Reconnection and its Relation to Auroral Physics Observation and Theory Uppsala, April 2004

Magnetospheric Field Line Structure (Empirical Tsyganenko Model) X (R E ) Z (R E ) Solar Wind B X-point Magnetopause Magnetosheath Bow Shock Lobes

The Meaning of Reconnection Axford 1984

Generalized Ohm´s Law (Fluid Approach) E + v  B -  j = (  0  pe 2 ) -1  t j +  (jv + vj – (en) -1 j j)} + (en) -1 { j  B -  P e + F epmf  Inertial term Hall term Wave pmf In quasi-equilibrium the electron pressure gradient term is the ion pressure term, for then: j  B -  P e   ·P i Assumptions: two-fluid (protons/electrons) ideal conditions ~ collisionless m e /m i <<1,   0 [ Wave ponderomotive force usually neglected without justification (?) May be important in a turbulent plasmasheet ]

Dispersion Relations No guide field: Alfvén whistler With guide field: Kinetic Alfvén wave Wang et al. JGR 105, 2000

Estimates of Reconnection Rate No guide field: HALLWith guide field: Pressure

Reconnection Models Sweet-Parker resistive Petschek resistive Hill variant of Petschek Sonnerup mixed non-resistive (Hall) Simulations –Resistive –Collisionless Hybrid – Vlasov – Full-Particle

Magnetospheric Requirements Location outside ionosphere Total non-collisionality mfp ~ 1 AU No Parker-Sweet Petschek only if anomalous  an =e 2 n/m e an –Localized resistivity –Problem of generation of anomalous collisions –No strong wave activity observed so far ! –Reconnection is (probably) collisionless Bursty Bulk Flows |v| ~ v A Generation of Field-Aligned Currents Acceleration of Ions and Electrons < 300 keV Fast reconnection (electron scales)

Runov et al Jetting and Field Line Curvature (Cluster Tail Observations)

Frey et al. (2003) Poleward Reconnection for Northward IMF (Cluster Observations)

Geotail/Equator-S Conjunction Phan et al., Nature 404, 848, 2000

Magnetopause Reconnection Phan et al., Nature 404, 848, 2000

Conditions for Hall Effect Hall effect exists only in region with distinct separation of electron and ion motion Hence in region where by some external means (e.g. geometry) the ions remain unmagnetized while the electrons are magnetized The required motion is the normal E  B drift in the collisionless case Otherwise also pressure gradient drifts contribute when the transverse pressure gradient generates a transverse electric potential RECONNECTION IS IDEALLY SUITED FOR HALL EFFECT IN RANGE e < L < i around the X-line as scales imposed by reconnection geometry here i.e. ions do really decouple from electron motion with electrons remaining frozen-in and moving inward towards the X-line where they locally decouple on scale L < e

Reconstruction of Hall Current System in the Magnetotail (Nagai et al., 1998, 2001) Electron Hall Current System i Unmagnetised Ions Unmagnetised Electrons e

Hall-Current System j H = 0 j H  0 Hall Currents Closure of Hall Currents Via Field Aligned Currents   O  O 

Relation between Hall/FACs and Field-aligned Electron Fluxes in Tail Reconnection V in = E  B v out ~ v A Hall Current j H FACs downward upward no FAC upward Electrons downward Electrons Slow E  B inflow implies narrow region of downward FAC/upward e - Fast reconnection outflow implies broad region of upward FAC/ downward e - - Fluxes (in this model) equatorward B

Hall-Effect in Magnetotail 1 Nagai et al., JGR 106, 25929, 2001 Received 12. July 2000

Hall-Effect in Magnetotail 2 Oieroset et al., Nature 412, 416, 2001 Received 1. May 2001

Hall-Electron Distribution Asano et al., JGR 109, A02212, 2004

Schematics of Tail-Hall-Region

Magnetopause Reconnection Mozer et al., PRL 89, 2002

Electron Acceleration in Magnetotail Reconnection Oieroset et al. (2002) FAC‘s connected to Hall Current Wrong ! No Hall current ! Reconnection Region Acceleration of Electrons

Lower-hybrid Waves at Magnetopause Bale et al., GRL 24, 2180, 2002

Lower-Hybrid-Drift Instability Shinohara et al., PRL 87, 2001

Lower-hybrid Drift Waves without and with Guide Field Scholer et al. PoP 10, 3521, 2003

Normal Magnetic Component in 3D Scholer et al. PoP 10, 3521, 2003 no guide fieldwith guide field

3D-Tail-Reconnection Pritchett & Coroniti JGR 109, 2004Scholer et al. PoP 10, 3521, 2003

Distribution Functions Drake et al. Science 299, 2003 Scholer et al. PoP 10, 3521, 2003 With guide field

Pritchett‘s 3D Simulation Distributions Stack plot of E|| Propagating wavesHeating and acceleration

Electron Velocity and E|| Pritchett & Coroniti 2004

3D-Reconnection Electron Distributions Pritchett & Coroniti 2004 outside X-linein X-line

Guide Field Simulation Drake et al. Science 299, 2003

Electric fields in guide field case Drake et al. Science 299, 2003

Non-Hall Reconnection m e =m i Schematic view Initialization Jaroschek et al. 2004

Reconnection Without Hall Effect: The Case m i = m e Magnetic Field Electric Induction Field Wave Electric Field — Evolution of magnetic islands (primary and secondary x-points) — Evolution of DC electric induction fields in regions of field conversion — Finite extent of DC electric field in the third (y) dimension — Evolution of Buneman and Drift Modes in the xy-plane — Particles accelerated in induction and wave electric field xz-plane xy-plane Jaroschek et al. 2004

Acceleration in No-Hall 3D-reconnection Jaroschek et al. PoP 11, 2004

3D Fields in Reconnection Jaroschek et al. PoP 11, 2004

Auroral zone physics Ergun et al. PoP 9, 2002

Auroral zone physics Ergun et al. PoP 9, 2002 Electric fieldElectron distribution

Evidence for Hall Region-Aurora Coupling Observed sequence in auroral current and flux Narrow upstream (downward current) electron flux regions versus broad (upward current) downstream (inverted V-event) regions Downward electrons  High energies (accelerated) Upward electrons  Low energies (ionospheric)

Ionospheric Signature of FA-Currents An Example from FAST

BB Field-aligned Currents Electron Flux downward upward down { e-e- 80 seconds Ionospheric Signature of FA-Currents An Example from FAST J  Low (ionospheric) energies High (accelerated) energies No flux-no FAC

Electron Distributions Oieroset et al., PRL 2002 Treumann et al., PoP 2004

Hu and Sonnerup JGR 108, 2003 Magnetopause Reconstruction

Lyon, Science 288, 2000

Nagai et al. (2002)

Tail-Hall-Reconnection Parameters

Kink-Mode Formation in Reconnection

Collisionless Reconnection Scaling

2D-Current Layers in Reconnection Lyon, Science 288, 2000 Ion current Electron current

Dispersive Waves in Reconnection Rodgers et al., PRL 87, 2001

Lower-hybrid Driven Reconnection Shinohara et al. PRL 87, 2001

Hall-MHD-Simulations Wang et al. JGR 105, 2000 J|| E|| Reconnection with guide field Ey Jy

Guide field in the simulation By Bz

Nonsymmetric MP Reconnection

Ergun et al. PoP 9, 2002 Auroral zone physics

Wind Observations of Hall Effect Øieroset et al. (2001) Hall Field

Particles in Hall-Reconnection Asano et al., 2004

3D Hall Region at Magnetopause Mozer et al. (2002) Hall-B y Field 3D-Signature in Hall E x Polar