Flux Uncertainty Quantification in Heterogeneous Turbulent Boundary-Layer Flows

The effects of surface heterogeneity on turbulent boundary-layer flows are complex and not well understood. Practical constraints often limit atmospheric studies to no more than one data collection tower. However, surface heterogeneities introduce significant variability in both surface momentum and sensible heat fluxes, indicating a strong need for multiple observation sites to capture the full statistics of a flow. We investigate a novel method for quantifying uncertainty in surface momentum and sensible heat fluxes as a function of the number of observations. Data from a 1 km × 1 km region were acquired over the desert playa at the Surface Layer Turbulence and Environmental Science Test (SLTEST, Dugway, UT, USA) facility as part of the Idealized Planar Array experiment for Quantifying Spatial heterogeneity (IPAQS 2019) field campaign to determine surface flux variability as a function of flux footprint density. In the idealized terrain at SLTEST, we find variations of over 400% in both momentum and sensible heat fluxes when comparing measurements to spatially averaged data. Additional tests have been conducted to understand the impact of atmospheric conditions on flux variability. These findings will inform the development of new numerical wall models and field experiment design.