Turbulence in the canopy roughness sublayer (CRSL) is the primary driving force of the exchange processes between terrestrial ecosystems and the atmosphere. These exchanges are vital components in global carbon and water cycles and climate change research. Previous studies of short crops have shown that the aeroelasticity of plants has a significant impact on CRSL turbulence structure. The aeroelasticity of trees, however, has not been formally considered in most turbulence models of CRSL, including state of the art large-eddy simulation models (LES). This is largely due to a lack of field experiments to quantify the elastic properties of trees and their complex damped sway behaviors, which differ from those in short crops. Improved understanding and modeling of the aerodynamic interactions between forest canopies and CRSL turbulence are also significant in order to investigate the multifaceted effects of winds on the structure and function of terrestrial forest ecosystems and their responses to and interactions with future climate change.

Intellectual merit: This collaborative project is an interdisciplinary effort built upon the experimental and numerical modeling expertise of forest ecologists and micrometeorologists at the University of Connecticut, East Carolina University and Louisiana State University. The research consists of a novel but labor intensive field experiment campaign over a period of 1.5 years at an established AmeriFlux forest site at Howland, Maine, and a computationally intensive modeling component to incorporate tree sway motion physics into a current LES. The investigators will develop improved numerical models of tree-sway and their coupling with the LES. The overall goal is to improve understanding and modeling of the mechanisms underlying the aerodynamic interactions between CRSL turbulence structures and tree sway motions in and above forest canopies.

The field campaign will measure the sway motions and the elastic and aerodynamic properties of a large array of trees and turbulence wind fields simultaneously. These measurements will be used to quantify the temporal and spatial characteristics of tree-sway motions and their aerodynamic interactions with coherent gusts in a forest canopy. The coupled LES-tree-sway-model will be used to quantify the influences of tree sway motions on airflow in and above a forest over a range of atmospheric conditions.

In addition, the PIs will conduct systematic investigations, using the coupled LES-tree-sway-model, to quantify the effects and the relative significances of atmospheric boundary layer height and stability, external horizontal pressure gradient force, canopy morphology and elastic properties of trees, on the characteristics of tree-sway motions and CRSL coherent structures and their interactions. The PIs will carry out a thorough and comprehensive set of analyses of field measurements and LES outputs to create both qualitative and quantitative descriptions of the spatial and temporal characteristics of the tree-sway motions and canopy-scale coherent structures, including their relations and interactions.

Broader impacts: This collaborative project will integrate teaching and research at multiple levels of education. To cultivate and nurture the pursuit of science at the grass roots, the PIs will carry out an education program specifically designed to engage primary school children with interactive instructions on how basic data are collected, analyzed and shared, and demonstrations of the linkages between weather, climate and forested ecosystems. This outreach via family public education program will excite future generations about scientific understanding of the world, and will utilize some of the knowledge, instruments and models applied in the research portion of this project.

This project will provide support to graduate students who will receive formal training in multiple research areas (micrometeorology, boundary-layer meteorology, forest meteorology, forest ecology), learn and practice important field measurement and numerical modeling and data analysis techniques.

Research results from this project will be used to develop undergraduate and graduate course modules in micrometeorology, forest meteorology and forest ecology at both universities, and made available through a project web site.

National Science Foundation (NSF)
Division of Atmospheric and Geospace Sciences (AGS)
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A. Gannet Hallar
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University South Carolina Research Foundation
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