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

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?

Observations

Sunspot NOAA 10886, 27 May 2006Wavelength: 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.

The sunspot AR 10886

27 May 2006 hl=7N, cmd~0

VTT with AO!

combined from spectral continuum of 3 scans

Mean Images

Left: Whitelight Right: UV 170 nm (log)

The magnetic field

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

Gamma

Magnetic inclination for

Si 1078.6 (upper panel) and

Fe 1078.3 (lower panel).

The field is less inclined in higher layers.

Mean Images

Left: Whitelight Right: UV 170 nm (log)

Whitelight movie

UV-Movie

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.

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.

LCT 4

Box width: 4 Pixel

Upper panels: WL

Lower: UV

Left: radial component,

Right: tangential component.

LCT 4

Box width: 4 Pixel

Subfield 220 x 200

Upper panels: WL

Lower: UV

Left: radial component,

Right: tangential component.

LCT 10

Box width: 10 Pixel

Upper panels: WL

Lower: UV

Left: radial component,

Right: tangential component.

LCT 10

Box width: 10 Pixel

Subfield 220x 200

Upper panels: WL

Lower: UV

Left: radial component,

Right: tangential component.

Radial dependence

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

Radial dependence

Same as before but for

boxsize 10.

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)

Outlook

Comparison with other methods ( Fisher & Welsch, or Bovelet & Wiehr).

New observations with 2D-spectropolarimeters. Need of higher spatial resolution GREGOR