Experimental Investigation of Small Scale Transport Mechanisms in the Stratosphere

Transport properties in the stratosphere were measured in an experimental program where smoke trails, deposited by rockets and aircraft, were recorded by time-lapse photography. This allowed winds, wind shears, and the rate of dispersion of the smoke to be calculated. Radial growth of the trails conformed to a turbulent diffusion rate; the effective diffusion coefficient at 20 km was approximately 0.7 nr sec. The spatial turbulence structure was determined from measured wind shears. Average energy spectra were obtained for total vertical profiles and segmented profiles of horizontal winds. A consistent finding was that the energy spectrum dependence exponent was close to n = 2.8. In the case of segmented profile spectra we found that 20% of the sample population showed n < 2.2 (indicating an inertial subrange). This is consistent with the presence of intermittent thin layers of efficient mixing in the 5-18 km height range. We also found an increase of wind shear and amplitude with altitude in this region.