Data selection techniques for non-comprehensive global geomagnetic field models
Thomson, Alan; Lesur, Vincent. 2006 Data selection techniques for non-comprehensive global geomagnetic field models. [Poster] In: GEOSPACE Consortium Meeting, BGS Edinburgh, 29-30 August 2006. (Unpublished)Before downloading, please read NORA policies.
The geomagnetic field contains contributions from various time-varying, spatially complex, sources external to the solid Earth. Non-comprehensive geomagnetic field models may fail to reflect the characteristics of these sources and lead to inaccurate internal field models, with consequences for interpretation of Earth structure and internal dynamics. Furthermore data from satellites in low Earth orbit may be obtained in the source regions of some fields and may therefore be improperly modeled using standard potential field techniques. Appropriate satellite data selection, to minimize the contribution of external sources, is one way of reducing the un-modeled external field 'noise' in internal field models. This has been historically a common approach to modeling, where all the sources are not explicitly modeled, and is achieved by selecting satellite data with reference to regional or global geomagnetic indices and during local nighttime. In this paper we examine whether this approach still has value in the modern era and we test this by producing high degree (up to spherical harmonic degree 60) global field models from Orsted and Champ satellite data. These models have both internal and external field components but do not, for example, model the ionosphere. We compare these global models with comprehensive models produced by other authors and also by reference to known crustal structures. We find that high latitude indices are useful but that the Dst index is unreliable, although the time rate of change of Dt is helpful. However such a data selection procedure inevitably leaves 'holes' in the spatial distribution of the satellite data. We therefore describe a re-selection technique, which fills these holes with slightly noisier data, and yet results in models with lower overall rms misfit. We show that there are still problems with the crustal field model for the Polar Regions and that further work on refining polar cap and auroral oval indices is therefore suggested. However the degree of agreement with the crustal model components of the (more) comprehensive models is encouraging. Future work will address the differences, by adding to model complexity and by further refining the data selection techniques.
|Item Type:||Conference or Workshop Item (Poster)|
|Programmes:||BGS Programmes > Seismology and Geomagnetism|
|NORA Subject Terms:||Earth Sciences|
|Date made live:||02 Nov 2012 11:17|
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