Physics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsm12b..02h&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #SM12B-02
Physics
[2475] Ionosphere / Polar Cap Ionosphere, [2744] Magnetospheric Physics / Magnetotail, [2788] Magnetospheric Physics / Magnetic Storms And Substorms, [2790] Magnetospheric Physics / Substorms
Scientific paper
Different magnetospheric dynamic processes, such as sawtooth events, isolated substorms, and steady magnetospheric convection (SMC), can occur under varying solar wind conditions. We have conducted a statistical analysis of the magnetotail parameters (total pressure, lobe magnetic field, and magnetic flux) measured by the Geotail satellite and the open magnetic flux in the polar cap measured by the IMAGE and Polar satellites during different magnetospheric modes. The magnetotail total pressure at the sawtooth onset is 2-3 times that of the quiet-time magnetotail, and the lobe magnetic field at the sawtooth onset is 8-10 nT higher than the value for isolated substorms. The average values of the total magnetic flux at the sawtooth and isolated substorm onsets are ~1 GWb and ~0.68 GWb, respectively, and the relative decrease of the magnetic flux from the maximum value at the onset to the minimum value after the onset is ~25%. The magnetospheric mode depends on the solar wind and on the maximum magnetic flux in the polar cap/magnetotail. Sawtooth events tend to occur at higher merging electrical field. Isolated substorms and SMC tend to occur at lower merging electrical field. Sawtooth events appear to be the only magnetospheric mode when the merging electric field is higher than 6 mV/m and/or when the corrected Dst index is less than -60 nT. The observations show that the sawtooth onset occurs when the magnetotail reaches a critical state. However, the maximum magnetotail total pressure and magnetic flux at the sawtooth/substorm onset is not a constant but increases with the merging electric field and with the corrected Dst index. The variations of the magnetotail parameters and polar cap magnetic flux are consistent with the energy loading-unloading scenario, but the magnetotail total pressure and magnetic flux must reach a larger value for the onset to occur during stronger solar wind driver because of the enhanced ring current. The results of this study provide reasonable explanation of the relatively constant period of sawtooth events. References: Huang, C.-S., and X. Cai (2009), Magnetotail total pressure and lobe magnetic field at onsets of sawtooth events and their relation to the solar wind, J. Geophys. Res., 114, A04204, doi:10.1029/2008JA013807. Huang, C.-S., A. D. DeJong, and X. Cai (2009), Magnetic flux in the magnetotail and polar cap during sawteeth, isolated substorms, and steady magnetospheric convection events, J. Geophys. Res., 114, A07202, doi:10.1029/2009JA014232.
Cai Xu
DeJong Anna D.
Huang Chan Chun
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