Abstract
The day-time eastward equatorial electric field (EEF) in the ionospheric E-region plays a crucial role in equatorial ionospheric dynamics. It is responsible for driving the equatorial electrojet (EEJ) current system, equatorial vertical ion drifts, and the equatorial ionization anomaly (EIA). Due to its importance, there is much interest in accurately measuring and modeling the EEF for both climatological and near real-time studies. The Swarm satellite mission offers a unique opportunity to estimate the equatorial electric field from measurements of the geomagnetic field. Due to the near-polar orbits of each satellite, the on-board magnetometers record a full profile in latitude of the ionospheric current signatures at satellite altitude. These latitudinal magnetic profiles are then modeled using a first principles approach with empirical climatological inputs specifying the state of the ionosphere. Since the EEF is the primary driver of the low-latitude ionospheric current system, the observed magnetic measurements can then be inverted for the EEF. This paper details the algorithm for recovering the EEF from Swarm geomagnetic field measurements. The equatorial electric field estimates are an official Swarm level-2 product developed within the Swarm SCARF (Satellite Constellation Application Research Facility). They will be made freely available by ESA after the commissioning phase.
Highlights
Electromagnetic fields in the Earth’s ionosphere are responsible for driving many interesting phenomena
Previous efforts to model the equatorial electrojet have found it necessary to increase the electron collision frequency νe by an empirical factor of 4 during typical day-time eastward electric field conditions, to account for unmodeled nonlinear instabilities in the electrojet stream (Gagnepain et al, 1977; Ronchi et al, 1990, 1991; Fang et al, 2008; Alken and Maus, 2010a, b). We adopt this same convention for the Swarm EEF chain when calculating the conductivities
This constraint has been found to yield more accurate electric fields (Alken and Maus, 2010a), since the EEF is primarily responsible for current structure near the magnetic equator, while the winds are primarily responsible for current structure at higher latitudes (Fambitakoye et al, 1976)
Summary
Due to the near-polar orbits of each satellite, the on-board magnetometers record a full profile in latitude of the ionospheric current signatures at satellite altitude. These latitudinal magnetic profiles are modeled using a first principles approach with empirical climatological inputs specifying the state of the ionosphere. The equatorial electric field estimates are an official Swarm level product developed within the Swarm SCARF (Satellite Constellation Application Research Facility). They will be made freely available by ESA after the commissioning phase
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