One important issue regarding the role of interstellar turbulence in
the star formation process is its distribution among the different
scales and its dissipation. In incompressible turbulence, the transfer
rate of the energy and its dissipation are intermittent in space and
time. For interstellar turbulence, magnetized and compressible,
intermittency is still an elusive concept. In this perspective,
observed statistical and structural signatures of intermittency are
presented and compared in two parsec-scale samples of gas, chosen in
different large scale environments, a high latitude cloud and a more
massive cloud, already forming stars.
Large and small scale properties are found to be coupled, the most
turbulent field at the parsec scale being the most intermittent at
small scale. Intermittent elongated structures are found in both
samples, parallel to the direction of the local magnetic field. In the
most turbulent field, the thinnest structures (less than 0.01 pc)
cluster into a thicker coherent pattern which extends over several
pc. A dissipation lengthscale is inferred from the comparison of these
data with recent numerical simulations. Such a scale, combined with
the special chemical and thermal properties observed in these
structures, supports the view that they are dissipative structures of
interstellar turbulence. These results raise several challenges that
will be addressed.
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