HR: 0800h
AN: SM31A-0390    [Abstracts]
TI: Small-Scale Flow Structures Associated with a Near-Earth Substorm Onset Observed During a Radial Conjunction between Polar and Cluster
AU: * Bonnell, J W
EM: jbonnell@ssl.berkeley.edu
AF: Space Sciences Laboratory, University of California, Berkeley, CA 94720 United States
AU: Mozer, F S
EM: fmozer@ssl.berkeley.edu
AF: Space Sciences Laboratory, University of California, Berkeley, CA 94720 United States
AU: Lin, N
EM: nlin@ssl.berkeley.edu
AF: Space Sciences Laboratory, University of California, Berkeley, CA 94720 United States
AB: The precession of the Polar spacecraft orbit has placed its apogee (~9 Re) near the equator during 2000-2003, allowing correlative studies of electric fields and plasmas between Polar and the satellites of the Cluster constellation (apogee ~19 Re). This has allowed us to preview the sorts of radial and azimuthal alignments planned for the inner satellites of the THEMIS mission, and to better understand the relationships between the in-situ plasma and field measurements and the ground-based signatures of substorm onset. A particularly clear example of correlated, rapid, and large-amplitude electric field fluctuations associated with strong plasma flows and ground signatures of substorm onset was observed on Polar and Cluster on 20 September 2003. This particular event has features that suggest important macro- and micro-scale ramifications of the electromagnetic fluctuations associated with substorm onset in the tail. The onset of electromagnetic fluctuations and strong flows at both Polar and Cluster are close to simultaneous, indicating a onset occurring between the two spacecraft, near 13 Re downtail. Ion temperatures Ion flows as measured by Cluster/CIS are a few hundred km/s in magnitude in a relatively high-temperature environment (~14 keV). ExB flows derived from both Polar EFI and Cluster EFW indicate much higher speed flows (1000 km/s), consistent with the observed time delays between Polar and Cluster. The relative amplitudes of the electric and magnetic fluctuations during the event indicate that significant small-scale structure below the acoustic gyroradius exists within these flows. Such small-scale structure can lead to local stochastic ion acceleration, and may also serve as a source for the observed sub-inertial perpendicular scale structure at auroral altitudes.
DE: 2723 Magnetic reconnection (7526, 7835)
DE: 2744 Magnetotail
DE: 2753 Numerical modeling
SC: SPA-Magnetospheric Physics [SM]
MN: Fall Meeting 2005