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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 34, issue 10
Ann. Geophys., 34, 887–900, 2016
https://doi.org/10.5194/angeo-34-887-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 34, 887–900, 2016
https://doi.org/10.5194/angeo-34-887-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Regular paper 18 Oct 2016

Regular paper | 18 Oct 2016

Can the comprehensive model phase 4 (CM4) predict the geomagnetic diurnal field for days away from quiet time?

Elvis Onovughe1,2 Elvis Onovughe
  • 1Department of Earth Sciences, Federal University of Petroleum Resources, Effurun, Nigeria
  • 2Jane Herdman Laboratories, University of Liverpool, Liverpool, L69 3GP, UK

Abstract. The most recent comprehensive model (CM4) of the geomagnetic field (Sabaka et al., 2004) has been used in conjunction with geomagnetic ground observatory station data to analyse and study the geomagnetic diurnal variation field for days away from quiet time and the CM4 prediction for these times. Even though much has been learnt about many components of the geomagnetic field, the diurnal variation field behaviour for days away from quiet time (moderately disturbed time) has not been intensively studied. Consequently, we analyse these, and the predictive ability of the CM4 for ground variations, and whether the CM4 prediction of the diurnal variation (whether at quiet time or away from quiet time) is valid outside the period of reference that from which the data were used in modelling. In carrying out the study, we compared the observatory station data and the CM4 prediction directly. Using the CM4 code, well-characterised internal and magnetospheric components were subtracted from the data, plots and global maps of the residual field generated and then compared with the CM4 to see how well the model performed in predicting the data at moderately disturbed time (Kp  ≤  5). The results show that the CM4 is valid and produces useful predictions outside the period covering the timespan of the model and during moderately disturbed time, despite the lack of active data in the original model dataset. The model predictability of the data increases as we move to higher spherical harmonic degree truncation, as the model–data misfit is reduced, but with increased roughness as a result of small-scale features incorporated. The observed results show that this relationship between the increase in spherical harmonic degree truncation and reduction in misfit can be restricted by data quality or quantity and global coverage or spread.

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We assess the CM4 of daily variation and whether it can be applied to times and activity levels outside of those that provide input data for the model. Our conclusion shows that the model works well at times outside those from which CM4 was produced and also performs better than expected at activity levels higher than that for which CM4 was designed, although it fails to predict short-period behaviour.
We assess the CM4 of daily variation and whether it can be applied to times and activity levels...
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