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3D Current Topology in the Vicinity of an Evening Arc

3D Current Topology in the Vicinity of an Evening Arc. O. Marghitu (1,3), G. Haerendel (2), B.Klecker (3), and J.P. McFadden (4) Institute for Space Sciences, Bucharest, Romania International University of Bremen, Germany Max-Planck-Inst. f. extraterr. Physik, Garching, Germany

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3D Current Topology in the Vicinity of an Evening Arc

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  1. 3D Current Topology in the Vicinity of an Evening Arc O. Marghitu (1,3), G. Haerendel (2), B.Klecker (3), and J.P. McFadden (4) • Institute for Space Sciences, Bucharest, Romania • International University of Bremen, Germany • Max-Planck-Inst. f. extraterr. Physik, Garching, Germany • Space Sciences Lab., Univ. of California at Berkeley, US EGS-AGU-EUG, Nice, April 9, 2003 Credit: Jan Curtis, http://climate.gi.alaska.edu/Curtis

  2. Acknowledgement C. Carlson – FAST R. Ergun – FAST Electric field R. Strangeway – FAST Magnetic field FAST Team J. Vogt, H. Frey – Optical data World Data Center for Geomagnetism, Kyoto – AE Index

  3. Contents • Experimental setup: FAST and ground based optics • Data: Optical and FASTmeasurements • Current topology • Summary • Prospects

  4. Setup: Ground Optics • Low-light CCD cameras developed at MPE, Garching • Wide-angle optics (86ox64o) • Pass band filter • Exposure time 40 ms multiplied with powers of 2 • Digitized images, 768x576x8 • Location: Deadhorse, Alaska, 70.22o LAT, 211.61o LON • Time: Feb. 9, 1997, 8:22UT Photo: courtesy W. Lieb, MPE

  5. Setup: FAST • 2nd NASA SMEX Mission • PI Institution UCB/SSL • Launch: August 21, 1996 • Lifetime: 1 year nominal; still operational • Orbit: 351 x 4175km, 83o • Spin axis perpendicular to the orbit plane • Electric field: three orthogonal boom pairs equipped with spherical probes • Magnetic field: a DC fluxgate and an AC search coil • Mass spectrometry: TEAMS – measures full H+ and O+ distributions in ½ spin and He+ in one spin • Plasma analyzers: IESA, EESA, SESA – high time resolution electron and ion data, with uninterrupted 360o coverage http://www-ssc.igpp.ucla.edu/fast

  6. Data: AE index, Feb. 9, 1997 http://swdcdb.kugi.kyoto-u.ac.jp

  7. Optical Data: 8 min N E Selection of images, 1 min apart, taken at UT 8:18 – 8:26. FAST crosses the camera´s FoV in the frames 4, 5, 6; the satellite´s ionospheric footprint is shown as a square. The limits of the ion beams detected by FAST are overlaid in all the frames, to provide a reference.

  8. Optical Data: 1 min Images 4 s apart during 8:22-8:23. FAST footprint is shown as a square. ´11´ and ´22´ are the limits of the first two ion beams. The arc is stable and drifts with ~200m/s, equivalent to ~10mV/m (assuming the arc has no proper motion).

  9. FAST Data: Trajectory Magnetic noon at the top N=magnetic pole X=arc FAST Path Auroral Oval Terminator at 110km

  10. FAST Data: Large Scale Top: Potential. Middle: Magnetic field in the Satellite Associated System (SAS). Bottom: Magnetic field in the Arc Associated System (AAS).

  11. FAST Data: Medium Scale Panel 1: Magnetic field. Panels 2-4: Electrons, energy. Panel 5: Electrons, p.-a. Panels 6: Ions, energy Panels 7: Ions, p.-a. Panel 8: Electric potential The arc is north of the convection reversal

  12. Current Configuration: FR vs. CR The relative positions of the FAC reversal (FR), the convection reversal (CR), and the arc. The CR is very close to the FR and just a negligible fraction of the downward FAC returns to the magnetosphere as upward FAC.

  13. Current Configuration: Flow Topology Type 1 Type 2 From Bostrom (1964) Current Electric field Plasma convection

  14. Current config: quantitative evaluation Conductance from particle precipitation + • Electric field • High-altitude data cannot be mapped to ionosphere when FAST crosses the AAR • FAST does not measure the E–W electric field • Method based on a parametric model of the arc, prezented in the poster session. In order to obtain consistent results one has to take into account, as a minimum: • Ionospheric polarization => Exnot const. => a1 , ..... , an • Hall current perpendicular to the arc => Ehnot 0 => b0 • Coupling FAC – electrojet => Jhnot divergence free => c1 Current

  15. Current config: quantitative evaluation Jx , Jh, J||

  16. Summary • 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 data suggests the standard Bostrom Type 2 (1B2) configuration, the current topology looks like 2 times Bostrom Type 1 (2B1)

  17. Prospects • Check the current topology for other orbits. First step: the relative positions of FR and CR. • Investigate the conditions under which the 1B2 topology develops. • Check the results with ground observations, when conjugated data exists.

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