Abstract
The objectives of this study are to establish a climatology of gravity waves in a forest and to gain insights into the dynamics of this motion type. The site is part of the BOREAS (Boreal EcosystemβAtmosphere Study) flux monitoring network. The analysis relies mainly on 5 Hz temperature time series observed with two arrays of fineβwire thermocouples deployed in the vertical (up to 40 m above the ground) and horizontal (separation up to 150 m) from July to November 1996. Supporting measurements include mean wind speed and direction at two heights above the forest.
Waves of various intensities are found over 40% of the nightβtime observations, emphasizing the need to understand its role in transporting momentum and masses between the vegetation and the atmosphere. These waves are shearβgenerated. They propagate in the direction of the mean wind at a speed that is most likely to fall between the mean wind speeds at z/h = 1.2 and 1.8, where z is the height above the ground and h is the mean tree height. The median values of wave speed, wavelength, wave vertical displacement, and wave frequency are 1.61 m s^β1^, 75 m, 10 m and 0.0214 Hz, respectively. The wave motion remains coherent in the horizontal over less than one wavelength but is in general persistent in time.