Scale dependence of tracer microstructure: PDFs, intermittency and the dissipation scale

The statistics of tracer variability on small scales (< 200 km) is investig ated using high resolution aircraft measurements of ozone in the northern w inter middle/high latitudes. Conditioning based on potential temperature is used to isolate the statistics of filamentation on isentropic surfaces fro m spurious variability due to cross-isentropic motion of the platform. The distribution of isentropic increments Delta (r)chi in the tracer field chi across a horizontal scale r have non-Gaussian tails and are consistent with stretched exponential functions of the form P(Delta (r)chi) similar to exp (-a \ Delta (r)chi \ (p)), where a is a scale-dependent parameter and the e xponent p increases overall with r. A scale break in the second order struc ture function suggests a dissipation scale r(d) similar to 20 km during nor thern winter 91-92, but the scale break is closer to 100 km during northern winter 88-89. Possible reasons for this are discussed.