  Recent observations suggest that magnetic flux cancellation may play a
crucial role in heating the Sun's upper atmosphere (chromosphere, transition
region, corona). Here, we intended to validate an analytic model for magnetic
reconnection and consequent coronal heating, driven by a pair of converging and
cancelling magnetic flux sources of opposite polarities. For this test, we
analyzed photospheric magnetic field and multi-wavelength UV/EUV observations
of a small-scale flux cancellation event in a quiet-Sun internetwork region
over a target interval of 5.2 hr. The observed cancellation event exhibits a
converging motion of two opposite-polarity magnetic patches on the photosphere
and red-shifted Doppler velocities (downflows) therein consistently over the
target interval, with a decrease in magnetic flux of both polarities at a rate
of 10$^{15}$ Mx s$^{-1}$. Several impulsive EUV brightenings, with differential
emission measure values peaked at 1.6-2.0 MK, are also observed in the shape of
arcades with their two footpoints anchored in the two patches. The rate of
magnetic energy released as heat at the flux cancellation region is estimated
to be in the range of (0.2-1)$\times$10$^{24}$ erg s$^{-1}$ over the target
interval, which can satisfy the requirement of previously reported heating
rates for the quiet-Sun corona. Finally, both short-term (a few to several tens
of minutes) variations and long-term (a few hours) trends in the magnetic
energy release rate are clearly shown in the estimated rate of radiative energy
loss of electrons at temperatures above 2.0 MK. All these observational
findings support the validity of the investigated reconnection model for plasma
heating in the upper solar atmosphere by flux cancellation.
