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Figure 1. A sunspot observed with Hinode Solar Optical Telescope.
A bright filamentary structure at the center of the square is "light bridge."(JAXA/NAOJ)
Sunspots - New chromospheric activities revealed in the light bridges -
keywords: hinode, solar
Sunspots (Figure 1) are the cross section of magnetic
flux bundles at the solar surface, originally emerged
from the solar interior. The strong magnetic flux
prevents the heat from transporting convectively
from the interior to the surface, resulting in lower temperature
and visually dark.
The solar observing satellite "Hinode" has been investigating
sunspots in details with high spatial resolution never
achieved so far. The sunspot movies sometimes show
the formation of light bridges in the sunspot umbrae.
The light bridges are one of the fundamental magnetic structures
in sunspots, separating two umbral regions with filamentary
structure or photospheric-like morphological features.
Hinode's Ca II H movie observations
have revealed that a sunspot light bridge produces
chromospheric plasma ejections intermittently and
recurrently for more than 1 day (Figure 2).
With detailed analysis of high-resolution magnetic field
measurements, we found very strong vertical electric
current density along the light bridge.
The observations suggest that current-carrying highly
twisted magnetic flux tubes are trapped below a cusp-shaped
magnetic structure along the light bridge.
The presence of trapped current-carrying flux tubes is essential
for causing long-lasting chromospheric plasma ejections at the interface
with pre-existing vertically oriented umbral fields.
Quantitative understanding of sunspot magnetic field
behaviors may give some hits for understanding various explosive
events observed in the universe and space plasma
For details, refer to Shimizu et al.
"Hinode observation ofthe magnetic fields in a sunspot light bridge accompanied by
long-lasting chromospheric plasma ejections," The Astrophysical
Journal, Vol. 696, L66-L69, 2009
Figure 2. Some Ca II H snapshots of chromospheric jets, which were observed
intermittently and recurrently at the sunspot light bridge. The field of view is same as the square in Figure 1.(JAXA/NAOJ)
Toshifumi Shimizu (ISAS/JAXA)
August,2009