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Stromkonfiguration in der N ähe eines Polarlichtbogens

Stromkonfiguration in der N ähe eines Polarlichtbogens. O. Marghitu (1, 3), G. Haerendel (2, 3), B.Klecker (3), and J.P. McFadden (4) Institute for Space Sciences, Bucharest, Romania International University of Bremen, Germany

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Stromkonfiguration in der N ähe eines Polarlichtbogens

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  1. Stromkonfiguration in der Näheeines Polarlichtbogens • O. Marghitu (1, 3), G. Haerendel (2, 3), B.Klecker (3), and J.P. McFadden (4) • Institute for Space Sciences, Bucharest, Romania • International University of Bremen, Germany • Max-Planck-Institut für extraterrestrische Physik, Garching, Germany • Space Sciences Lab., Univ. of California at Berkeley, USA • AEF Tagung, Kiel, März 11, 2004 Photo: Jan Curtis, http://climate.gi.alaska.edu/Curtis

  2. Type 1 Type 2 Preamble From Bostrom (1964) Type 1: Substorm current wedge, convection electrojets Type 2: Auroral arcs, large scale Birkeland currents Our case: The current circuit resembles Type 1 in the vicinity of a wide, stable, winter evening arc.

  3. Outline • Experimental setup and data • Current configuration • Summary and prospects

  4. http://swdcdb.kugi.kyoto-u.ac.jp Growth phase of a small substorm Magnetic noon at top; N=Magnetic pole X=Arc: Deadhorse, AK, 70.22o x 211.61o Time: Feb. 9, 1997, 8:22UT FAST; Aur. Oval ; Terminator at 110km Kp = 2 Dst = -27 A Conjunction Map and Geophysical Data A

  5. N E Photo: courtesy W. Lieb, MPE Images 4s apart, 8:22 – 8:23. FAST footprint shown as a square. The arc is stable and drifts southward, ~200m/s, equivalent to ~10mV/m westward (if the arc has no proper motion). A Optical Data A • Low-light CCD cameras developed at MPE • Wide-angle optics (86ox64o) • Pass band filter, 650nm • Exposure time 20ms • Digitized images, 768x576x8

  6. (a) Electrons (b) Ions http://www-ssc.igpp.ucla.edu/fast (c) Potential (d) Sheet current (e) Mag. Perturb. A FAST Data A • 2nd NASA SMEX Mission • PI Institution UCB/SSL • Launch: August 21, 1996 • Lifetime: 1 year nominal; still alive • Orbit: 351 x 4175km, 83o • Full set of plasma and field sensors CR very close to FR. Just a small bit of the dwd. FAC returns to magnetosphere as upwd. FAC.

  7. Type 1 Type 2 B Current and Plasma Flow Topology B Current; Electric field; Plasma convection FR=FAC reversal; CR=Convection reversal AS, AN=Southern and northern arc edges

  8. Conductance from particle precipitation + • Electric field • Data cannot be mapped to ionosphere when FAST crosses the AAR • FAST does not measure the DC E–W electric field • The new ALADYN method, based on a parametric arc model, can be used north of the CR: • Polarization => Exnot const. • El. field parallel to arc => Ehnot 0 • FAC – EJ coupling => Jhnot div free Current B Quantitative Evaluation B

  9. B Tentative Equatorial Mapping B From Heelis and Hanson, 1980 Convection studies based on Atmospheric Explorer C data From Heelis et al., 1980

  10. C Summary C • Because of the close proximity of the CR and FR the downward and upward FACs appear to be electrically separated in the ionosphere. • The current continuity is achieved at the expense of the electrojets. • Although the magnetic field signature suggests the standard ’Type 2’ configuration, the current topology resembles the ’Type 1’, in a modifed realisation, with the FAC distributed along the arc.

  11. C Prospects C • Current topology for other FAST orbits. First step: FR vs. CR. • Check the results with conjugated ground data, when available. • Is there any association with the substorm growth phase? • Model the complete current circuit, including the magnetospheric closure.

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