Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsm51b2104p&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SM51B-2104
Physics
[2724] Magnetospheric Physics / Magnetopause And Boundary Layers, [2752] Magnetospheric Physics / Mhd Waves And Instabilities, [2784] Magnetospheric Physics / Solar Wind/Magnetosphere Interactions
Scientific paper
The coast phase configuration of the five THEMIS spacecraft turned out to be particularly useful for the reconstruction of the radial motion of the magnetopause (MP) over extended periods of time. It could be shown that the MP moves preferentially with some distinct, sometimes called "magic" frequencies known from geomagnetic pulsations. Their appearance at the MP has raised the question, if MP surface waves (Kruskal-Schwarzschild-modes) standing between the northern and southern ionospheres could be responsible for the frequency selection observed. We present results of the THEMIS observations of the MP motion as well as related calculations of the mode structure of the standing Kruskal-Schwarzschild-modes in the rectified geometry of the box magnetosphere, where two half spaces of different but homogeneous plasma conditions are separated by a MP plane. One of the half spaces is further restricted by planar ionospheric boundaries at which reflection of the MP surface waves takes place. Their wave structure is computed in the approximation of the ideal, incompressible, and single-fluid MHD. It is found that the MP resembles a membrane under tension when oscillating due to a standing Kruskal-Schwarzschild-mode; these modes represent the eigenmodes of oscillation of the MP membrane. The ionospheres act here as supporting points of the membrane. A comparison of the MP oscillations observed by THEMIS with solar wind data from NASA's OMNI database showed that the dayside MP moves with higher probability with the "magic" frequencies when the IMF has a northward component and a low cone angle. We show why these conditions are favorable for the excitation of Kruskal-Schwarzschild-modes and, hence, are able to present a consistent picture of the THEMIS MP-observations, the corresponding solar wind conditions and the theory developed.
Angelopoulos Vassilis
Glassmeier K.-
Plaschke Ferdinand
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