Cliff–Ramp Patterns and Kelvin–Helmholtz Billows in Stably Stratified Shear Flow in the Upper Troposphere: Analysis of Aircraft Measurements

Cliff–ramp patterns (CR) are a common feature of scalar turbulence, characterized by a sharp temperature increase (cliff) followed by a more gradual temperature decrease (ramp). Aircraft measurements obtained from NOAA best aircraft turbulence probes (BAT) were used to characterize and compare CR patterns observed under stably stratified conditions in the upper troposphere, a region for which there are few such studies. Experimental data were analyzed for three locations, one over Wales and two over southern Australia, the latter in correspondence with the Southern Hemisphere winter subtropical jet stream. Comparison of observed CR patterns with published direct numerical simulations (DNS) revealed that they were likely signatures of Kelvin–Helmholtz (KH) billows, with the ramps associated with the well-mixed billows and the cliffs marking the highly stretched braids. Strong correlation between potential temperature and horizontal velocity supported the KH link, though expected correlations with ...