HR: 14:35h
AN: SM33C-04    [Abstracts]
TI: Two-Stage Oscillatory Response of the Magnetopause to a Current/Vortex Sheet Followed by Northward IMF: Cluster Observations
AU: * Farrugia, C
EM: charlie.farrugia@unh.edu
AF: Space Science Center, University of New Hampshire, College Rd, Durham, NH 03824, United States
AU: Gratton, F
EM: fgratton@arnet.com.ar
AF: Instituto de Fisica del Plasma, CONICET, and University of Buenos Aires, Ciudad Universitaria, Buenos Aires, C1428EHA, Argentina
AU: Lund, E
EM: eric.lund@unh.edu
AF: Space Science Center, University of New Hampshire, College Rd, Durham, NH 03824, United States
AU: Torbert, R
EM: roy.torbert@unh.edu
AF: Space Science Center, University of New Hampshire, College Rd, Durham, NH 03824, United States
AU: Sandholt, P
EM: p.e.sandholt@fys.uio.no
AF: Department of Physics, University of Oslo, Blindern, Oslo, N-0316, Norway
AU: Cowley, S
EM: swhc1@ion.le.ac.uk
AF: Department of Physics and Astronomy, University of Leicester, University Rd, Leicester, LE1 7RH, United Kingdom
AU: Gnavi, G
EM: ggnavi@arnet.com.ar
AF: Instituto de Fisica del Plasma, CONICET, and University of Buenos Aires, Ciudad Universitaria, Buenos Aires, C1428EHA, Argentina
AU: Bilbao, L
EM: luis.bilbao@arnet.com.ar
AF: Instituto de Fisica del Plasma, CONICET, and University of Buenos Aires, Ciudad Universitaria, Buenos Aires, C1428EHA, Argentina
AU: Mouikis, C
EM: chris.muoikis@unh.edu
AF: Space Science Center, University of New Hampshire, College Rd, Durham, NH 03824, United States
AU: Kistler, L
EM: lynn.kistler@unh.edu
AF: Space Science Center, University of New Hampshire, College Rd, Durham, NH 03824, United States
AU: Mann, I
EM: imann@phys.ualberta.ca
AF: Department of Physics, University of Alberta, Avadh Bhatia Physics Laboratory, Edmonton, AB T6G 2J1, Canada
AU: Watermann, J
EM: jfw@dmi.dk
AF: Atmosphere Space Research Division, Danish Meteorological Institute, Lyngbyvej 100, Kobenhavn, 2100, Denmark
AU: Singer, H
EM: Howard.Singer@Noaa.gov
AF: NOAA Space Environment Center, 325 Broadway, Boulder, CO 80305, United States
AB: We discuss the motion and structure of the magnetopause/boundary layer observed by Cluster in response to a joint tangential discontinuity/vortex sheet (TD/VS) observed by the ACE spacecraft on December 7, 2000. The observations are then supplemented by theory. Sharp polarity reversals in the east-west components of the field and flow ,B_y and V_y, occurred at the discontinuity. These rotations were followed by a period of strongly northward IMF. These two factors elicited a two-stage response at the magnetopause, as observed by Cluster situated in the boundary layer at the duskside terminator. First, the magnetopause suffered a large deformation from its equilibrium position, with large-amplitude oscillations of ~3 min period being set up. These are argued to be mainly the result of tangential stresses associated with Δ V_y, the contribution of dynamic pressure changes being small in comparison. This strengthens recent evidence of the importance to magnetospheric dynamics of changes in azimuthal solar wind flow. The TD/VS impact caused a global response seen by ground magnetometers in an MLT range spanning at least 12 hours. The response monitored on ground magnetometers is similar to that brought about by magnetopause motions driven by dynamic pressure changes. Second, Cluster recorded higher frequency waves (~79 s). Two clear phases could be distinguished from the spectral power density, which decreased by a factor of ~3 in the second phase. Applying compressible, linearized MHD theory, we show that these perturbations are consistent with surface waves originating from the Kelvin-Helmholtz instability. Varying the local magnetic shear at the Cluster locale, as suggested by the temporal profile of the IMF clock angle, we find that locally stability was reinstated, so that the reduced power in the second phase is argued to be due residual KH activity arriving from locations farther to the dayside.
DE: 2109 Discontinuities (7811)
DE: 2471 Plasma waves and instabilities (2772)
DE: 2784 Solar wind/magnetosphere interactions
SC: SPA-Magnetospheric Physics [SM]
MN: 2007 Fall Meeting