Science and Technology News

Wednesday, January 25, 2012

Simulation From High-resolution Forest-wind Model (Image 2)

This is one of a series of illustrations that are the result of a high-resolution wind model. The model calculates the speed and direction of wind flow in and above the forest and also includes the effects of the forest itself on the wind. By forming an obstacle to the flow, the leaves and stems of trees in the forest slow down the wind and break large wind gusts to smaller eddies. Leaves also emit heat and water vapor that mix with the air as the wind blows past the leaves and change the air properties.

The images in the series illustrate a sub-section of a virtual forest, roughly 100x100x100 m^3 large. The trees in the forest were generated using a computer model, and the tree-tops are visualized as a green sheet in the picture. Leaves fill the space between the tree-tops and the ground (green floor) but are not illustrated. The white stream lines of wind inside the forest canopy illustrate the directions of the wind flow. The side walls illustrate humidity (moist is white, dry- blue) and the back wall shows the patterns of air temperature (hot is red, cold blue). The movie clip runs for 80 seconds. It illustrates a special pattern of wind in the forest called "momentum ejection." It is caused by wind being pushed from above into the canopy which in turn, pushes moist and warm air upward, outside of the canopy and into the atmosphere above. "Momentum ejections" are the major way in which moisture and heat that are released from the leaves into the canopy air are mixed with the atmosphere above the forest, and also the major way to provide fresh carbon dioxide supply into the canopy air where plants can breathe it during the photosynthesis process. Using this computer model, Gil Bohrer in the department of civil and environmental engineering and geodetic science at Ohio State University discovered that the structure of the forest and the location of gaps within it change the locations and strength at which those momentum ejections happen.

The model used for these simulations was developed with National Science Foundation (NSF) funding (grant DEB 04-53665) and the study--the results of which are depicted in these images--was supported by NSF grants DEB 09-18869 and DEB 09-11461.

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