Scale-Aware Evaluation of Complex Mountain Boundary Layer Flow From Observations and Simulations

Abstract

Boundary layers over complex, mountainous terrain are characterized by multi-scale, complex flow structures, where the characterization of individual flow modes poses a fundamental challenge. We apply the novel multi-resolution coherent spatio-temporal scale separation (mrCOSTS) method to LIDAR observations and numerical data of the velocity components of complex mountain boundary-layer flow. Using three distinct time scales (turbulent scales, mountain boundary layer, and diurnal scales) the underlying physical processes are explored. Furthermore, we identified the dominant flow patterns for each time scale, for example, down- and up-valley flows, cross-valley vortices, small-scale turbulence, and large evening transition eddies. Applying mrCOSTS to simulated velocity components enables us to identify how coherent structures and the flow patterns are represented at various mesh sizes in the model. Using mrCOSTS we trivially retrieved complex dynamics that were previously difficult to resolve, enabling a direct, scale-aware evaluation between the LIDAR observations and model results.