (extremely low frequency) signatures arising from space vehicle disturbances of the ionosphere". Canadian Journal of Physics 69, nr 8-9 (1.08.1991): 959–65. http://dx.doi.org/10.1139/p91-151.

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We report on observations of extremely low-frequency (ELF) signatures during exit or reentry of space vehicles through the ionosphere. The two modes regularly observed gave signals that peaked at 5.6 and 11.2 Hz. The evidence points to the lower ionosphere, i.e., the D- and E-layers, as the generator of these signals. The measurements were performed using ground-based multiturn coil sensors located in Reno and San Diego. The nature of these signals is unclear at present but it is surmised that we are detecting either the evanescent fields of hydromagnetic waves traveling in the ionosphere or the oscillating geomagnetic field associated with these hydromagnetic waves.

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Di Mauro, Domenico, Mauro Regi, Stefania Lepidi, Alfredo Del Corpo, Guido Dominici, Paolo Bagiacchi, Giovanni Benedetti i Lili Cafarella. "Geomagnetic Activity at Lampedusa Island: Characterization and Comparison with the Other Italian Observatories, Also in Response to Space Weather Events". Remote Sensing 13, nr 16 (6.08.2021): 3111. http://dx.doi.org/10.3390/rs13163111.

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Regular automatic recordings of the time series of the magnetic field, together with routine manual absolute measurements for establishing dynamic baselines at Lampedusa Island—south of Sicily—Italy (geographic coordinates 35°31′N; 12°32′E, altitude 33 m a.s.l.), show a signature of very low electromagnetic noise. The observatory (provisional IAGA code: LMP) lays inside a restricted and remote wildlife reserve, far away from the built-up and active areas of the island, which at present is the southernmost location of the European territory for such observations. The availability of high-quality data from such site, whose survey started in 2005, is valuable for filling the spatial gap due to the lack of observatories in the whole south Mediterranean and North African sectors. We compare observations at Lampedusa, in both time and frequency domains, with those at the other Italian observatories (Castello Tesino and Duronia-L’Aquila), operating since the 1960s of last century, allowing us to report even the secular variation. Using data recorded in the last few years, we investigate higher frequency variations (from diurnal to Pc3-4 pulsations) in order to magnetically characterize the Italian territory and the local response to external forcing. In particular, we present a characterization in terms of diurnal variation and its seasonal dependence for the three observatories. This latter feature is in good agreement with a geomagnetic Sq-model, leading us to speculate about the position of the north Sq-current system vortex and its seasonal displacement with respect to the geographic positions of the observatories. We also study the geomagnetic individual response to intense space weather events by performing Superposed Epoch Analysis (SEA), with an ad-hoc significance test. Magnetic responses in the Ultra Low Frequency range (ULF) from spectral, local Signal-to-Noise Ratio (SNR) analyses under different local time, and polarization rates are computed. These latter studies lead us to search for possible signatures of magnetic field line resonances during intense space weather events, using cross-phase multi-observatory analysis, revealing the promising detection capability of such technique even at low latitudes. The geomagnetic observatories prove to be important points of observation for space weather events occurring at different spatial and time scales, originating in both upstream and ionospheric regions, here analyzed by several well-established methodologies and techniques. The quiet environmental site of LMP, providing high-quality geomagnetic data, allows us such investigations even at inner Earth’s magnetospheric shell.

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Mannucci, A. J., B. T. Tsurutani, O. Verkhoglyadova, A. Komjathy i X. Pi. "Use of radio occultation to probe the high latitude ionosphere". Atmospheric Measurement Techniques Discussions 8, nr 2 (23.02.2015): 2093–121. http://dx.doi.org/10.5194/amtd-8-2093-2015.

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Abstract. We have explored the use of COSMIC data to provide valuable scientific information on the ionospheric impacts of energetic particle precipitation during geomagnetic storms. Ionospheric electron density in the E region, and hence ionospheric conductivity, is significantly altered by precipitating particles from the magnetosphere. This has global impacts on the thermosphere-ionosphere because of the important role of conductivity on high latitude Joule heating. Two high-speed stream (HSS) and two coronal mass ejection (CME) storms are examined with the COSMIC data. We find clear correlation between geomagnetic activity and electron density retrievals from COSMIC. At nighttime local times, the number of profiles with maximum electron densities in the E layer (below 200 km altitude) is well correlated with geomagnetic activity. We interpret this to mean that electron density increases due to precipitation are captured by the COSMIC profiles. These "E layer dominant ionosphere" (ELDI) profiles have geomagnetic latitudes that are consistent with climatological models of the auroral location. For the two HSS storms, that occurred in May of 2011 and 2012, a strong hemispheric asymmetry is observed, with nearly all the ELDI profiles found in the southern, less sunlit, hemisphere. Stronger aurora and precipitation have been observed before in winter hemispheres, but the degree of asymmetry deserves further study. For the two CME storms, occurring in July and November of 2012, large increases in the number of ELDI profiles are found starting in the storm's main phase but continuing for several days into the recovery phase. Analysis of the COSMIC profiles was extended to all local times for the July 2012 CME storm by relaxing the ELDI criterion and instead visually inspecting all profiles above 50° magnetic latitude for signatures of precipitation in the E region. For nine days during the July 2012 period, we find a signature of precipitation occurs nearly uniformly in local time, although the magnitude of electron density increase may vary with local time. The latitudinal extent of the precipitation layers is generally consistent with auroral climatology. However, after the storm main phase on 14 July 2012, the precipitation tended to be somewhat more equatorward than predicted by the climatology (by about 5–10° latitude). We conclude that, if analyzed appropriately, high latitude COSMIC profiles have the potential to contribute to our understanding of MI coupling processes and extend and improve existing models of the auroral region.

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Hall, C. M. "Complexity signatures in the geomagnetic <i>H</i> component recorded by the Tromsø magnetometer (70° N, 19° E) over the last quarter of a century". Nonlinear Processes in Geophysics 21, nr 5 (22.10.2014): 1051–58. http://dx.doi.org/10.5194/npg-21-1051-2014.

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Abstract. Solar disturbances, depending on the orientation of the interplanetary magnetic field, typically result in perturbations of the geomagnetic field as observed by magnetometers on the ground. Here, the geomagnetic field's horizontal component, as measured by the ground-based observatory-standard magnetometer at Tromsø (70° N, 19° E), is examined for signatures of complexity. Twenty-five year-long 10 s resolution data sets are analysed for fluctuations with timescales of less than 1 day. Quantile–quantile plots are employed first, revealing that the fluctuations are better represented by Cauchy rather than Gaussian distributions. Thereafter, both spectral density and detrended fluctuation analysis methods are used to estimate values of the generalized Hurst exponent, α. The results are then compared with independent findings. Inspection and comparison of the spectral and detrended fluctuation analyses reveal that timescales between 1 h and 1 day are characterized by fractional Brownian motion with a generalized Hurst exponent of ~1.4, whereas including timescales as short as 1 min suggests fractional Brownian motion with a generalized Hurst exponent of ~1.6.

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43

Pallamraju, D., S. Chakrabarti i C. E. Valladares. "Magnetic storm-induced enhancement in neutral composition at low latitudes as inferred by O(<sup>1</sup>D) dayglow measurements from Chile". Annales Geophysicae 22, nr 9 (23.09.2004): 3241–50. http://dx.doi.org/10.5194/angeo-22-3241-2004.

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Abstract. We describe the effect of the 6 November 2001 magnetic storm on the low latitude thermospheric composition. Daytime red line (OI 630.0nm) emissions from Carmen Alto, Chile showed anomalous 2-3 times larger emissions in the morning (05:30-08:30 Local Time; LT) on the disturbed day compared to the quiet days. We interpret these emission enhancements to be caused due to the increase in neutral densities over low latitudes, as a direct effect of the geomagnetic storm. As an aftereffect of the geomagnetic storm, the dayglow emissions on the following day show gravity wave features that gradually increase in periodicities from around 30min in the morning to around 100min by the evening. The integrated dayglow emissions on quiet days show day-to-day variabilities in spatial structures in terms of their movement away from the magnetic equator in response to the Equatorial Ionization Anomaly (EIA) development in the daytime. The EIA signatures in the daytime OI 630.0nm column-integrated dayglow emission brightness show different behavior on days with and without the post-sunset Equatorial Spread F (ESF) occurrence.

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Neudegg, D. A., B. J. Fraser, F. W. Menk, G. B. Burns, R. J. Morris i M. J. Underwood. "Magnetospheric sources of Pc1-2 ULF waves observed in the polar ionospheric waveguide". Antarctic Science 14, nr 1 (marzec 2002): 93–103. http://dx.doi.org/10.1017/s0954102002000627.

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Energy from the outer regions of the magnetosphere may be transferred to the polar ionosphere by plasma waves. A magnetometer array operated during the Antarctic winter observed Ultra-Low-Frequency (ULF) plasma waves in the Pc 1–2 (0.1–10.0 Hz) frequency range, propagating parallel to the surface of the Earth in a waveguide or duct centred at ∼300 km altitude in the ionosphere. These compressional fast mode plasma waves most likely originated in the outer magnetosphere as shear mode plasma waves guided along the geomagnetic field. The region of origin in the magnetosphere for the waves is not certain as several widely spaced volumes map along geomagnetic field lines to a relatively close ensemble in the polar ionosphere. This paper compares the direction of propagation for the waves with signatures of magnetospheric regions geomagnetically projecting onto the ionosphere. Regions such as the polar cusp, low latitude boundary layer and mantle were observed by DMSP spacecraft and a SuperDARN high-frequency radar. The most likely region in the polar ionosphere for the fast mode waves to have originated from is equatorwards of the polar cusp, suggesting the field guided waves originated just inside the magnetopause. A case is made for association of the observed Pc1-2 ULF waves with post-noon, field-aligned-current systems driven by reconnection of the solar Interplanetary Magnetic Field (IMF) and the geomagnetic field near the magnetopause.

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Villante, U., P. Francia i S. Lepidi. "Pc5 geomagnetic field fluctuations at discrete frequencies at a low latitude station". Annales Geophysicae 19, nr 3 (31.03.2001): 321–25. http://dx.doi.org/10.5194/angeo-19-321-2001.

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Abstract. A statistical analysis of the geomagnetic field fluctuations in the Pc5 frequency range (1–5 mHz) at a low latitude station (L = 1.6) provides further evidence for daytime power peaks at discrete frequencies. The power enhancements, which become more pronounced during high solar wind pressure conditions, may be interpreted in terms of ground signatures of magnetospheric cavity/waveguide compressional modes driven by solar wind pressure pulses. In this sense, the much clearer statistical evidence for afternoon events can be related to corotating structures mainly impinging the postnoon magnetopause. A comparison with results obtained for the same time intervals from previous investigations at higher latitudes and in the Earth’s magnetosphere confirms the global character of the observed modes.Key words. Magnetospheric physics (MHD waves and instabilities; solar wind-magnetospheric interactions)

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Villante, U., i P. Francia. "Low frequency geomagnetic field fluctuations at low latitude during the passage of a higher pressure solar wind region". Annales Geophysicae 15, nr 6 (30.06.1997): 656–61. http://dx.doi.org/10.1007/s00585-997-0656-3.

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Abstract. The passage of a higher pressure solar wind region at the Earth's orbit marked the onset of low latitude (L=1.6) fluctuations in the frequency range (0.8–5.5 mHz) for both the horizontal geomagnetic field components. Spectral peaks mostly occur at the same frequencies as the spectral enhancements which appeared in the long term analysis of experimental measurements from the same station and were tentatively interpreted in terms of ground signatures of global magnetospheric modes. A comparison with simultaneous observations discussed by previous investigations allows us to conclude that the same set of frequencies is enhanced in a wide portion of the Earth's magnetosphere.

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47

Mannucci, A. J., B. T. Tsurutani, O. Verkhoglyadova, A. Komjathy i X. Pi. "Use of radio occultation to probe the high-latitude ionosphere". Atmospheric Measurement Techniques 8, nr 7 (16.07.2015): 2789–800. http://dx.doi.org/10.5194/amt-8-2789-2015.

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Abstract. We have explored the use of COSMIC data to provide valuable scientific information on the ionospheric impacts of energetic particle precipitation during geomagnetic storms. Ionospheric electron density in the E region, and hence ionospheric conductivity, is significantly altered by precipitating particles from the magnetosphere. This has global impacts on the thermosphere–ionosphere because of the important role of conductivity on high-latitude Joule heating. Two high-speed stream (HSS) and two coronal mass ejection (CME) storms are examined with the COSMIC data. We find clear correlation between geomagnetic activity and electron density retrievals from COSMIC. At nighttime local times, the number of profiles with maximum electron densities in the E layer (below 200 km altitude) is well correlated with geomagnetic activity. We interpret this to mean that electron density increases due to precipitation are captured by the COSMIC profiles. These "E-layer-dominant ionosphere" (ELDI) profiles have geomagnetic latitudes that are consistent with climatological models of the auroral location. For the two HSS storms that occurred in May of 2011 and 2012, a strong hemispheric asymmetry is observed, with nearly all the ELDI profiles found in the Southern, less sunlit, Hemisphere. Stronger aurora and precipitation have been observed before in winter hemispheres, but the degree of asymmetry deserves further study. For the two CME storms, occurring in July and November of 2012, large increases in the number of ELDI profiles are found starting in the storm's main phase but continuing for several days into the recovery phase. Analysis of the COSMIC profiles was extended to all local times for the July 2012 CME storm by relaxing the ELDI criterion and instead visually inspecting all profiles above 50° magnetic latitude for signatures of precipitation in the E region. For 9 days during the July 2012 period, we find a signature of precipitation occurs nearly uniformly in local time, although the magnitude of electron density increase may vary with local time. The latitudinal extent of the precipitation layers is generally consistent with auroral climatology. However, after the storm main phase on 14 July 2012 the precipitation tended to be somewhat more equatorward than the climatology (by about 5–10° latitude) and equatorward of the auroral boundary data acquired from the SSUSI sensor onboard the F18 DMSP satellite. We conclude that, if analyzed appropriately, high-latitude COSMIC profiles have the potential to contribute to our understanding of MI coupling processes and extend and improve existing models of the auroral region.

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Neudegg, D. A., S. W. H. Cowley, S. E. Milan, T. K. Yeoman, M. Lester, G. Provan, G. Haerendel i in. "A survey of magnetopause FTEs and associated flow bursts in the polar ionosphere". Annales Geophysicae 18, nr 4 (30.04.2000): 416–35. http://dx.doi.org/10.1007/s00585-000-0416-0.

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Abstract. Using the Equator-S spacecraft and SuperDARN HF radars an extensive survey of bursty reconnection at the magnetopause and associated flows in the polar ionosphere has been conducted. Flux transfer event (FTE) signatures were identified in the Equator-S magnetometer data during periods of magnetopause contact in January and February 1998. Assuming the effects of the FTEs propagate to the polar ionosphere as geomagnetic field-aligned-currents and associated Alfvén-waves, appropriate field mappings to the fields-of-view of SuperDARN radars were performed. The radars observed discrete ionospheric flow channel events (FCEs) of the type previously assumed to be related to pulse reconnection. Such FCEs were associated with \\sim80% of the FTEs and the two signatures are shown to be statistically associated with greater than 99% confidence. Exemplary case studies highlight the nature of the ionospheric flows and their relation to the high latitude convection pattern, the association methodology, and the problems caused by instrument limitations.Key words: Ionosphere (polar ionosphere) · Magnetospheric physics (magnetosphere-ionosphere interaction; solar wind-magnetosphere interactions)

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Aveiro, H. C., C. M. Denardini i M. A. Abdu. "Signatures of 2-day wave in the E-region electric fields and their relationship to winds and ionospheric currents". Annales Geophysicae 27, nr 2 (9.02.2009): 631–38. http://dx.doi.org/10.5194/angeo-27-631-2009.

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Abstract. We analyze the effects of the 2-day wave activity in the EEJ using one coherent scatter radar and eight magnetometer stations located close to the dip equator. The wavelet analysis of the magnetometer data reveals a 2-day signature in the semidiurnal geomagnetic tide. The E-region zonal background ionospheric electric field, derived from coherent radar measurements, shows 2-day oscillations in agreement with such oscillations in the magnetometers data. An anticorrelation between the amplitude of the tidal periodicites (diurnal and semidiurnal) and that of the 2-day signature is also shown in the electric fields. The results are compared with simultaneous observations of 2-day planetary wave in meridional winds and ionosonde data. Further, our results are discussed based on the analysis of the magnetic activity.

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Kotulak, Kacper, Irina Zakharenkova, Andrzej Krankowski, Iurii Cherniak, Ningbo Wang i Adam Fron. "Climatology Characteristics of Ionospheric Irregularities Described with GNSS ROTI". Remote Sensing 12, nr 16 (14.08.2020): 2634. http://dx.doi.org/10.3390/rs12162634.

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At equatorial and high latitudes, the intense ionospheric irregularities and plasma density gradients can seriously affect the performances of radio communication and satellite-based navigation systems; that represents a challenging topic for the scientific and engineering communities and operational use of communication and navigation services. The GNSS-based ROTI (rate of TEC index) is one of the most widely used indices to monitor the occurrence and intensity of ionospheric irregularities. In this paper, we examined the long-term performance of the ROTI in terms of finding the climatological characteristics of TEC fluctuations. We considered the different scale temporal signatures and checked the general sensitivity to the solar and geomagnetic activity. We retrieved and analyzed long-term time-series of ROTI values for two chains of GNSS stations located in European and North-American regions. This analysis covers three full years of the 24th solar cycle, which represent different levels of solar activity and include periods of intense geomagnetic storms. The ionospheric irregularities’ geographical distribution, as derived from ROTI, shows a reasonable consistency to be found within the poleward/equatorward boundaries of the auroral oval specified by empirical models. During magnetic midnight and quiet-time conditions, the equatorward boundary of the ROTI-derived ionospheric irregularity zone was observed at 65–70° of north magnetic latitude, while for local noon conditions this boundary was more poleward at 75–85 magnetic latitude. The ionospheric irregularities of low-to-moderate intensity were found to occur within the auroral oval at all levels of geomagnetic activity and seasons. At moderate and high levels of solar activity, the intensities of ionospheric irregularities are larger during local winter conditions than for the local summer and polar day conditions. We found that ROTI displays a selective latitudinal sensitivity to the auroral electrojet activity—the strongest dependence (correlation R > 0.6–0.8) was observed within a narrow latitudinal range of 55–70°N magnetic latitude, which corresponded to a band of the largest ROTI values within the auroral oval zone expanded equatorward during geomagnetic disturbances.

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