  The interaction of fluids with surface-mounted obstacles in canopy flows
leads to strong turbulence that dominates dispersion and mixing in the
neutrally stable atmospheric surface layer. This work focuses on intermittency
in the Lagrangian velocity statistics in a canopy flow, which is observed in
two distinct forms. The first, small scale intermittency, is expressed by
non-Gaussian and not self-similar statistics of the velocity increments. The
analysis shows an agreement in comparison with previous results from
homogeneous isotropic turbulence (HIT) using the multifractal model, extended
self-similarity, and acceleration autocorrelations. These observations suggest
that the picture of small-scale Lagrangian intermittency in canopy flows is
similar to that in HIT, and therefore, they extend the idea of universal
Lagrangian intermittency to certain inhomogeneous and anisotropic flows.
Second, it is observed that the RMS of energy increments along Lagrangian
trajectories depend on the direction of the trajectories' time-averaged
turbulent velocity. Subsequent analysis suggests that the flow is attenuated by
the canopy drag while leaving the structure function's scaling unchanged. This
observation implies the existence of large-scale intermittency in Lagrangian
statistics. Thus, this work presents a first empirical evidence of intermittent
Lagrangian velocity statistics in a canopy flow that exists in two distinct
senses and occurs due to different mechanisms.
