Magnetic Flux Transport and the Hemispheric Pattern of Filaments - PowerPoint PPT Presentation

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Magnetic Flux Transport and the Hemispheric Pattern of Filaments

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    1. Magnetic Flux Transport and the Hemispheric Pattern of Filaments

    3. BACKGROUND

    4. The hemispheric pattern Filaments can be assigned a chirality:

    5. Photospheric flux transport Normal magnetic field at photosphere evolves according to surface flux transport model (Wang, Sheeley, DeVore):

    6. Previous work Mackay & van Ballegooijen (2005): systematic study of pair of idealised bipolar regions; using flux transport and magneto-frictional model - coronal field responds to photospheric motions by relaxing toward series of force-free equilibria.

    7. Hypothesis The hemispheric pattern of quiescent filament chirality is caused by: photospheric transport of magnetic flux; dominant helicities (Pevtsov, Canfield & Metcalf 1995); dominant bipole tilt angles (Joys Law).

    8. OBSERVATIONS

    9. Observed filaments Sample of 254 filaments over 5 month period from daily Big Bear H? images. Positions identified on Kitt Peak synoptic magnetograms (CR1949 to CR1954).

    10. Observed filament chiralities 99 filaments have definite chirality (statistically significant) based on observations of barbs, 64 dextral and 35 sinistral.

    11. Aim of this project (1) Model observed evolution of surface magnetic field over many rotations, including emerging flux with correct helicity. (2) Simulate coupled evolution of 3D coronal field through sequence of nonlinear force-free equilibria. (3) Compare chirality of flux rope structures with corresponding observed filaments.

    12. SIMULATION OF SURFACE MAGNETIC FIELD

    13. Application to real photosphere Attempt to simulate evolution of real Br on photosphere with spherical flux transport code. Start from observed magnetogram (corrected for differential rotation) ...

    14. Previous work Mackay, Gaizauskas & van Ballegooijen (2000) applied the model to filament formation in an observed activity complex.

    15. Evolution over longer periods Example evolution with no resetting to potential at each rotation. Accuracy in strong field regions is lost after one rotation due to newly emerging flux.

    16. Emerging flux Developed a semi-automated procedure: compare successive magnetograms; find new bipolar regions; measure key properties; insert as ideal bipoles into simulation.

    17. Simulation with emerging flux

    18. Where next? We have developed a new technique for simulating the global coronal magnetic field evolution over an extended period, with 3D non-potential modelling based on observed photospheric magnetograms. We apply the model to a specific 5 month period to study the origin of the hemispheric pattern of filaments: dynamic photospheric boundary conditions complete; data on observed filaments is collected;