SHA vs. SCHA for Modelling Secular Variation in a Small Region Such as Italy

Santis, Angelo De; Falcone, C.; Torta, J. M.

doi:10.5636/jgg.49.359

Cited by 11 publications

(8 citation statements)

References 13 publications

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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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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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“…The method is claimed to be valid over any spherical cap at any altitude above the Earth's surface. On the basis of these assertions, SCHA has been widely used for producing magnetic anomaly maps (De Santis et al, 1997;Hwang and Chen, 1997;Korte and Haak, 2000).…”

Section: Spherical Cap Harmonic Modelingmentioning

confidence: 99%

Observing, Modeling, and Interpreting Magnetic Fields of the Solid Earth

Mandea

Purucker

2005

Surv Geophys

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Many Earth system processes generate magnetic fields, either primary magnetic fields or in response to other magnetic fields. The largest of these magnetic fields is due to the dynamo in the Earth's core, and can be approximated by a geocentric axial dipole that has decayed by nearly 10% during the last 150 years. This is an order of magnitude faster than its natural decay time, a reflection of the growth of patches of reverse flux at the core-mantle boundary. The velocity of the North magnetic pole reached some 40 km/yr in 2001. This velocity is the highest recorded so far in the last two centuries. The second largest magnetic field in the solid Earth is caused by induced and remanent magnetization within the crust. Controlled in part by the thermo-mechanical properties of the crust, these fields contain signatures of tectonic processes currently active, and those active in the distant past. Recent work has included an estimate of the surface heat flux under the Antarctic ice cap. In order to understand the recent changes in the Earth's magnetic field, new high-quality measurements are needed to continue those being made by Ørsted (launched in 1999), CHAMP and the Ørsted-2 experiment onboard SAC-C (both launched in 2000). The present paper is motivated by the advent of space surveys of the geomagnetic field, and illustrates how our way of observing, modeling, and interpreting the Earth's magnetic field has changed in recent years due to the new magnetic satellite measurements.

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“…The method is claimed to be valid over any spherical cap at any altitude above the Earth's surface. On the basis of these assertions, SCHA has been widely used for getting regional magnetic maps (De Santis et al 1997; Hwang & Chen 1997; Korte & Haak 2000). However, two kinds of difficulties are to be taken into account when SCHA is performed.…”

Section: State Of the Problem: Global And Regional Modellingmentioning

confidence: 99%

“…In the geodetic literature, Hwang & Chen (1997) introduced fully normalized SCHA to analyse sea‐level data. Applications are also found for regional gravity field representation (De Santis & Torta 1997), for example, over China (Li et al 1995). Another approach was developed to deal with the problem of off‐polar orbits in satellite geodesy, leading to polar gaps in the data, and to study bounded domains such as the oceans.…”

Section: State Of the Problem: Global And Regional Modellingmentioning

confidence: 99%

Wavelet frames: an alternative to spherical harmonic representation of potential fields

Chambodut¹,

Panet

Mandea³

et al. 2005

Geophysical Journal International

120

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S U M M A R YPotential fields are classically represented on the sphere using spherical harmonics. However, this decomposition leads to numerical difficulties when data to be modelled are irregularly distributed or cover a regional zone. To overcome this drawback, we develop a new representation of the magnetic and the gravity fields based on wavelet frames.In this paper, we first describe how to build wavelet frames on the sphere. The chosen frames are based on the Poisson multipole wavelets, which are of special interest for geophysical modelling, since their scaling parameter is linked to the multipole depth (Holschneider et al.). The implementation of wavelet frames results from a discretization of the continuous wavelet transform in space and scale. We also build different frames using two kinds of spherical meshes and various scale sequences. We then validate the mathematical method through simple fits of scalar functions on the sphere, named 'scalar models'. Moreover, we propose magnetic and gravity models, referred to as 'vectorial models', taking into account geophysical constraints. We then discuss the representation of the Earth's magnetic and gravity fields from data regularly or irregularly distributed. Comparisons of the obtained wavelet models with the initial spherical harmonic models point out the advantages of wavelet modelling when the used magnetic or gravity data are sparsely distributed or cover just a very local zone.Magnetic and gravity observations are of great importance for the understanding of geodynamic activity of our planet. Measurements of the Earth's magnetic and gravity fields undertaken by satellites (without forgetting those on land, sea and air) are of particular interest, as they provide a global and uniform survey of these fields and of their temporal evolution.Models of the magnetic field have been derived by means of several Earth's satellite missions, which have been carrying magnetic sensors. Satellite-borne magnetometers provide information on strength and direction of the internal and external Earth's magnetic field and its time variations. The Earth is surrounded by a large and complicated field caused to a large extent by a dynamo operating in the fluid core. Currents flowing in the ionosphere, magnetosphere and oceans and magnetized rocks also influenced the geomagnetic field.Three magnetic missions (Ørsted-launched in 1999, CHAMP and SAC-C-launched in 2000) have collected measurements providing new insights into the composition and the processes in the interior, and surrounding of the planet. These observations are also used in a range of applications, including navigation systems, resource exploration drilling, spacecraft attitude control systems and assessments of the impact of space weather. The coming decade will see further missions planned for more in-depth, dedicated studies of magnetic field including DEMETER, 2004; ESPERIA, 2006; Swarm, 2008; etc. Gravity field observations from space can advance our knowledge of the geoid and its time variations. The g...

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SHA vs. SCHA for Modelling Secular Variation in a Small Region Such as Italy

Cited by 11 publications

References 13 publications

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

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

Observing, Modeling, and Interpreting Magnetic Fields of the Solid Earth

Wavelet frames: an alternative to spherical harmonic representation of potential fields

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