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Periods of planetary waves in geomagnetic variations  [cached]
A. Kohsiek,K. H. Glassmeier,T. Hirooka
Annales Geophysicae (ANGEO) , 2003,
Abstract: Periods of planetary waves, especially the 10- and 16-day waves, were found in Fourier analyses of 10-year geomagnetic time series from two mid-latitude stations in the northern hemisphere. This suggests that planetary waves influence geomagnetic variations. Cross-spectral analysis of magnetic time series from seven stations located at around 50°N at the beginning of 1979, when a 16-day wave occurred in the stratosphere, also shows a 16-day oscillation. However, study of the phases does not reveal the horizontal direction of wave propagation. Furthermore, the temporal variations of the 16-day oscillation in magnetic time series are presented as dynamic spectra and the results are compared with global investigations of geopotential height data at 1 hPa (around 48 km) with respect to the 16-day wave for the same time interval. In some cases this comparison suggests a clear correlation between geomagnetic variations and planetary waves as well as a propagation of the 16-day wave up to the dynamo region (100-170 km).
Parallel Computation of Spatio-Temporal Variations of Geomagnetic Field Using One-Minute Time Resolution Dataset  [PDF]
Felix Ale,Oye Ibidapo-Obe,Theophilus A. Fashanu,Olufemi A. Agboola
International Journal of Engineering and Technology , 2012,
Abstract: This work presents a novel method for analyzing spatio-temporal variations of geomagnetic field using parallel computing. One-minute resolution geomagnetic dataset of 1996 was obtained from INTERMAGNET global network of 64 observatory stations. In effect, large and three dimensional arrays of geomagnetic observations are to be processed. Thus, sequential and parallel algorithms were developed using MATLAB 2012a, interfaced with the well-known kriging method for efficient geostatistical data gridding and mapping of solar quiet (Sq) daily variations. The runtime of the sequential algorithm on a processor took 18.5 minutes while the corresponding parallel algorithm took 2.95 minutes using eight Intel Xeon E5410 2.33GHz processors in parallel. The efficiency profile of the model is logarithmic in nature. This was further optimized using quadratic polynomial interpolation. The results show that 13 processors will process the Sq in less than one minute, thus providing effective near real-time observation of Space weather. In addition, the foci of the generated finer Sq(H) plots revealed temporal variability that is consistently maximized at local noon at every location on this geomagnetic environment as demonstrated in the 2D visual display.
Research of geomagnetic spatial-temporal variations in China by the NOC method

GU Zuo-Wen,CHEN Bin,GAO Jin-Tian,XIN Chang-Jiang,YUAN Jie-Hao,DI Chuan-Zhi,

地球物理学报 , 2009,
Abstract: The geomagnetic data at 36 observatories in China during 1995~2006 were calculated by using the natural orthogonal component (NOC) method. We have obtained the eigenvalues and their corresponding eigenvectors in the space and time domains for the above-mentioned data matrix. A comparative analysis between its spatial-temporal distribution and the China Geomagnetic Model (CGM) is made, and its physical meaning is studied. The research shows that the these observational data contain rich information of the internal and external geomagnetic source fields. The first and the second eigenvalues of the geomagnetic field components F, D and I, and the temporal variations of the geomagnetic main field described by the first and the second eigenvalues of the corresponding spatial-temporal domains coincide fairly well with the CGM.
PAMELA's measurements of geomagnetic cutoff variations during solar energetic particle events  [PDF]
A. Bruno,O. Adriani,G. C. Barbarino,G. A. Bazilevskaya,R. Bellotti,M. Boezio,E. A. Bogomolov,M. Bongi,V. Bonvicini,S. Bottai,U. Bravar,F. Cafagna,D. Campana,R. Carbone,P. Carlson,M. Casolino,G. Castellini,E. C. Christian,C. De Donato,G. A. de Nolfo,C. De Santis,N. De Simone,V. Di Felice,V. Formato,A. M. Galper,A. V. Karelin,S. V. Koldashov,S. Koldobskiy,S. Y. Krutkov,A. N. Kvashnin,M. Lee,A. Leonov,V. Malakhov,L. Marcelli,M. Martucci,A. G. Mayorov,W. Menn,M. Mergè,V. V. Mikhailov,E. Mocchiutti,A. Monaco,N. Mori,R. Munini,G. Osteria,F. Palma,B. Panico,P. Papini,M. Pearce,P. Picozza,M. Ricci,S. B. Ricciarini,J. M. Ryan,R. Sarkar,V. Scotti,M. Simon,R. Sparvoli,P. Spillantini,S. Stochaj,Y. I. Stozhkov,A. Vacchi,E. Vannuccini,G. I. Vasilyev,S. A. Voronov,Y. T. Yurkin,G. Zampa,N. Zampa,V. G. Zverev
Physics , 2015,
Abstract: Data from the PAMELA satellite experiment were used to measure the geomagnetic cutoff for high-energy ($\gtrsim$ 80 MeV) protons during the solar particle events on 2006 December 13 and 14. The variations of the cutoff latitude as a function of rigidity were studied on relatively short timescales, corresponding to single spacecraft orbits (about 94 minutes). Estimated cutoff values were cross-checked with those obtained by means of a trajectory tracing approach based on dynamical empirical modeling of the Earth's magnetosphere. We find significant variations in the cutoff latitude, with a maximum suppression of about 6 deg for $\sim$80 MeV protons during the main phase of the storm. The observed reduction in the geomagnetic shielding and its temporal evolution were compared with the changes in the magnetosphere configuration, investigating the role of IMF, solar wind and geomagnetic (Kp, Dst and Sym-H indexes) variables and their correlation with PAMELA cutoff results.
The development of a regional geomagnetic daily variation model using neural networks  [PDF]
P. R. Sutcliffe
Annales Geophysicae (ANGEO) , 2003,
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)
Multifractal analysis of low-latitude geomagnetic fluctuations
M. J. A. Bolzan, R. R. Rosa,Y. Sahai
Annales Geophysicae (ANGEO) , 2009,
Abstract: The technique of large deviation multifractal spectrum has shown that the high-latitude (77.5° N, 69.2° W) geomagnetic fluctuations can be described from direct dissipation process or loading-unloading regimes of the solar wind-magnetosphere coupling. In this paper, we analyze the H-component of low-latitude (22.4° S, 43.6° W) geomagnetic field variability observed during the month of July 2000 at the Geomagnetic Observatory, Vassouras, RJ, Brazil. The variability pattern during this period is a mixture of quiet and disturbed days including the Bastille Day intense geomagnetic storm on 15 July. Due to the complexity of this data, we pursue a detailed analysis of the geomagnetic fluctuations in different time scales including a multifractal approach using the singular power spectrum deviations obtained from the wavelet transform modulus maxima (WTMM). The results suggest, as observed from high-latitude data, the occurrence of low-latitude multifractal processes driving the intermittent coupling between the solar wind-magnetosphere and geomagnetic field variations. On finer scales possible physical mechanisms in the context of nonlinear magnetosphere response are discussed.
An analysis of geomagnetic field variations (3 min-2 h) at a low-latitude observatory (L=1.6)  [cached]
P. Francia,U. Villante,A. Meloni
Annales Geophysicae (ANGEO) , 2003,
Abstract: An analysis of the geomagnetic field variations between 3 min and 2 h at L'Aquila (L=1.6) shows that the power level in the low-frequency range (i.e. for periods longer than approximately 10 min) at solar maximum (1989/90) is much higher than at solar minimum (1985/86). Conversely, at solar minimum, it emerges that there is a greater relative importance of fluctuations with periods smaller than 10 min which might be related to the greater percentage of solar wind speeds greater than approximately 540 km s–1. Diurnal, seasonal and solar cycle variations of both the high- and the low-frequency power are also discussed. We found that several aspects of these variations might be correlated with ionospheric features such as the ionisation of the F2 layer and the location and the intensity of the S current system.
The temporal and spatial variations of low frequency geomagnetic pulsations at polar cusp and cap latitudes  [cached]
N. G. Kleimenova,P. Francia,U. Villante,O. V. Kozyreva
Annals of Geophysics , 1999, DOI: 10.4401/ag-3747
Abstract: Geomagnetic field measurements at two Antarctic stations are compared during two weeks in the local summer (January 1-15, 1992). Low frequency (0.6-6 mHz) pulsations are observed at each station near local magnetic noon. The same wave packets appear in some cases also at the other station, although with a significant attenuation, more clearly in the morning sector; the waves show a near noon reversal of the polarization sense from counter-clockwise in the morning to clockwise in the afternoon indicating a westward and an eastward propagation, respectively.
Mid-latitude ionosphere during two great geomagnetic storms
I. M. Vasiljevic,L. R. Cander
Annals of Geophysics , 1996, DOI: 10.4401/ag-4014
Abstract: The ionospheric disturbances observed at many European ionosonde stations in association with the severe geomagnetic storms occurring on 19-20 December 1980 and 11-12 April 1981 were investigated by using the available ionospheric and geomagnetic data. During these storms the ionospheric F region underwent major changes at all mid-latitudes. However, the variations from storm to storm were much larger at lower mid-latitudes. These results support the view that even in assessing the response of the mid-latitude ionosphere to severe geomagnetic storms it is necessary to distinguish carefully between global, regional and local behaviour.
Afternoon mid-latitude current system and low-latitude geomagnetic field asymmetry during geomagnetic storms  [PDF]
A. Grafe,P. A. Bespalov,V. Y. Trakhtengerts,A. G. Demekhov
Annales Geophysicae (ANGEO) , 2003,
Abstract: For four geomagnetic storms of middle intensity the relationship between the low-latitude magnetic field asymmetry using ASY indices and the intensity of the auroral eastward and westward electrojet was considered. It was asked whether there exists a connection between ASY and the eastward electrojet. To answer this question equivalent current systems were estimated in mid-latitudes. It was found that the observations obviously show no correlative relationship between the low-latitude magnetic-field asymmetry and the eastward electrojet, whereas one exists between ASY and the westward electrojet. To explain the generally accepted common three-dimensional current system between the partial ring current and the eastward electrojet, a condensor model of the three-dimensional current system was developed. It could be shown that the short periodic variations of the partial ring current are shielded by the condensor and cannot influence the eastward-electrojet current.
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