Filament channels coincide with large-scale polarity inversion lines of the
photospheric magnetic field, where flux cancellation continually takes place.
High-cadence Solar Dynamics Observatory (SDO) images recorded in He II
30.4 nm and Fe IX 17.1 nm in August 2010 reveal numerous transient
brightenings occurring along the edge of a filament channel within a decaying
active region, where SDO line-of-sight magnetograms show strong
opposite-polarity flux in close contact. The brightenings are elongated
along the direction of the filament channel, with linear extents of several
arcseconds, and typically last a few minutes; they sometimes have the form
of multiple two-sided ejections with speeds on the order of 100 km/s.
Remarkably, some of the brightenings rapidly develop into larger scale
events, forming sheetlike structures that are eventually torn apart by
the diverging flows in the filament channel and ejected in opposite
directions. We interpret the brightenings as resulting from reconnections
among filament-channel field lines having one footpoint located in the
region of canceling flux. In some cases, the flow patterns that develop
in the channel may bring successive horizontal loops together and cause
a cascade to larger scales.