HR: 0800h
AN: SM31B-1235    [Abstracts]
TI: The Saturation of Dayside Magnetosphere Erosion
AU: Muehlbachler, S
EM: muehlbachler@mps.mpg.de
AF: S. Muehlbachler, Max-Planck-Institute for Solar System Research, Max-Planck-Str. 2, Katlenburg-Lindau, D37191 Germany
AU: * Farrugia, C J
EM: charlie.farrugia@unh.edu
AF: C. J. Farrugia, Institute for the Study of Earth, Oceans, and Space, Space Science Center, Univ. of New Hampshire, 39 College Road , Durham, 03824 United States
AB: We carry out a statistical investigation relating the depression of the geostationary magnetic field near noon to the strength of the southward component of the IMF ($B_z$). We use measurements made by GOES, WIND, ACE and ground-based magnetograms. The period studied is 1996--2003. Events have been selected during intervals with (1) a steady dynamic pressure, $P_{dyn}$; (2) a steady and negative IMF $B_z$; (3) when one of the GOES spacecraft was within 2 hours of local noon; and (4) during substorm growth phase (as ascertained by readings from nightside ground magnetometers). The investigation starts with a correction of raw values of the total geostationary field, $B_{tot}$, for the compression due to $P_{dyn}$. To do this, we chose a number of ``reference" days encompassing a wide range of $P_{dyn}$ values when the IMF was strongly northward (clock angle $<$ 45$^{\circ}$), and fitted $B_{tot}$ to the functional form $B_{tot} = a + b P_{dyn}^{1/2}$. We then fit the corrected $\Delta B_{tot}$ values as a function of $B_z$. This work extends the investigation of {\sl M\"uhlbachler et al., 2004} by a set of events with extremly large and negative $B_z$ in the range of [0,-52]nT. Thus, we find that saturation of erosion occurs for $B_z$ in the range -12 to -16 nT. We fit the data in several ways and find $\Delta B_{tot} = -27.76 + 26.1 \exp(0.012 B_{z})$ to lie closest to our set of data.
DE: 2700 MAGNETOSPHERIC PHYSICS
SC: SPA-Magnetospheric Physics [SM]
MN: 2004 AGU Fall Meeting