Mixing parameters in CLaMS, are adjusted on the CRISTA observations
by using the probability density function technique (PDF)
quantifying the statistics of N_{2}O fluctuations.
The PDF derived from CRISTA observations at 700 K and on the horizontal scales
of the order 200 km is characterized by a
Gaussian core and non-Gaussian tails indicating filamentary structures
typical for 2d turbulence. The PDFs obtained from
CLaMS simulations strongly depend on the critical deformation switching mixing on
but only weakly on the model resolution tested between
45 and 200 km.
The results indicate that scale collapse followed by significant
mixing has to be expected in flow regions where horizontal
scales of the order 200 km are shrunk or elongated by the factor
less than 0.5 or greater than 2, respectively,
on time scales of the order 10 hours.

To quantify mixing in terms of the diffusivity,
CLaMS simulations are compared with in situ aircraft observations
at the edge of the northern polar vortex during the SOLVE/THESEO-2000 campaign.
Using the concept of effective diffusion to represent vertical
mixing processes in the isentropic (2d) simulations of the stratosphere,
the lateral (across the wind) effective diffusion
coefficient was estimated to be of the order 10^{3} m^{2}s^{-1}.
Mixing in CLaMS generalizes the idea of the
(bulk) effective diffusivity to a more realistic
inhomogeneous (i.e. driven by spatial and time dependent
flow deformations) and anisotropic
(i.e. dependent on the wind direction) mixing.

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