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| Titel |
Harmonic quiet-day curves as magnetometer baselines for ionospheric current analyses |
| VerfasserIn |
M. Kamp |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
2193-0856
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| Digitales Dokument |
URL |
| Erschienen |
In: Geoscientific Instrumentation, Methods and Data Systems ; 2, no. 2 ; Nr. 2, no. 2 (2013-11-29), S.289-304 |
| Datensatznummer |
250084927
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| Publikation (Nr.) |
 copernicus.org/gi-2-289-2013.pdf |
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| Zusammenfassung |
This paper presents a novel method to determine a baseline for magnetometer
data. This baseline consists of all magnetic field components not related to
ionospheric and magnetospheric disturbances, i.e. all field components due
to solar quiet variations and other background variations, such as tidal and
secular variations, as well as equipment effects. Extraction of this
baseline is useful when the magnetic field variations due to solar
disturbances are analysed. This makes magnetometer data suitable, for
instance, for the calculation of ionospheric equivalent currents related to
geomagnetic storms and substorms.
The full baseline is largely composed of two main constituents: the diurnal
baseline and the long-term baseline. For the diurnal baseline, first
"templates" are derived, based on the lowest few harmonics of the daily
curves from the quietest days. The diurnal variation of the baseline is
obtained by linear interpolation between these templates; this method
ensures a smooth baseline at all times, avoiding any discontinuities at
transitions between days. The long-term baseline is obtained by linear
interpolation between the daily median values of the data; this way the
baseline is ensured to follow long-term trends, such as seasonal and tidal
variations, as well as equipment drift. The daily median values are
calculated for all days except the most disturbed ones; a procedure for this
selection is included.
The method avoids many problems associated with traditional baseline methods
and some of the other recently published methods, and is simpler in
procedure than most other recent ones. As far as can be compared, the
distribution of the resulting field after removal of the baseline is largely
similar to that using other recent baseline methods. However, the main
advantage of the method of this paper over others is that it removes
equipment drift and other artefacts efficiently without discarding too much
data, so that even low-quality data from remote unmanned magnetometers can
be made suitable for analysis. This can give valuable contributions to the
database of ionospheric equivalent currents, especially in the area near the
polar cap boundary. |
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