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The Moat Flow Observed in Two Different TRACE-Filters

The Moat Flow Observed in Two Different TRACE-Filters. Horst Balthasar Astrophysikalisches Institut Potsdam 1 July 2008. Partner involved:. Karin Muglach, ARTEP, NAVAL Research Laboratory. Reasons for these investigations.

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The Moat Flow Observed in Two Different TRACE-Filters

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  1. The Moat Flow Observed in Two Different TRACE-Filters Horst Balthasar Astrophysikalisches Institut Potsdam 1 July 2008

  2. Partner involved: • Karin Muglach, ARTEP, NAVAL Research Laboratory

  3. Reasons for these investigations The moat flow is well known. Outflow around sunspots with ´normal´ penumbra of ~300-500 m/s Moving magnetic features (MMF) with up to 2 km/s. There are extended polarimetric investigations of a special small sunspot with VTT and THEMIS (see Hauskolloquium 2007). Question: Can we learn something about the dynamics in and around this sunspot?

  4. Observations Sunspot NOAA 10886, 27 May 2006 Wavelength: TRACE-filters, WL and UV 170 nm. UV is formed next to the temperature minimum. Cadence: 1 minute, 409 images each. Duration: 6 h 40 m, 00:39 - 07:19 UT Pixel width: 0.5 arcsec. Data are corrected for spikes (hot pixel, particle events,....) Solar rotation and TRACE-orbit effects are removed. Solar oscillations are filtered out in WL, but not in UV.

  5. The sunspot AR 10886 27 May 2006 hl=7N, cmd~0 VTT with AO! combined from spectral continuum of 3 scans

  6. Mean Images Left: Whitelight Right: UV 170 nm (log)

  7. The magnetic field Total magnetic field strength derived from the two lines: Upper panel: Si 1078.6 Max: 2180 G Min(PU): 316 G Lower panel: Fe 1078.3 Max: 2308 G Min(PU): 423 G

  8. Gamma Magnetic inclination for Si 1078.6 (upper panel) and Fe 1078.3 (lower panel). The field is less inclined in higher layers.

  9. Mean Images Left: Whitelight Right: UV 170 nm (log)

  10. Whitelight movie

  11. UV-Movie

  12. Local Correlation Tracking Local correlation tracking (LCT) is a well-established technique to determine proper motions. Select a subfield in one image, identify it by best correlation in another image. Here: delta t = 8 min.

  13. LCT Results LCT delivers horizontal velocities in Cartesian coordinates, 401 maps each. These values are transformed into a radial and a tangential component. Averaging all 401 maps.

  14. LCT 4 Box width: 4 Pixel Upper panels: WL Lower: UV Left: radial component, Right: tangential component.

  15. LCT 4 Box width: 4 Pixel Subfield 220 x 200 Upper panels: WL Lower: UV Left: radial component, Right: tangential component.

  16. LCT 10 Box width: 10 Pixel Upper panels: WL Lower: UV Left: radial component, Right: tangential component.

  17. LCT 10 Box width: 10 Pixel Subfield 220x 200 Upper panels: WL Lower: UV Left: radial component, Right: tangential component.

  18. Radial dependence Intensity, radial and tangetial velocity component, averaged over azimuth. Solid line: whitelight, dashed: UV 170 nm. Dotted: error ranges. (for boxsize 4 pixels)

  19. Radial dependence Same as before but for boxsize 10.

  20. Summary • We see an outflow everywhere in the moat. • For the inner moat we find higher velocities in UV, and vice versa in the outer moat. • Both outflow curves, WL and UV, reach zero at the same distance from the spot center. • The velocities are higher if a larger tracking box is selected. • Compared to other spots, this moat is rather extended (~4 radii)

  21. Outlook • Comparison with other methods ( Fisher & Welsch, or Bovelet & Wiehr). • New observations with 2D-spectropolarimeters. • Need of higher spatial resolution  GREGOR

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