S. Eriksson 1 , G. Provan 2 , F. J. Rich 3 , C. Mouikis 4 ,

1. S. Eriksson1, G. Provan2, F. J. Rich3, C. Mouikis4, M. W. Dunlop5, M. Kuznetsova6, S. Massetti7, B. Anderson8, M. Lester2, J. T. Gosling1, H. Reme9, and A. Balogh10 1LASP, University of Colorado, Boulder, CO, USA 2University of Leicester, Leicester, UK 3AFRL, Hanscom AFB, MA, USA 4SSC, University of New Hampshire, Durham, NH, USA 5Rutherford Appleton Laboratory, Chilton, UK 6NASA/GSFC, Greenbelt, MD, USA 7Istituto di Fisica dello Spazio Interplanetario, Roma, Italy 8JHU/APL, Laurel, MD, USA 9Centre d’Etude Spatiale des Rayonnements, Toulouse, France 10The Blackett Laboratory, Imperial College, London, UK Ionospheric Convection Response to High-Latitude Reconnection and Electrodynamics of a Split-Transpolar Aurora Contact: eriksson@lasp.colorado.edu

2. Outline Part I – Global Observations • Cluster lobe reconnection observations: 14 February 2003 1840-2000 UT • BATSRUS MHD simulation 1830-2030 UT http://ccmc.gsfc.nasa.gov [c.f. “Stefan”] • SuperDARN noon response to IMF 1940-2200 UT: Schematic NBZ field-aligned current (FAC) and ExB flow driven by lobe reconnection • Iridium Birkeland Currents • Summary – Part I

3. Outline Part II – Electrodynamics • Polar UVI & All-sky Camera observations • DMSP F13 observations: 2107-2114 UT -- ExB drift velocity -- FAC system -- Electron precipitation • Summary – Part II

4. Part I – Global Observations

5. Lobe Reconnection SchematicDungey [1963] (courtesy of J. C. Dorelli, UNH)

6. Side view View from above 20 UT 19 18 Solar Direction Solar Direction Solar Direction Cluster C1 Cluster C2 Cluster C3 Cluster C4

7. Cusp Schematic - Cluster FGM Lobe field Cluster C1 Cluster C3 Dayside closed field z x Direction of magnetic field

8. Vx Vy Vz Bx By Bz

9. Walen Test: Quantitative agreement with high-latitude magnetic reconnection Vx Vy Vz x-comp y-comp z-comp Bx By Bz

10. Walen Test: Quantitative agreement with high-latitude magnetic reconnection magnetosheath z Bn x magnetotail lobe

12. YZ GSM Plane B Vx Jpar Vy

13. YZ GSM Plane B Vx Cluster C1 position ~1800-1900 UT Jpar Vy

14. Vx Vy XZ GSM Plane P

15. XZ GSM Plane

16. XZ GSM Plane Cluster C3 18, 19, 20 UT Cluster C1 18, 19, 20 UT

17. SuperDARN noon-sector flow in agreement with Cluster C3 observations at 1940 UT and 1950 UT….one clockwise lobe cell is present in the dayside sector with sunward and dawnward flow across 12 MLT.

18. How does the sunward flow in the noon sector respond as the IMF clock angle changes? 78o 13 12 11 MLT 80o 82o

19. 78o 13 12 11 MLT 80o 82o

20. IMF during SuperDARN high-latitude noon convection changes TPA: Transpolar Aurora (Polar UVI) Red Vertical Line: Time of DMSP F13 TPA Observation TPA TPA

21. IMF during SuperDARN high-latitude noon convection changes A: Two-cell pattern B: Strong predominantly dawnward flow C: One clockwise global lobe cell D: One counterclockwise postnoon dayside lobe cell E: Two dayside lobe cells (reverse dayside flow) C D E A B

22. A: Two-cell pattern B: Strong predominantly dawnward flow C: One clockwise global lobe cell D: One counterclockwise postnoon dayside lobe cell E: Two dayside lobe cells (reverse dayside flow)

23. A: Two-cell pattern B: Strong predominantly dawnward flow C: One clockwise global lobe cell D: One counterclockwise postnoon dayside lobe cell E: Two dayside lobe cells (reverse dayside flow)

24. A: Two-cell pattern B: Strong predominantly dawnward flow C: One clockwise global lobe cell D: One counterclockwise postnoon dayside lobe cell E: Two dayside lobe cells (reverse dayside flow)

25. A: Two-cell pattern B: Strong predominantly dawnward flow C: One clockwise global lobe cell D: One counter- clockwise postnoon dayside lobe cell E: Two dayside lobe cells (reverse dayside flow)

26. A: Two-cell pattern B: Strong predominantly dawnward flow C: One clockwise global lobe cell D: One counterclockwise postnoon dayside lobe cell E: Two dayside lobe cells (reverse dayside flow)

27. A: Two-cell pattern B: Strong predominantly dawnward flow C: One clockwise global lobe cell D: One counterclockwise postnoon dayside lobe cell E: Two dayside lobe cells (reverse dayside flow)

28. A: Two-cell pattern B: Strong predominantly dawnward flow C: One clockwise global lobe cell D: One counterclockwise postnoon dayside lobe cell E: Two dayside lobe cells (reverse dayside flow) downward NBZ upward NBZ

29. Iridium Configuration downward upward

30. Iridium Configuration R2 R1 NBZ R1 R2 downward upward

31. MHD simulation of NBZ development

32. B: Strong predominantly dawnward flow IMF clock angle +90 C: One clockwise global lobe cell IMF clock angle +45 E: Two dayside lobe cells (reverse dayside flow) IMF clock angle 0 F: One anti-clockwise global lobe cell ??? IMF clock angle -45 Proposed model: The sunward flow and the bounding NBZ FAC system are directly driven by lobe reconnection. As the IMF By changes during positive Bz, so does the lobe reconnection site and thus the location and deflection of the joint sunward flow channel and NBZ system. A TPA is expected within the upward NBZ system. See also: Southwood, 1987; Vennerstrom et al., 2005

33. Summary Part I • The IMF from ACE and Cluster is strongly northward and duskward. The IMF Bx is negative in the solar wind (ACE) and in the magnetosheath (Cluster C1). Lobe reconnection is favored tailward of the northern cusp. Following a southward IMF Bz excursion, the IMF By decreases gradually toward By~0. • The Cluster s/c moved through the northern cusp at the beginning of the event. Two s/c (C1 and C3) observed enhanced sunward and dawnward velocity in agreement with high-latitude lobe reconnection tailward of the cusp. • MHD simulations confirm the general magnetic field and flow topology consistent with these Cluster observations. NBZ-type FACs are suggested on either side of the MHD lobe reconnection region and in the duskside ionosphere. • SuperDARN ExB drift is sunward and dawnward across the 12 MLT meridian at the time of the Cluster C3 flow enhancements. • The subsequent direction of SuperDARN noon sector flows (after a southward excursion) tracks the IMF clock angle changes well with different time delays. A faster response time is suggested to the southward (100 to 156 deg) turning (3-6 min) than either the duskward (135 to 34 deg) or due northward (45 to 8 deg) turnings that take 8-9 min and 12-14 min, respectively.

34. Part II – Electrodynamics

36. Polar UVI

37. Polar UVI

38. All-sky Camera, Daneborg (DNB)

39. All-sky Camera, Daneborg (DNB)

40. All-sky Camera, Daneborg (DNB)

41. All-sky Camera, Daneborg (DNB)

44. Clockwise Lobe Cell

45. R1 NBZ R1 R2 Clockwise Lobe Cell

47. DMSP Electron Precipitation

48. DMSP Electron Precipitation

49. DMSP Electron Precipitation

50. Summary Part I-II • SuperDARN verified a sunward flow channel over the TPA as part of a clockwise global lobe cell that covered much of the polar cap. This is consistent with the positive IMF By and northward IMF Bz (~30-50 deg clock angle). • A DMSP F13 dusk-to-dawn pass verified a structured sunward lobe cell flow channel over the split-TPA and an NBZ current system on either side of it [Iijima and Shibaji, JGR, 1987; Southwood, 1987]. The TPA was found within the upward NBZ region. • Two inverted Vs were detected in agreement with sunward flow shear and local upward FAC filaments at each of the two Sun-aligned arcs of the split-TPA. The high-latitude current system poleward of the duskside R2 system was locally balanced assuming a Pedersen closure. • The increased Pedersen conductance at both arcs self-consistently explains the structured sunward drift velocity.