Abstract
Abstract. Field-aligned currents (FACs) in the magnetosphere–ionosphere (M–I) system exhibit a range of spatial and temporal scales that are linked to key dynamic coupling processes. To disentangle the scale dependence in magnetic field signatures of auroral FACs and to characterize their geometry and orientation, Bunescu et al. (2015) introduced the multiscale FAC analyzer framework based on minimum variance analysis (MVA) of magnetic time series segments. In the present report this approach is carried further to include in the analysis framework a FAC density scalogram, i.e., a multiscale representation of the FAC density time series. The new technique is validated and illustrated using synthetic data consisting of overlapping sheets of FACs at different scales. The method is applied to Swarm data showing both large-scale and quiet aurora as well as mesoscale FAC structures observed during more disturbed conditions. We show both planar and non-planar FAC structures as well as uniform and non-uniform FAC density structures. For both synthetic and Swarm data, the multiscale analysis is applied by two scale sampling schemes, namely the linear and logarithmic scanning of the FAC scale domain. The local FAC density is compared with the input FAC density for the synthetic data, whereas for the Swarm data we cross-check the results with well-established single- and dual-spacecraft techniques. All the multiscale information provides a new visualization tool for the complex FAC signatures that complements other FAC analysis tools.
Highlights
The dynamics of the magnetosphere–ionosphere (M–I) system at auroral latitudes is essentially controlled by solar wind–magnetosphere (S–M) coupling, subject to ionospheric feedback
This paper extends the MSMVA framework (Bunescu et al, 2015) with the addition of a field-aligned currents (FACs) density scalogram, i.e., a multiscale representation of the FAC density that takes into account the orientation derived from MSMVA
Because we address the multiscale aspect of the FAC signatures and in order to have good statistics at smaller scales, we use the highest-resolution data provided by vector field magnetometer (VFM), namely the 50 Hz data (0.02 s sampling)
Summary
The dynamics of the magnetosphere–ionosphere (M–I) system at auroral latitudes is essentially controlled by solar wind–magnetosphere (S–M) coupling, subject to ionospheric feedback. The transfer of energy and momentum in the system is mediated by field-aligned currents (FACs) flowing along the ambient magnetic field lines and driving the formation of ionospheric (Hall and Pedersen) currents. The entire chain of the energy flow and conversion mechanisms is governed by a multiscale behavior in both time and space. The multiscale character is observed in all the measurable quantities associated with the system, like magnetic field measurements from above (spacecraft) and below (ground) the ionosphere. While above the ionosphere one measures the magnetic perturbation of the field-aligned current (closed in the ionosphere mainly by the Pedersen current), the magnetic perturbation observed on ground is related mainly to the Hall component of the ionospheric current. The multiscale character is observed in the measurements of optical emissions, associated in turn with a multiscale particle precipitation pattern
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
