Field-aligned currents play a fundamental role in conveying stress and electric field in the coupled solar wind- magnetosphere-ionosphere-thermosphere system, as well as providing the channel for energy and momentum transfer between these systems. Knowledge of the field-aligned current (FAC) structure and dynamics is a key to understanding how solar wind energy is transferred from the magnetosphere to the ionosphere and thermosphere. In the last decade these current systems were extensively investigated based on the observations from low-orbiting satellites, CHAMP, Ørsted, DMSP, Iridium constellation, as well as inferred from SuperDARN radars and ground-based magnetometer network observations. Although significant progress has been made in our understanding of the statistical distribution, source regions, and evolution of the current systems in response to external condition changes, there are still many open questions in need of investigation. In addition, uncertainties in accuracy and temporal resolution of the current estimations remain to be studied. So far little attention has been paid to small and medium-scale FACs. Due to their large amplitudes they are believed to play an important role for the energy input to the upper atmosphere.

In this project we plan to combine the observations from different missions, including and most notably from ESA’s recently launched multi-spacecraft mission Swarm, which provides the most accurate estimates of small and medium-scale FACs to date. We will combine observations from low-Earth orbiting satellites, SuperDARN, and ground-based magnetometers to investigate FACs, ionospheric electrodynamics, and thermospheric response; use observations from Cluster, THEMIS, and Van Allen Probes to investigate current sources in the magnetosphere; and employ MHD modelling and mapping techniques to relate magnetospheric, ionospheric, and thermospheric observations. We will compare different techniques for the current estimations and try a common calibration against the most reliable estimates. We aim to bring together scientists with diverse backgrounds in order to address the following questions:

• What is the large-scale morphology of R0/R1/R2 current systems and what are the factors influencing the strength and distribution of large-scale current systems in both hemispheres?
• What are the relations between large and small-scale FAC systems?
• What are the generation mechanisms of the Region 0 (polar cap) current systems and what are the common external conditions for their existence?
• What are the generation mechanisms of the cusp and cleft currents, and what is the ionospheric and thermospheric response to these filamentary FAC systems?
• How do the FAC systems evolve in response to sudden changes in the external conditions and what is the mechanism of the FAC saturation during magnetic storms?
• What are the magnetospheric sources of the FAC current systems?

Full proposal is here.