Multi-instrument observations of the dynamics of auroral arcs: a case study |
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| Affiliation: | 1. Department of Communication Systems, Lancaster University, Lancaster LA1 4YR, UK;2. Physics Department, University of Wales, Aberystwyth SY23 3BZ, UK;3. EISCAT group, Rutherford Appleton Laboratory, Didcot OX11 0QX, UK;4. Physics Department, University of Sussex, Brighton BN1 9QH, UK;5. Max Planck Institut für Aeronomie, Katlenburg-Lindau, Germany;1. Pamukkale University, Faculty of Education, 20070, Denizli, Turkey;2. Pamukkale University, School of Foreign Languages, 20070, Denizli, Turkey;1. Institute of Opto-Mechatronics Engineering, National Central University, Taoyuan City 32001, Taiwan;2. Institute of Mechanical Engineering, National Central University, Taoyuan City 32001, Taiwan;3. ViewMove Technologies, Inc., Taoyuan City 32001, Taiwan;4. Institute of Space Science, National Central University, Taoyuan City 32001, Taiwan;5. Center for Astronautical Physics and Engineering, National Central University, Taoyuan City 32001, Taiwan |
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| Abstract: | We present results from a multi-instrument study of events on February 13–14, 1996. The data were taken by the EISCAT incoherent-scatter radar, the Sussex, MPI and FMI all-sky cameras, the IRIS riometer and the IMAGE and SAMNET magnetometer networks. Observations from the various instruments are compared to establish the concurrency of the radar, optical and absorption signatures of arcs, and to make a detailed study of their dynamics. The distribution of electric field strength near each arc is determined and the drift velocity of each arc is compared with EISCAT measurements of F-region plasma velocity. Two multiple-onset substorms are studied in detail, the behaviour of each arc depends on the phase of the substorm in which it is observed. Our major points are: (1) All arcs observed during the growth or recovery phases are seen to drift at velocities close to the average convection velocity. In contrast, arcs observed during the expansion phase travel at a significantly different velocity. (2) There is strong qualitative evidence that arcs which drift with the convection are optically less bright than arcs with a large relative velocity with respect to the surrounding plasma so that arc brightening at substorm onset is clearly associated with a sharp increase in relative velocity. (3) The observations confirm the current electrodynamics model of arcs and, moreover, we notice a difference in the conductivity behaviour with respect to the direction of the arc movement. It is generally true that when the band of enhanced electric field is in advance of a moving arc the gradient in conductivity is very sharp at the leading edge of the arc and hence the largest electric fields are seen very close to the arc. When, however, the band of enhanced field follows the moving arc the increase in Pedersen conductivity is more gradual, and in such cases too the maximum electric field strength is observed at greater distances from the optical arc itself. |
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