  There is evidence that coronal heating is highly intermittent, and flares are
the high energy extreme. The properties of the heat pulses are difficult to
constrain. Here hydrodynamic loop modeling shows that several large amplitude
oscillations (~ 20% in density) are triggered in flare light curves if the
duration of the heat pulse is shorter that the sound crossing time of the
flaring loop. The reason is that the plasma has not enough time to reach
pressure equilibrium during the heating and traveling pressure fronts develop.
The period is a few minutes for typical solar coronal loops, dictated by the
sound crossing time in the decay phase. The long period and large amplitude
make these oscillations different from typical MHD waves. This diagnostic can
be applied both to observations of solar and stellar flares and to future
observations of non-flaring loops at high resolution.
