Analysis of turbulence and turbulence kinetic energy dynamics in complex terrain

Boundary layer processes and turbulence in a complex terrain are influenced by thermally driven flows, as well as dynamically forced flows when ambient wind interacts with orography. This paper investigates the variability in turbulence kinetic energy (TKE) with elevation and topography in a shallow high mountain valley in the Canadian Rockies. The Fortress Mountain Research Basin in the Kananaskis Valley, Alberta, was chosen for this study. Data from three high‐frequency eddy‐covariance systems at a northwest‐facing slope, and at two ridgetops at the south and north valley sidewalls were used for the analysis, and combined with large‐eddy simulations at 90 m horizontal grid spacing. The observed data and simulations focused on a sunny summer day when turbulence was well‐developed, and cross‐ridge flows interacted with thermally driven circulations. The observed TKE time series compared reasonably well with simulations at the northwest‐facing slope and southern ridgetop. The model was then used to evaluate the vertical and horizontal TKE‐budget equation. Analysis of the TKE budget showed that horizontal shear production and advection of TKE driven by horizontal wind‐gradients in cross‐ridge flows, and the interaction of these flows with the up‐valley flow could be an important source of TKE production on the northwest‐facing slope station in the Fortress Valley. The variability observed in TKE budget components across different locations within this high mountain basin indicates the significance of both horizontal and vertical exchange processes in the mechanisms governing TKE production.