Air exchange between forests and the lower atmosphere plays an important role in the transport of heat, moisture, momentum and trace gases between the ground surface and the atmosphere, thereby directly impacting human life and the environment. Much remains to be learned about the mechanisms of air exchange within the forest canopy layer, and its interaction with the overlying deeper atmospheric boundary layer. The generally weak nature of subcanopy winds and mechanical barrier presented by the network of tree branches forming the canopy render conceptual frameworks for turbulent transfer (such as commonly applied similarity theories) inadequate. The common generation of turbulence by shear on a variety of time scales, poor exchange between the subcanopy and above-canopy air, and short-circuiting of the energy cascade are not included in similarity theory that forms the basis for turbulent fluxes in models. Moreover, ubiquitous background "submesoscale" motions with spatial scales from tens of meters to several kilometers become important and can lead to unpredictable sudden wind direction changes, intermittent mixing, and non-equilibrium turbulence. No current physical concept describes the nature of these motions. Cases of weak airflow in concert with limited vertical mixing can result in high concentrations of contaminants near the surface.
Intellectual merit: New field observations will be collected and analyzed at various contrasting sites to generalize findings with the objective to:
i) identify forcing mechanisms of submesoscale motions, ii) evaluate the impact of plant canopies of different overstory density on the wind, temperature, and humidity fields, and iii) improve predictors for mixing in plant canopies that incorporate the important physical mechanisms.
These investigations are key steps toward the long-term goal to develop a novel improved framework to describe the flow and resulting transport under weak-wind conditions for a range of overstory density and stratification. Observations will be made with a unique combination of new and standard techniques, including optical fiber measurement of temperature structure, acoustic remote sensing, ultrasonic anemometers, and laser-illuminated flow visualizations. The research will be integrated with educational activities in the classroom. A new graduate-level field course will be developed and taught for students from several disciplines. Both classroom and field activities will help spark the students' curiosity and interest to better understand interactions between the lower atmosphere and the land surface. The curricula will be enriched by connecting theoretical concepts with hands-on research experience based on access to state-of-the-art instrumentation.
Broader Impacts: The novel framework and new analysis techniques will lead to improved formulations of turbulent fluxes applicable in non-ideal boundary layer conditions. These generalized formulations will be designed for use in regional and large-scale models, as well as dispersion and diffusion models. A set of practical recommendations will be developed for the applied flux community to reduce uncertainties in scalar budgets and predictions of water availability. Two graduate students will be trained in theoretical and observational boundary layer meteorology. This skill set is in high demand and demand likely will grow if/when monitoring of greenhouse gases becomes mandatory. The hands-on field education will foster critical thinking, improve retention of concepts, and help many students to reach technical proficiency. One Oregon K-12 high school teacher will be actively involved in field research and data analysis by partnering with the Oregon Natural Resources Education program at Oregon State University. This teacher's involvement will be leveraged to reach large numbers of K-12 students in addition to the hundreds of students directly connected to the participating teacher. Shared interests in air movement across the forested landscape will stimulate an exchange of information with the Willamette National Forest personnel.
