Steady magnetospheric convection (SMC)

spaceweb@oulu.fi - last update: 27 November 1998, 2310 UT (RR)

Observations have shown that, under steady southward IMF conditions lasting several hours, the whole magnetosphere can remain in a state where no substorms occur at all (e.g., Sergeev, 1977). These periods have been called "steady magnetospheric convection" or SMC events (Yahnin et al., 1994). They are interesting because many theoretical considerations have indicated that such a steady state is not possible (e.g., Erickson and Wolf, 1980).

One SMC event, from 24 November, 1981, was studied by Yahnin et al. (1994). The IMF Bz was about -5 nT for more than 10 hours without any substorms occurring. DE 1 imager observations show very stable level of magnetic flux threading the polar cap for at least 3.5 hours during the event. The equivalent current system showed a two-cell convection pattern usually seen during the growth phase, and the dayside auroral oval was at unexpectedly low latitudes. On the other hand, the auroral display during the period was similar to that seen at maximum stage of substorm expansion phase. The most active region was located at the nightside, high-latitude part of the auroral oval, and it formed a bulgelike feature. On the evening side it was bordered by a surgelike structure and, on the morning side, by depletion of auroral precipitation. This may indicate precense of field aligned currents resembling, for example, substorm current wedge (SCW). The localized active region was suggested to correspond to the ionospheric image of the far tail reconnection region.

References

Erickson, G. M. and R. A. Wolf, Is steady convection possible in the Earth's magnetotail?, Geophys. Res. Lett., 7, 897-900, 1980.
Sergeev, V. A., On the state of the magnetosphere during prolonged period of southward oriented IMF, Phys. Solarterr., 5, 39-, 1977.
Yahnin, A., M. V. Malkov, V. A. Sergeev, R. J. Pellinen, O. Aulamo, S. Vennerström, E. Friis-Christensen, K. Lassen, C. Danielsen, J. D. Craven, C. Deehr, and L. A. Frank, Features of steady magnetospheric convection, J. Geophys. Res., 99, 4039-4051, 1994.