  Infrared variability is common among young stellar objects, with surveys
finding daily to weekly fluctuations of a few tenths of a magnitude.
Space-based observations can produce highly sampled infrared light curves, but
are often limited to total baselines of about a month due to the orientation of
the spacecraft. Here we present observations of the Chameleon I cluster whose
low declination makes it observable by the Spitzer space telescope over a 200
day period. We observe 30 young stellar objects with a daily cadence to better
sample variability on timescales of months. We find such variability is common,
occurring in ~80% of the detected cluster members. The change in [3.6]-[4.5]
color over 200 days for many of the sources falls between that expected for
extinction and fluctuations in disk emission. With our high cadence and long
baseline we can derive power spectral density curves covering two orders of
magnitude in frequency and find significant power at low frequencies, up to the
boundaries of our 200 day survey. Such long timescales are difficult to explain
with variations driven by the interaction between the disk and stellar magnetic
field, which has a dynamical timescale of days to weeks. The most likely
explanation is either structural or temperature fluctuations spread throughout
the inner ~0.5 au of the disk, suggesting that the intrinsic dust structure is
highly dynamic.
