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Magnetic Tongues, Magnetic Helicity and Twist in Active Regions.

Flux Emergence Workshop 2011 SSL, Berkeley, CA, USA 22nd August 2011. Magnetic Tongues, Magnetic Helicity and Twist in Active Regions. É. Pariat & P. Démoulin LESIA, CNRS, Observatoire de Paris, France. Outline. Introduction: twist in actives regions Magnetic tongues

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Magnetic Tongues, Magnetic Helicity and Twist in Active Regions.

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  1. Flux Emergence Workshop 2011 SSL, Berkeley, CA, USA 22nd August 2011 Magnetic Tongues, Magnetic Helicity and Twist in Active Regions. É. Pariat & P. Démoulin LESIA, CNRS, Observatoire de Paris, France

  2. Outline • Introduction: twist in actives regions • Magnetic tongues • Magnetic helicity: measurement methods • Observational properties of injected helicity • Observed helicity flux distribution 22/08/11 - FEW 2011 - E. Pariat

  3. Global view Conjecture: To limit the buildup of Hcorona H has to be ejected via CMEs ICMEs magnetic clouds flux tubes need twist, so H, ( Rust 1994, Low 1997 ) to cross the CZ ( Emonet & Moreno Insertis 1998, Cheung et al. 2006 ) observed photospheric H flux : best measurement of H ( the photosphere is the only region where 2D maps of B are measured ) H cascade to large scales very low dissipation dissipate on the global resistive time scale ( > 100 years ) H is a conserved quantity ( Frisch et al. 1975, Berger 1984, Alexakis et al. 2006 ) 22/08/11 - FEW 2011 - E. Pariat

  4. Evidences of twist * Shift / J-shape of ribbons * Magnetic tongues I.L. Shift ( Lopez et al. 2000 Green et al. 2007 ) ( Moore et al. 1995, Démoulin et al. 1996 ) * feet/barbs of filaments * magnetic clouds MC B// ( Bothmer & Schwenn 1998, Dasso et al. 2006 ) ( Martin et al. 1994, Aulanier et al. 1999 ) * Sunspot whorls *vector magnetograms ( Hale 1925, Chae 2001, Nakagawa et al. 1971 ) ( Hagyard et al. 1990, Metcalf et al. 2005 ) * coronal loops * X-ray sigmoids sunspot ( Brown et al. 2003, Schmieder et al. 1996 ) ( Manoharan et al. 1996, Canfield et al. 1999 ) All have H > 0, for H < 0 : mirror symmetry 22/08/11 - FEW 2011 - E. Pariat

  5. Quantitative methods to estimate twist What is the amount of twist of the active regions magnetic fields? • (Non-linear) Force Free extrapolation: e.gabestparameters(eg. Pevtsov et al. 02) • Total Magnetic Helicity • Properties of UV coronal loops(e.g. Chae & Moon 05) • Geometricalshape and distribution of coronal loopscompared to (N)LFFF model (e.g. Malanushenko et al. 09, 09b, 11)  Anna’s Talk • Magnetic helicity injection • MagneticTongues (?) • Shear/Rotation of the polarities(e.g. Magara & Tsuneta 08, Magara 09) (Chae & Moon 05) Model-based (Magara 09) Obs-based 22/08/11 - FEW 2011 - E. Pariat

  6. Outline • Introduction: twist in actives regions • Magnetic tongues • Magnetic helicity: measurement methods • Observational properties of injected helicity • Observed helicity flux distribution 22/08/11 - FEW 2011 - E. Pariat

  7. MagneticTongues Luoni et al. 11 • Magnetic tongue: extensions of the approximately round magnetic field polarities (López Fuentes et al. 00, Démoulin & Pariat 09, Luoni et al. 11) • ~ horizontal Taijitu (yin-yang) symbol: ☯ • angle formed between the global PIL and the axis of the main magnetic polarities • Large scale property of the magnetic field: • Less obvious when considering small scale structures at the PIL: e.g. sea-serpents • Less obvious but still present in complex/multipolar AR Hood et al. 2009 22/08/11 - FEW 2011 - E. Pariat Magara & Tsuneta 08

  8. Interpretation of magnetic tongues MDI Magnetograms AR 8015b • Magnetic tongues: direct signature of the emergence of a twisted flux tube • Elongation is due to the projection of the azimuthal field on the vertical direction H>0 AR 8015c H<0 • Two possible configuration depending only on the chirality/helicity of the twisted FT AR 8203 H<0 AR 8011 H>0 H<0 Luoni et al. 11 22/08/11 - FEW 2011 - E. Pariat Hood et al. 09

  9. MagneticTonguesevolution • Typical feature of the early phase of “standard” (i.e. bipolar) active regions emergence • Tongue are present while appex of the FT is crossing the photosphere • Obs. retraction & disappearance of the tongue: projection of the azimuthal field decrease Luoni et al. 11 22/08/11 - FEW 2011 - E. Pariat Hood et al. 09

  10. Quantitative estimation? • Analytically, for a given model of the emerging FT the twist directly sets • the angle between the tongue and the axis of the polarity: d~arctan(1/2Nturn) • Uniform twist= dis constant • tongues extension • Observationally, itsextremelydifficult to retrieve the twist • Difficult to define the location of the PIL and the center of polarities • Tongue onlyobservedduring a relatively short period. • Angle d change because the twist islikely not uniform in the FT • Extremelydifficult to fit a simplisticemerging flux tube model to actual observation Nturn=0.2 Nturn=1 Nturn=6 • Pariat et al. 05 • Luoni et al. 11 22/08/11 - FEW 2011 - E. Pariat

  11. Outline • Introduction: twist in actives regions • Magnetic tongues • Magnetic helicity: measurement methods • Observational properties of injected helicity • Observed helicity flux distribution 22/08/11 - FEW 2011 - E. Pariat

  12. Definition of H Coronal field Reference field (usually potential field ) S S Boundary condition : same magnetogram ( normal component ) relative magnetic helicity (to a reference field) ( Barnes 1988, Berger 1988 ) Equivalent IF 22/08/11 - FEW 2011 - E. Pariat

  13. Measuring Helicity in AR: extrapolations • Direct measurements of magnetic helicity are not possible • Magnetic field almost only estimated in the photosphere •  Magnetic field Extrapolation (Green et al. 02) • Linear force free field assumption • Use of longitudinal magnetograms only • LFFF Linearized equation (Green et al. 02) (Lim et al. 07) • Nlfff & Non-force free fields • Needs to numerically integrate A and AP in a box with the proper condition on A, AP, B & BP • Carefull choice of the gauge (DeVore et al. 00, Rudenko & Myshyakov, Thalmann et al. 11 , Valori et al 11, 12) 22/08/11 - FEW 2011 - E. Pariat (Thalmann et al. 11 )

  14. Measurementsprecision • Coronal helicity computation: • Relies on extrapolation methods and are hence subject to their validity & caveats (DeRosa et al. 09) •  :Very sheared/twisted structures (highest helicity) are the most difficult to obtain • : Helicity is a large scale quantity stored in large scale structures easier to get • Different extrapolation methods (Regnier at al. 05) : • H varies by a factor 2 • : Helicity computation in a small box is very sensitive to the choice of the gauge at the boundary: different choice  different sign of H (Valori et al. 11) • : New understanding of how to compute H in a boxed domain (Rudenko & Myshyakov, Thalmann et al. 11 , Valori et al 11, 12) 22/08/11 - FEW 2011 - E. Pariat

  15. Measuring Helicity in AR: photospheric flux (Chae et al. 04) A better proxy of the helicity flux density is : ( Pariat et al. 2005 ) Magnetogram + velocity ( arrows )  Rotation rate x’ B// > 0 B// < 0 Helicity flux density: summation of the relative rotation of all the elementary flux tubes, weighted by their magnetic fluxes x • Magnetic helicity can be estimated by time-integrating the flux of magnetic helicity through the photosphere.(Chae 01) • Flux of helicity: 22/08/11 - FEW 2011 - E. Pariat

  16. Measuring Helicity in AR: photospheric flux • How to measure the Helicity flux? • B is given from spectropolarimetry (magnetograms) • Udeduced with methods based on Local Correlation Tracking(November & Simons, 1989) LCT: basic method to deduce velocities. More sophisticated methods solving the induction equation (Welsh et al. 07) *Induction Method Kusano et al. (2002, 2004) * Inductive LCTWelsch et al. (2004) *Minimum Energy Fit Longcope (2004), Ravindra et al. (2008) *Differential Affine Velocity Estimator Schuck(2005, 2006) *DAVE for Vector Magnetogram Schuck (2008) *Non-linear Affine Velocity Estimator Chae & Sakurai (2008) 22/08/11 - FEW 2011 - E. Pariat

  17. Measurementsprecision • Photospheric helicity flux measurements: • Relies on flux transport velocity methods (Welsh et al. 07) • : Helicity poorly estimated in shootout: wrong sign and/or an order of magnitude difference • : LCT methods mostly capture Vperp • : Improved methods (e.g. Schuck 08, Chae 08) • Sensitive to data cadence, resolution, noise levels (e.g. Zhang et al. 08, Yamamoto & Sakurai 09, Chandra et al. 10, Romano et al. 11, Tian et al. 11) : Helicity given with a factor 2-3 •  : Cannot recover helicity flux along the isocontours of B: twisting motions (high helicity flux) (Green at al. 02) • : New data set with higher cadence/resolution (Lim et al 07) • Comparison of helicity flux and coronal helicity computations (Lim et al 07, Park et al. 10) : • Results agree within a factor 2 22/08/11 - FEW 2011 - E. Pariat

  18. Outline • Introduction: twist in actives regions • Magnetic tongues • Magnetic helicity: measurement methods • Observational properties of injected helicity • Observed helicity flux distribution 22/08/11 - FEW 2011 - E. Pariat

  19. Differential rotation : theory 0 dH/dt < 0 dH/dt > 0 H time Hmutual dominant =>H > 0 H north south bipole dH/dt > 0 dH/dt < 0 0 time diff. rot. ( DeVore 2000, Démoulin et al. 2002 ) H = Hself + Hmutual Competition between: * Hself : rotation of each polarity * Hmutual : relative rotation of one polarity / the other one with differential rotation : Hself . Hmutual< 0 east-west bipole Hself dominant =>H < 0 diff. rot. Differential rotation: Time-independent shearing flow BUT: time dependant input of magnetic helicity + can change of sign 22/08/11 - FEW 2011 - E. Pariat

  20. Differential rotation : AR case studies Helicity injection rate ( 1040 Mx2 h-1 ) 0 only differential rotation without differential rotation Helicity injection by differential rotation: * smaller than the helicity injected by internal motions (typical ~ 1/10 to 1/2 ) *not enough for launched CMEs / MCs * could have the opposite sign than Hcoronal ( Chae et al. 2001, Jeong & Chae2007, Labonté et al. 07, Tian & Alexander 2008 ) ( Démoulin et al. 2002, Nindos et al. 2002, 2003 ) ( Green et al. 2002, Tian & Alexander, 2007 ) In most ARs, differential rotation cannot provides Hcoronal AR 8668 Hcoronal < 0 Hinjected < 0 22/08/11 - FEW 2011 - E. Pariat

  21. Hemisphericrule ? ( Pevtsov 2002 ) • Due to the solar rotation: • H<0 in the North • H>0 in the South • Independently of the solar cycle • True mostly for quiet sun features! • For active features the rules is only marginally validated H < 0 Whythisdifference ? H > 0 independent of solar cycle • Magnetic helicity studies close to equipartition • Labonté et al. 07: 57-60% of 393 ARs. • Yang et al. 09: 56-57% of 58 emerging ARs. • Weak correlation likely due to the diff. Rot. at the surface Mechanism generating the twist in emerging flux tube is likely not correlated to the W effect of the solar rotation Labonté et al. 07 22/08/11 - FEW 2011 - E. Pariat

  22. AR emergence H injected ( 1042 Mx2 ) low high AR 10831 Magnetic tongues: H< 0 low high Total magnetic flux ( 1022 Mx) -H injected ( 1042 Mx2 ) ( Jeong & Chae 2007 ) high high ( Tian & Alexander, 2007 ) low low low low Helicity injection follows a low-high-low evolution. high high Significant helicity injection is delayed ~ 2 days compared to magnetic flux low low low low 22/08/11 - FEW 2011 - E. Pariat

  23. Photospheric flux of magnetic helicity Similar peaks of helicity flux Helicity flux Helicity flux simple analytical evolution longitudinal magnetograms 3D MHD simulation emergence of a twisted flux tube constant vertical velocity emergence of AR 10365 ( Pariat et al. 2005 ) ( Cheung et al. 2005 ) ( Chae 2004 ) high high high low low low low low low H injection evol. can be interpreted by the emergence of a globally twisted FT 22/08/11 - FEW 2011 - E. Pariat

  24. AR recurrences CMEs with low H later on? Rather: Not enough injected helicity measured in evolved ARs ? 22/08/11 - FEW 2011 - E. Pariat

  25. Helicity injection in ARs Helicity flux over 6 days ( Mx2 ) 345 non-X-flaring ARs 48 X-flaring ARs Twisted flux tube with n turns Magnetic flux ( Mx ) ( Yang et al. 2009 ) • Statisticalstudies of helicity injection assuming a single twisted flux tube: • Yamamoto et al. 05: n=0.01-0.02/day • 7 ARs, averaged injection • Jeong & Chae 07: n=0.07, • 6 ARsfollowed over a few days • Labonté et al. 07: n=0.02 • 393 ARs over 5-6 days • Verylowcad.  underestimation • Tian et al. 08: • 23 sigmoidalARs: n=0.08 • 18 justemergedARs: n=0.03 • Yang et al. 09: n=0.04 • 58 emerging AR over 2-8 days (F=(|F+|+|F-|)/2) H = 0.039F2 22/08/11 - FEW 2011 - E. Pariat ( Labontéet al. 2007 )

  26. Helicity accumulation in ARs. How much helicity isinjected in ARs?  H=0.005-0.02 F2/days •  1 turn in 100 days(3 Carrington Rotations) • Helicity accumulated in AR over their passage on disk: • <DH>~0.08-0.2 F2 • Typical instantaneous flux of Helicity in AR: • <dH/dt> ~ 1042 Mx².day-1 but large variation ; <dH/dt> ~ 10-2 F²/day (F = 1022Mx) • Total helicity accumulated in AR over several rotation (Démoulin et al. 02, Lim et al. 07) • <DH>~1-100 x1044 Mx² ; <DH>~ 0.5-2 F² • Is the normalisation by F2 valid?: Not fully! • Jeong & Chae 07: a=1.3 • Labonté et al. 07: a =1.8 • Yang et al. 09: a=1.85 • Why? lifetime of ARs increases significantly with their amount of magnetic flux hence helicity accumulation not fullyobserved for largerARs 22/08/11 - FEW 2011 - E. Pariat

  27. Outline • Introduction: twist in actives regions • Magnetic tongues • Magnetic helicity: measurement methods • Observational properties of injected helicity • Observed helicity flux distribution 22/08/11 - FEW 2011 - E. Pariat

  28. Evolution of helicity flux density ( Pariat et al. 2006 ) AR 9144 • In most active region, helicitty injection isrelativelyunipolar: only helicity of one signisinjected! •  Constraint on the emerging flux tube generationmechanism Coherent evolution AR 10955 AR 8375 AR 8210 22/08/11 - FEW 2011 - E. Pariat

  29. Asymmetricinjection (?) • Helicity is asymmetricaly injected: 3-10 more helicity flux in the leading magnetic polarity (Tian & Alexander 09, Tian et al. 11) • Origin (Fan et al. 09) : stronger field in the leading leg of the Ω-shaped emerging flux tube • Field lines wind about each other more smoothly  more coherent values of the local twist, • greater Alfvén speed: faster rotation • However… Helicity flux density per unit surface is not a physically meaningful quantity!! • Helicity flux density is only defined for a given flux tube: defining a different helicity at both footpoint of a field line is incorrect •  It’s not an asymmetry of Magnetic Helicity • Result is very likely physical because proxies of helicity flux density may carry more information than magnetic helicity • Results obtained with 2 proxies of helicity flux density with very different properties  puzzling! • Part of the asymmetry just results may just results from the weighting of in region of higher field strength 22/08/11 - FEW 2011 - E. Pariat

  30. A puzzlingmagneticcloud • Geoeffectivemagneticcloud of 20 November 03 a positive helicity (e.g. Gopalswamy et al. 05;Yurchyshyn et al. 05, Möstl et al. 08 ) • AR 10501, at the source of the CME has a global negative helicity. •  How can a negativemagnetic helicity AR generate a positive helicity magneticcloud? • Mixed helicity signs in the southern filaments Global negative helicity accumulation in AR 10501 Wind Data: Positive helicity MC Grad-Shafranov reconstruction M flares Chandra et al. 10 22/08/11 - FEW 2011 - E. Pariat Möstl et al. 08

  31. Mixed helicity in filaments • Topological analyze: existence of a close connectivity domain where is the South filament • Helicity injection in the south filament: localized positive injection. •  Ejected South filament forms the observed magnetic cloud South Filament Localized positive helicity acc. in South filament 22/08/11 - FEW 2011 - E. Pariat

  32. Mixed helicity in filaments ( Romano et al. 2011 ) • Filament in AR 9862 • Eruption on 01/11/01 • Mixed sign of helicity during the eruption • Helicity injection: • Whole active region: H<0 • Injection in filament footpoints: H<0 • Mixed helicity: larger energy may be released (e.g Linton et al. 01). •  Filament eruption in mixed helicity region (Kusano et al. 04) BBSO Ha, 31/10/01 MDI Helicity map Whole AR: H>0 A+B: H<0 22/08/11 - FEW 2011 - E. Pariat

  33. Dynamo : coupling of the hemisphere north: H < 0 south: H > 0 but why dominance of only 60 % ? Helicity budget ( H is a conserved quantity ) Hcorona from magnetic extrapolation Observed photospheric H flux HMC from magnetic cloud modelling Maps of H injected in ARs Why some ARs have H < 0, and some H > 0 ?  constraints on the solar dynamo Conclusion corona interplanetary space photosphere tachocline dynamo : produce H <0 & H >0 H stored in the corona, then ejected via CMEs H in ICMEs & Magnetic Clouds B emergence & H transfert Helicity storage in the solar corona Improved method to compute H in 3D domain • Mixed helicity regions few examples of mixed helicity region associated with large eruptions Flux of helicity through the photosphere H=0.005-0.02 F2/days  constraint for models Why CME rate is constant over several carrington rotation while H injection decrease? Is the eruptivity of mixed helicity region particular? Does all the helicity of emerging FT cross the photosphere ? Is there H accumulating bellow?

  34. 22/08/11 - FEW 2011 - E. Pariat

  35. Flux density of magnetic helicity All previous studies with GA maps : simultaneous injections of both sign of magnetic helicity. True ? GA & Bn GA & velocity GA & velocity ( Chae 2004 ) ( Kusano et al. 2002 ) ( Nindos et al. 2003 ) Total H flux : well established physical meaning Flux density : Does it had a physical meaning ? 22/08/11 - FEW 2011 - E. Pariat

  36. Simplest example: a translated magnetic flux tube Flux tube u u Photosphere u Example of an observed AR --> ( Kusano et al. 2002 ) => GA is NOT a good proxy of the flux density ! ( Pariat et al. 2005 ) GA introduces fake signal of both signs in equal amount Only the total flux of helicity is reliable Bn > 0 While no helicity is injected ! GA 22/08/11 - FEW 2011 - E. Pariat

  37. Flux density of magnetic helicity A better proxy of the helicity flux density is : ( Pariat et al. 2005 ) Rotation rate Magnetogram + velocity ( arrows )  Helicity flux density: summation of the relative rotation of all the elementary flux tubes, weighted by their magnetic fluxes x’ B// > 0 B// < 0 x + Double integration on the magnetogram => 22/08/11 - FEW 2011 - E. Pariat

  38. Magnetic helicity flux : theory B Phostosphere Simple interpretation of : photospheric footpoint motion of magnetic flux tubes Corona Corona emergence emergence Photosphere Photosphere Helicity flux emergence horizontal motions Can always define : => 22/08/11 - FEW 2011 - E. Pariat

  39. Which velocities are measured by LCT ? *Mostly the horizontal motions : ( Ravindra et al. 2008, Shuck 2008 ) =>Miss a large part of the helicity flux ! This conclusion comes from testing LCT with an anelastic MHD simulation Limitation: B field dominated by the convection => similar to super-granule cells Would need an AR-like B field to test LCT *The footpoint motions of flux tubes: ( suppose simple emergence ) ( Démoulin & Berger 2003 ) =>Full helicity flux from longitudinal magnetogram time series ( close to centre disk ) But emergence is a complex phenomena e.g. it involves magnetic reconnection ( Magara 2004, Pariat et al 2005, Archontis et al. 2007 ) 22/08/11 - FEW 2011 - E. Pariat

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