HR: 1400h
AN: SM23C-04    [Abstracts]
TI: The relationship between substorm onset location and the polar cap boundary
AU: * Mende, S
EM: mende@ssl.berkeley.edu
AF: Space Sciences Lab, University of California at Berkeley, 7 Gauss Way, Berkeley, CA 94720, United States
AU: Frey, H
EM: hfrey@ssl.berkeley.edu
AF: Space Sciences Lab, University of California at Berkeley, 7 Gauss Way, Berkeley, CA 94720, United States
AU: Carlson, C
EM: cwc@mail.SSL.Berkeley.EDU
AF: Space Sciences Lab, University of California at Berkeley, 7 Gauss Way, Berkeley, CA 94720, United States
AB: A topological difference between the classical near earth neutral line (1) and current disruption (2) substorm models is the latitude position of the open closed field line boundary (OCFB) immediately after substorm onset. In model 1 the OCFB should be near the onset point which is the location of the reconnection between open and closed field lines while in model 2 the onset and subsequent poleward expansion should take place in a regions of closed field lines and where the expansion move towards the OCFB. Data sets were examined in which a NASA FAST satellite magnetic footprint occurred within 2000 km of a substorm onset point as determined from auroral brightening in the global images obtained by the NASA IMAGE spacecraft. The OCFB was determined from the FAST electron and proton precipitation poleward boundary. The latitude difference between the OCFB and the onset latitude was plotted against the time difference of the FAST observation and the substorm onset. From the resulting scatter plot it can be seen that nearest to onset there is a large difference between the latitude of the OCFB and the onset. This is consistent with prior observations of substorm onsets occurring deep in a closed field line region of the magnetosphere. However there is a trend that for FAST passes occurring soon (within a few minutes) after onset the OCFB is very close to the onset latitude just as if the closed field line region poleward of the onset had disappeared. For FAST passes later than 5 minutes after the OCFB is observed more and more poleward consistent with snapshots of poleward expanding surges located at the OCFB during the substorm expansion phase.
DE: 2407 Auroral ionosphere (2704)
DE: 2723 Magnetic reconnection (7526, 7835)
DE: 2740 Magnetospheric configuration and dynamics
DE: 2744 Magnetotail
DE: 2790 Substorms
SC: SPA-Magnetospheric Physics [SM]
MN: 2007 Joint Assembly