Unicorn (Developing a Novel Framework for understanding near-surface turbulence in complex terrain)

Atmospheric turbulence is the processes that dominantly controls the exchange of heat, mass (e.g., CO2, water vapor, pollutants) and momentum between the Earth’s surface and the atmosphere, and therefore drives phenomena as diverse as climate, storm systems, hydrological cycle, air pollution, and glacial melt. Still, Monin-Obukhov similarity theory that stands as the cornerstone of our understanding of turbulence over flat and horizontally homogenous terrain, fails over more complex surfaces, such as mountains. Thus, for the majority of our planetary surface no viable theory of turbulence is available, and approaches that are known to be inadequate are nevertheless applied.

Unicorn addresses this knowledge gap to create a novel framework extending the existing theory of near-surface turbulence to complex terrain. Based on the ground-breaking hypothesis that the directionality of turbulent exchange (anisotropy) encodes the boundary conditions and thus provides a unifying element in scaling over all surface types, Unicorn will identify the key physical processes that cause anisotropy in complex terrain to differ from that over flat terrain. Thus Unicorn will systematically explore the parameter space of different sources of complexity, such as topography, flow conditions and heterogeneity, using unprecedented analysis of over sixty measurement datasets over flat and complex terrain coupled with machine learning approaches, sensitivity studies using state-of-the-art high resolution numerical modelling, and reduced order theoretical derivations. This synergistic approach incorporating the effects of complex terrain into a framework based on turbulence anisotropy will bring a much-needed breakthrough for understanding turbulence in complex terrain. Findings will have the potential to revolutionise near-surface turbulence representation in numerical models, leading to better predictive capability in numerous societally and scientifically relevant topics, such as climate, extreme weather and air pollution.

Unicorn is a 5-year project funded through an ERC Consolidator Grant and is led by Ivana Stiperski at the Department of Atmospheric and Cryospheric Sciences of the University of Innsbruck.