  Downflows with high velocities occur in the transition region above many
sunspots; however, how these signatures evolve over short time-scales in both
spatial and spectral terms is still unknown. In this article, we investigate
the evolution of downflows detected within the transition region on time-scales
of the order minutes and search for clues as to their formation mechanisms in
co-temporal imaging data. The high-resolution spectral and imaging data used to
identify downflows here were sampled by IRIS on the 20th and 21st May 2015.
Imaging data from the Hinode and SDO satellites provided context about the
wider solar atmosphere. Four downflows were identified and analysed. The
potential super-sonic components of these downflows had widths of around 2" and
evolved over time-scales of the order minutes. The measured apparent downflow
velocities were structured both in time and space, with the highest apparent
velocities occurring above a bright region detected in Si IV 1400 {\AA} images.
Downflows with apparent velocities below 50 km s^{-1} were observed to extend a
few arcsecs away from the foot-points suggesting the potential super-sonic
components are linked to larger-scale flows. The electron density and mass flux
for these events were within the ranges 10^{9.6}-10^{10.2} cm^{-3} and
10^{-6.81}-10^{-7.48} g cm^{-2} s^{-1}, respectively. Each downflow formed at
the foot-point of thin `fingers' extending out around 3-5" in Si IV 1400 {\AA}
data with smaller widths (<1") than the super-sonic downflows. Downflows can
appear, disappear, and recur within time-scales of less than one hour in
sunspots. As potential super-sonic downflow signatures were detected at the
foot-points of both extended fingers in Si IV 1400 {\AA} SJI data and sub-sonic
downflows in Si IV 1394 \AA\ spectra, it is likely that these events are linked
to flows within structures such as coronal loops.
