The Monin-Obukhov similarity theory (MOST) is widely used to quantify turbulence structures in steady, homogeneous atmospheric surface layers (ASL). Recent studies have identified some features that are, more or less, inconsistent with MOST of turbulence structures due to its limitations under non-ideal conditions. One major cause is that MOST is framed in terms of local parameters and is only applicableied for locally-generated turbulence, which, therefore, implyingies that the large, non-locally generated motions in the atmospheric boundary layer (ABL) have no significant effects on the turbulent flows in the ASL. In the ASL,, these large-scale motions, which are sensitive to outer-layer parameters (e.g., BL depth) and, thus, obey outer-layer scaling, may co-exist with the shear-produced, small scale turbulence that obeys inner-layer scaling (ILS). Under these circumstances (i.e., the disturbed ASL), turbulence structures deviate more or less from those predicted by MOST with the degree of departure degrees depending on how the larger motions interact with ASL turbulence. Our research aims to study how large eddies interact and modulate turbulence structures in disturbed ASLs by using the datasets from the Energy Balance Experiment (EBEX) and other field campaigns...[More coming soon]
Complex terrain poses significant problems to eddy covariance measurements above forest canopies. Improving eddy covariance measurements over complex terrain requires a better understanding of how complex terrain influences spatial and temporal variability in turbulent flows above and within forest canopies. This will lead to improvements in measurements of the exchange of momentum, heat, and scalars between the atmosphere and vegetation, so that reliable interpretations/assessments of the surface energy balance, water cycle, and carbon budget over complex terrain can be made over various temporal and spatial scales. Currently, there is no clear understanding of how the simultaneous action of complex terrain, dynamic and thermodynamic conditions of inflows, and plant canopies modulate turbulence structures and thus transport of momentum, heat, water vapor, and carbon dioxide. In this research, we will examine turbulence in the forest canopy-atmosphere interface over a complex terrain by conducting analyses of the data measured from our field campaigns ...[More coming soon]
Terrain-induced flows are often highly intermittent, three-dimensional (3-D), and localized in nature as indicated by previous studies from analytical and numerical models, field campaigns, and laboratory experiments, and numerical models over idealized hills with neutrally stratified background flows. Compared with flows over forested flat terrain, flows over forested hills are characterized by topography-induced horizontal pressure perturbations, which distorts the mean flows and generates turbulent eddies with different scales. The presence of a canopy generally modifies flow dynamics through altering the no-slip lower boundary condition and introducing the influence of canopy elements on turbulence generation (e.g., pressure and form drag, wake production, spectral short-circuiting of energy cascade, coupling of turbulence between above and within the canopy, etc). Our research aims to improve the Weather Research and Forecasting Model (WRF) Large Eddy Simulation (LES) for simulating canopy flows over complex terrain. To accomplish this objective, we have incorporated the immersed boundary method (IBM) into WRF-LES to eliminate the restrictions of WRF-LES simulations on gentle terrain , thus enabling WRF-LES to deal with high-resolution simulations over highly complex topography. We are developing a multi-layer canopy module in WRF-LES to provide vertical variability in sources/sinks of momentum, heat, H2O, and CO2 inside the canopy. We will construct 3-D mean/turbulent flows and spatiotemporal patterns of the total fluxes, source/sinks, horizontal/vertical advections, and flux divergence of momentum and scalars (i.e., all terms in the conservation equations for momentum and scalars) under neutral, unstable, and stable conditions. These spatiotemporal patterns of different quantities parameters will enable us to quantify the relative contributions of different mechanisms to momentum and scalars transfer...[Read more]
Drylands in arid and semiarid regions are home to more than 38% of the total global population and are one of the most sensitive areas to climate change and human activities. Higher occurrences of long sustained droughts and warming events as a result of climate change have brought national and international attention to impacts on agriculture and populated municipalities. These drought and warming events present severe threats to sustainable agriculture, wildlife, ecosystem services, and human activities worldwide, particularly over arid and semiarid regions such as the Pacific Northwest. With limited water resources, establishing adaptation and mitigation strategies relies heavily on our understanding of how ecosystem-atmosphere interactions respond to climate change and the variability in these arid and semiarid regions. Through a close collaboration with an interdisciplinary team from Pacific Northwest National Laboratory (PNNL) Subsurface Biogeochemical Research (SBR) Scientific Focus Area (SFA), we are conducting eddy covariance measurements to study the hydrological impacts of groundwater-surface water interactions on ecosystem-atmosphere exchange processes over the arid and semiarid region of the Pacific Northwest (PNW) in USA...[Read more]
Inland waters (lakes, reservoirs, wetlands, etc.) act as hotspots in exchanges of energy, water vapor, and trace gases. It remains unexplored how turbulent processes affect water-atmosphere interactions, water surface energy budget, and lake evaporation, and how air-side and water-side processes regulate CO2 emissions. In collaboration with Jackson State University Mississippi and Pearl River Valley Water Supply District, we are making long-term eddy covariance measurements over the Ross Barnett reservoir in Mississippi to quantify CO2 emissions and the surface energy budget and understand mechanisms for their diurnal, subseasonal, and interannual variations...[Read more]
Contact Us: Dr. Heping Liu (heping.liu@wsu.edu) Phone: (509) 335-1529 Office: PACCAR 450