HR: 09:10h
AN: SM21B-05    [Abstracts]
TI: Transition from Substorm Growth to Substorm Expansion Phase as Observed with a Radial Configuration of ISTP and Cluster Spacecraft
AU: Sergeev, V
EM: victor@geo.phys.spbu.ru
AF: S.Petersburg State University, Ulyanovskaya 1, Petrodvoretz, St.Petersburg, 198504 Russian Federation
AU: Kubyshkina, M
EM: kubysh@geo.phys.spbu.ru
AF: S.Petersburg State University, Ulyanovskaya 1, Petrodvoretz, St.Petersburg, 198504 Russian Federation
AU: Baumjohann, W
EM: baumjohann@oeaw.ac.at
AF: Austrian Academy Science, Space Research Inst., Schmiedlstrasse 6, Graz, 8042 Austria
AU: * Nakamura, R
EM: rumi.nakamura@oeaw.ac.at
AF: Austrian Academy Science, Space Research Inst., Schmiedlstrasse 6, Graz, 8042 Austria
AU: Amm, O
EM: olaf.amm@fmi.fi
AF: Finnish Meteorological Inst, POB 503 Helsinki, Helsinki, 00101 Finland
AU: Pulkkinen, T
EM: tuija.pulkkinen@fmi.fi
AF: Finnish Meteorological Inst, POB 503 Helsinki, Helsinki, 00101 Finland
AU: Angelopoulos, V
EM: vassilis@ssl.berkeley.edu
AF: Univ California, Space Science Lab., 7 Gauss Way, Berkeley, CA 94720-7450 United States
AU: Mende, S
EM: mende@ssl.berkeley.edu
AF: Univ California, Space Science Lab., 7 Gauss Way, Berkeley, CA 94720-7450 United States
AU: Klecker, B
EM: berndt.klecker@mpe.mpg.de
AF: Max Planck Institut fur Extraterr.Phys., Garching, Munchen, D-85741 Germany
AU: Nagai, T
EM: nagai@geo.titech.ac.jp
AF: Tokyo Inst Technology, Ookayama 2-12-1 Meguro, Tokyo, 152-8551 Japan
AU: Sauvaud, J
EM: sauvaud@cesr.fr
AF: CESR, 9 Ave Colonel Roche, Toulouse, 31028 France
AU: Slavin, J
EM: james.a.slavin.l@gsfc.nasa.gov
AF: NASA GSFC, Greenbelt, MD, 20771 United States
AU: Thomsen, M
EM: mthomsen@lanl.gov
AF: Los Alamos Natl Lab, MS D466, Los Al;amos, NM 87545 United States
AB: Transition from the growth phase to the substorm expansion during a well-isolated substorm with a strong growth phase is investigated using a unique radial (THEMIS-like)spacecraft constellation near midnight, including the probing of the tail current at ~16 Re with Cluster, of the transition region at ~9 Re with Geotail and Polar spacecraft, and of the inner region at 6.6 Re with two LANL spacecraft. The activity development in both global scale and near the spacecraft footpoints was controlled with global auroral images (from the IMAGE spacecraft) and the ground network. The magnetospheric models tuned using in situ observations indicated a strong tail stretching and plasma sheet thinning, which included the growth of the near-Earth current (approaching 30 nA/m2) and possible formation of the local B minimum in the neutral sheet (~5nT) at ~10-12 Re near the substorm onset. However, the time delays around the distinct substorm onset show the propagation from the midtail to the inner magnetosphere suggesting that this strongly enhanced current was not spontaneously disrupted. The earliest perturbations near the onset observed at Cluster just outside the thinned plasma sheet are interpreted as the being due to localized Earthward-contracting newly-reconnected plasma tubes produced by the impulsive reconnection in the midtail plasma sheet. A peculiar feature of this substorm was that 12 min prior to this distinct onset, a clear soft plasma injection to the GEO orbit was recorded which has little associated effects both in the ionosphere and in the transition region at ~9Re. This pseudobreakup was probably due to either localized ballooning-type activity or due to the braking of very narrow BBF whose signatures were also recorded by the Cluster. This event manifested the (previously unknown) phenomenon, a strong tail overloading (excessive storage of magnetic energy) contrasted to the modest energy dissipation and plasma acceleration, which both are discussed and interpreted as the consequences of cold/dense and thick pre-substorm plasma sheet which often occurs after the long quiet period. The lessons of using the radial spacecraft configurations in substorm onset studies are also discussed.
DE: 2407 Auroral ionosphere (2704)
DE: 2740 Magnetospheric configuration and dynamics
DE: 2764 Plasma sheet
DE: 2788 Storms and substorms
SC: SPA-Magnetospheric Physics [SM]
MN: 2004 AGU Fall Meeting