Interpretation of sigmoid structure and evolution

Sigmoid evolution across disk:

  • Yohkoh movie
  • TRACE movie
  • EIT movie
  • BBSO H-alpha movie- sigmoidal filament forms and evolves - also see high cadence movies for BBSO observations of filament development
  • MDI magnetic field movie
    • Summary: Sigmoid is most visible in very hot backwards S-shaped loops and a cold backwards S-shaped filament (i.e., X-ray and in absorption) for most of its disk passage, except during brightening of August 21 - then a backwards S shape is visible in emission at a range of temperatures.

    Mature sigmoid filament:

    August 19 ~ 14:00 UT - 18:00 mature filament:

    Images:  BBSO 16:30 UT, BBSO 17:02 UT, MLSO/PICS(dPmon) 18:05, MLSO/CHIP 17:02

    Overlays

    Comments on overlays:
    1) The dark sigmoidal filament seen in H-alpha is also observed in absorption in TRACE 171 and 284 and the CDS lines .
    2) The filament lies along a neutral line separating negative (yellow) and positive (blue) polarity field (although things get messy towards the bottom of the sigmoid).
    3) Sigmoidal loops in emission are only really visible in X-ray SXT observations. Backwards-S shaped loops appear to connect the negative (yellow) and positive (blue) poles - both in a more compact "northward" sigmoid that extends to the strong and compact positive sunspot pole, and "southward" loop extensions that appear to extend to the more diffuse positive field down and to the right of the compact positive spot.  Loops connecting to both the northward and southward positive poles are found in a linear force-free extrapolation of the magnetic field by Mandrini et al and the nonlinear force-free extrapolation by Liu et al.  An even more pronounced double S (northward and southward) is found the sigmoid structure of August 21, when cooler lines saw loops outlining the "northward" sigmoid, and the bulk of the hottest X-ray lines saw a "southward", or more extended sigmoid - see below.
    4) The filament appears to lie between the "northward" and "southward" sigmoid on August 19.

    Sigmoid filament disappearance and brightening:

    August 19-20 - disappearing filament:

    August 21 ~ 18:21 UT - disappearing filament and S-shaped brightening: Comments on movies:
    1) During Aug 21 brightening, some filament seems to remain/reappear/slosh back and forth in middle of S (see BBSO movie) and also may be visible in absorption down the middle of the S in CDS He1.  The trigger for the flare may be the emerging magnetic flux near the center of the S, where small H-alpha loops across the S are visible and a bipolar magnetic field region can be seen to emerge (see particularly frames 110-120 in the MDI magnetic movie).
    2) TRACE movies of the August 21 brightening show loops both sheared along the S, and more "bipolar" ones in the middle perpendicular to the S shape.
    Overlays:
  • CDS: Variation of bright sigmoid with wavelength, overlay of Fe 19 contour on other lines
  • CDS and TRACE: CDS contours overlaid on TRACE 171, 284
  • SXT and TRACE: SXT contours overlaid on TRACE 171, 284
  • CDS, SXT, and TRACE: CDS and SXT contours overlaid on TRACE 284
  • BBSO and SXT:SXT contours overlaid on BBSO H-alpha
  • BBSO and TRACE: TRACE 284 contours overlaid on BBSO H-alpha
  • BBSO and MDI: MDI contours overlaid on BBSO
  • MDI and SXT: SXT contours overlaid on MDI
  • SXT and MDI: MDI contours overlaid on SXT
  • SXT and Mg10: CDS Mg10 contours overlaid on SXT
  • MDI and Mg10: CDS Mg10 contours overlaid on MDI
  • Mg10 and MDI: MDI contours overlaid on CDS Mg10
  • He1 and MDI: MDI contours overlaid on CDS He1
  • O5 and MDI: MDI contours overlaid on CDS O5
  • MDI and O5 and He1: CDS O5 and He1 overlaid on MDI
  • BBSO and O5 and He1: CDS O5 and He1 overlaid on BBSO
    • Comments on overlays:
    1) Rotation of structure (clockwise, cold->hot) is observed in CDS lines.
    2) Emerging bipolar region just above the center of the sigmoid shows dark H-alpha loops across the sigmoid connecting the small bipole's negative (yellow) to positive (blue).  This emerging region is also seen as a transition region brightening - most apparent in CDS He1 and O5.
    3) Downward slanting spur sticking out from center of "northward" sigmoid (associated with extension of negative polarity (black) magnetic field) with dark patch below is visible at all wavelengths during brightening (possible exception is X-ray emission)
    4) Overlays of CDS lines on TRACE 171&284 shows that the cold lines (He1,O5) pick up the moss (footpoints?) and the hot lines pick up the (higher?) central "loops".
    5) SXT loops extend below the more compact sigmoid seen in cooler lines, meeting the "southward" positive (white) magnetic pole down and to the right of the main compact positive sunspot near which most of the sigmoids seen in other lines terminate .  It is possible that there are SXT loops connected to both the "northward" and the "southward" positive poles, as is the case for August 19, but this is difficult to determine with the quarter resolution SXT image available. TRACE movies do show brightening along both the main sigmoid structure connecting to the "northward" compact positive pole, and the lower loops that connect to the "southward" pole.  This can be compared to a linear force-free extrapolation of the magnetic field by Mandrini et al- both the northward and southward loops are apparent.
    6) Remnant of the filament still lies along a neutral line, in a similar position but lacking the upper portion of the mature filament of August 19.

    Jet associated with sigmoid region:

    August 26 >~ 21:00 UT - jet eruption:

    Movies: CDS, EIT/LASCO, MLSO/CHIP, TRACE
    Overlays
    Further analysis of jet

    Sigmoid working group