Turbulence Fine Structure, Intermittency, and Large-Scale Interactions in the Stable Boundary Layer and Residual Layer: Correlative High-Resolution Measurements and Direct Numerical Simulations.

摘要

The research employed stable boundary layer measurements using the DataHawk UAV and high-resolution direct numerical simulations (DNS) to examine the interactions and instabilities occurring in multi-scale flows that drive intermittent turbulence events in the stable atmosphere. Both measurements and the DNS revealed the occurrence and persistence of sheet-and-layer structures in the temperature and velocity fields that arise from, and drive, successive instabilities including Kelvin-Helmholtz instabilities (KHI), gravity wave breaking (GWB), and more general fluid intrusions. Comparisons of measurements and modeling revealed many similarities and enabled an interpretation of a number of features of the observed flows. Also examined using the DNS results was the relationship between the Thorpe scale and the Ozmidov scale in such multi-scale flows. This revealed that the assumption that the ratio of these scales is approximately constant employed by many researchers is violated strongly on a case-by-case basis and may only be approximate for long spatial and temporal averages over turbulence events.