  As observed in spectral lines originating from the chromosphere, transition
region, and low corona, active regions are surrounded by an extensive
"circumfacular" area which is darker than the quiet Sun. We examine the
properties of these dark moat- or canopy-like areas using \ion{Fe}{9} 17.1 nm
images and line-of-sight magnetograms from the {\it Solar Dynamics
Observatory}. The 17.1 nm canopies consist of fibrils (horizontal fields
containing EUV-absorbing chromospheric material) clumped into featherlike
structures. The dark fibrils initially form a quasiradial or vortical pattern
as the low-lying field lines fanning out from the emerging active region
connect to surrounding network and intranetwork elements of the opposite
polarity. The area occupied by the 17.1 nm fibrils expands as supergranular
convection causes the active region flux to spread into the background medium;
the outer boundary of the dark canopy stabilizes where the diffusing flux
encounters a unipolar region of the opposite sign. The dark fibrils tend to
accumulate in regions of weak longitudinal field and to become rooted in
mixed-polarity flux. To explain the latter observation, we note that the
low-lying fibrils are more likely to interact with small loops associated with
weak, opposite-polarity flux elements in close proximity, than with high loops
anchored inside strong unipolar network flux. As a result, the 17.1 nm fibrils
gradually become concentrated around the large-scale polarity inversion lines
(PILs), where most of the mixed-polarity flux is located. Systematic flux
cancellation, assisted by rotational shearing, removes the field component
transverse to the PIL and causes the fibrils to coalesce into long PIL-aligned
filaments.
