Pseudobreakups

SpaceWeb@SkyNet.oulu.fi - last update: 5 June 1996, 2100 UT (RR)

Pseudobreakups (Akasofu, 1964) are short-lived auroral substorm-like events that don't grow to the strength of a substorm. They can occur as

substorm precursors (e.g., Koskinen et al., 1993)
isolated events during quiet times (Sergeev et al., 1986)
isolated events during Steady Magnetospheric Convection (SMC) times
- SMCs are periods of enhanced non-substorm activity during prolonged southward IMF

Pseudobreakups have most of the signatures found in real substorms, like

injections (localized)
dipolarization (localized)
current disruption (localized, possibly partly closed within plasmasheet)
- Ohtani et al. (1993) propose that the major difference between pseudobreakups and substorms is the absense of the expansion of the current disruption
thin current sheet (TCS)
- Sergeev (ICS-3) suggested that the lenght of TCS in the x-direction might be shorter for pseudobreakups than for substorms
ground-based magnetic disturbances up to several hundred nT
Pi2 pulsations (weak)
quasi-neutral current sheet
reconnection (but possibly only local plasma sheet reconnection bursts, and no open flux reconnection or plasmoids)

However, only substorms are associated with a significant poleward expansion of auroras and currents in the ionosphere. The spatial scale of the substorms in the longitudinal direction is, on the other hand, more complicated thing (Koskinen et al., 1993).

At least two reasons have been suggested why pseudobreakups don't grow into a real substorm:

Amount of energy stored in the tail is not sufficient (Ohtani et al., 1993; Nakamura et al. 1994)
- however, some claim that there is always enough energy for a substorm !
Ionosphere prohibits real SCW formation (Koskinen et al., 1993)

References

Akasofu, S.-I., The development of auroral substorm, Planet. Space Sci., 12, 273-, 1964.
Koskinen, H. E. J., R. E. Lopez, R. J. Pellinen, T. I. Pulkkinen, D. N. Baker, and T. Bösinger, Pseudobreakups and substorm growth phase in the ionosphere and magnetosphere, J. Geophys. Res., 98, 5801-5813, 1993.
Nakamura, R., D. N. Baker, T. Yamamoto, R. D. Belian, E. A. Bering III, J. R. Benbrook, and J. R. Theall, Particle and field signatures during pseudobreakup and major expansion onset, J. Geophys. Res., 99, 207-221, 1994.
Ohtani, S., B. J. Anderson, D. G. Sibeck, P. T. Newell, L. J. Zanetti, T. A. Potemra, K. Takahashi, R. E. Lopez, V. Angelopoulos, R. Nakamura, D. M. Klumpar, and C. T. Russell, A multisatellite study of a pseudo-substorm onset in the near-Earth magnetotail, J. Geophys. Res., 98, 19355-19367, 1993.
Sergeev, V. A., A. G. Yahnin, R. A. Rakhmatulin, S. I. Solovjev, F. S. Mozer, D. J. Williams, and C. T. Russell, Permanent flare activity in the auroral zone, Planet. Space Sci., 34, 1169-, 1986.