Atmospheric Boundary Layer Turbulence

Turbulence research has a long history in both the engineering and the geophysical communities. While there are many similarities between atmospheric turbulence and laboratory flows (e.g. over an airfoil or in a pipe), atmospheric boundary layers have the added complications of thermal stratification, diurnal variability, and complex surface boundary conditions, such as land surface heterogeneity, topography, or plant canopies. One major focus of research in our group is on turbulence organization in both convective and stable atmospheric boundary layers, and implications for scaling laws (that relate turbulent fluxes to mean vertical gradients) and turbulent transport.

Turbulence in Clouds

While turbulence in dry, cloud-free air is already a fascinating and challenging problem, clouds have the added complications of scalar transport (of temperature and humidity), phase change, and turbulent transport of particles, which may differ from that of the fluid phase due to particle inertia. Moreover, turbulent fluctuations of momentum, temperature, humidity, and droplet concentrations have been found to have major implications for precipitation formation and large-scale cloud properties. Current research in our group is focusing on improving subgrid-scale models of turbulent-microphysics interactions in clouds in large eddy simulation; we are using laboratory data and high-resolution direct numerical simulations of turbulence as benchmark datasets to understand the governing physics.

Particle-Laden Flows

Related to the previous topic, another component of research in our group is turbulent particle-laden flows in the atmosphere. Heavy particles of interest in the atmosphere include dust and sand, biogenic particles (pollen, seeds, and spores), cloud droplets, and hydrometeors. The behavior of heavy particles differs significantly from the transport of trace gases due to their settling velocities and inertia, leading to relative velocities between the particles and the fluid. In our current research, we are studying turbulent particle-laden flows in clouds, as well as snow transport through saltation and suspension, and we are developing new models to study these flows with large eddy simulation which capture the underlying physics. More broadly, we are interested in the fluid dynamics of particle-laden flows and their implications for weather and climate, hydrology, cloud processes, and human health.

Large Eddy Simulations

While ground-truth observations will always play a critical role in advancing our understanding of atmospheric turbulence, in situ measurements are typically taken at only a few locations in many experiments and therefore cannot fully characterize the spatial variability that occurs in real atmospheric boundary layers. A promising approach for studying these flows is large eddy simulation (LES), a computational technique where the largest turbulent motions (responsible for a large fraction of the transport) are resolved explicitly, while the effects of the smaller scales are modeled.

We use large eddy simulation to investigate the physics of idealized ABLs such as the nocturnal stable boundary layer or daytime convective boundary layer over flat, horizontally homogeneous terrain. We also are able to perform simulations of more complex ABLs, such as those over complex topography or urban areas, by using simulations that are able to represent the effects of complex topography on the ABL. Furthermore, we also work on representing additional physics in large eddy simulation in order to perform accurate, physically-based simulations of more complex ABLs. Our ongoing work in this area includes improving subgrid scale models for LES and developing new modules for passive scalar and heavy particle transport that capture the underlying physics.