STABLEST - Stable Boundary Layer Separation and Turbulence


FWF Project: STABLEST - Stable Boundary Layer Separation and Turbulence, 2012-2015 

The boundary layer is the region of the atmosphere closest to the Earth’s surface and is characterized by highly turbulent air motions.

Wave-induced boundary-layer separation (BLS) is the process by which near-surface flow detaches from the ground as a consequence of adverse pressure gradients, owing their origin to internal gravity waves that are generated as the air passes over a mountain. The occurrence of BLS is often associated with vigorous perturbations of the atmospheric flow, such as wave breaking, and the generation of atmospheric rotors, which pose a serious threat to air and ground transportation on the lee side of mountains.

The interaction of internal-gravity waves generated by airflow over orography with the flow within the atmospheric boundary layer has been pointed out as one of the major outstanding problems for the improvement of mountain weather forecasting. Furthermore, besides being a challenging geophysical fluid dynamics problem, wave-induced BLS also has relevant practical implications. Beyond the aforementioned safety of air and ground transportation, BLS can exert a significant impact on the efficiency of wind power production in mountainous areas by generating intense turbulence, which normally reduces the yield of wind turbines.

In the STABLEST project, high-resolution numerical simulation is combined with the analysis of observational data to gain insight into the factors governing BLS. Particular attention is devoted to those aspects of BLS which are currently not well understood, in particular its possible non-stationarity, its dependence on the heat exchanges between the ground and the atmosphere and its evolution when occurring over obstacles with a complex three-dimensional shape.

Numerical simulations will be performed using large-eddy simulation (LES), the most advanced approach nowadays available to model turbulent flows in the atmosphere. Plans include both idealized simulations, where the conditions leading to the onset of BLS are deliberately simplified in order to improve the understanding of the phenomenon, and real case studies. The latter will initially refer to events for which high-resolution observations are already available.

The field observations to be analyzed during STABLEST include airborne in situ measurements and wind speed estimates from a Doppler cloud radar, which were collected during recent campaigns by a team at the University of Wyoming and are available to the STABLEST investigators by virtue of an existing partnership. Research efforts in this context are mostly directed towards the estimation of turbulence parameters from the radar data, in order to enable their comparison with the results of numerical simulations for verification purposes.

A distinctive feature of the STABLEST project is the wide network of international cooperation that it builds upon. Research partners include the US National Center for Atmospheric Research, the consortium of north-American universities participating in the MATERHORN project, the University of Wyoming and the University of Innsbruck. The proposed research connections will lead to the acquisition and analysis of novel observational evidence of BLS, both with a Doppler lidar in a natural environment and with particle image velocimetry in a laboratory.



Stefano Serafin
Lukas Strauss
Johannes Sachsperger
Vanda Grubišić
Samuel Haimov (University of Wyoming)


Recent research contribution


 Further Information