Energy Conversion in the Auroral Energy Conversion in the Auroral MagnetosphereMagnetosphere

O. Marghitu (1, 2), M. Hamrin (3), B.Klecker (1) M. André (4),O. Marghitu (1, 2), M. Hamrin (3), B.Klecker (1) M. André (4),S. Buchert (4), J. McFadden (5), H. Vaith (1), S. Buchert (4), J. McFadden (5), H. Vaith (1),

(1) Max-Planck-Institut f(1) Max-Planck-Institut fürür extraterrestrische Physik, Garching, Germany extraterrestrische Physik, Garching, Germany

(2) Institute for Space Sciences, Bucharest, Romania(2) Institute for Space Sciences, Bucharest, Romania

(3) Physics Department, Umeå University, Sweden(3) Physics Department, Umeå University, Sweden

(4) Swedish Institute of Space Physics, Uppsala, Sweden(4) Swedish Institute of Space Physics, Uppsala, Sweden

(5) Space Sciences Lab., University of California at Berkeley, USA(5) Space Sciences Lab., University of California at Berkeley, USA

DPG – AEF DPG – AEF Spring Spring Meeting, Meeting, Berlin, MarchBerlin, March 44, 200, 20055

Outline

A Motivation

B Event on September 20, 2001: Conjunction geometry

C Event study: Data, E•J signature

D Summary and prospects

There is a significant number of theoretical studies on the auroral generator region:

• Analytical => e.g. Rostoker and Boström, 1976

• Semi-analytical => e.g. Lysak, 1985, Vogt et al., 1999

• Numerical simulations => e.g. Birn et al, 1996, Birn and Hesse, 1996

A Motivation A

However, to our knowledge, the experimental investigations of the generator region are missing, as far as the evaluation of E•J is concerned:

• The one s/c missions before Cluster could not fully resolve J

• Both J and (mainly) E are close to the instrumental detection limit

The energy flux of a strong aurora, ~10-2 W/m2, maps to ~10-5 W/m2 in the tail (mapping factor ~1000). If the generator region extends 107 – 108 m along the magnetic field line, the power density is ~10-13 – 10-12 W/m3.

A Motivation A

B Conjunction Geometry B

Cluster in the tail, at ~20RE; FAST above the auroral oval, at ~0.5RE

B Conjunction Geometry B

No ground optical data.No optical data from IMAGE or Polar.

C Event Study: Data C

16 mW/m2 1 mW/m2

C Event Study: E•J C

E•J 5 •10 -13

The signature E•J < 0 not seen in EFW, because it comes mainly form Cluster 1, where ASPOC is off.

D Summary and Prospects D

First experimental evidence for the crossing of an auroral generator region.

The signature in E•J consistent with the order of magnitude

estimate.

Extension of the time interval to 5h => includes two additional

conjunctions with FAST

Potential for a statistical investigation of several events in September – October 2001.

Potential for application to other generator regions (LLBL, ...)