Auroral activity associated with Kelvin-Helmholtz instability at the inner edge of the low-latitude boundary layer
- NASA/Goddard Space Flight Center, Greenbelt, MD (United States)
- Univ. of Oslo (Norway)
Auroral activity occurred in the late afternoon sector ({approximately} 16 MLT) in the northern hemisphere during the passage at Earth of an interplanetary magnetic cloud on January 14, 1988. The auroral activity consisted of a very dynamic display which was preceded and followed by quiet auroral displays. During the quiet displays, discrete rayed arcs aligned along the geomagnetic L shells were observed. In the active stage, rapidly evolving spiral forms centered on magnetic zenith were evident. The activity persisted for many minutes and was characterized by the absence of directed motion. They were strongly suggestive of intense filaments of upward field-aligned currents embedded in the large-scale region 1 current system. The authors assess as possible generating mechanisms three nonlocal sources known to be associated with field-aligned currents. Of these, partial compressions of the magnetosphere due to variations of solar wind dynamic pressure seem an unlikely source. The possibility that the auroral forms are due to reconnection is investigated but is excluded because the active aurora were observed on the closed field line region just equatorward of the convection reversal boundary. To support this conclusion further, the authors apply recent results on the mapping of ionosphere regions to the equatorial plane based on the Tsyganenko 1989 model. They find that for comparable magnetic activity the aurora map to the equatorial plane at X{sub GSM} = {approximately} 3 R{sub E} and {approximately} 2 R{sub E} inward of the magnetopause, that is, the inner edge of the boundary layer close to dusk. Since the auroral forms are manifestly associated with magnetic field shear, a vortical motion at the equatorial end of the flux rope is indicated, making the Kelvin-Helmholtz instability acting at the inner edge of the low-latitude boundary layer the most probable generating source. 47 refs., 5 figs.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 50529
- Journal Information:
- Journal of Geophysical Research, Vol. 99, Issue A10; Other Information: PBD: 1 Oct 1994
- Country of Publication:
- United States
- Language:
- English
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