IN-SITU OBSERVATIONS OF MAGNETIC RECONNECTION IN PLASMA TURBULENCE

Transcription

1 IN-SITU OBSERVATIONS OF MAGNETIC RECONNECTION IN PLASMA TURBULENCE Z. Vörös 1,2,3 E. Yordanova 4 A. Varsani 2, K. Genestreti 2 1 Institute of Physics, University of Graz, Austria 2 Space Research Institute, Austrian Academy of Sciences, Graz, Austria; 3 Geodetic and Geophysical Institute, RCAES, Hungarian Academy of Sciences, Sopron, Hungary; 4 Swedish Institute of Space Physics, Uppsala, Sweden IWF.OEAW.AC.AT Our mysterious Sun: magnetic coupling between solar interior and atmosphere September 25-29, 2017, Tbilisi, Georgia

2 OUTLINE - Remote vs. in-situ observations of magnetic reconnection - Field and plasma structures in the turbulent magnetosheath flow jets and current sheets - Fluid and kinetic signatures of magnetic reconnection in the turbulent magnetosheath IWF.OEAW.AC.AT 2

3 Magnetic reconnection: remote vs. in-situ measurements < 100 km Retino et al., 2007 vandriel Gesztelyi, 2008 Benz, 2008 Shibata 1998 Plasma inflow towards reconnection: Yokoyama et al., 2001 Filament Reconnection outflows: McKenzie and Hudson, 1999 HXR Asai et al., 2004 TRACE-vanDriel Gesztelyi, 2008 Flare ribbons IWF.OEAW.AC.AT 3

4 Magnetic reconnection: in-situ measurements Solar wind Magnetosphere Magnetic cloud Flux rope Otto, 2005 Lavraud, 2014 Turbulence Gosling, 2012 Magnetic reconnection at the large-scale boundaries and reconnection in turbulence are the same? IWF.OEAW.AC.AT 4

5 Karimabadi et al., 2014 IWF.OEAW.AC.AT 5

6 GLOBAL HYBRID SIMULATIONS Q magnetosheath structures (Karimabadi et al. 2014) Jets Waves Vortices Magnetic islands (Flux ropes) Reconnecting current sheets IWF.OEAW.AC.AT 6

7 MMS OBSERVATIONS OF FAST JETS Q magnetosheath jets (Plaschke et al. 2017) IWF.OEAW.AC.AT - Sub-magnetosonic jets in the plasma frame no fast shocks - Evidence for jets pushing and stirring the ambient plasma generating even sunward flows. - Jet plasma and current sheets move differently 7

8 COLLISSIONLESS TURBULENCE SIMULATIONS Turbulence generates intermittent coherent structures: J/Jmax: 2D MHD Dissipation: 2D MHD flux ropes current sheets, etc. J/Jmax: 2.5D PIC Dissipation: 2.5D PIC Retino et al., Nature,2007; Sundquist et al., PRL, 2007; Greco et al., GRL, 2008; Servidio et al., PRL, 2009; Greco et al., ApJL, 2009; Servidio et al., JGR, 2011; Wan et al., PRL, 2015; Matthaeus et al.,ptrsa, 2015 etc. IWF.OEAW.AC.AT Wan et al., PoP,2016 8

9 How to find potential reconnection events in turbulence? Large-scale boundaries are absent! (magnetopause, tail current sheet) 1.step: detect currents Partial variance of increments (Greco et al., 2008, 2009) [discontinuity detector]: Magnetic rotation angle Structure/gradient detector Jcurl IWF.OEAW.AC.AT 9

10 SIMILAR PVIs trajectory SIMULATIONS AND OBSERVATIONS: Servidio et al., 2011 PVI: simulations large PVI~MR!! Cluster observations: March 27, 2002 Threshold CLUSTER 1 hour in the MS IWF.OEAW.AC.AT An example of a current sheet (E,B fields) Vörös et al., ApJL

11 CONCLUSIONS I Using PVI and magnetic rotation angles the current sheets can be find in turbulence. The statistics of the strongest discontinuities resembles the statistics in simulations IWF.OEAW.AC.AT 11

12 MMS mission - 4 spacecraft, tetrahedron configuration ~ 10 km dist. - combined fluxgate & search-coil magnetic data: 1 khz res. - E-field 8 khz - ion moments and VDFs 150 ms - electron moments and VDFs 30 ms IWF.OEAW.AC.AT 12

13 Reconnection event I -current sheet thinning -electron scale structures (~ 0.7 km; 26Hz) -electron-ion differential motion EARTH Yordanova et al., GRL, 2016 IWF.OEAW.AC.AT 13

14 N L M IWF.OEAW.AC.AT 14

15 BULLETED LISTS IWF.OEAW.AC.AT Yordanova et al., GRL,

16 IWF.OEAW.AC.AT 16

17 CONCLUSIONS II Within the electron scale structures we see ion demagnetization electron jets electron heating VDF agyrotropy suggesting that the MMS spacecraft observed reconnection signatures. IWF.OEAW.AC.AT 17

18 Reconnection event II EARTH IWF.OEAW.AC.AT 18

19 Where is reconnection? IWF.OEAW.AC.AT 19

20 RD Outflow? RD Gosling, 2012 MVA Walen test IWF.OEAW.AC.AT 20

21 RD Outflow? RD MVA Correlations OK How to interpret the two slopes? Walen test IWF.OEAW.AC.AT 21

22 The event in LMN coordinates (MVA and multi-point timing) L M N Outflows? V L is not necessarily reconnection outflow Outflows? V L has to be perpendicular to the local B Crossing? IWF.OEAW.AC.AT

23 Perp inflows outflows ion/electron demagnetizations Hall field temperature anisotropy trajectory?? IWF.OEAW.AC.AT Vörös et al., JGR, under review 23

24 IWF.OEAW.AC.AT Vörös et al., JGR, under review

25 Parallel current Parallel E Energy conversion dissipation Electron agyrotropy electron energization IWF.OEAW.AC.AT Vörös et al., JGR, under review

26 Electrons (30 ms) anistropy: thermal electrons agyrotropy: suprathermal electrons IWF.OEAW.AC.AT Vörös et al., JGR, under review

27 Ions (150 ms) D-shaped ion VDFs in the outflow region IWF.OEAW.AC.AT Vörös et al., JGR, under review

28 CONCLUSIONS III We observed two reconnection events in the turbulent magnetosheath clear reconnection signatures reconnection in turbulence resembles reconnection at large scale boundaries However, the LMN coordinate system might not always exist (more 3D case in turbulence) the events can be easily overlooked even in MMS data the events might not be seen in data sets from previous missions (data resolution issue) IWF.OEAW.AC.AT 28