The use of low altitude satellite data bases for modeling of core and crustal fields and the separation of external and internal fields

Langel, R. A.

doi:10.1007/bf01044077

Cited by 26 publications

(14 citation statements)

References 49 publications

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“…The IGRF-90 (Langel, 1992) secular-variation model was used to adjust all measurements to the common epoch of 1992.0. The data were further separated into summer (December, January and February), and winter (June, July and August) intervals.…”

Section: Spherical Cap Harmonic Analysis (Scha)mentioning

confidence: 99%

“…Although these equations may represent the major portion of the magnetospheric field, the external field is extremely variable. This means that the model just described, which is simply a fit to the residuals and is not a potential field analysis, may not account for fields resulting from Sq and equatorial electrojet currents, which flow below the satellite's orbit (Langel, 1993). The method of Mayhew (1979) was followed by removing a linear trend from each pass-segment over Southern Africa after removing the external field computed from Eqs.…”

Section: Characterization Of Pogs External Fields By Schamentioning

confidence: 99%

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Modelling and Analysis of POGS Data over Southern Africa by Spherical Cap Harmonic Analysis

Kotzé

Barraclough

1997

J. geomagn. geoelec

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POGS total intensity data were analysed over the Southern African region between 10° South and 45° South in latitude and between 5° East and 40° East in longitude. Satellite data were selected corresponding to magnetically quiet conditions during local night times before carrying out an analysis of external fields by subdividing winter and summer data into Dst bins 5 nT wide, centred at multiples of 5 nT. Spherical Cap Harmonic Analysis (SCHA) was then applied to each of these Dst data bins to obtain external field coefficients corresponding to k = 1. Residual POGS data were downward continued by means of the equivalent layer magnetization model and modelled by SCHA to reveal component data at ground level.

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Section: Spherical Cap Harmonic Analysis (Scha)mentioning

confidence: 99%

Section: Characterization Of Pogs External Fields By Schamentioning

confidence: 99%

Modelling and Analysis of POGS Data over Southern Africa by Spherical Cap Harmonic Analysis

Kotzé

Barraclough

1997

J. geomagn. geoelec

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“…While filtering allows us to eliminate the long wavelength fields associated with the magnetospheric ring current and solar quiet variations, the amplitudes and wavelengths of the ionospheric and crustal fields are similar. In order to isolate the ionospheric contribution to the magnetic field, we subtract a crustal field model derived by the equivalent source point technique ) using the averaged POGO data; however, it is possible that removing a crustal field model may eliminate, or at least underestimate, the amplitude of the EE (Langel, 1993). Because the crustal field model may contain some of the EE signal we are looking for, we create two data sets: in the first we subtract the main field model from the POGO data and then apply the long-wavelength filtering correction described above.…”

Section: Data Processingmentioning

confidence: 99%

A study of local time and longitudinal variability of the amplitude of the equatorial electrojet observed in POGO satellite data

Kim

King

2014

Earth Planet Sp

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The local time and longitudinal variations of the amplitude of the equatorial electrojet (EE) are investigated using the POGO series satellite data. An iterative normalization scheme is developed to separate the variations of the amplitude of the EE with respect to longitude and local time. The resulting local time variation of the EE compares favorably with observatory based studies; however, the longitudinal variation is not well resolved. The altitude of the satellite is another factor that affects the amplitude of the EE. We use a simple linear scaling of amplitude of the EE with the inverse of the satellite altitude. An experiment including only the satellite passes below 450 km altitude indicates that there may be problems in correcting the data from higher altitudes. The reason behind the discrepancy between the results from the data limited to below 450 km and the full data set is not understood and requires further investigation.

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“…The geomagnetic field measured at the surface of the Earth is a superposition of the fields raising from various sources having a wide variety of spatial and temporal characteristics (see e.g., Langel, 1993). The geomagnetic variation field is contributed by external currents in the ionosphere and magnetosphere, and internal telluric currents induced in the Earth.…”

Section: Introductionmentioning

confidence: 99%

Separation of the geomagnetic variation field on the ground into external and internal parts using the spherical elementary current system method

2014

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Traditionally the separation of the ground geomagnetic field variations into external and internal parts is carried out by applying methods using harmonic functions. However, these methods may require a separate field interpolation and extrapolation, can be computationally slow, and require a minimum wavelength to be specified to which the spatial resolution is limited globally. A novel method that utilizes elementary current systems can overcome these shortcomings. The basis is the fact that inside a domain free of current flow, the magnetic field can be continued to any selected plane in terms of equivalent currents. Two layers of equivalent currents, each composed of superposition of spherical elementary systems, are placed to reproduce the ground magnetic field: One above the surface of the Earth representing the field of ionospheric origin, and one below it representing the field caused by induced currents in the Earth. The method can be applied for single time steps and the solution of the associated underdetermined linear system is found to be fast and reliable when using singular value decomposition. The applicability of the method is evaluated using synthetic magnetic data computed from different ionospheric current models and associated image currents placed below the surface of the Earth. Following these tests, the method is applied to the measurements of Baltic Electromagnetic Array Research (BEAR) (June-July 1998). External and internal components of geomagnetic variations were computed for the entire measurement period. Also the adequacy of the sparser IMAGE magnetometer network for the full field separation was tested.

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The use of low altitude satellite data bases for modeling of core and crustal fields and the separation of external and internal fields

Cited by 26 publications

References 49 publications

Modelling and Analysis of POGS Data over Southern Africa by Spherical Cap Harmonic Analysis

Modelling and Analysis of POGS Data over Southern Africa by Spherical Cap Harmonic Analysis

A study of local time and longitudinal variability of the amplitude of the equatorial electrojet observed in POGO satellite data

Separation of the geomagnetic variation field on the ground into external and internal parts using the spherical elementary current system method

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