Journal Article

Investigation of Space Weather Effects by Swarm Magnetic Field Data: The SFAC Index

Dunlop, Malcolm W., Gjerloev, Jesper W., Marghitu, Octav, Blăgău, Adrian, Rauberg, Jan, Kervalishvili, Guram, Constantinescu, Vlad

2025

Overview

The three Swarm satellites provide an optimum, low Earth orbit (LEO) and multi‐spacecraft platform, to explore for the first time the local correlation between field‐aligned currents (FACs), auroral electrojets, and magnetic perturbations at the Earth's surface. By combining Swarm and ground magnetic field data, one can investigate systematically the full correlation chain, whose final link controls the ground induced currents and related space weather effects. We introduce an integrated FAC product, the Sheet FAC (SFAC) index, as a convenient measure of the in‐situ FAC data, and explore the correlations SFAC‐AE, SFAC‐PEJ and SFAC‐dH, with AE the standard auroral electrojet index, PEJ the local, Swarm based, polar electrojet index, and dH the horizontal magnetic field perturbation at the Earth's surface. Given the good SFAC‐dH correlation, we also suggest an extension of SFAC to higher LEO satellites, which cannot observe any more the electrojet currents, but are fully capable to monitor SFAC. Plain Language Summary ‘Space weather’ resembles, to some extent, ordinary weather. Likewise, storms in space, termed ‘magnetic storms’, have common features with ordinary storms. Just like ordinary storms, magnetic storms can cause damage, and similar to ordinary weather, space weather needs to be monitored and, ideally, predicted. The SFAC index, introduced in the paper, is shown to be a potentially useful tool for such goals, able to capture local effects. This is essential for efficient monitoring. Moreover, the SFAC index can be extended to many satellites, which is important too. Just like for ordinary weather, space weather prediction requires measurements of key parameters that are used as input by specific models. The more and denser the measurements, the better the output, namely the prediction. Key Points The newly introduced SFAC index is shown to be robust and appropriate for space weather monitoring by low Earth orbit satellites SFAC appears to be able to capture local features related to magnetospheric dynamics, as driven, in particular, by bursty bulk flows While the introduction of SFAC takes advantage of Swarm features, the index can be extended to other low Earth orbit satellites

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Auroral electrojet / Auroral electrojets / bursty bulk flow and magnetospheric dynamics / Correlation / Earth orbit / Earth orbits / Earth surface / electrojet current / Electrojets / fielld‐aligned current / Geomagnetic storms / ground magnetic perturbation / Low earth orbits / Magnetic field / Magnetic fields / Magnetic storms / Perturbation / Satellite observation / Satellites / Space weather / Spacecraft / Storms / Swarm mission and low Earth orbit satellites / Weather / Weather effects / Weather forecasting