Westward moving dynamic substorm features observed with the IMAGE magnetometer network and other ground-based instruments

Abstract

Abstract. We present the ground signatures of dynamic substorm features with particular emphasis on the event interpretation capabilities provided by the IMAGE magnetometer network. This array covers the high latitudes from the sub-auroral to the cusp/cleft region. An isolated substorm on 11 Oct. 1993 during the late evening hours exhibited many of well-known features such as the Harang discontinuity, westward travelling surge and poleward leap, but also discrete auroral forms, known as auroral streamers, appeared propagating westward along the centre of the electrojet. Besides the magnetic ®eld measurements, there were auroral observations and plasma¯ow and conductivity measurements obtained by EISCAT. The data of all three sets of instruments are consistent with the notion of upward ®eld-aligned currents associated with the moving auroral patches. A detailed analysis of the electrodynamic parameters in the ionosphere, however, reveals that they do not agree with the expectations resulting from commonly used simplifying approximations. For example, the westward moving auroral streamers which are associated with ®eld-aligned current ®laments, are not collocated with the centres of equivalent current vortices. Furthermore, there is a clear discrepancy between the measured plasma¯ow direction and the obtained equivalent current direction. All this suggests that steep conductivity gradients are associated with the transient auroral forms. Also self-induction eects in the ionosphere may play a role for the orientation of the plasma¯ows. This study stresses the importance of multi-instrument observation for a reliable interpretation of dynamic auroral processes.

Rapid fluctuations of stratospheric electric field following a solar energetic particle event

“…A payload position inside the transition region gives us the possibility to explore electrical effects in the stratosphere as rigidity cut-offs shift location with respect to the balloon. Significant(>100 nT), sudden decreases in the northward component in ground-based IMAGE magnetometer data [Lühr et al, 1998] at the same time as MINIS observes the rapid vertical electric field jumps can be seen in Figure 3. These sharp decreases indicate a large-scale shift in the geomagnetic field that could be responsible for shifts in SEP rigidity cutoffs.…”

A statistical analysis of ionospheric velocity and magnetic field power spectra at the time of pulsed ionospheric flows

“…[12] This survey is based on velocity data from the CUTLASS Finland radar of the SuperDARN network [Greenwald et al, 1995] and magnetic field data from the IMAGE magnetometer network [Lühr et al, 1998]. …”

Pc5 geomagnetic pulsations, pulsating particle precipitation, and VLF chorus: Case study on 24 November 2006

“…[9] We used the ground-based multi-point magnetic recordings from several IMAGE stations located along the geomagnetic meridian of ∼107-110° [Lühr et al, 1998]. The station code and the corrected geomagnetic latitude of each given station are indicated in Figures 2, 3, 5, and 6.…”