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Null-singular line reconnection configuration reconstructed from Cluster spacecraft observations

Null-singular line reconnection configuration reconstructed from Cluster spacecraft observations.

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Null-singular line reconnection configuration reconstructed from Cluster spacecraft observations

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  1. Null-singular line reconnection configuration reconstructed from Cluster spacecraft observations He J.-S.， Tu C.-Y.*， Tian H.， Xiao C.-J.， Wang X.-G.， Pu Z.-Y.，Ma Z.-W., Zong Q.-G., Zhao H., Zhou G.-P., Wang J.-X., Fu S.-Y., Liu Z.-X., M. W. DUNLOP, K-H. GLASSMEIER, H. REME, I. DANDOURAS, C. P. ESCOUBET * School of Earth and Space Sciences, Peking University

  2. Outline • Importance of magnetic field configuration in magnetic reconnection • 2-D & 3-D magnetic reconnection configuration in theoretical aspect • A new method to reconstruct the magnetic reconnection configuration based on Cluster observations • Characteristics of observed 3-D magnetic reconnection configuration • Characteristic of the 3-D null • Characteristic of singular line connected to the 3-D null • Figure out a picture of Cluster motions in the magnetic configuration • Validity and applicability of this new method

  3. 1. Importance of magnetic configuration in magnetic reconnection • Dissipation of magnetic energy and its conversion to kinetic energy and thermal energy • Piling up before reconnection and scattering of magnetic flux after reconnection； • Change of magnetic layout across the shock in the expansion/compression of fast/slow modes during the reconnection； • Impact of guide magnetic field on reconnection rate and acceleration of electrons；

  4. 2. Reconnection configuration predicted by theories (1) • 2-D magnetic reconnection configuration • Y-type magnetic structure; • X-type magnetic structure; • Including Hall-quadrupoles Y-type: long diffusion length, increased diffusion time, slow reconnection rate Hall-quadrupoles: ion un-magnetized, electron magnetized, X-type: short diffusion length, decreased diffusion time, fast reconnection rate

  5. 2. Reconnection configuration predicted by theories (2) • 3-D reconnection configuration • Singular line reconnection structure • Spine reconnection structure • Fan reconnection structure • Separator reconnection structure

  6. 3. New method to reconstruct magnetic configuration based on Cluster observations • 4 satellites, 4 magnetic vectors at every moment: • {B1x, B1y, B1z; B2x, B2y, B2z; B3x, B3y, B3z; B4x, B4y, B4z} • Design a set of fitting function Bx/y/z(a1,a2,…, a12; x, y, z) to fit the above 12 magnetic field components: • Divergence-free condition； • Magnetic configuration associated with Harris current sheet (magnetotail situation) • Residual magnetic field without current sheet contribution，residual magnetic field is the gradient field of potential function; • Expressed with spherical harmonic series • Fitting function consisted of Harris current sheet function and spherical harmonic series;

  7. 3. New method to reconstruct magnetic configuration based on Cluster observations • height z0 and thickness Lz of Harris current sheet to be fixed in other ways; • Fitting function expression： • From GSM cartesian coordinate to spherical coordinate system; • Bx/y/z(a1,a2,…,a12; x,y,z)=> Br/θ/φ(a1,a2,…,a12; r,θ,φ) • Fitting coefficients {a1,a2,…,a12}, namely {qnm, hnm, B0, B1}, is obtained through solving linear equations A(12x12)*Coeff(12x1)’=Br/θ/φ(12x1);

  8. 4. Characteristics of observed 3-D reconnection configuration • Reconstruction of magnetic configuration in a reconnection event on Sep 15, 2001

  9. 4. Characteristics of 3-D reconnection configuration Appearing as X-type magnetic field lines arranged along X-line; A 3-D null may be embeded in the X-line;

  10. 4. Characteristic of observed 3-D null Location of 3-D null： Eigen-values of magnetic configuration near null： Eigen-vectors of magnetic configuration near null： B-Null

  11. 4. Further identification of 3-D null Poincare analysis in the vicinity of 3-D null；

  12. 4. Characteristic of singular line Singular line may connect the already identified 3-D null to another possibly existed 3-D null； Guide field B < 5nT on a segment of the singular line，this event is less ；

  13. 5. Cluster motions in the magnetic configuration (1) Estimation of Cluster position projected on X-Z plane：

  14. 5. Cluster motions in the magnetic configuration (2) Motions of Cluster in 3-D magnetic configuration

  15. 5. Cluster motions in the magnetic configuration (3) Comparison of Cluster real measurements of magnetic field in real magnetic structure with Cluster virtual measurement in reconstructed magnetic structure

  16. 6. Validity and applicability of this new reconstruction method Model Fitting result O-type X-type Uniform such fitting function made up of Harris current sheet contribution and spherical harmonic series can be applied to reconstruct local magnetic configuration in magnetotail; After conversion to LMN-coordinate system specified by current sheet, such method can be used in anywhere in magnetosphere；

  17. The End Thanks

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