  We present a numerical scheme to study the dynamics of slow light and light
storage in an electromagneticallyinduced- transparency (EIT) medium at finite
temperatures. Allowing for the motional coupling, we derive a set of coupled
Schr\"{o}dinger equations describing a boosted closed three-level EIT system
according to the principle of Galilean relativity. The dynamics of a uniformly
moving EIT medium can thus be determined by numerically integrating the coupled
Schr\"odinger equations for atoms plus one ancillary Maxwell-Schr\"odinger
equation for the probe pulse. The central idea of this work rests on the
assumption that the loss of ground-state coherence at finite temperatures can
be ascribed to the incoherent superposition of density matrices representing
the EIT systems with various velocities. Close agreements are demonstrated in
comparing the numerical results with the experimental data for both slow light
and light storage. In particular, the distinct characters featuring the decay
of ground-state coherence can be well verified for slow light and light
storage. This warrants that the current scheme can be applied to determine the
decaying profile of the ground-state coherence as well as the temperature of
the EIT medium.
