GRAVITY-WAVES IN A FOREST - A LINEAR-ANALYSIS

Wavelike oscillations are a common form of air motion in the forest ca nopy at night. This paper investigates the canopy wave phenomenon usin g a two-dimensional inviscid Linear wave model taking into account the drag force exerted on the wave wind components by plant elements and the plant-air heat exchange induced by temperature wave oscillations. The model appears to have adequately reproduced the salient features o f a wave event in a boreal aspen forest. The wave dynamics are investi gated as functions of parameters of the background states er;pressed i n analytical form. It is shown that canopy waves are generated by wind shear near the treetops and share features of a Kelvin-Helmholtz dist urbance. Because it is located close to the inflection point of the me an wind, the ground exerts a strong stabilizing effect on the wave mot ions, particularly in a sparse forest. The main role of the canopy dra g in the wave dynamics is the creation of the inflection point. its da mping effect on wave oscillations themselves is limited to disturbance s of wavelengths shorter than that of the fastest growing waves. Wavel ength, phase speed, and period of the fastest growing waves, those tha t are most likely to dominate observations, appear insensitive to stat ic stability.