HR: 11:50h
AN: SM21C-06    [PDF]
TI: Alfv\'en wave modulation of Substorms and outflowing O+ ions Observed by Cluster: Bulk Parameter View
AU: * Parks, G K
EM: parks@ssl.berkeley.edu
AF: Space Sciences Laboratory, University of California, Berkeley, CA 94720 United States
AU: Lee, E
AF: Space Sciences Laboratory, University of California, Berkeley, CA 94720 United States
AU: Wilber, M
AF: Space Sciences Laboratory, University of California, Berkeley, CA 94720 United States
AU: McFadden, J
AF: Space Sciences Laboratory, University of California, Berkeley, CA 94720 United States
AU: Dandouras, J
AF: CESR, Paul Sabatier University, Toulouse, 00000 France
AU: Reme, H
AF: CESR, Paul Sabatier University, Toulouse, 00000 France
AU: Sauvaud, J
AF: CESR, Paul Sabatier University, Toulouse, 00000 France
AU: Bosqued, J
AF: CESR, Paul Sabatier University, Toulouse, 00000 France
AU: Kistler, L
AF: Space Sciences, University of New Hampshire, Durham, NH 03712 United States
AU: Moebius, E
AF: Space Sciences, University of New Hampshire, Durham, NH 03712 United States
AU: Klecker, B
AF: MPE, MPE, Garching, 11111 Germany
AU: Bavassano, M B
AF: IFSI, IFSI, Frascati, 1234 Italy
AU: Korth, A
AF: MPAE, MPAE, Lindau, 12345 Germany
AU: Lundin, R
AF: SISP, SISP, Kiruna, 23456 Sweden
AU: McCarthy, M
AF: Earth and Planaetary Sciences, University of Washington, Seattle, WA 98195 United States
AB: The Cluster spacecraft often encounters the current sheet in the geomagnetic tail. This talk will discuss the behavior of a substorm that occurred on October 1, 2001. Cluster observed the substorm from onset through the recovery phase. This talk will highlight the behavior of bulk parameters (density, mean velocity annd temperature) and the subsequent talk by E. Lee et al. will expand the discussion to kinetic features.The substorm onset occurred $\approx$0927 UT (AE index) and at synchronous altitude it was signified by large pulse-like variations in the magnetic field at $\approx$0930 UT. Cluster detected the onset signature at $\approx$0927 UT at geocentric coordinates (-16.1, 6.2, 4.9)$R_E$. Cluster first crossed the current sheet at $\approx$0938 UT and subsequently Alfv\'en waves modulated the tail allowing Cluster to move back and forth across the current sheet several times. Outflowing ionospheric O+ show periodic bursts of $\approx$1-2 minutes associated with the Alfv\'en wave oscillation indicating strong MI coupling. Longer period modulations ($\approx$6-10 minutes) were observed in energetic particles injected at synchronous altitudes. Prior to the first current sheet crossing, mean velocities $\langle{\bf v}\rangle$ of ion distributions were $\approx$500 km/s in the tailward direction. As Cluster crossed into the southern hemisphere, mean ion velocities $\langle{\bf v}\rangle$ reached values of $\approx$1000 km/s but in the earthward direction, and remained in that direction through the end of the recovery. However, these velocity moments do not mean the plasma was flowing because kinetic features show Cluster was close to the high latitude boundary of the plasma sheet. The time delay between the synchronous altitude and Cluster indicates that the substorm onset was located between the synchronous altitude and the Cluster orbit.
DE: 2431 Ionosphere/magnetosphere interactions (2736)
DE: 2471 Plasma waves and instabilities
DE: 2736 Magnetosphere/ionosphere interactions
SC: SPA - Magnetospheric Physics [SM]
MN: 2003 Fall Meeting