  Solar flares involve the sudden release of magnetic energy in the solar
corona. Accelerated nonthermal electrons have often been invoked as the primary
means for transporting the bulk of the released energy to the lower solar
atmosphere. However, significant challenges remain for this scenario,
especially in accounting for the large number of accelerated electrons inferred
from observations. Propagating magnetohydrodynamics (MHD) waves, particularly
those with subsecond/second-scale periods, have been proposed as an alternative
means for transporting the released flare energy, likely alongside the electron
beams, while observational evidence remains elusive. Here we report a possible
detection of such waves in the late impulsive phase of a two-ribbon flare. This
is based on ultrahigh cadence dynamic imaging spectroscopic observations of a
peculiar type of decimetric radio bursts obtained by the Karl G. Jansky Very
Large Array. Radio imaging at each time and frequency pixel allows us to trace
the spatiotemporal motion of the source, which agrees with the implications of
the frequency drift pattern in the dynamic spectrum. The radio source,
propagating at 1000--2000 km s$^{-1}$ in projection, shows close spatial and
temporal association with transient brightenings on the flare ribbon. In
addition, multitudes of subsecond-period oscillations are present in the radio
emission. We interpret the observed radio bursts as short-period MHD wave
packets propagating along newly reconnected magnetic flux tubes linking to the
flare ribbon. The estimated energy flux carried by the waves is comparable to
that needed to account for the plasma heating during the late impulsive phase
of this flare.
