Abstract
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)
Highlights
The transient bursty bulk flows (BBFs) provide the largest contribution to the plasma and magnetic flux transport in the plasma sheet (Angelopoulos et al, 1992; Baumjohann, 1993)
Was a close temporal-spatial relationship found for auroras and isolated BBF events, but the absence of perpendicular plasma flows in the plasma sheet in the absence of the auroral activations was shown (Ieda et al, 2003)
This study provides the parameters of streamer-related convection, field-aligned currents and precipitation, which are important for addressing the generation mechanisms of auroral streamers and constraining the corresponding models
Summary
The transient bursty bulk flows (BBFs) provide the largest contribution to the plasma and magnetic flux transport in the plasma sheet (Angelopoulos et al, 1992; Baumjohann, 1993). A close relationship between the fast bursty plasma sheet flows (BBFs) and auroral activations was confirmed observationally for a wide range of activity and for different types of transient auroral structures, including the localized auroral brightenings and pseudobreakups, and north-south auroras (or auroral streamers) (Fairfield et al, 1999; Ieda et al, 2001; Nakamura et al, 2001b; Sergeev et al, 2000, 2001; Lyons et al, 1999). Many important questions concerning the character of the precipitation (especially ion precipitation), its relationship with the convection structure, and field-aligned currents still remain open These questions could be better addressed with the precipitation, electric and magnetic fields probed simultaneously by the low altitude spacecraft. This is the purpose of our study in which we analyse a dozen streamer crossings made by three DMSP spacecraft that occured while their dynamics were monitored by the Polar UVI instrument
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