HR: 11:35h
AN: SM22A-05    [Abstracts]
TI: Simultaneous Observations of Substorm Onset by the Alignment of Cluster, IMAGE, GOES, and Canadian Ground Based Instruments.
AU: * Voronkov, I
EM: igor@phys.ucalgary.ca
AF: University of Calgary, Dept. of Physics and Astronomy, 2500, University Drive, NW, Calgary, AB T2N1N4, Canada
AU: Runov, A
EM: Andrei.Runov@oeaw.ac.at
AF: Space Research Institute, Schmiedlstrasse 6, Graz, A-8042, Austria
AU: Meurant, M
EM: matthieu@phys.ucalgary.ca
AF: University of Calgary, Dept. of Physics and Astronomy, 2500, University Drive, NW, Calgary, AB T2N1N4, Canada
AB: Several recent studies of substorm onset suggested that in fact this process may comprise two distinct activations seen both in situ and on the ground. It has been asserted that the one activation is associated with the near-Earth breakup and the other - with the mid-tail plasma sheet reconnection (or NENL). We will present an event study of onset with a fortunate alignment of several satellites and ground-based observatories. GOES 8 and Cluster (19 RE down the tail) were in the near-midnight magnetotail conjugate to hi-resolution photometers and magnetometers in the Canadian sector. The IMAGE satellite provided contemporaneous global auroral images throughout the interval. During this event, double onset was clearly seen by all instruments. The first one, detected by ground-based magnetometers, GOES, and IMAGE, was a near-Earth breakup (or equator-most auroral breakup) which followed by a tailward flow, bipolar magnetic field variations, and extreme thinning of the current sheet observed by Cluster. The second, observed roughly 5 min later on, led to a much larger activation with a fully developed WTS and electrojet. This onset was observed by Cluster as a sharp flow reversal from tailward to Earthward with a quadrupolar magnetic field structure and intensive ion heating. This can be interpreted as the Hall-type CPS reconnection tailward of the spacecraft. Prior to this reconnection, the current sheet half-thickness decreased to a minimum on the order of 1000 km. At the time of reconnection a large auroral vortex, on the scale of the auroral oval width, formed. It was rapidly followed by the formation of a double oval and gradual transition to the recovery phase. We assert that we have, for this event, identified ionospheric signatures of mid-tail reconnection in the substorm. Further, we assert that these ionospheric and ground-based signatures of the mid-tail reconnection are distinct from those of the near-Earth breakup.
DE: 2704 Auroral phenomena (2407)
DE: 2736 Magnetosphere/ionosphere interactions (2431)
DE: 2764 Plasma sheet
DE: 2790 Substorms
SC: SPA-Magnetospheric Physics [SM]
MN: 2007 Joint Assembly