HR: 1330h
AN: SH42A-0475    [PDF]
TI: Interplanetary Magnetic Clouds Observed by Wind and Helios 1 \& 2: Influence of the Magnetic Field Strength on the Stand-off Distance
AU: Leitner, M
EM: martin.leitner@stud.uni-graz.at
AF: Institute for Geophysics, Astrophysics, and Meteorology, University of Graz, Universit\"atsplatz 5, Graz, 8010 Austria
AU: Leitner, M
EM: martin.leitner@stud.uni-graz.at
AF: Space Research Institute, Austrian Academy of Sciences, Schmiedlstr. 6, Graz, 8042 Austria
AU: * Farrugia, C J
AF: Institute of the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, NH 02824 United States
AU: Biernat, H K
AF: Institute for Geophysics, Astrophysics, and Meteorology, University of Graz, Universit\"atsplatz 5, Graz, 8010 Austria
AU: Biernat, H K
AF: Space Research Institute, Austrian Academy of Sciences, Schmiedlstr. 6, Graz, 8042 Austria
AU: Biernat, H K
AF: Institute for Theoretical Physics, University of Graz, Universit\"atsplatz 5, 8010, Graz Austria
AB: We study the extent of the sheath region of interplanetary magnetic clouds over the heliospheric distance range 0.3 - 1.0 AU and, in particular, the effect of the magnetic field on the stand-off distance of the shock which fast magnetic clouds drive. For this study we use data on these ejecta acquired by Wind at 1 AU and the Helios 1 and 2 probes at 0.3 - 1 AU. Modelling the ejecta as straight-cylindrical objects, we first apply a hydrodynamic approximation to obtain the stand-off distance of 50 magnetic clouds as a function of sonic Mach number. In a second step we follow Burlaga (1988) and model magnetic clouds as cylindrical-symmetric, force-free magnetic structures of constant alpha, i.e. a 2-component field, $\bf$ satisfying $\nabla \bf B = \alpha \bf B$. Least-squares fit of this model to the data then determines several parameters of the model magnetic cloud, such as the total field strength on the axis and the distance the spacecraft passes from the axis of the cylinder. Using this information and comparing the measurements with the hydrodynamic limit of zero $\bf B$, we derive the effect of the magnetic field on the stand-off distance of the shock. Burlaga, L.F., Magnetic clouds and force-free fields with constant alpha, J. Geophys. Res., 93, 7217, 1988. This work is supported by NASA Living with a Star under grant NAG 5-10883.
DE: 2111 Ejecta, driver gases, and magnetic clouds
DE: 2139 Interplanetary shocks
SC: SPA - Solar and Heliospheric Physics [SH]
MN: 2003 Fall Meeting