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

The statistics of tracer variability on small scales (< 200 km) is investigated using high resolution aircraft measurements of ozone in the northern winter middle/high latitudes. Conditioning based on potential temperature is used to isolate the statistics of filamentation on isentropic surfaces from spurious variability due to cross-isentropic motion of the platform. The distribution of isentropic increments Δ_rא in the tracer field א across a horizontal scale r have non-Gaussian tails and are consistent with stretched exponential functions of the form P(Δ_rא) ∼ exp(-a/Δrא/^p), where a is a scale-dependent parameter and the exponent p increases overall with r. A scale break in the second order structure function suggests a dissipation scale r_d ∼ 20 km during northern winter 91-92, but the scale break is closer to 100 km during northern winter 88-89. Possible reasons for this are discussed.