Solar Physics

, 270:45 | Cite as

Twisted Flux Tube Emergence Evidenced in Longitudinal Magnetograms: Magnetic Tongues

  • M. L. LuoniEmail author
  • P. Démoulin
  • C. H. Mandrini
  • L. van Driel-Gesztelyi


Bipolar active regions (ARs) are thought to be formed by twisted flux tubes, as the presence of such twist is theoretically required for a cohesive rise through the whole convective zone. We use longitudinal magnetograms to demonstrate that a clear signature of a global magnetic twist is present, particularly, during the emergence phase when the AR is forming in a much weaker pre-existing magnetic field environment. The twist is characterised by the presence of elongated polarities, called “magnetic tongues”, which originate from the azimuthal magnetic field component. The tongues first extend in size before retracting when the maximum magnetic flux is reached. This implies an apparent rotation of the magnetic bipole. Using a simple half-torus model of an emerging twisted flux tube having a uniform twist profile, we derive how the direction of the polarity inversion line and the elongation of the tongues depend on the global twist in the flux rope. Using a sample of 40 ARs, we verify that the helicity sign, determined from the magnetic polarity distribution pattern, is consistent with the sign derived from the photospheric helicity flux computed from magnetogram time series, as well as from other proxies such as sheared coronal loops, sigmoids, flare ribbons and/or the associated magnetic cloud observed in situ at 1 AU. The evolution of the tongues observed in emerging ARs is also closely similar to the evolution found in recent MHD numerical simulations. We also found that the elongation of the tongue formed by the leading magnetic polarity is significantly larger than that of the following polarity. This newly discovered asymmetry is consistent with an asymmetric Ω-loop emergence, trailing the solar rotation, which was proposed earlier to explain other asymmetries in bipolar ARs.


Active regions, magnetic fields Corona, structures Helicity, magnetic Helicity, observations 

Supplementary material

(MPG 1.068 kb).

(MPG 1.786 kb).

(MPG 2.021 kb).

(MPG 1.307 kb).

(MPG 1.386 kb).


  1. Abbett, W.P., Fisher, G.H., Fan, Y.: 2001, The effects of rotation on the evolution of rising omega loops in a stratified model convection zone. Astrophys. J. 546, 1194 – 1203. doi: 10.1086/318320. ADSCrossRefGoogle Scholar
  2. Archontis, V., Hood, A.W.: 2010, Flux emergence and coronal eruption. Astron. Astrophys. 514, A56. doi: 10.1051/0004-6361/200913502. ADSCrossRefGoogle Scholar
  3. Archontis, V., Moreno-Insertis, F., Galsgaard, K., Hood, A., O’Shea, E.: 2004, Emergence of magnetic flux from the convection zone into the corona. Astron. Astrophys. 426, 1047 – 1063. doi: 10.1051/0004-6361:20035934. ADSCrossRefGoogle Scholar
  4. Archontis, V., Hood, A.W., Savcheva, A., Golub, L., Deluca, E.: 2009, On the structure and evolution of complexity in sigmoids: a flux emergence model. Astrophys. J. 691, 1276 – 1291. doi: 10.1088/0004-637X/691/2/1276. ADSCrossRefGoogle Scholar
  5. Asai, A., Shibata, K., Ishii, T.T., Oka, M., Kataoka, R., Fujiki, K., Gopalswamy, N.: 2009, Evolution of the anemone AR NOAA 10798 and the related geo-effective flares and CMEs. J. Geophys. Res. 114, A00A21. doi: 10.1029/2008JA013291. CrossRefGoogle Scholar
  6. Attrill, G.D.R., Harra, L.K., van Driel-Gesztelyi, L., Démoulin, P.: 2007, Coronal “wave”: magnetic footprint of a coronal mass ejection? Astrophys. J. Lett. 656, 101 – 104. doi: 10.1086/512854. ADSCrossRefGoogle Scholar
  7. Aulanier, G., Török, T., Démoulin, P., DeLuca, E.E.: 2010, Formation of torus-unstable flux ropes and electric currents in erupting sigmoids. Astrophys. J. 708, 314 – 333. doi: 10.1088/0004-637X/708/1/314. ADSCrossRefGoogle Scholar
  8. Berdichevsky, D.B., Farrugia, C.J., Thompson, B.J., Lepping, R.P., Reames, D.V., Kaiser, M.L., Steinberg, J.T., Plunkett, S.P., Michels, D.J.: 2002, Halo-coronal mass ejections near the 23rd solar minimum: Lift-off, inner heliosphere, and in situ (1 AU) signatures. Ann. Geophys. 20, 891 – 916. doi: 10.5194/angeo-20-891-2002. ADSCrossRefGoogle Scholar
  9. Burnette, A.B., Canfield, R.C., Pevtsov, A.A.: 2004, Photospheric and coronal currents in solar active regions. Astrophys. J. 606, 565 – 570. doi: 10.1086/382775. ADSCrossRefGoogle Scholar
  10. Caligari, P., Moreno-Insertis, F., Schussler, M.: 1995, Emerging flux tubes in the solar convection zone. 1: Asymmetry, tilt, and emergence latitude. Astrophys. J. 441, 886 – 902. doi: 10.1086/175410. ADSCrossRefGoogle Scholar
  11. Canfield, R.C., Hudson, H.S., McKenzie, D.E.: 1999, Sigmoidal morphology and eruptive solar activity. Geophys. Res. Lett. 26, 627 – 630. doi: 10.1029/1999GL900105. ADSCrossRefGoogle Scholar
  12. Canou, A., Amari, T., Bommier, V., Schmieder, B., Aulanier, G., Li, H.: 2009, Evidence for a pre-eruptive twisted flux rope using the THEMIS vector magnetograph. Astrophys. J. Lett. 693, 27 – 30. doi: 10.1088/0004-637X/693/1/L27. ADSCrossRefGoogle Scholar
  13. Chae, J.: 2001, Observational determination of the rate of magnetic helicity transport through the solar surface via the horizontal motion of field line footpoints. Astrophys. J. Lett. 560, 95 – 98. doi: 10.1086/324173. ADSCrossRefGoogle Scholar
  14. Chae, J., Moon, Y.J., Park, Y.D.: 2004, Determination of magnetic helicity content of solar active regions from SOHO/MDI magnetograms. Solar Phys. 223, 39 – 55. doi: 10.1007/s11207-004-0938-9. ADSCrossRefGoogle Scholar
  15. Chandra, R., Schmieder, B., Aulanier, G., Malherbe, J.M.: 2009, Evidence of magnetic helicity in emerging flux and associated flare. Solar Phys. 258, 53 – 67. doi: 10.1007/s11207-009-9392-z. ADSCrossRefGoogle Scholar
  16. Chandra, R., Pariat, E., Schmieder, B., Mandrini, C.H., Uddin, W.: 2010, How can a negative magnetic helicity active region generate a positive helicity magnetic cloud? Solar Phys. 261, 127 – 148. doi: 10.1007/s11207-009-9470-2. ADSCrossRefGoogle Scholar
  17. Cheung, M., Schüssler, M., Moreno-Insertis, F.: 2005, 3D magneto-convection and flux emergence in the photosphere. In: Innes, D.E., Lagg, A., Solanki, S.A. (eds.) Chromospheric and Coronal Magnetic Fields, ESA SP-596, paper 54.1 (on CDROM). Google Scholar
  18. Cheung, M.C.M., Moreno-Insertis, F., Schüssler, M.: 2006, Moving magnetic tubes: fragmentation, vortex streets and the limit of the approximation of thin flux tubes. Astron. Astrophys. 451, 303 – 317. doi: 10.1051/0004-6361:20054499. ADSzbMATHCrossRefGoogle Scholar
  19. Cheung, M.C.M., Schüssler, M., Tarbell, T.D., Title, A.M.: 2008, Solar surface emerging flux regions: A comparative study of radiative MHD modeling and Hinode SOT observations. Astrophys. J. 687, 1373 – 1387. doi: 10.1086/591245. ADSCrossRefGoogle Scholar
  20. Cristiani, G., Martinez, G., Mandrini, C.H., Giménez de Castro, C.G., da Silva, C.W., Rovira, M.G., Kaufmann, P.: 2007, Spatial characterisation of a flare using radio observations and magnetic field topology. Solar Phys. 240, 271 – 281. doi: 10.1007/s11207-006-0337-5. ADSCrossRefGoogle Scholar
  21. Cristiani, G., Giménez de Castro, C.G., Mandrini, C.H., Machado, M.E., Silva, I.D.B.E., Kaufmann, P., Rovira, M.G.: 2008, A solar burst with a spectral component observed only above 100 GHz during an M class flare. Astron. Astrophys. 492, 215 – 222. doi: 10.1051/0004-6361:200810367. ADSCrossRefGoogle Scholar
  22. Delaboudiniére, J.-P., Artzner, G.E., Brunaud, J., Gabriel, A.H., Hochedez, J.F., Millier, F., et al.: 1995, EIT: Extreme-ultraviolet imaging telescope for the SOHO mission. Solar Phys. 162, 291 – 312. doi: 10.1007/BF00733432. ADSCrossRefGoogle Scholar
  23. Démoulin, P., Pariat, E.: 2009, Modelling and observations of photospheric magnetic helicity. Adv. Space Res. 43, 1013 – 1031. doi: 10.1016/j.asr.2008.12.004. ADSCrossRefGoogle Scholar
  24. Démoulin, P., Priest, E.R., Lonie, D.P.: 1996, Three-dimensional magnetic reconnection without null points 2. Application to twisted flux tubes. J. Geophys. Res. 101, 7631 – 7646. doi: 10.1029/95JA03558. ADSCrossRefGoogle Scholar
  25. Démoulin, P., Mandrini, C.H., van Driel-Gesztelyi, L., Thompson, B.J., Plunkett, S., Kovári, Z., Aulanier, G., Young, A.: 2002, What is the source of the magnetic helicity shed by CMEs? The long-term helicity budget of AR 7978. Astron. Astrophys. 382, 650 – 665. doi: 10.1051/0004-6361:20011634. ADSCrossRefGoogle Scholar
  26. Emonet, T., Moreno-Insertis, F.: 1998, The physics of twisted magnetic tubes rising in a stratified medium: two-dimensional results. Astrophys. J. 492, 804 – 821. doi: 10.1086/305074. ADSCrossRefGoogle Scholar
  27. Fan, Y.: 2008, The three-dimensional evolution of buoyant magnetic flux tubes in a model solar convective envelope. Astrophys. J. 676, 680 – 697. doi: 10.1086/527317. ADSCrossRefGoogle Scholar
  28. Fan, Y.: 2009, The emergence of a twisted flux tube into the solar atmosphere: Sunspot rotations and the formation of a coronal flux rope. Astrophys. J. 697, 1529 – 1542. doi: 10.1088/0004-637X/697/2/1529. ADSCrossRefGoogle Scholar
  29. Fan, Y., Fisher, G.H., Deluca, E.E.: 1993, The origin of morphological asymmetries in bipolar active regions. Astrophys. J. 405, 390 – 401. doi: 10.1086/172370. ADSCrossRefGoogle Scholar
  30. Georgoulis, M.K., LaBonte, B.J.: 2006, Reconstruction of an inductive velocity field vector from Doppler motions and a pair of solar vector magnetograms. Astrophys. J. 636, 475 – 495. doi: 10.1086/497978. ADSCrossRefGoogle Scholar
  31. Gibson, S.E., Fan, Y., Mandrini, C., Fisher, G., Démoulin, P.: 2004, Observational consequences of a magnetic flux rope emerging into the corona. Astrophys. J. 617, 600 – 613. doi: 10.1086/425294. ADSCrossRefGoogle Scholar
  32. Glover, A., Ranns, N.D.R., Harra, L.K., Culhane, J.L.: 2000, The onset and association of CMEs with sigmoidal active regions. Geophys. Res. Lett. 27, 2161 – 2164. doi: 10.1029/2000GL000018. ADSCrossRefGoogle Scholar
  33. Gopalswamy, N., Kaiser, M.L., Sato, J., Pick, M.: 2000, Shock wave and EUV transient during a flare. In: Ramaty, R., Mandzhavidze, N. (eds.) High Energy Solar Physics Workshop – Anticipating HESSI, ASP Conf. Ser. 206, 351 – 354. Google Scholar
  34. Green, L.M., Kliem, B.: 2009, Flux rope formation preceding coronal mass ejection onset. Astrophys. J. Lett. 700, 83 – 87. doi: 10.1088/0004-637X/700/2/L83. ADSCrossRefGoogle Scholar
  35. Green, L.M., López Fuentes, M.C., Mandrini, C.H., Démoulin, P., Van Driel-Gesztelyi, L., Culhane, J.L.: 2002, The magnetic helicity budget of a CME-prolific active region. Solar Phys. 208, 43 – 68. doi: 10.1023/A:1019658520033. ADSCrossRefGoogle Scholar
  36. Green, L.M., Kliem, B., Török, T., van Driel-Gesztelyi, L., Attrill, G.D.R.: 2007, Transient coronal sigmoids and rotating erupting flux ropes. Solar Phys. 246, 365 – 391. doi: 10.1007/s11207-007-9061-z. ADSCrossRefGoogle Scholar
  37. Hood, A.W., Archontis, V., Galsgaard, K., Moreno-Insertis, F.: 2009, The emergence of toroidal flux tubes from beneath the solar photosphere. Astron. Astrophys. 503, 999 – 1011. doi: 10.1051/0004-6361/200912189. ADSCrossRefGoogle Scholar
  38. Jeong, H., Chae, J.: 2007, Magnetic helicity injection in active regions. Astrophys. J. 671, 1022 – 1033. doi: 10.1086/522666. ADSCrossRefGoogle Scholar
  39. Jouve, L., Brun, A.S.: 2009, Three-dimensional nonlinear evolution of a magnetic flux tube in a spherical shell: Influence of turbulent convection and associated mean flows. Astrophys. J. 701, 1300 – 1322. doi: 10.1088/0004-637X/701/2/1300. ADSCrossRefGoogle Scholar
  40. LaBonte, B.J., Georgoulis, M.K., Rust, D.M.: 2007, Survey of magnetic helicity injection in regions producing X-class flares. Astrophys. J. 671, 955 – 963. doi: 10.1086/522682. ADSCrossRefGoogle Scholar
  41. Leamon, R.J., Canfield, R.C., Pevtsov, A.A.: 2002, Properties of magnetic clouds and geomagnetic storms associated with eruption of coronal sigmoids. J. Geophys. Res. 107(A9), SSH1-1. doi: 10.1029/2001JA000313. CrossRefGoogle Scholar
  42. Li, H., Schmieder, B., Song, M.T., Bommier, V.: 2007, Interaction of magnetic field systems leading to an X1.7 flare due to large-scale flux tube emergence. Astron. Astrophys. 475, 1081 – 1091. doi: 10.1051/0004-6361:20077500. ADSCrossRefGoogle Scholar
  43. Liu, J., Zhang, H.: 2006, The magnetic field, horizontal motion and helicity in a fast emerging flux region which eventually forms a delta spot. Solar Phys. 234, 21 – 40. doi: 10.1007/s11207-006-2091-0. ADSCrossRefGoogle Scholar
  44. Liu, J., Zhang, Y., Zhang, H.: 2008, Relationship between powerful flares and dynamic evolution of the magnetic field at the solar surface. Solar Phys. 248, 67 – 84. doi: 10.1007/s11207-008-9149-0. ADSCrossRefGoogle Scholar
  45. Longcope, D.W., Welsch, B.T.: 2000, A model for the emergence of a twisted magnetic flux tube. Astrophys. J. 545, 1089 – 1100. doi: 10.1086/317846. ADSCrossRefGoogle Scholar
  46. López Fuentes, M.C., Démoulin, P., Mandrini, C.H., van Driel-Gesztelyi, L.: 2000, The counterkink rotation of a non-Hale active region. Astrophys. J. 544, 540 – 549. doi: 10.1086/317180. ADSCrossRefGoogle Scholar
  47. López Fuentes, M.C., Démoulin, P., Mandrini, C.H., Pevtsov, A.A., van Driel-Gesztelyi, L.: 2003, Magnetic twist and writhe of active regions. On the origin of deformed flux tubes. Astron. Astrophys. 397, 305 – 318. doi: 10.1051/0004-6361:20021487. ADSCrossRefGoogle Scholar
  48. Luoni, M.L., Mandrini, C.H., Dasso, S., Démoulin, P., Van Driel-Gesztelyi, L.: 2007, From the photosphere to the interplanetary medium: The magnetic helicity sign from observations. Bol. Asoc. Argent. Astron. 50, 43 – 46. ADSGoogle Scholar
  49. MacTaggart, D., Hood, A.W.: 2009, On the emergence of toroidal flux tubes: general dynamics and comparisons with the cylinder model. Astron. Astrophys. 507, 995 – 1004. doi: 10.1051/0004-6361/200912930. ADSzbMATHCrossRefGoogle Scholar
  50. Magara, T.: 2001, Dynamics of emerging flux tubes in the Sun. Astrophys. J. 549, 608 – 628. doi: 10.1086/319073. ADSCrossRefGoogle Scholar
  51. Magara, T.: 2004, A model for dynamic evolution of emerging magnetic fields in the Sun. Astrophys. J. 605, 480 – 492. doi: 10.1086/382148. ADSCrossRefGoogle Scholar
  52. Magara, T., Longcope, D.W.: 2003, Injection of magnetic energy and magnetic helicity into the solar atmosphere by an emerging magnetic flux tube. Astrophys. J. 586, 630 – 649. doi: 10.1086/367611. ADSCrossRefGoogle Scholar
  53. Manchester, W. IV, Gombosi, T., DeZeeuw, D., Fan, Y.: 2004, Eruption of a buoyantly emerging magnetic flux rope. Astrophys. J. 610, 588 – 596. doi: 10.1086/421516. ADSCrossRefGoogle Scholar
  54. Mandrini, C.H., Démoulin, P., van Driel-Gesztelyi, L., Green, L., López Fuentes, M.C.: 2004, Magnetic helicity budget of solar-active regions from the photosphere to magnetic clouds. Astrophys. Space Sci. 290, 319 – 344. doi: 10.1023/B:ASTR.0000032533.31817.0e. ADSzbMATHCrossRefGoogle Scholar
  55. Mandrini, C.H., Pohjolainen, S., Dasso, S., Green, L.M., Démoulin, P., van Driel-Gesztelyi, L., Copperwheat, C., Foley, C.: 2005, Interplanetary flux rope ejected from an X-ray bright point. The smallest magnetic cloud source-region ever observed. Astron. Astrophys. 434, 725 – 740. doi: 10.1051/0004-6361:20041079. ADSCrossRefGoogle Scholar
  56. Moore, R.L., Sterling, A.C., Hudson, H.S., Lemen, J.R.: 2001, Onset of the magnetic explosion in solar flares and coronal mass ejections. Astrophys. J. 552, 833 – 848. doi: 10.1086/320559. ADSCrossRefGoogle Scholar
  57. Moreno-Insertis, F., Caligari, P., Schuessler, M.: 1994, Active region asymmetry as a result of the rise of magnetic flux tubes. Solar Phys. 153, 449 – 452. doi: 10.1007/BF00712518. ADSCrossRefGoogle Scholar
  58. Murray, M.J., Hood, A.W.: 2008, Emerging flux tubes from the solar interior into the atmosphere: Effects of non-constant twist. Astron. Astrophys. 479, 567 – 577. doi: 10.1051/0004-6361:20078852. ADSCrossRefGoogle Scholar
  59. Murray, M.J., Hood, A.W., Moreno-Insertis, F., Galsgaard, K., Archontis, V.: 2006, 3D simulations identifying the effects of varying the twist and field strength of an emerging flux tube. Astron. Astrophys. 460, 909 – 923. doi: 10.1051/0004-6361:20065950. ADSCrossRefGoogle Scholar
  60. Nindos, A., Zhang, J., Zhang, H.: 2003, The magnetic helicity budget of solar active regions and coronal mass ejections. Astrophys. J. 594, 1033 – 1048. doi: 10.1086/377126. ADSCrossRefGoogle Scholar
  61. Pariat, E., Démoulin, P., Berger, M.A.: 2005, Photospheric flux density of magnetic helicity. Astron. Astrophys. 439, 1191 – 1203. doi: 10.1051/0004-6361:20052663. ADSCrossRefGoogle Scholar
  62. Pariat, E., Aulanier, G., Schmieder, B., Georgoulis, M.K., Rust, D.M., Bernasconi, P.N.: 2004, Resistive emergence of undulatory flux tubes. Astrophys. J. 614, 1099 – 1112. doi: 10.1086/423891. ADSCrossRefGoogle Scholar
  63. Parker, E.N.: 1979, Sunspots and the physics of magnetic flux tubes. IX – Umbral dots and longitudinal overstability. Astrophys. J. 234, 333 – 347. doi: 10.1086/157501. ADSCrossRefGoogle Scholar
  64. Pevtsov, A.A.: 2002, Sinuous coronal loops at the Sun. In: Martens, P.C.H., Cauffman, D. (eds.) Multi-Wavelength Observations of Coronal Structure and Dynamics, COSPAR Colloq. Ser. 13, 125 – 134. CrossRefGoogle Scholar
  65. Pevtsov, A.A., Canfield, R.C., McClymont, A.N.: 1997, On the subphotospheric origin of coronal electric currents. Astrophys. J. 481, 973 – 977. doi: 10.1086/304065. ADSCrossRefGoogle Scholar
  66. Rust, D.M., Kumar, A.: 1996, Evidence for helically kinked magnetic flux ropes in solar eruptions. Astrophys. J. Lett. 464, 199 – 203. doi: 10.1086/310118. ADSCrossRefGoogle Scholar
  67. Scherrer, P.H., Bogart, R.S., Bush, R.I., Hoeksema, J.T., Kosovichev, A.G., Schou, J., et al.: 1995, The solar oscillations investigation – Michelson Doppler Imager. Solar Phys. 162, 129 – 188. doi: 10.1007/BF00733429. ADSCrossRefGoogle Scholar
  68. Strous, L.H., Scharmer, G., Tarbell, T.D., Title, A.M., Zwaan, C.: 1996, Phenomena in an emerging active region. I. Horizontal dynamics. Astron. Astrophys. 306, 947 – 959. ADSGoogle Scholar
  69. Tian, L., Alexander, D.: 2006, Role of sunspot and sunspot-group rotation in driving sigmoidal active region eruptions. Solar Phys. 233, 29 – 43. doi: 10.1007/s11207-006-2505-z. ADSCrossRefGoogle Scholar
  70. Tian, L., Alexander, D.: 2008, On the origin of magnetic helicity in the solar corona. Astrophys. J. 673, 532 – 543. doi: 10.1086/524129. ADSCrossRefGoogle Scholar
  71. Tian, L., Alexander, D.: 2009, Asymmetry of helicity injection flux in emerging active regions. Astrophys. J. 695, 1012 – 1023. doi: 10.1088/0004-637X/695/2/1012. ADSCrossRefGoogle Scholar
  72. Tian, L., Alexander, D., Nightingale, R.: 2008, Origins of coronal energy and helicity in NOAA 10030. Astrophys. J. 684, 747 – 756. doi: 10.1086/589492. ADSCrossRefGoogle Scholar
  73. Tian, L., Liu, Y., Yang, J., Alexander, D.: 2005b, The role of the kink instability of a long-lived active region AR 9604. Solar Phys. 229, 237 – 253. doi: 10.1007/s11207-005-6884-3. ADSCrossRefGoogle Scholar
  74. Tian, L., Démoulin, P., Alexander, D., Zhu, C.: 2011, On asymmetry of magnetic helicity in emerging active regions: High-resolution observations. Astrophys. J. 727, 28. doi: 10.1088/0004-637X/727/1/28. ADSCrossRefGoogle Scholar
  75. Titov, V.S., Démoulin, P.: 1999, Basic topology of twisted magnetic configurations in solar flares. Astron. Astrophys. 351, 707 – 720. ADSGoogle Scholar
  76. Tsuneta, S., Acton, L., Bruner, M., Lemen, J., Brown, W., Caravalho, R., et al.: 1991, The soft X-ray telescope for the SOLAR-A mission. Solar Phys. 136, 37 – 67. doi: 10.1007/BF00151694. ADSCrossRefGoogle Scholar
  77. van Driel-Gesztelyi, L., Petrovay, K.: 1990, Asymmetric flux loops in active regions. Solar Phys. 126, 285 – 298. doi: 10.1007/BF00153051. ADSCrossRefGoogle Scholar
  78. Wu, G.P., Huang, G.L., Tang, Y.H., Xu, A.A.: 2005, The observational evidence on the loop interaction in a flare CME event on April 15, 1998. Solar Phys. 227, 327 – 337. doi: 10.1007/s11207-005-2512-5. ADSCrossRefGoogle Scholar
  79. Yamamoto, T.T., Kusano, K., Maeshiro, T., Yokoyama, T., Sakurai, T.: 2005, Magnetic helicity injection and sigmoidal coronal loops. Astrophys. J. 624, 1072 – 1079. doi: 10.1086/429363. ADSCrossRefGoogle Scholar
  80. Yang, S., Büchner, J., Zhang, H.: 2009a, Magnetic helicity exchange between neighboring active regions. Astrophys. J. Lett. 695, 25 – 30. doi: 10.1088/0004-637X/695/1/L25. ADSCrossRefGoogle Scholar
  81. Yang, S., Zhang, H., Büchner, J.: 2009b, Magnetic helicity accumulation and tilt angle evolution of newly emerging active regions. Astron. Astrophys. 502, 333 – 340. doi: 10.1051/0004-6361/200810032. ADSzbMATHCrossRefGoogle Scholar
  82. Zwaan, C.: 1985, The emergence of magnetic flux. Solar Phys. 100, 397 – 414. doi: 10.1007/BF00158438. ADSCrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media B.V. 2011

Authors and Affiliations

  • M. L. Luoni
    • 1
    Email author
  • P. Démoulin
    • 3
  • C. H. Mandrini
    • 1
    • 2
  • L. van Driel-Gesztelyi
    • 3
    • 4
    • 5
  1. 1.Instituto de Astronomía y Física del EspacioCONICET-UBABuenos AiresArgentina
  2. 2.Facultad de Ciencias Exactas y NaturalesFCEN-UBABuenos AiresArgentina
  3. 3.Observatoire de Paris, LESIAUMR8109 (CNRS)Meudon Principal CedexFrance
  4. 4.UCL – Mullard Space Science LaboratoryDorkingUK
  5. 5.Konkoly Observatory of the Hungarian Academy of SciencesBudapestHungary

Personalised recommendations