In-situ observations of magnetic reconnection in solar system plasma

1. In-situ observations of magnetic reconnection in solar system plasma What can we export to other astrophysical environments? Alessandro Retinò, R. Nakamura and W. Baumjohann Space Research Institute, Austrian Academy of Sciences, Graz, Austria A. Vaivads Swedish Institute of Space Physics, Uppsala, Sweden D. Sundkvist and F. S. Mozer Space Sciences Laboratory, University of California, Berkeley, USA F. Sahraoui Laboratory of Physics of Plasmas, CNRS, Paris, France MFPO conference - Krakow 2010 alessandro.retino@oeaw.ac.at

2. Outline • Motivation • Magnetic reconnection: basics, importance, universality • Collisionless reconnection in near-Earth space • In-situ observations of turbulent reconnection: • first evidence • energy dissipation • particle acceleration • Possible comparisons with other astrophysical environments: • heating of the solar corona • cosmic ray acceleration • Summary MFPO conference - Krakow 2010 alessandro.retino@oeaw.ac.at

3. Motivation • Magnetic forms produce activity and violence in the otherwise • serene thermal degradation of the cosmic landscape[E.N. Parker] • [NASA/HBT-FCO in UV] • [NASA/HBT in UV] • [ESA/SOHO-EIT in EUV] • Magnetized plasma ubiquitous in the universe • Key processes in magnetized plasma: dynamo, reconnection, MHD instabilities ,... • In-situ observations required to understand the basic physics • Synergy between in-situ & remote observations important MFPO conference - Krakow 2010 alessandro.retino@oeaw.ac.at

4. Reconnection: basics Violation of the frozen-in condition • Frozen-in • E' =E+VxB=0 • E||=0 • No frozen-in • E' =E+VxB=J/ • E||≠0 • ( conductivity in the diffusion region) [ Paschmann, Nature, 2006] MFPO conference - Krakow 2010 alessandro.retino@oeaw.ac.at

5. Reconnection: importance • Breaking of frozen-in condition -> • ->local topology change -> • ->large-scale: • reconfiguration of magnetic fields • energy conversion/dissipation: • plasma acceleration (Alfvénic) • plasma heating • particle acceleration • plasma transport E' E' [Vaivads et al., Space Sci. Rev., 2006] E' is the reconnection rate MFPO conference - Krakow 2010 alessandro.retino@oeaw.ac.at

6. Reconnection: universality X near - Earth space [Paschmann et. Al, Nature, 1979] [Hones et al., Geophy. Res. Lett., 1984] [Phan et al., Nature, 2006] [Retinò et. al, Nature Physics, 2007] also observed at Mercury, Mars & Saturn X X Laboratory plasma [Intrator et al., Nature Physics, 2009] Solar corona [Yokoyama et. al., ApJ Lett., 2001] X mfp ~ 1 A. U. collisionless plasma

7. In-situ vs remote observations • LABNEAR-EARTHSUNASTRO • Direct measur. of E & B yesyes (high res) no no • Direct measur. of f(v) no yes (high res) no no • Imaging no noyes (high res)yes • Boundary conditions controlled natural naturalnatural • Repeatability yesnonono • Number of objects a few oneonemany • direct mesurements of E, B and f(v) required to resolve the basic physics of reconnection! • near-Earth space best laboratory (so far) • comparison with remote observations important MFPO conference - Krakow 2010 alessandro.retino@oeaw.ac.at

8. Near-Earth observations: Cluster spacecraft • ESA cornerstone mission • first 4 spacecraft mission ! • distinguish temporal/spatial variations • measurement of 3D quantities: J=(1/μ0) xB, • B = 0, EJ, ... • tetrahedrical configuration with changeable spacecraft separation 100-10000 km -> measurements at different scales http://sci.esa.int/science-e/www/area/index.cfm?fareaid=8 • 4 sets of 11 identical instruments to measure: • magnetic field • electric field • thermal particle distribution functions • suprathermal particle distribution functions FGM magnetometer MFPO conference - Krakow 2010 alessandro.retino@oeaw.ac.at

9. Collisionless reconnection large-scale laminar current sheet (e.g. magnetotail) anomalous conductivity ? MHD Hall electron pressure ? electron inertia ? Three scales: MHD ( >> i) 103 – 104 km ion ( ~i ) 50-500 km electron ( ~e) 1-10 km [NASA/MMS]

10. Reconnection rate Reconnection first proposed by Giovanelli [Nature, 1946] to explain solar flares Sweet-Parker reconnection: rate ~ (Rm)-1/2~ ()-1/2 depends on resistivity -> SLOW (flare ~100s) Collisionless reconnection: rate ~ 0.1 independent on resistivity -> FAST !!! Numerical simulations [Birn, JGR, 2001] Spacecraft data [Mozer et. al., Phys. Rev. Lett., 2002] [Vaivads et al., Phys. Rev. Lett., 2004] [Retinò et al., Nature Physics, 2007]

11. Turbulent reconnection: importantfor astrophysical plasma? • Turbulence and reconnection ubiquitous in the universe: turbulent reconnection should be common in astrophysical plasmas • Turbulent configuration could increase the reconnection rate wrt laminar case: faster reconnection • Turbulent reconnection could be important for energy dissipation • Larger electric fields and small-scale irregularities could enhance particle acceleration MFPO conference - Krakow 2010 alessandro.retino@oeaw.ac.at

12. Turbulent reconnection Small-scale laminar current sheet in turbulent plasma • Turbulence in laminar current sheets • Turbulent current sheet B [Matthaeus, Phy. Fluids, 1986] [adopted from Lazarian & Vishniac,1999] [Bale et al. 2002, Vaivads et al., 2004, Retinò et al., 2006] • Which configuration ? MFPO conference - Krakow 2010 alessandro.retino@oeaw.ac.at

13. In-situ evidence of turbulent reconnection Firstevidence ! energetic ions volume-filling current sheets cartoon of current sheet formation in turbulent plasma (contours are magnetic field lines) reconnecting current sheets [Retinò et al., Nature Physics,2007] also in solar wind [Gosling et al., ApJ,, 2007]

14. Small-scale laminar current sheet in turbulent plasma turbulent current sheet ? turbulence ? R ~ 0.1 (fast rec) four spacecraft (assumptions: planarity & stationarity) SC separation ~ 100 km single spacecraft MFPO conference - Krakow 2010 alessandro.retino@oeaw.ac.at

15. Intermittency Gaussian i i Energy dissipation Turbulence properties Large number of reconnection regions E&B Kolmogorov-like Alfvenic turbulence (E/B ~Va) [ Servidio et al., Phy. Plasma, 2010] measured dissipation rate <EJ> comparable with that expected from waves around ion gyrofrequency: turbulentreconnection in volume-filling current sheets can be important energy dissipation mechanism ! [ Sundkvist et al., PRL,2007]

16. Particle acceleration Particle acceleration in small-scale current sheet in turbulent plasma [Dmitruk & Matthaeus, JGR, 2006] B suprathermal ions First order Fermi acceleration during fast reconnection in turbulent current sheet [Lazarian et al., 2010] No clear evidence (so far) of particle acceleration from in-situ data !

17. Comparison with other astrophysical plasma • Can we directly export results • from in-situ observations • to other astrophysical • environments? • Caution is needed: (most)solar • system plasma are: • fully ionized • mainly H+, e- • not relativistic (Va<<c) • collisionless [Vaivads et al., Plasma Phys. Contr. Fus., 2009] MFPO conference - Krakow 2010 alessandro.retino@oeaw.ac.at

18. Possible comparisons (TBD) • Heating of the solar • chromosphere/corona: • small-scale reconnection events • [Shibata et. al, Science, 2007] The magnetic carpet on the Sun [From SOHO/SOI http://soi.stanford.edu] • Cosmic ray acceleration: • Giant radio galaxies[Kronberg et al., Ap. J. Lett., 2004] • Anomalous cosmic rays (5-100 MeV/nucleon) [Lazarian et. al, ApJ, 2009; Drake et al., ApJ, 2010] MFPO conference - Krakow 2010 alessandro.retino@oeaw.ac.at

19. Summary • Reconnection universal energy conversion/dissipation process • In-situ observations required to resolve the basic physics • Fast collisionless reconnection is observed in-situ in the solar system e.g. in near-Earth space • First experimental evidence of turbulent reconnection obtained in near-Earth space. Turbulent reconnection important for energy dissipation and (possibly) for particle acceleration. • Results from in-situ observations may be exported to distant astrophysical environments but much caution is needed. Crucial first to understand differencies and similarities between environments. • Possible examples for turbulent reconnection: heating of solar corona and cosmic ray acceleration MFPO conference - Krakow 2010 alessandro.retino@oeaw.ac.at