Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsm23b1691h&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #SM23B-1691
Physics
2740 Magnetospheric Configuration And Dynamics, 2744 Magnetotail, 2760 Plasma Convection (2463), 2784 Solar Wind/Magnetosphere Interactions, 2788 Magnetic Storms And Substorms (7954)
Scientific paper
Sawtooth events in the Earth's magnetosphere are global, large-amplitude oscillations of energetic plasma particle fluxes at geostationary orbit and represent periodic magnetospheric substorms with a typical period of ~3 hours. Sawtooth events generally occur during intense magnetic storms when the magnetosphere is continuously driven by strong southward IMF and high-speed solar wind stream. It has not been well understood how the magnetotail parameters (the total pressure, the lobe magnetic field, and the tail lobe total magnetic flux) at the onset of sawtooth events are related to the solar wind driver. We have conducted a statistical analysis of the magnetotail parameters measured by the Geotail satellite during sawtooth events over 1998-2006. At the onset of sawtooth events (storm-time substorms), the magnetotail total pressure and lobe magnetic field decrease exponentially with the radial distance and increase with the solar wind pressure and merging electric field, and the total magnetic flux in the tail lobe increases linearly with the merging electric field and interplanetary electric field. Empirical formulas of the relationship of the magnetotail parameters at the sawtooth onset with the tail distance and the solar wind are derived for the first time. We have also made a superposed epoch analysis. The magnetotail total pressure and lobe magnetic field take ~50 min for gradual buildup and then ~30 min for rapid increase before the substorm onset, and they decrease for ~80 min after the onset. We have compared our results with previous studies on quiet-time tail behavior and isolated substorms. The magnetotail total pressure at the sawtooth onset is 2-3 times that of the quiet-time magnetotail, the lobe magnetic field at the sawtooth onset is 8-10 nT higher than the value for isolated substorms, and the total lobe magnetic flux at the sawtooth onset is systematically higher than the flux at isolated substorms. The results imply that the sawtooth onset occurs when the magnetotail reaches a critical state and that the critical state depends on the solar wind parameters. Our finds provide new insight into the storm-time magnetospheric dynamics and important guidance for model simulations.
Cai Xu
Huang Chan Chun
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