Determining polar ionospheric electrojet currents from Swarm satellite constellation magnetic data

Cecilie Drost Aakjær,Christopher C. Finlay,Nils Olsen

doi:10.1186/s40623-016-0509-y

Cecilie Drost Aakjær, Christopher C. Finlay + Show 1 more

Open Access

https://doi.org/10.1186/s40623-016-0509-y

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Abstract

We determine the strength and location of the ionospheric currents responsible for the polar electrojets from magnetic data collected by the Swarm satellite constellation on an orbit-by-orbit basis. The ionospheric currents are modelled using a simple, yet robust, method by a series of line currents at 110 km altitude (corresponding to the ionospheric E-layer) perpendicular to the satellite orbit, separated by $$1^\circ$$ (about 113 km). We assess the reliability of our method, with the aim of a possible near-real-time application. A study of the effect of different regularization methods is therefore carried out. An $$L_1$$ model regularization of the second-order spatial differences, and robust treatment of the data (to account for non-Gaussian error distributions), yields the most encouraging results. We apply our approach to two three-weekly data periods in March 2014 (geomagnetic quiet conditions) and March 2015 (more disturbed conditions), respectively. Our orbit-by-orbit approach also allows the temporal evolution of the polar electrojets to be investigated. We find remarkable agreement of the ionospheric activity in Northern and Southern polar regions, with correlation exceeding 0.9 for periods longer than two days. Reliability of the approach is shown by three key results: (1) a common regularization parameter for all orbits with enough data coverage, (2) 0.95 squared coherence with the Auroral Electrojet index, and (3) 0.97 squared coherence is found between the side-by-side flying satellites, Alpha and Charlie, indicating a method invariant to small changes in data input. All these results indicate a possible automated near-real-time application.

Highlights

Geomagnetic reference models provide a good description of the main parts of Earth’s magnetic field, including contributions from the core and crust, as well as the large-scale magnetospheric (e.g. Finlay et al 2016; Lesur et al 2010; Olsen et al 2014)
Model parameterization We describe the polar ionospheric currents by a series of line currents placed at an altitude of 110 km in the ionospheric E-layer, perpendicular to the satellite track and separated in horizontal direction by
The magnetic field disturbance caused by a superposition of the contributions from single line currents described by Eq (1) results in a model of the form d = Gm where d is the data vector consisting of the N observations, δFn, with n = 1, . . . , N, m is the vector of the M model parameters, jk, with k = 1, . . . , M, and G is the design matrix of size N × M

Summary

Introduction

Geomagnetic reference models provide a good description of the main parts of Earth’s magnetic field, including contributions from the core and crust, as well as the large-scale magnetospheric (e.g. Finlay et al 2016; Lesur et al 2010; Olsen et al 2014). We applied the line current model of Olsen (1996) to Swarm satellite magnetic data and investigated how different regularization methods affect the model results. The magnetic field disturbance caused by a superposition of the contributions from single line currents described by Eq (1) results in a model of the form d = Gm where d is the data vector consisting of the N observations, δFn, with n = 1, .

Results

Conclusion