reconnection and its relation to auroral physics observation and theory uppsala, april 2004
TRANSCRIPT
Reconnection and its Relation to Auroral Physics
Observation and Theory
Uppsala, April 2004
Magnetospheric Field Line Structure (Empirical Tsyganenko Model)
X (RE)
Z (
RE)
Solar Wind
B
X-point
Magnetopause
Magnetosheath
Bow S
hock
Lobes
1
3
2
1
3
The Meaning of Reconnection
Axford 1984
Generalized Ohm´s Law(Fluid Approach)
E + v B - j = (0pe2)-1t j + (jv + vj – (en)-1j j)} + (en)-1{ j B - Pe + Fepmf
Inertial term Hall term Wave pmf
In quasi-equilibrium the electron pressure gradient term is the ion pressure term, for then:
j B - Pe ·Pi
Assumptions: two-fluid (protons/electrons)
ideal conditions ~ collisionless
me/mi <<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: HALL With 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=e2n/mean
– Localized resistivity– Problem of generation of anomalous collisions – No strong wave activity observed so far !– Reconnection is (probably) collisionless
• Bursty Bulk Flows |v| ~ vA
• Generation of Field-Aligned Currents• Acceleration of Ions and Electrons < 300 keV
• Fast reconnection (electron scales)
Runov et al. 2003
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-lineas scales imposed by reconnection geometry herei.e. ions do really decouple from electron motion
with electrons remaining frozen-in and moving inward towards the X-linewhere 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
jH = 0
jH = 0
jH = 0
jH 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
Vin = E B
vout ~ vA
Hall Current jH
FACs
downward
upward
no FAC
upward Electrons
downward Electrons
Slow EB 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 field with guide field
3D-Tail-Reconnection
Pritchett & Coroniti JGR 109, 2004 Scholer 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
DistributionsStack plot of E||
Propagating waves Heating and acceleration
Electron Velocity and E||
Pritchett & Coroniti 2004
3D-Reconnection Electron Distributions
Pritchett & Coroniti 2004
outside X-line in 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 me=mi
Schematic view Initialization
z
y
x
Lx
Ly
0
Jaroschek et al. 2004
Reconnection Without Hall Effect: The Case mi = me
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 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 field Electron 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
Field-aligned Currents
Electron Flux
downwarddownwardupward
upward upwarddown
{e-
80 seconds
Ionospheric Signature of FA-Currents An Example from FAST
J
J
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-By Field
3D-Signature in Hall Ex
Polar