New representation of geomagnetic secular variation over restricted regions by means of spherical cap harmonic analysis: application to the case of Spain

Torta, J. M.; García, Alicia García; Curto, J. J.; Santis, Angelo De

doi:10.1016/0031-9201(92)90011-j

Cited by 27 publications

(37 citation statements)

References 8 publications

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“…statistically significant at the F-level 4, results that are similar to those of TORTA et al (1992). The coefficients of the new SV model are listed in Table 1, where their second subscript refers directly to the order q of the temporal expansion of (2).…”

Section: Secular Variation Field Analysessupporting

confidence: 52%

“…The main advantage of this procedure is to avoid the possible crustal contamination in nearsurface main-field observations which can bias the determination of the temporal coefficients. Recent work TORTA et al, 1992) has shown two new procedures to obtain a model of the SV (for Spain) using spherical cap harmonic analysis (SCHA). The data, observatory annual means and measurements from repeat stations, were restricted to a cap of half-angle 16 centered at 34°N, 7°W.…”

Section: Secular Variation Field Analysesmentioning

confidence: 99%

“…Later, TORTA et al (1992) found that a problem in applying SCHA was the lack of long wavelength harmonic functions in a SCH SV model defined for a relatively small cap. This is due to the fact that the lowest values of the harmonic degree nk(m) over a small cap region are not as low as those typical of the SV field.…”

Section: Secular Variation Field Analysesmentioning

confidence: 99%

“…The new data comprise 7 new three-component observatory annual means (Coimbra, 1989;San Pablo, Almeria, andSanta Cruz de Tenerife, 1988 and and 58 repeat station data, including some values from the Italian magnetic network (Istituto Nazionale di Geofisica, Italy, personal communication). The analysis of the first differences was again carried out as described in TORTA et al (1992) with maximum spatial index K= 4, and temporal degree Q = 2, over a 45° cap, with data limited to the 16° cap, from 1970 onwards. The model was referenced to 1990.0; the previous one was referenced to 1987.5.…”

Section: Secular Variation Field Analysesmentioning

confidence: 99%

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A Geomagnetic Reference Field for Spain at 1990.

Torta

García

Santis

1993

J. geomagn. geoelec

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A Spanish Geomagnetic Reference Field for epoch 1990 has been produced using the technique of spherical cap harmonic analysis (SCHA). The data set on which the model is based includes both Magsat and ground (observatory and repeat-station) three-component data. The field data have been updated to 1990 by means of a spherical cap harmonic model of secular variation for a spherical cap of half-angle 16° for the time interval 1970-1989.5. Due to the poor distribution of the ground data (almost entirely restricted to the mainland areas) we have confined the analysis to a smaller cap (8°). Before applying SCHA, field values from the IGRF 1985, evaluated at 1990, were removed from the data and only the residuals were analyzed. We found that the removal of a trend from the satellite residuals improved the fit of the resulting model to the ground data; we also found some difficulties using SCHA to extrapolate Magsat measurements to the ground. Appropriate solutions to this problem are presented. Charts of the elements of the 1990 Spanish Geomagnetic Reference Field (after the addition of the field values computed using the IGRF model) are shown, along with the secular variation maps for that epoch as deduced from the secular variation model.

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Section: Secular Variation Field Analysessupporting

confidence: 52%

Section: Secular Variation Field Analysesmentioning

confidence: 99%

Section: Secular Variation Field Analysesmentioning

confidence: 99%

Section: Secular Variation Field Analysesmentioning

confidence: 99%

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A Geomagnetic Reference Field for Spain at 1990.

Torta

García

Santis

1993

J. geomagn. geoelec

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“…While the ground magnetic field or the ground equivalent currents by themselves can only be used qualitatively for the estimation of ionospheric electrodynamic parameters, the height-continued equivalent currents at the ionospheric level can be combined with information of the ionospheric electric field via Ohm's law to spatially obtain quantitative results on ionospheric conductances, true ionospheric currents, and field-aligned currents (e.g., Richmond and Baumjohann, 1983;Inhester et al, 1992;Amm, 1998). Field continuation in general (not only from the ground to the ionosphere) is also an important tool for the construction of three-dimension geomagnetic reference models (e.g., Haines, 1985a, Torta et al, 1992, De Santis et al, 1997, or for geological applications such as to study crustal magnetic anomalies by means of satellite data (e.g., De Santis et al, 1989), or the Earth's conductivity structure (e.g., Torta and De Santis, 1996). As we shall see, the technique described in this paper can be applied to such problems as well with small modifications.…”

Section: Introductionmentioning

confidence: 99%

Ionospheric disturbance magnetic field continuation from the ground to the ionosphere using spherical elementary current systems

2014

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A new technique for continuation of the ground magnetic field caused by ionospheric currents to the ionosphere in spherical geometry is presented that makes use of elementary ionospheric current systems, which were introduced by Amm (1997) in extension of an earlier work by Fukushima (1976). The measured ground magnetic disturbance is expanded in terms of the ground magnetic effect of a spatial distribution of such elementary current systems. Using a matrix inversion technique, the scaling factors for each elementary current system, and therefrom the ionospheric equivalent currents are calculated. The technique can be applied to both global and local scales. Its advantages compared to the common field continuation techniques with Fourier (local scale), spherical cap (local to medium scale), or spherical (global scale) harmonic expansions are: 1) No fixed limitation of the spectral content has to be given for the whole analysis area, as it has to be done for the other techniques by truncation of a series expansion.2) The locations of the elementary current systems can be chosen freely, such that they are most suitable with respect to the available measurement sites or the type of current system to be analysed. Results of the new technique are discussed in comparison to results of the spherical cap harmonic expansion method for a model of a Cowling channel.

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Spherical Cap Harmonic Analysis of the Geomagnetic Field With Application for Aeronautical Mapping

Torta

Gaya–Piqué

Santis

2006

Geomagnetics for Aeronautical Safety

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The Spherical Cap Harmonic Analysis (SCHA) is a regional modeling technique based on appropriate functions which are solutions of Laplace's equation over a constrained, cap-like region of the Earth. The concept was introduced in 1985 in the context of geomagnetism as a local or regional extension of the classic global spherical harmonic analysis. Starting from the basic principles in which the analysis method is founded, this paper describes the latest applications for the modeling of the main magnetic field and its secular variation. Although examples of applications over small areas will be given, it will be shown that, in general, the bigger the region the more appropriate the technique. Therefore, this paper focuses on the results and perspectives over continental areas, like Antarctica or Europe. The possible application to the derivation of isogonic charts for navigational purposes with suitable time predictions will be emphasized. At the same time, the limitations of the method will be examined. Although recent revisions of the technique seem to solve some of the problems, our present research focuses on the quest for solutions to the still unanswered questions.

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New representation of geomagnetic secular variation over restricted regions by means of spherical cap harmonic analysis: application to the case of Spain

Cited by 27 publications

References 8 publications

A Geomagnetic Reference Field for Spain at 1990.

A Geomagnetic Reference Field for Spain at 1990.

Ionospheric disturbance magnetic field continuation from the ground to the ionosphere using spherical elementary current systems

Spherical Cap Harmonic Analysis of the Geomagnetic Field With Application for Aeronautical Mapping

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