PFISR observations of strong azimuthal flow bursts in the ionosphere and their relation to nightside aurora |
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| Authors: | S Zou LR Lyons MJ Nicolls CJ Heinselman |
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| Institution: | 1. Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, CA 90095, USA;2. Center for Geospace Studies, SRI International, Menlo Park, CA 94025, USA;1. CoRA, NWRA, Boulder, CO 80301, USA;2. SRI International, Menlo Park, CA 94025, USA;3. SRI International, Menlo Park, CA 94025, USA;4. MIT Haystack Observatory, Westford MA 01886, USA;1. Department of Physics, Landmark University, P.M.B. 1001, Omu Aran, Kwara State, Nigeria;2. Department of Physics, University of Ilorin, P.M.B. 1515, Ilorin, Kwara State, Nigeria;1. Centre for Space and Atmospheric Research, Embry-Riddle Aeronautical University, 600 S. Clyde Morris Blvd., Daytona Beach 32114, FL, USA;2. Aalto University, POBox 17800, 00076 AALTO, Finland;1. Astronomical Observatory Zagreb, Croatia;2. Faculty of Science, University of Zagreb, Croatia;3. Royal Belgian Institute for Space Aeronomy (Space Physics and STCE), Brussels, Belgium;4. Earth and Life Institute, TECLIM, Université Catholique de Louvain, Louvain-La-Neuve, Belgium;5. Department of Astronomy and Space Science, Chungbuk National University, Cheongju-si, South Korea;1. Space Research Institute of RAS, Profsoyuznaya ul., 84/32, 117997, Moscow, Russia;2. The Yu.G. Shafer Institute of Cosmophysical Research and Aeronomy, SB of RAS, Yakutsk, Russia;3. Pushkov Institute of Terrestrial Magnetism, The Ionosphere and Radio Wave Propagation Russian Academy of Sciences, Troitsk, Moscow, Russia |
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| Abstract: | Flow bursts within the ionosphere are the ionospheric signatures of flow bursts in the plasma sheet and have been associated with poleward boundary intensifications (PBIs). Some PBIs extend equatorward from the polar cap boundary, where they can be roughly divided into north–south-aligned and east–west-aligned structures. In this paper, we present two flow burst events observed by the new Poker Flat Advanced Modular Incoherent Scatter Radar (PFISR) in the pre-midnight auroral zone on 28 April 2007, one towards the west and the other towards the east. In both cases, enhanced flows lasted for about 8–10 min with peak velocities exceeding 1500 m/s. The concurrently measured electron density showed that the flow bursts occurred in low conductivity regions. However, near the poleward (equatorward) edge of the westward (eastward) flow burst, strong electron density enhancements were observed in the E region, indicating the presence of discrete auroral arcs. Auroral images from the Polar spacecraft were available at the time of the eastward flow burst and they indicate that this burst was associated with an east–west-aligned auroral structure that connected at later MLT to a north–south structure. In addition, simultaneous precipitating particle energy spectrum measured by the the Defense Meteorological Satellites Program (DMSP) F13 satellite reveals that this auroral structure resulted from mono-energetic electron precipitation associated with a significant field-aligned potential drop. These observations show direct evidence of the relationship between flow bursts, field-aligned currents and auroral intensifications, and suggest that eastward/westward flow bursts are associated with east–west-oriented PBI structures that have extended well within the plasma sheet. This is in contrast to the equatorward-directed flow that has been previously inferred for PBIs near the polar cap boundary and for north–south auroral structures. This paper illustrates the use of the PFISR radar for studying the magnetosphere–ionosphere coupling of flow bursts. |
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