Magnetic reconnection is thought to be responsible for
eruptive events on the Sun, from large-scale CMEs to
small-scale events that are barely resolved. The height in
the solar atmosphere where the reconnection takes place may
significantly influence the morphology and appearance of the
events. This might be the main distinction between events
such as e.g. Ellerman bombs, IRIS bombs, or explosive events
which are observed in spectral lines forming at different
temperatures showing different line profile characteristics.
Here we report a prolonged reconnection event caused by a
magnetic feature moving from a sunspot to an adjacent pore.
Data-driven nonlinear force-free field extrapolations and
magneto-frictional models suggest that the strong dominant
sunspot and the pore of the same polarity lead to a
canopy-type field structure at low heights. The moving
magnetic feature of the opposite polarity reconnects with
the overlying canopy. The models suggest a height of the
reconnection only about 500 km above tau=1. The IRIS
observations of this event show complex Mg II, C II, and Si
IV line profiles, in part similar to those reported earlier
for IRIS bombs. We find evidence for strong spatial,
velocity discontinuities from red to blueshifts in the Si IV
Dopplergrams at the reconnection site. Additionally,
multiple blueshifted components along the same line of sight
are also observed. Further, there is evidence that the
downflowing plasma from the reconnection site interacts with
chromospheric plasma, increasing the apparent brightness of
the structure. The magnetic modelling of these events
supports the earlier suggestions that the location of the
reconnection of these active region UV bursts is very low in
the atmosphere, in the low chromosphere or even in the
photosphere. Small-scale events like this may give insights
into the dynamics and complex evolution of large-scale
eruptive events on the Sun.
