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Just as magnetic storms are composed of substorms, the substorms themselves seem to be composed of smaller scale events. The concept of "multiple substorm onsets" was even included in the substorm definition by Rostoker et al. (1980), and there is a huge amount of studies verifying the existense of substorm finestructure. Processes with two different time scales seem to be operating but, as yet, there is no concensus on the terminology.

5-10 min (recurrence time 10-20 min)

  • Called as
    • intensification (Rostoker et al., 1980)
    • microsubstorm (Sergeev, 1977)
  • Observed as
    • steplike expansion of the auroral bulge (Vorobjev and Rezenov, 1973; Sergeev and Yahnin, 1979; Murphree and Cogger, 1992; Nakamura et al., 1993)
    • changes in the substorm related electrojet intensity and riometer absorption (Sergeev, 1974; Wiens and Rostoker, 1975)
    • appearance of Pi 2's (Pytte et al., 1976)
    • bursts of bremsstrahlung X-rays (Lazutin et al., ICS-3)
    • multiple injections of high energy particles in the near-Earth tail
    • bursty bulk flows (BBF)
  • Separate auroral intensifications may occur at different local time sectors; however, an intensification itself is localized also in space (Yahnin et al., 1990)

1 min (recurrence time 1.5-3 min)

  • Called as
    • impulsive dissipation event (IDE; Sergeev et al., 1996)
    • elementary event (Sergeev et al., 1986a,b)
    • activation (Lazutin et al., manuscript 1996)
  • Observed as
    • auroral arc flares at the front of the auroral bulge, i.e., formation of new arcs at the poleward boundary (Sergeev and Yahnin, 1979; Yahnin et al., 1990)
    • Pi B bursts (Bösinger et al., 1981; Bösinger and Yahnin, 1987)
    • fine structure in the bursts of bremsstrahlung X-rays (Lazutin et al., ICS-3)
    • injection finestructure (Belian et al., 1984; Yahnin et al., 1990; Lazutin et al., ICS-3)
    • flow bursts (FB)

The impulsive character of substorms has also been investigated by Murphree and Elphinstone (1988), Williams et al. (1990), Shephard et al. (1990); Sauvaud et al. (1987); Krimigis et al. (1979), Scholer and Roth (1987); Sergeev (1977).

References

  • Belian, R. D., D. N. Baker, E. W. Hones, P. R. Highbie, High-energy proton drift echoes: Multiple peak structure, J. Geophys. Res., 89, 9101-9106, 1984.
  • Bösinger, T., K. Alanko, J. Kangas, H. J. Opgenoorth, and W. Baumjohann, Correlation between Pi type magnetic micropulsations, auroras, and equivalent current structures during two isolated substorms, J. Atmos. Terr. Phys., 43, 933-945, 1981.
  • Bösinger, T., and A. G. Yahnin, Pi1B type magnetic pulsations as a high time resolution monitor of substorm development, Ann. Geophysicae, 5A, 231-238, 1987.
  • Krimigis, S. and E. T. Sarris, Energetic particle bursts in the Earth's magnetotail, in "Dynamics of the magnetosphere", ed. S.-I. Akasofu, pp. 599-618, 1979.
  • Murphree, J. S. and L. L. Cogger, Observation of substorm onset, Proceedings of the International Conference on Substorms (ISC-1), ESA SP-335, 207-212, 1992.
  • Murphree, J. S. and R.D. Elphinstone, Correlative studies using the VIKING imagery, Adv. Space Res., 8, (9)9-(9)19, 1988.
  • Nakamura, R., T. Oguti, T. Yamamoto, and S. Kokubun, Equatorward and poleward expansion of the auroras during auroral substorms, J. Geophys. Res., 98, 5743-5759, 1993.
  • Pytte, T., R. L. McPherron, and S. Kokubun, The ground signatures of the expansion phase during multiple onset substorms, Planet. Space Sci., 24, 1115-1132, 1976.
  • Rostoker, G., S.-I. Akasofu, J. C. Foster, R. A. Greenwald, Y. Kamide, K. Kawasaki, A. T. Y. Lui, R. L. McPherron, and C. T. Russell, Magnetospheric substorms-definition and signatures, J. Geophys. Res., 85, 1663-1668, 1980.
  • Sauvaud, J. A., J. P. Treilhou, A. Saint-Marc, J. Dandouras, H. Reme, A. Korth, G. Kremser, G. K. Parks, A. N. Zaitsev, V. Petrov, L. Lazutin, and R. Pellinen, Large scale response of the magnetosphere to a southward turning of the interplanetary magnetic field, J. Geophys. Res., 92, 2365-2376, 1987.
  • Sergeev, V. A., On the classification of magnetospheric disturbance phenomena, Phys. Solariterr., 4, 19-36, 1977.
  • Sergeev, V. A., On the longitudinal localization of substorm active region and its changes during the substorm, Planet. Space Sci., 22, 1341-1343, 1974.
  • Sergeev, V. A., T. Bösinger, and A. T. Y. Lui, Impulsive processes in the magnetotail during substorm expansion, J. Geophys., 60, 175-185, 1986a.
  • Sergeev, V. A., R. J. Pellinen, T. Bösinger, W.Baumjohann, P. Stauning, and A. T. Y. Lui, Spatial and temporal characteristics of impulsive structure of magnetospheric substorms, J. Geophys., 60, 186-198, 1986b.
  • Sergeev, V. A., T. I. Pulkkinen, and R. J. Pellinen, Coupled-mode model for the magnetospheric substorms, submitted to J. Geophys. Res., 1996.
  • Sergeev, V. A. and A. G. Yahnin, The features of auroral bulge expansion, Planet. Space Sci., 27, 1429-1440, 1979.
  • Shepard, G. G. and M. S. Murphree, Diagnosis of auroral dynamics using global auroral imaging with emphasis on localized and transient features, in "Auroral Physics", eds. C.-I. Meng, M. J. Rycroft and L. A. Frank, Cambridge Univ. Press, Cambridge, U.K., pp. 289-298, 1990.
  • Scholer, M. and D. Roth, A simulation on reconnection and small-scale plasmoid formation, J. Geophys. Res., 92, 3223-3233, 1987.
  • Vorobjev, V. G. and B. V. Rezhenov, Progressive westward displacement of the region of the auroral substorm localization in conjunction with impulsive variations of the magnetic field, Inst. Ass. Geomagn. Aeron., 34, 441-449, 1973.
  • Wiens, R. G. and G. Rostoker, Characteristics of the development of the westward electrojet during the expansion phase of the magnetospheric substorm, J. Geophys. Res., 80, 2109-2128, 1975.
  • Williams, P. J. S., T. S. Virdi, S. W. H. Cowley, and M. Lester, Short-lived bursts of plasma velocity in the auroral zone. 1. Observational evidence from radar measurements, J. Atmos. Terr. Phys., 52, 421-430, 1990.
  • Yahnin, A. G., T. Bösinger, J. Kangas, and R. D. Belian, Some implications on substorm dynamics inferred from correlations between multiple flux peaks of drifting high-energy proton clouds and ground observations, Ann. Geophysicae, 8, 327-336, 1990.
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