Reconnection and its Relation to Auroral Physics

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

2. Magnetospheric Field Line Structure (Empirical Tsyganenko Model) SolarWind Magnetosheath Z (RE) Bow Shock Lobes 3 2 X-point 1 1 3 Magnetopause B X (RE)

3. The Meaning of Reconnection Axford 1984

4. Generalized Ohm´s Law(Fluid Approach) Assumptions:two-fluid (protons/electrons) ideal conditions ~ collisionless me/mi <<1,   0 E + v  B - j = (0pe2)-1t j + (jv + vj – (en)-1j j)} + (en)-1{ j  B - Pe + Fepmf  Hall term Inertial term Wave pmf In quasi-equilibrium the electron pressure gradient term is the ion pressure term, for then: j  B -Pe ·Pi [ Wave ponderomotive force usually neglected without justification (?) May be important in a turbulent plasmasheet ]

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

6. No guide field: HALL With guide field: Pressure Estimates of Reconnection Rate

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

8. Magnetospheric Requirements • Location outside ionosphere • Total non-collisionality mfp ~ 1 AU • No Parker-Sweet • Petschek only if anomalous an=e2n/mean • 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)

10. Jetting and Field Line Curvature (Cluster Tail Observations) Runov et al. 2003

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

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

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

14. 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

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

16. Hall-Current System jH = 0   O jH 0 jH = 0 jH = 0   O Hall Currents Closure of Hall Currents Via Field Aligned Currents

17. Relation between Hall/FACs and Field-aligned Electron Fluxes in Tail Reconnection FACs upward Electrons downward B Vin = E B noFAC upward Hall Current jH downward Electrons vout ~ vA 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

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

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

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

21. Schematics of Tail-Hall-Region

22. Magnetopause Reconnection Mozer et al., PRL 89, 2002

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

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

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

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

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

28. 3D-Tail-Reconnection Pritchett & Coroniti JGR 109, 2004 Scholer et al. PoP 10, 3521, 2003

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

30. Pritchett‘s 3D Simulation Distributions Stack plot of E|| Propagating waves Heating and acceleration

31. Electron Velocity and E|| Pritchett & Coroniti 2004

32. 3D-Reconnection Electron Distributions outside X-line in X-line Pritchett & Coroniti 2004

33. Guide Field Simulation Drake et al. Science 299, 2003

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

35. Non-HallReconnection me=mi Schematic view Initialization Jaroschek et al. 2004

36. Reconnection Without Hall Effect: The Case mi = me xy-plane xz-plane xz-plane 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 Jaroschek et al. 2004

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

38. 3D Fields in Reconnection Jaroschek et al. PoP 11, 2004

40. Auroral zone physics Ergun et al. PoP 9, 2002

41. Auroral zone physics Electric field Electron distribution Ergun et al. PoP 9, 2002

42. 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)

43. Ionospheric Signature of FA-Currents An Example from FAST

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

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

47. Magnetopause Reconstruction Hu and Sonnerup JGR 108, 2003

48. Lyon, Science 288, 2000

49. Nagai et al. (2002)

50. Tail-Hall-Reconnection Parameters