55 research outputs found
Experimental investigation of auroral generator regions with conjugate Cluster and FAST data
Here and in the companion paper, Hamrin et al.&nbsp;(2006), we present experimental evidence for the crossing of auroral generator regions, based on conjugate Cluster and FAST data. To our knowledge, this is the first investigation that concentrates on the evaluation of the power density, <i><b>E</b></i>&middot;<i><b>J</b></i>, in auroral generator regions, by using in-situ measurements. The Cluster data we discuss were collected within the Plasma Sheet Boundary Layer (PSBL), during a quiet magnetospheric interval, as judged from the geophysical indices, and several minutes before the onset of a small substorm, as indicated by the FAST data. Even at quiet times, the PSBL is an active location: electric fields are associated with plasma motion, caused by the dynamics of the plasma-sheet/lobe interface, while electrical currents are induced by pressure gradients. In the example we show, these ingredients do indeed sustain the conversion of mechanical energy into electromagnetic energy, as proved by the negative power density, <i><b>E</b></i>&middot;<i><b>J</b></i>&lt;0. The plasma characteristics in the vicinity of the generator regions indicate a complicated 3-D wavy structure of the plasma sheet boundary. Consistent with this structure, we suggest that at least part of the generated electromagnetic energy is carried away by Alfv&#233;n waves, to be dissipated in the ionosphere, near the polar cap boundary. Such a scenario is supported by the FAST data, which show energetic electron precipitation conjugated with the generator regions crossed by Cluster. A careful examination of the conjunction timing contributes to the validation of the generator signatures
Analysis of three-spacecraft data using planar reciprocal vectors: methodological framework and spatial gradient estimation
Multiscale estimation of the field-aligned current density
Field-aligned
currents (FACs) in the magnetosphereâionosphere (MâI)
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.</p
Multiple current sheets in a double auroral oval observed from the MAGION-2 and MAGION-3 satellites
Multiple current sheets in a double auroral oval observed from the MAGION-2 and MAGION-3 satellites
- âŠ