Abstract
We present simultaneous ground‐based and in situ measurements of a train of meso‐scale (about 100–300 km) auroral arc undulations, occurring in the postmidnight sector (∼1 MLT) between 0040 UT and 0054 UT on September 21, 2009. The undulations appeared at the auroral poleward boundary, and then moved eastward with a speed of 0.9–2.2 km s−1. Dynamic behaviors of the associated meso‐scale ionospheric plasma flows and current systems were also detected with the ground‐based magnetometer and radar measurements within the all‐sky camera field‐of‐view. During the interval of interest, simultaneous Cluster observations in the central near tail region (11–14 RE down tail) were available, and especially the ionospheric footprint of Cluster 2 (CL2) was close to the optical auroral forms. CL2 observed strong fluctuations in the in situ magnetic field with amplitude of 5–10 nT whenever a bright arc area, and its trailing adjacent area, of the auroral undulations passed its ionospheric footprint. Such in situ magnetic field changes at CL2 could be considered as a manifestation of localized upward and downward field‐aligned current sheets moving eastward at the central near‐Earth tail boundary, linked to the meso‐scale auroral undulation structures.
Highlights
[2] A series of large-scale bright auroral undulations with wavelengths of 400–1000 km is frequently seen in the postmidnight to early morning sector during substorm recovery phase
A06213 ionosphere and magnetosphere, they suggested that that Alfvén waves in the plasma sheet $8 RE tailward of the Earth are responsible for the generation of field-aligned currents (FACs) that cause omega bands/Ps6 pulsations observed on the ground
[15] Here, let us first discuss the ionospheric electrodynamics in the vicinity of the meso-scale auroral arc undulations presented here, on the basis of the combined groundbased optical, magnetometer, and radar observations
Summary
[2] A series of large-scale bright auroral undulations with wavelengths of 400–1000 km is frequently seen in the postmidnight to early morning sector during substorm recovery phase. Jorgensen et al [1999] presented a case in which Ps6 pulsations were observed simultaneously on the ground and in the magnetospheric equatorial plane around geosynchronous orbit Their results suggested that the magnetospheric counterpart of omega bands/Ps6 pulsations originates from a localized region in the near-Earth magnetotail. A recent study by Wild et al [2011] compared the ground-based allsky imager measurements of omega bands with the in situ field and plasma measurements form the conjugate region in the near-Earth magnetotail. They did not find a clear one-to-one correspondence between variations in the. In order to link the FAC signatures at CL2 with the eastward drifting auroral undulations, we discuss the near-Earth tail FAC features, especially from the viewpoints of electromagnetic energy and longitudinal motion, by combining in situ observations at Cluster 1 which was separated $2 RE dawnward of CL2
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