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 ~ 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: :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 VTT with AO! AR 10886 27 May 2006 hl=7N, cmd~0
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
Max: 2180 G
Min(PU): 316 G
Lower panel: Fe
Max: G
Min(PU): 423 G

8. Gamma Magnetic inclination for Si 1078.6 (upper panel) and
Fe (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