München 1997 – scientific programme
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EP: Extraterrestrische Physik
EP 2: Magnetosph
äre 1
EP 2.8: Talk
Monday, March 17, 1997, 10:15–10:30, 302
Fine Structure of Field-Aligned Currents Associated with a Westward Travelling Surge — •M. Rother1, H. Lühr1, J.S. Murphree2, and T. Hughes3 — 1GeoForschungsZentrum Potsdam, Telegrafenberg, D-14473 Potsdam — 2University of Calgary, Canada — 3Hertzberg Institute of Astrophysics, Ottawa, Canada
A westward travelling surge (WTS) is an intense auroral feature which shows up close to magnetic midnight at the onset of a substorm. The WTS propagates westward at a high speed of several km/s and marks the westward boundary of the substorm-enhanced polar electrojet. On 11. Dec. 1992 we had the unique opportunity of a Freja satellite pass right through the head of a WTS. The combination of the measurements from several instruments allows us to draw a detailed picture of the associated currents. As mentioned above, the WTS is a moving object, therefore we determine its position and velocity, as deduced from ground-based magnetometer observations. From the interpretation of Freja magnetic field measurements in terms of currents we can estimate the field-aligned current (FAC) structures. On medium scales we find a good agreement between upward FAC and auroral features, as expected. Looking into the fine-scale structure of the FACs associated with the WTS reveals some surprises. Inside of the well-known intens upward directed FAC there seems to be a return current. Such a current configuration resembling a co-axial cable suggests a twisting force acting on the flux tube which connects the WTS with the magnetospheric source region.