[1] Airborne measurements were conducted above the UK during May and June 2000 in order to investigate turbulence and mixing in the tropopause region. Measurements of temperature frequently exhibited a periodic series of ramps that resembled a sawtooth pattern. These repeating structures were only observed in or near patches of intense shear-generated turbulence associated with the jet-stream. In each observed case the temperature ramps had the same orientation with respect to the wind shear. The temperature increased gradually in the direction of the shear, dropped suddenly, and the pattern repeated with wavelengths of about 1 to 1.2 km. Numerical simulation was applied to demonstrate that the observed temperature ramps are a signature of growing KelvinHelmholtz waves that are just beginning to overturn in transition to turbulence. The fluctuations in wind became increasingly three-dimensional along the direction of the shear with coherent oscillations that are consistent with the shear-aligned vortices found in laboratory experiments and numerical simulations.

[1] An airborne monitoring system has been used to observe fine-scale filamentation in the ozone field between 370 and 390 K isentropic levels. The Australian long-range, highaltitude research aircraft, the Egrett, was used to record multiple atmospheric properties with a high spatial resolution. Toward the end of 5 June 2000, an intrusion of low-ozone air was recorded over Aberystwyth, between 360 and 390 K. On the same day, a Rossby wave was observed to be breaking over western Europe with both poleward and equatorward components. We suggest that the low ozone at $380 K was caused by the poleward component of the breaking Rossby wave, stretching from southwestern Ireland to Iceland. On the eastern flank of the subtropical intrusion the in situ ozone measurements observed by the Egrett showed distinctive step and trough structures that were not expected from conventional model analyses. Using Reverse Domain-Filled (RDF) trajectory analyses to produce a fine-scale view of potential vorticity, we show how breaking of small-scale Rossby waves along the flank of the main wave over the northeastern United States, followed by a strong zonal compression, produced fine-scale filaments responsible for the structures observed in the Egrett ozone measurements.

[1] An airborne ozone lidar has been used to observe layering in the ozone field between 350 and 400 K northward of the subtropical jet stream. An ozone-poor layer between 370 and 400 K was observed over western Europe on 21 April 1999. On this day a Rossby wave was observed to be breaking over the eastern North Atlantic and western Europe, with both poleward and equatorward components. We propose that the low ozone at $400 K was caused by a poleward breaking Rossby wave stretching from Spain to the south coast of Britain. Isentropic back-trajectory calculations suggest a tropical upper tropospheric origin for the air within this wave, over North America. We suggest that Rossby waves generate layering in the lower stratosphere because of vertical gradients in the background wind fields, which govern the growth in amplitude and breaking characteristics of the waves.