Behaviour of Field Aligned Currents during a geomagnetic storm: Swarm observations

Field-aligned currents (FACs) flowing from Earth’s outer magnetosphere to the high latitude ionosphere along the geomagnetic field lines, are driven by solar wind and interplanetary magnetic field and allow a direct coupling of Earth’s ionosphere with outer plasma regions. This coupling is strongly enhanced during geomagnetic storms, when the energy transfer from solar wind to inner magnetosphere increases significantly and the ionospheric convection / currents are enhanced as well.

In addition to geomagnetic indexes computed from magnetic perturbations measured from ground-based observatories, also the behaviour of FACs can provide relevant information on energy transfer and coupling mechanisms during geomagnetic storms.

In this work we use data from Swarm satellites, which include very accurate measures of field-aligned currents, to characterize the geomagnetic storm that occurred between the 3rd and the 4th of November 2021.

In particular, we investigated the behaviour of FACs at different spatial scales as a function of solar wind conditions, and in comparison with the main geomagnetic indexes (e.g. the Dst and SYM-H indices). We discuss our findings in the context of main results reported in previous literature.