3D magnetic reconnection: geometry and In situ measurements

1. 3D magnetic reconnection: geometry and In situ measurements 肖池阶1 , 王晓钢2, 濮祖荫3,马志为4, 汪景琇1, 赵辉1, 周桂萍1 , 傅绥燕3, M.G. Kivelson5, 刘振兴6, 宗秋刚7,K.H. Glassmeier8, A.Balogh9, A. Korth10, H. Reme11,C. P. Escoubet12 1 中国科学院国家天文台; 2 北京大学物理学院; 3 北京大学地球与空间科学学院; 4 浙江大学物理系; 5 IGPP, UCLA, USA; 6中国科学院空间科学与应用研究中心; 7 Center for Atmospheric Research, U. of Massachusetts Lowell, USA 8 IGM, TU Branuschweig, German; 9 SAPG, Imperial College, UK; 10 Max Planck Institute for Solar System Research, Lindau, German; 11CESR/CNRC, France; 12 ESA/ESTEC, The Netherlands

2. Outline • Introduction: 2D v.s. 3D Reconnection • 3D nulls and null-null lines detection • Conclusions

3. 太阳风 磁层顶 等离子体片 尾瓣 磁尾 磁鞘 Reconnection is essential in Sun, Magnetosphere, Fusion

4. North x  Sun Earth Z Y • d magnetotail GSM coordinates system: From Kivelson et al., 1995

5. North x  Sun Earth Z Y Reconnection Regions magnetotail GSM coordinates system: From Kivelson et al., 1995

6. In-Situ Observations of MR  High-speed plasma flows, energization of particles and other MR signatures were observed long ago by in-situ measurements (Phan et al., 2000; Hultqvist, 2000).  Evidences of collisionless MR have been detected by Geotail and Wind spacecraft (Deng et al., 2001; Øieroset et al., 2001 ). 4-spacecraft of Cluster mission provides unique opportunity to study MR, with the MR events in/near the diffusion region being of great interest.

7. 2D Collisionless Reconnection Outside the diffusion Region Traditional MHD theory holds Diffusion Region: Ion inertial region (width di) – Hall current and quadrupole By  Electron inertial region (width de)

8. Magnetic null • the magnetic vector field: spine fan Lau Y. T., & Finn, J. M. 1990, ApJ, 350,672

9. Magnetic field lines near the null spine spine fan fan Pontin, D. I., Hornig G. andPriest, E. R., ESA SP-575: SOHO 15 Coronal Heating, 507, 2004 Lau Y. T., & Finn, J. M. ApJ, 350, 672, 1990,

10. 3D Reconnection at the null: Fanreconnection Spinereconnection Reconnection at the A-B null line: Separatorreconnection Lau Y. T., & Finn, J. M., ApJ, 350, 672, 1990

11. Lau Y. T., & Finn, J. M., ApJ, 350, 672, 1990

12. 3D PIC simulation Buchner J., Astrophys. and Space Sci., 264, 25-42, 1999 Cai D.S., et al., Earth Planets Space, 53, 1011–1019, 2001

13. Nulls detection in the solar atmosphere S. K. Antiochos, ApJ, 502:L181–L184, 1998 Filippov, B, Sol. Phys., 185, 297, 1999 Zhao h., et al., ChJAA, 5, 443-447, 2005 Aulanier G., et al., ApJ, 540, 1126, 2000

14. How to detect the “Null” ? • A mathematical isolated singular point • Hard to determine the null based on magnetic field data in a local point. 1) right at the null, the relative measurement error is infinite with any small error-bar of data. 2) a single point measurement can’t distinguish the isolated null from a magnetic neutral line or a neutral sheet. • The null is associated with the topological property of its neighborhood. After J.M. Greene ( 1988, 1992 , 993), Garth, C. et al. (2004) , Zhao et al. (2005), etc. • The Poincare index method • The linear interpolation method

15. Poincare Index— 3D Calculating the index of a singularity by enclosing it with a surface small enough not to contain any other singularities. Poincare index = ∑ solid angles / 4p Greene, 1992, C. Garth, X. 2004, zhao, 2005

16. 2001-09-15 event • Bs null detection • Bipolar structure • scale of structure

17. Cluster Location at 05:00 UT on 01-09-15 DZ14=322km C3 X = -18.7RE Y = 3.5RE Z = -2.9RE

18. Overview of B-V: 2D Hall reconnection 05:03:36 UT—— Cluster around the X-point Xiao C.J., et al., GRL, 2007

19. Null point detected by Cluster : possible frame 05:03:36 UT—— Cluster around the X-point

20. Poincare index calculation 4s FGM data 0.04s FGM data

21. Find null position based on “Linear Interpolation”

22. Bs Null – theoretical structure at 05:03:36(UT):

23. Bipolar structure Near the reversal point 05:03:36(UT) Scale of the bipolar structure ~di

24. 2001-10-1 event (1) A, As and B nulls detection (2) A-B, As-B null lines detection (3) Lower Hybrid wave detection

25. Cluster Location at 09:50 UT on 2001-10-01 Y Y C3 X = -16.2RE Y = 7.9RE Z = -0.5RE

26. 2001-10-1 eventOverview

27. A null 09:48:25.593UT B null 09:48:28.447 UT As null 09:48:32.104 UT

28. Characteristics of the null pair observed on 2001-10-01

29. B-As null line 09:48:28.447 UT- 09:48:32.104 UT A-B null line 09:48:25.593 UT-09:48:28.447 UT

30. Null positions in the Cluster frame—— via the linear interpolation

31. The lower-hybrid oscillation: wLH ~ 13 Hz (with magnetic field 20 nT); a maximum power at 10-15Hz 13Hz 12Hz

32. Conclusions • All four types of nulls, A, B, As and Bs, have been detected by Cluster in situ measurements; • Typical 3D geometry feature of Bs-type null (flux tube) has been captured; The scale of structure is about the order of local di • An A-B null pair and a Bs-A null pair with their neighbouring geometry are identified in a typical reconnection event. • The separation between the nulls is measured as ~ 0.7±0.3 di, • A lower hybrid oscillation is also identified in the immediate vicinity of the line with a wavelength of ~ de, It is the first in situ evidence for complete 3D reconnection geometry and associated electron dynamics

33. Thanks for your attention!

34. Ref. : • Xiao C. J., et al., Nature Physics, 3(9), 609-613, doi:10.1038/nphys650, 2007 • Xiao C. J., et al.,Geophys. Rev. Lett., 34 , L01101, doi:10.1029/ 2006GL028006, 2007. • Xiao C. J., et al., Nature Physics, 2, 478-483, doi:10.1038/nphys342, 2006.