  The second Hi-C flight (Hi-C2.1) provided unprecedentedly-high spatial and
temporal resolution ($\sim$250km, 4.4s) coronal EUV images of Fe IX/X emission
at 172 \AA, of AR 12712 on 29-May-2018, during 18:56:21-19:01:56 UT. Three
morphologically-different types (I: dot-like, II: loop-like, III:
surge/jet-like) of fine-scale sudden-brightening events (tiny microflares) are
seen within and at the ends of an arch filament system in the core of the AR.
Although type Is (not reported before) resemble IRIS-bombs (in size, and
brightness wrt surroundings), our dot-like events are apparently much hotter,
and shorter in span (70s). We complement the 5-minute-duration Hi-C2.1 data
with SDO/HMI magnetograms, SDO/AIA EUV images, and IRIS UV spectra and slit-jaw
images to examine, at the sites of these events, brightenings and flows in the
transition-region and corona and evolution of magnetic flux in the photosphere.
Most, if not all, of the events are seated at sites of opposite-polarity
magnetic flux convergence (sometimes driven by adjacent flux emergence),
implying likely flux cancellation at the microflare's polarity inversion line.
In the IRIS spectra and images, we find confirming evidence of field-aligned
outflow from brightenings at the ends of loops of the arch filament system. In
types I and II the explosion is confined, while in type III the explosion is
ejective and drives jet-like outflow. The light-curves from Hi-C, AIA and IRIS
peak nearly simultaneously for many of these events and none of the events
display a systematic cooling sequence as seen in typical coronal flares,
suggesting that these tiny brightening-events have
chromospheric/transition-region origin.
