  Continuous observations of sunspot penumbrae with the Solar Optical Telescope
aboard \textit{Hinode} clearly show that the outer boundary of the penumbra
fluctuates around its averaged position. The penumbral outer boundary moves
inward when granules appear in the outer penumbra. We discover that such
granules appear one after another while moving magnetic features (MMFs) are
separating from the penumbral ``spines'' (penumbral features that have stronger
and more vertical fields than those of their surroundings). These granules that
appear in the outer penumbra often merge with bright features inside the
penumbra that move with the spines as they elongate toward the moat region.
This suggests that convective motions around the penumbral outer boundary are
related to the disintegration of magnetic flux in the sunspot. We also find
that dark penumbral filaments frequently elongate into the moat region in the
vicinity of MMFs that detach from penumbral spines. Such elongating dark
penumbral filaments correspond to nearly horizontal fields extending from the
penumbra. Pairs of MMFs with positive and negative polarities are sometimes
observed along the elongating dark penumbral filaments. This strongly supports
the notion that such elongating dark penumbral filaments have magnetic fields
with a ``sea serpent''-like structure. Evershed flows, which are associated
with the penumbral horizontal fields, may be related to the detachment of the
MMFs from the penumbral spines, as well as to the formation of the MMFs along
the dark penumbral filaments that elongate into the moat region.
