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Storm-time magnetic field variations observed by the ETS-VI satellite


To study the ring current structure in the inner magnetosphere, we have statistically examined the magnetic field data acquired by ETS-VI (the Engineering Test Satellite-VI). During a magnetic storm, the Dst index shows a rapid recovery of its amplitude for about 9 hours on average after the main phase and a subsequent long-lasting slow recovery. We have investigated this “two-step recovery” of the Dst index by obtaining magnetic field vectors and calculating the current structure in the inner magnetosphere for each magnetic storm phase determined by the Dst index. From this study, following results are obtained: (1) Throughout the storm-time, disturbed magnetic fields exhibit clear day-night asymmetry with strong peak in the nightside. (2) During the main phase, southward perturbed field components have a relative bump in the nightside region between ~2000 and ~0400 MLT and between ~4.0 and 6.4 RE (geocentric distances in Earth radii). (3) The initial rapid recovery of the Dst index is considerably influenced by the nightside currents flowing between ~1800 and ~0600 MLT and between 5.6 and 7.2 RE. These currents are thought to be mainly composed of the particles that escape the magnetosphere on the duskside flank, which are simulated in particle tracing in a realistic magnetosphere.


  • Akasofu, S.-I., S. Chapman, and D. Venkatesan, The main phase of great magnetic storms, J. Geophys. Res., 68, 3345–3350, 1963.

    Article  Google Scholar 

  • Fok, M.-C., T. E. Moore, J. U. Kozyra, G. C. Ho, and D. C. Hamilton, Three-dimensional ring current decay model, J. Geophys. Res., 100, 9619–9632, 1995.

    Article  Google Scholar 

  • Hamilton, D. C., G. Gloeckler, F. M. Ipavich, W. Stüdemann, B. Wilken, and G. Kremser, Ring current development during the great geomagnetic storm of February 1986, J. Geophys. Res., 93, 14343–14355, 1988.

    Article  Google Scholar 

  • Iijima, T., T. A. Potemra, and L. J. Zanetti, Large-scale characteristics of magnetospheric equatorial currents, J. Geophys. Res., 95, 991–999, 1990.

    Article  Google Scholar 

  • Kozyra, J. U., M.-C. Fok, E. R. Sanchez, D. S. Evans, D. C. Hamilton, and A. F. Nagy, The role of precipitation losses in producing the rapid early recovery phase of the Great Magnetic Storm of February 1986, J. Geophys. Res., 103, 6801–6814, 1998.

    Article  Google Scholar 

  • Langel, R., J. Berbert, T. Jennings, and R. Horner, Magsat data processing: A report for investigators, NASA Tech. Memo., 82160, 1981.

  • Lui, A. T. Y., R. W. McEntire, and S. M. Krimigis, Evolution of the ring current during two geomagnetic storms, J. Geophys. Res., 92, 7459–7470, 1987.

    Article  Google Scholar 

  • Mead, G. D. and D. H. Fairfield, A quantitative magnetospheric model derived from spacecraft magnetometer data, J. Geophys. Res., 80, 523–542, 1975.

    Article  Google Scholar 

  • Nagai, T., T. Ondoh, H. Matsumoto, T. Goka, T. Fukuda, M. Nosé, T. Iyemori, K. Takahashi, and S. Kokubun, ETS-VI magnetic field observations of the near-Earth magnetotail during substorms, J. Geomag. Geoelectr., 48, 741–748, 1996.

    Article  Google Scholar 

  • Nakai, H., Y. Kamide, and C. T. Russell, Statistical nature of the magnetotail current in the near-Earth region, J. Geophys. Res., 102, 9573–9586, 1997.

    Article  Google Scholar 

  • Roelof, E. C., Energetic neutral atom image of a storm-time ring current, Geophys. Res. Lett., 14, 652–655, 1987.

    Article  Google Scholar 

  • Sibeck, D. G., R. W. McEntire, A. T. Y. Lui, R. E. Lopez, S. M. Krimigis, R. B. Decker, L. J. Zanetti, and T. A. Potemra, Energetic magnetospheric ions at the dayside magnetopause: leakage or merging? J. Geophys. Res., 92, 12097–12114, 1987.

    Article  Google Scholar 

  • Sugiura, M. and D. J. Poros, A magnetospheric field model incorporating the OGO 3 and 5 magnetic field observations, Planet. Space Sci., 35, 1763–1773, 1973.

    Article  Google Scholar 

  • Takahashi, S. and T. Iyemori, Three-dimensional tracing of charged particle trajectories in a realistic magnetospheric model, J. Geophys. Res., 94, 5505–5509, 1989.

    Article  Google Scholar 

  • Takahashi, S., T. Iyemori, and M. Takeda, A simulation of the storm-time ring current, Planet. Space Sci., 38, 1133–1141, 1990a.

    Article  Google Scholar 

  • Takahashi, S., T. Iyemori, and M. Takeda, Ring current response to impulsive southward IMF: a cause of second development of the Dst index, J. Geomag. Geoelectr., 42, 1325–1331, 1990b.

    Article  Google Scholar 

  • Tsyganenko, N. A., Global quantitative models of the geomagnetic field in the cislunar magnetosphere for different disturbance levels, Planet. Space Sci., 35, 1347–1358, 1987.

    Article  Google Scholar 

  • Tsyganenko, N. A., Effects of the solar wind conditions on the global magnetospheric configuration as deduced from data-based field models, in Proc. of 3rd International Conference on Substorms (ICS-3), Versailles, France, 12–17 May 1996, ESA SP-389, 181–185, 1996.

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Correspondence to N. Terada.

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Terada, N., Iyemori, T., Nosé, M. et al. Storm-time magnetic field variations observed by the ETS-VI satellite. Earth Planet Sp 50, 853–864 (1998).

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