O. Marghitu (1, 3), G. Haerendel (2, 3), B.Klecker (3), and J.P. McFadden (4)O. Marghitu (1, 3), G. Haerendel (2, 3), B.Klecker (3), and J.P. McFadden (4)

(1)(1) Institute for Space Sciences, Bucharest, RomaniaInstitute for Space Sciences, Bucharest, Romania

(2)(2) International University of Bremen, GermanyInternational University of Bremen, Germany

(3)(3) Max-Planck-Institut fMax-Planck-Institut fürür extraterrestrische Physik, Garching, Germany extraterrestrische Physik, Garching, Germany

(4)(4) Space Sciences Lab., Univ. of California at Berkeley, USASpace Sciences Lab., Univ. of California at Berkeley, USA

AEF Tagung, Kiel, MAEF Tagung, Kiel, Määrz 11, 2004rz 11, 2004

Stromkonfiguration in der NStromkonfiguration in der Näheäheeines Polarlichtbogenseines Polarlichtbogens

Photo: Jan Curtis, http://climate.gi.alaska.edu/Curtis

Preamble

Type 1 Type 2

From Bostrom (1964)

Type 1: Substorm current wedge, convection electrojetsType 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.

A. Experimental setup and data

B. Current configuration

C. Summary and prospects

Outline

A Conjunction Map and Geophysical Data A

Magnetic noon at top; N=Magnetic poleX=Arc: Deadhorse, AK, 70.22o x 211.61o

Time: Feb. 9, 1997, 8:22UTFAST; Aur. Oval ; Terminator at 110km

http://swdcdb.kugi.kyoto-u.ac.jp

Kp = 2Dst = -27

Growth phase of a small substorm

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

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).

NE

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

http://www-ssc.igpp.ucla.edu/fast

(a) Electrons(b) Ions

(c) Potential(d) Sheet current(e) Mag. Perturb.

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

Current; Electric field; Plasma convectionFR=FAC reversal; CR=Convection reversalAS, AN=Southern and northern arc edges

B Quantitative Evaluation B

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 => E not const. • El. field parallel to arc => E not 0• FAC – EJ coupling => J not div free

Current

Conductance from particle precipitation

+

B Tentative Equatorial Mapping B

From Heelis and Hanson, 1980

From Heelis et al., 1980

Convection studies based on Atmospheric Explorer C data

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

•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.