caa a22 4500 445346051 CHVBK 20180317142829.0 cr unu---uuuuu 170323e20110501xx s 000 0 eng 10.1007/s11207-011-9731-8 doi (NATIONALLICENCE)springer-10.1007/s11207-011-9731-8 Twisted Flux Tube Emergence Evidenced in Longitudinal Magnetograms: Magnetic Tongues [Elektronische Daten] [M. Luoni, P. Démoulin, C. 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 1AU. 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. Springer Science+Business Media B.V., 2011 Active regions, magnetic fields nationallicence Corona, structures nationallicence Helicity, magnetic nationallicence Helicity, observations nationallicence Luoni M. Instituto de Astronomía y Física del Espacio, CONICET-UBA, CC. 67, Suc. 28, 1428, Buenos Aires, Argentina aut Démoulin P. Observatoire de Paris, LESIA, UMR8109 (CNRS), 92195, Meudon Principal Cedex, France aut Mandrini C. Instituto de Astronomía y Física del Espacio, CONICET-UBA, CC. 67, Suc. 28, 1428, Buenos Aires, Argentina aut van Driel-Gesztelyi L. Observatoire de Paris, LESIA, UMR8109 (CNRS), 92195, Meudon Principal Cedex, France aut Solar Physics Springer Netherlands 270/1(2011-05-01), 45-74 0038-0938 270:1<45 2011 270 11207 https://doi.org/10.1007/s11207-011-9731-8 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s11207-011-9731-8 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Luoni M. Instituto de Astronomía y Física del Espacio, CONICET-UBA, CC. 67, Suc. 28, 1428, Buenos Aires, Argentina aut NATIONALLICENCE 700 1- Démoulin P. Observatoire de Paris, LESIA, UMR8109 (CNRS), 92195, Meudon Principal Cedex, France aut NATIONALLICENCE 700 1- Mandrini C. Instituto de Astronomía y Física del Espacio, CONICET-UBA, CC. 67, Suc. 28, 1428, Buenos Aires, Argentina aut NATIONALLICENCE 700 1- van Driel-Gesztelyi L. Observatoire de Paris, LESIA, UMR8109 (CNRS), 92195, Meudon Principal Cedex, France aut NATIONALLICENCE 773 0- Solar Physics Springer Netherlands 270/1(2011-05-01), 45-74 0038-0938 270:1<45 2011 270 11207 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer