  This work addresses the problem of plasma condensation and ``catastrophic
cooling'' in solar coronal loops. We have carried out numerical calculations of
coronal loops and find several classes of time-dependent solutions (static,
periodic, irregular), depending on the spatial distribution of a temporally
constant energy deposition in the loop. Dynamic loops exhibit recurrent plasma
condensations, accompanied by high-speed downflows and transient brightenings
of transition region lines, in good agreement with features observed with
TRACE. Furthermore, these results also offer an explanation for the recent EIT
observations of De Groof et al. (2004) of moving bright blobs in large coronal
loops. In contrast to earlier models, we suggest that the process of
catastrophic cooling is not initiated by a drastic decrease of the total loop
heating but rather results from a loss of equilibrium at the loop apex as a
natural consequence of heating concentrated at the footpoints of the loop, but
constant in time.
