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Emergence of Small-Scale Magnetic Loops in the Quiet Sun Internetwork

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Emergence of Small-Scale Magnetic Loops in the Quiet Sun Internetwork. R. Centeno, H Socas-Navarro, B. Lites, M. Kubo High Altitude Observatory (NCAR), Boulder CO 80301, USA. Z. Frank, R. Shine, T. Tarbell, A. Title Lockheed Martin Space and Astrophysics Laboratory, Palo Alto, CA, USA. - PowerPoint PPT Presentation

Text of Emergence of Small-Scale Magnetic Loops in the Quiet Sun Internetwork

  • Emergence of Small-Scale Magnetic Loops in the Quiet Sun InternetworkR. Centeno, H Socas-Navarro, B. Lites, M. KuboHigh Altitude Observatory (NCAR), Boulder CO 80301, USA

    K. Ichimoto, S. Tsuneta, Y. Katsukawa, Y. SuematsuNational Astronomical Observatory of Japan, Tokyo, JapanT. ShimizuJapan Aerospace Exploration Agency, Tokyo, JapanS. NagataKwasan and Hida Observatories, Kyoto University, JapanPresented by Angelo P. VerdoniCenter for Solar-Terrestrial Research Fall 2007The Astrophysical Journal, Volume 666, Issue 2, pp. L137-L140. Z. Frank, R. Shine, T. Tarbell, A. TitleLockheed Martin Space and Astrophysics Laboratory, Palo Alto, CA, USA

    FALL 2007CSTR Journal Club09/27/07

    IntroductionPresented in this paper is clear evidence of the emergence and temporal evolution of a small-scale InterNetwork (IN) magnetic loop in the quiet Sun photosphere.

    The nature of InterNetwork (IN) magnetic fields is currently a hot topic of debate:Strong kG field strengths associated with small filling factorsaPredominance of weak magnetic fields (~300 500 G)b

    Litesc , using the Advanced Stokes Polarimeter (ASP), reports Horizontal Internetwork Fields (HIFs) with typical sizes of 1 and lifetimes of ~ 5 minutes, suggesting small magnetic loops are being advected towards the surface by the upward motion of the plasma inside the granule.

    Measurement of the full topology of a magnetic loop requires accurate 2-D spectropolarimetric maps of the four Stokes parameters, with high S/N ratio (~ 10-3 continuum intensity), high spatial resolution and good consistent seeing conditions. The Spectro-Polarimetr (SP) of the Solar Optical Telescope (SOT) on board Hinoded meets all of these requirements.

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    Observations: Hinode SP/SOTFigures taken from: http://solarb.msfc.nasa.gov/documents/Tarbell_SolarB.pdf

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    Observations

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    Magnetic Flux Density and Field Topology To quantify the magnetic flux density and its topology, full Stokes LTE inversions ( using LILIAe ) of pixels with non-negligible linear or circular polarization signals.

    LTE inversions should give reliable magnetic flux density values. However, some of the signals are marginally above noise level.

    By adjusting various parameters ( one example, keeping field height constant or allowing linear variation in height ) different values of the flux density were calculated. So, the apparent transverse and longitudinal flux densities were computed from the integrated polarization signalsf and the LTE inversione was used to determine the field topology (which remained consistently independent of parameter variation).

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    Magnetic Flux Density and Field Topology Figure shows ( for the 4 X 4 region ) the time sequence of the longitudinal and transverse flux density ( 1st and 2nd row respectively ). The bottom row shows the field orientation with color-coded pixels representing inclination values and arrows representing the direction of positive polarity.

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    Magnetic Flux Density and Field Topology t = 0, barely any magnetic signal present in the granular region centered at approximately (1,2) t = 2 min, new concentration of mostly horizontal ( transverse ) flux density appears. The field is parallel to the surface and azimuth makes angle ~ 60 degrees with E-W direction t = 4 min, magnetic feature has stretched in the linear direction. Magnetic poles now apparent. t = 6 min, transverse flux is not detectable with vertical dipoles visibly drifting towards granule boundary.

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    Magnetic Flux Density and Field Topology Due to the azimuth ambiguity there are two possible topology configurations for the magnetic loop seen at t = 6 min.

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    ConclusionsObservational evidence is presented of an emergent magnetic loop structure at quiet sun disk center. The flux emerges within granular region showing strong horizontal magnetic signal flanked by traces of two vertical opposite polarities.

    This event brings ~ 1017 Mx of apparent longitudinal magnetic flux and does not seem to have any major influence on the shape of the underlying granulation pattern. In agreement with simulationsg where small scale magnetic loop structures with less than 1018 Mx of longitudinal flux are not sufficiently buoyant to rise coherently against the granulation, and produce no visible disturbances.

    The convective motions carry the vertical magnetic flux towards the intergranular lanes, where it stays confined for longer times. This could explain why transverse magnetic flux (observed at disk center) is in general co-spatial with granules while longitudinal flux tends to be concentrated in the intergranular lanes.

    FALL 2007CSTR Journal Club09/27/07

    References

    Sanchez Almeida, J., Lites, B.W., ApJ, 532, 1215

    Lin, H, 1995, ApJ, 446, 421 Lin, H., Rimmele, T., 1999, ApJ, 514, 448

    Lites, B.W., Leka, K.D., Skumanich, A., Martinez Pillet, V., Shimizu, T., 1996, ApJ, 460, 1019

    Kosugi, T. et al, 2007, Solar Physics, submitted

    Socas-Navarro, H., 2001, in Advanced Solar Polarimetry-Theory, Observation and Instrumentation, edited by M. Sigwarth, 236, 487

    Lites, B.W. et al, 2007, ApJ, submitted

    Cheung, M.C.M., et al, 2007, A&A, 467, 703

    X and y axis are in arc seconds and the color coded bars on the right represent (from top to bottom) 1. Longitudinal apparent flux density units of Mx cm-2 ranges from -70 to -702. Transverse apparent flux density units of Mx cm-2 ranges from 0 to 2003. Magnitude of inclination in degrees from 0 to 180 degrees.

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