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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 he eines polarlichtbogens
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

preamble

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.

outline
Outline
  • Experimental setup and data
  • Current configuration
  • Summary and prospects
a conjunction map and geophysical data a

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
a optical data a

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
a fast data a

(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.

b current and plasma flow topology b

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

b quantitative evaluation b

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
b tentative equatorial mapping b
B Tentative Equatorial Mapping B

From Heelis and Hanson, 1980

Convection studies based on Atmospheric Explorer C data

From Heelis et al., 1980

c summary c
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.
c prospects c
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.