Abstract

AbstractLow-latitude ionospheric electric currents produce prominent signatures in the magnetic field measurements made by low Earth-orbiting satellites. Analyzing these magnetic signatures not only provides insight into the currents themselves, but also many other important and interesting phenomena in the low-latitude ionosphere and thermosphere. The low-latitude currents are modulated by thermospheric winds, so attaining a global knowledge of the spatial structure of the currents can give insight into the neutral tidal harmonics present at ionospheric altitudes. Furthermore, the equatorial electrojet (EEJ) current is driven by an equatorial electric field which in turn is generated by a dynamo process. This electric field is additionally responsible for the vertical plasma fountain and equatorial ionization anomaly at low-latitudes. Magnetic measurements of the EEJ, therefore, allows the study of low-latitude plasma motion in the E and F regions of the ionosphere. This chapter will present techniques developed for processing magnetic measurements of the EEJ to extract information about the low-latitude currents and their driving electric fields. This chapter will present a line current approach to recover the EEJ current strengths, with an emphasis on cleaning the satellite data and minimizing magnetic fields from other internal and external sources. The electric fields will be determined using a combination of physical modeling and fitting the EEJ current strengths from the satellite measurements.

Highlights

  • This chapter will be concerned with the calculation of ionospheric current flow and electric fields at low-latitudes, using magnetic field measurements from low Earth orbiting (LEO) satellite missions, such as Swarm (Friis-Christensen et al 2006)

  • We have presented a methodology of inverting scalar magnetic measurements from LEO near-polar orbiting satellites for EEJ equivalent current flow at low-latitudes

  • This method is based on modeling the magnetically eastward current flow with straight line segments placed along lines of constant quasi-dipole latitude

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Summary

11.1 Introduction

This chapter will be concerned with the calculation of ionospheric current flow and electric fields at low-latitudes, using magnetic field measurements from low Earth orbiting (LEO) satellite missions, such as Swarm (Friis-Christensen et al 2006). About 120 km altitude, the Hall conductivity decreases substantially, since the reduced density of neutral particles result in less ion-neutral collisions, and the ions are essentially free to move with the electrons This effect causes a nonconducting layer at the top of the E-region, and so the charge will accumulate at about 120 km altitude near the magnetic equator. This charge accumulation will cause a strong vertical polarization electric field which will drive zonal electron drift. Because the vertical polarization electric field is typically about 10 times stronger than the eastward component, the zonal E × B drift results in a strong current system, the EEJ. These current estimates will be inverted using a physics-based modeling procedure in order to recover the eastward component of the equatorial electric field

11.2 Satellite Data Preprocessing
11.3 Removing the Sq Field
11.4 Estimating EEJ Flow with Line Currents
11.5 Estimating Low-Latitude Electric Fields
11.5.1 Ionospheric Electrostatic Modeling
11.5.2 Estimating the Electric Field
11.6 Conclusion

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