1. Structure and Dynamics in Sunspot Light Bridges
Hirzberger　et al. (2002)
Berger & Berdyugina (2003)

2. Introduction -
Knowing physical processes in fine structure of sunspot is crucial for understanding the subphotospheric structure of sunspots
Systematic reduction of magnetic field strength compared with the surrounding umbra
Light bridge consists of a chain of umbral dots - -
Muller (1979) -
Positive correlation between brightness and upward velocities Rimmele (1997)

3. Hirzberger　et al. (A&A 383, p275, 2002)
- SVST on La Palma
- 30 June, 1995
NOAA 7886
- 66 min duration
20 sec interval
- 57" x 48" FOV
0".062/pix sampling
- White Light with real time frame selection

4. Trajectories of Grains in Light Bridge
Dark end
position of birth
Bright end
position of death

5. Histogram of Mean Velocities

6. Regularity in Appearance-
Chains of five or more grains ( > 2")
Decay in a few minutes
Recur many times (not always exactly same position) - -

7. Results - Irregular motion of grains (up to 1.5 km/s)
Regularity in appearance
“Structure of convective cell is strongly dependent on the magnetic field strength”
Weiss et al.(1996)

8. Berger & Berdyugina (ApJ 589, L117, 2003)
Swedish 1m Solar Telescope with AO system

9. Observation - 25 Sept., 2002 (NOAA 10132) - Time resolution : 20 sec
- Spatial resolution: 110 km
- TiO band (705.7 nm)
- Real time frame selection

10. Mm Mm

11. Time-slice of the Light Bridge

12. Results - Unidirectional motion of grains in TiO images
From time-slice : 0.15 – 4.5 km/s (mean 0.9 km/s) From LCT : 0 – 2.3 km/s (mean 0.4 km/s)
"Sloshing back-and-forth" motion in 160nm
Some grains break from the light bridge to become umbral dots - -