  We investigate the variability of the brightness distribution and the
changing density structure of the protoplanetary disk around DR Tau, a
classical T Tauri star. DR Tau is known for its peculiar variations from the
ultraviolet (UV) to the mid-infrared (MIR). Our goal is to constrain the
temporal variation of the disk structure based on photometric and MIR
interferometric data. We observed DR Tau with the MID-infrared Interferometric
instrument (MIDI) at the Very Large Telescope Interferometer (VLTI) at three
epochs separated by about nine years, two months, respectively. We fit the
spectral energy distribution and the MIR visibilities with radiative transfer
simulations. We are able to reproduce the spectral energy distribution as well
as the MIR visibility for one of the three epochs (third epoch) with a basic
disk model. We were able to reproduce the very different visibility curve
obtained nine years earlier with a very similar baseline (first epoch), using
the same disk model with a smaller scale height. The same density distribution
also reproduces the observation made with a higher spatial resolution in the
second epoch, i.e. only two months before the third epoch.
