Using "Ground-Truth" Magnetic Fields To Derive Ionospheric Equivalent Currents
Abstract
The Hall currents in the high-latitude ionosphere are the primary driver of the magnetic field perturbations that are observed at the surface of the Earth. These currents and their ground effects are an important aspect of the magnetosphere-ionosphere coupling process. Through use of known inversion techniques, magnetic field measurements can be used to derive maps of the "ionospheric equivalent currents,'' a mathematical representation of the Hall currents on a thin shell. Through a comparison with electric field field-aligned current measurements, the equivalent currents may be useful for estimating the ionospheric conductivity values. Additionally, these currents can be compared with the results from simulation models as as means of validation. In this presentation the method of inversion using a spherical harmonic potential function is reviewed. It is shown the the use of both internal and external current sources is required when fitting the spherical harmonic series to the ground-level magnetic field data, otherwise the ionospheric currents will be overestimated. It is shown that the inversion needs to compensate for magnetic effects of the magnetospheric ring current, otherwise this current shows up as an ionospheric current. Going in other direction, if the internal, telluric currents are ignored by numerical models when calculating the magnetic perturbations, then they will underestimate the horizontal magnetic fields and over-predict the levels of the vertical magnetic fields. It is suggested that future validation studies of geomagnetic predictions include a comparison with the equivalent current, or an evaluation of the vertical component of the magnetic field in the metric scores.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMSA33B3466W
- Keywords:
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- 0355 Thermosphere: composition and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 3315 Data assimilation;
- ATMOSPHERIC PROCESSESDE: 2447 Modeling and forecasting;
- IONOSPHEREDE: 2736 Magnetosphere/ionosphere interactions;
- MAGNETOSPHERIC PHYSICS