2003 Fiscal Year Final Research Report Summary
A study of magnetotail dynamics during substorms using high-time resolution data
| Project/Area Number |
13640449
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Space and upper atmospheric physics
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| Research Institution | Nagoya University |
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Principal Investigator |
SHIOKAWA Kazuo Nagoya University, Solar-Terrestrial Environment Laboratory, Associate Professor, 太陽地球環境研究所, 助教授 (80226092)
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| Project Period (FY) |
2001 – 2003
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| Keywords | magnetosphere / substorm / magnetic perturbation / inner magnetosphere / neutral sheet / magnetic reconnection |
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| Research Abstract |
We have investigated various characteristics of magnetic and plasma fluctuations for 21 events of substorm-associated near-Earth dipolarization at Xgsm=-8 --11 Re and |Ygsm|<5 Re, using high-time-resolution data for the magnetic field (1/16 s), plasma moment (12 s), and electric field (3 s) measured by the GEOTAIL satellite in 1995-2000. The dipolarizations are always accompanied by intense fluctuations of the magnetic field. The amplitude of the fluctuations is larger for smaller B (closer to the cross-tail current sheet). We found several events in which the magnetic field elevation angles decreased rapidly prior to the dipolarization (explosive growth phase (EGP)-like features). The magnetic fluctuations are not sinusoidal curves but are spikes of a sudden decrease and increase with a time scale of seconds. In quite a few cases, the fluctuations are accompanied by Earthward convective plasma flow. The spectral shape of the fluctuations has a steeper slope (f^-2.7) at 1.0-0.2 Hz than at 0.01-0.2 Hz (f^-2.0). From the correlation between plasma velocity and magnetic field fluctuations, we estimate the parallel scale sizes of waves with periods of 60 s and 15 s to be about 10 Re and 5 Re, respectively. For the 60-s waves, the magnetic and plasma pressure variations are clearly anti-phase. The total pressure tends to decrease gradually before the dipolarization and increase during and after the dipolarization.
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