Time-domain, spherical harmonic-finite element approach to transient three-dimensional geomagnetic induction in a spherical heterogeneous Earth

Velı́mský, Jakub; Martinec, Z.

doi:10.1111/j.1365-246x.2005.02546.x

Cited by 46 publications

(44 citation statements)

References 23 publications

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“…The early solutions were based on a spectral method (Hamano 2002;Velimsky and Martinec 2005) in which the quantities of interest were expanded in spherical harmonics to represent their lateral variations. More recently a method relying on the Fourier transform of frequency-domain IE results Kuvshinov et al (2006a) has been presented.…”

Section: Prediction Of Magnetic and Electric Fieldsmentioning

confidence: 99%

3-D Global Induction in the Oceans and Solid Earth: Recent Progress in Modeling Magnetic and Electric Fields from Sources of Magnetospheric, Ionospheric and Oceanic Origin

2008

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Electromagnetic induction in the Earth's interior is an important contributor to the near-Earth magnetic and electric fields. The oceans play a special role in this induction due to their relatively high conductivity which leads to large lateral variability in surface conductance. Electric currents that generate secondary fields are induced in the oceans by two different processes: (a) by time varying external magnetic fields, and (b) by the motion of the conducting ocean water through the Earth's main magnetic field. Significant progress in accurate and detailed predictions of the electric and magnetic fields induced by these sources has been achieved during the last few years, via realistic three-dimensional (3-D) conductivity models of the oceans, crust and mantle along with realistic source models. In this review a summary is given of the results of recent 3-D modeling studies in which estimates are obtained for the magnetic and electric signals at both the ground and satellite altitudes induced by a variety of natural current sources. 3-D induction effects due to magnetospheric currents (magnetic storms), ionospheric currents (Sq, polar and equatorial electrojets), ocean tides, global ocean circulation and tsunami are considered. These modeling studies demonstrate that the 3-D induction (ocean) effect and motionally-induced signals from the oceans contribute significantly (in the range from a few to tens nanotesla) to the near-Earth magnetic field. A 3-D numerical solution based on an integral equation approach is shown to predict these induction effects with the accuracy and spatial detail required to explain observations both on the ground and at satellite altitudes.

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Section: Prediction Of Magnetic and Electric Fieldsmentioning

confidence: 99%

3-D Global Induction in the Oceans and Solid Earth: Recent Progress in Modeling Magnetic and Electric Fields from Sources of Magnetospheric, Ionospheric and Oceanic Origin

2008

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“…Under the above mentioned pair of conditions, the induced Sq signal should stack coherently in local time. A determination of the underlying mantle electrical conductivity structure that causes the induced Sq signal can be investigated in the frequency domain using 1‐D and 3‐D forward modeling codes [ Kuvshinov et al , 1999; Velimsky and Martinec , 2005] that have recently been published.…”

Section: Discussionmentioning

confidence: 99%

Local time stacking of geomagnetic solar daily variations

Everett

2006

J. Geophys. Res.

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[1] Regular geomagnetic solar daily variations, the Sq signal, is used in electromagnetic induction studies to investigate the electrical conductivity structure of Earth's upper mantle. Traditionally, Sq induction studies employ observatory magnetic data from a few quiet days in which the overprint on the regular Sq ionospheric current vortices from various irregular disturbances is minimal. Active days are typically discarded, a procedure which results in a gappy time series that is difficult to analyze. Furthermore, the quiet day selection is largely arbitrary since daily geomagnetic activity levels range continuously from very quiet to very active. This fact precludes the establishment of rigorous quiet/active thresholds. The average local time variation on active days resembles typical quiet day variations except for a multiplicative scaling factor. A multiyear stack of yearlong geomagnetic time series aligned with respect to local time incorporates ''regular active'' days while greatly attenuating the effects of irregular geomagnetic disturbances. External and internal current systems that rise and fall in step with the Sun's transit across the sky above an observatory contribute coherently to the local time stack. All other current systems are incoherent and tend to stack out. An exact 1-year-long stack preserves the seasonal variation. The resulting stacked time series contains no gaps, is dominated by regular solar daily variations, and can be used for improved Sq induction studies and comprehensive geomagnetic field modeling. Hourly geomagnetic values from Niemegk, Boulder, Mbour, and Meanook observatories between 1970 and 2002, along with the ap index, are used in this study.

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“…The forward problem solver is based on a spherical harmonic finite element approach (cf. Velimsky and Martinec 2005) and is employed in all works by Velimsky and Martinec to be discussed below.…”

Section: Constable and Constablementioning

confidence: 99%

Deep Electromagnetic Studies from Land, Sea, and Space: Progress Status in the Past 10 Years

Kuvshinov

2011

Surv Geophys

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This review paper summarizes advances in deep electromagnetic studies of the Earth in the past decade. The paper reports progress in data interpretation, with special emphasis on three-dimensional and quasi one-dimensional developments, and results. The results obtained from data of different origin-geomagnetic observatories, long-period magnetotelluric experiments, submarines cables, and from low-Earth orbiting geomagnetic satellite missions-are described. Both frequency-domain and time-domain approaches are addressed. Perspectives for the future are also discussed.Keywords Observatory, MT, cable, and satellite induction data Á Electrical conductivity in the mantle Á Water in upper mantle and transition zone Á Sources of magnetospheric, ionospheric and oceanic origin Á Global EM inversion Á Multi-dimensional conductivity models Á Frequency-and time-domain approaches 1 Introduction

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Time-domain, spherical harmonic-finite element approach to transient three-dimensional geomagnetic induction in a spherical heterogeneous Earth

Cited by 46 publications

References 23 publications

3-D Global Induction in the Oceans and Solid Earth: Recent Progress in Modeling Magnetic and Electric Fields from Sources of Magnetospheric, Ionospheric and Oceanic Origin

3-D Global Induction in the Oceans and Solid Earth: Recent Progress in Modeling Magnetic and Electric Fields from Sources of Magnetospheric, Ionospheric and Oceanic Origin

Local time stacking of geomagnetic solar daily variations

Deep Electromagnetic Studies from Land, Sea, and Space: Progress Status in the Past 10 Years

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