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Ann. Geophys., 22, 537-548, 2004
www.ann-geophys.net/22/537/2004/
© European Geosciences Union 2004
Auroral streamers: characteristics of associated precipitation,convection and field-aligned currents
V. A. Sergeev1, K. Liou2, P. T. Newell2, S.-I. Ohtani2, M. R. Hairston3, and F. Rich4
1Institute of Physics, St. Petersburg State University, Ulyanovskaya 1, Petrodvoretz, 198504, St. Petersburg, Russia
2The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, 20723, USA
3Center for Space Sciences, University of Texas at Dallas, USA
4AFRL, Hanscom Air Force Base, MA 01731, USA
Abstract. During the long-duration steady convection activity on 11 December 1998,
the development of a few dozen auroral streamers was monitored by
Polar UVI instrument in the dark northern nightside ionosphere. On many
occasions the DMSP spacecraft crossed the streamer-conjugate regions
over the sunlit southern auroral oval, permitting the investigation of the
characteristics of ion and electron precipitation, ionospheric
convection and field-aligned currents associated with the streamers. We
confirm the conjugacy of streamer-associated precipitation, as well as
their association with ionospheric plasma streams having a substantial
equatorward convection component. The observations display two basic
types of streamer-associated precipitation. In its polewardmost half,
the streamer-associated (field-aligned) accelerated electron
precipitation coincides with the strong (≥2–7μA/m2) upward
field-aligned currents on the westward flank of the convection stream,
sometimes accompanied by enhanced proton precipitation in the adjacent
region. In the equatorward portion of the streamer, the enhanced
precipitation includes both electrons and protons, often without
indication of field-aligned acceleration. Most of these characteristics
are consistent with the model describing the generation of the streamer
by the narrow plasma bubbles (bursty bulk flows) which are contained on
dipolarized field lines in the plasma sheet, although the mapping is
strongly distorted which makes it difficult to quantitatively interprete
the ionospheric image. The convective streams in the ionosphere, when
well-resolved, had the maximal convection speeds ∼0.5–1km/s,
total field-aligned currents of a few tenths of MA, thicknesses of a few
hundreds km and a potential drop of a few kV across the stream. However,
this might represent only a small part of the associated flux transport
in the equatorial plasma sheet.
Key words. Ionosphere (electric fiels and currents). Magnetospheric
physics (aurroal phenomena; energetic particles,
precipitating)
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