TURBULENCE SPECTRA AND DISSIPATION RATES ABOVE AND WITHIN A FOREST CANOPY ⋆ SHUHUA LIU ⋆⋆ and HEPING LIU State Key Laboratory of Severe Storm Research, Department of Geophysics, Peking University, Beijing 100871, China M. XU and M. Y. LECLERC Laboratory for Environmental Physics, University of Georgia, 1109 Experiment Street, Griffin, GA 30223-1797, U.S.A. TINGYAO ZHU and CHANGJIE JIN Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110015, China ZHONGXIANG HONG, JUN LI and HUIZHI LIU State Key Laboratory of Atmosphere Physics and Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China (Received in final form 18 April 2000) Abstract. Three velocity components and temperature were measured using three-dimensional sonic anemometers/thermometers at two levels, above and within a forest canopy, in the Changbai Moun- tains of northeast China. Turbulence spectral structure, local isotropy and dissipation rates above and within the forest canopy were calculated using the eddy correlation method. Results show that the normalized turbulent spectral curves have −2/3 slopes in the inertial subrange. While the shapes of the spectra are in good agreement with the Kansas flat terrain results, the atmospheric turbulence is anisotropic above the forest canopy. Due to breaking down of large eddies by the foliage, branches and trunks, the spectral peak frequencies for velocity and temperature are higher within than above the forest canopy. Compared with measurements from previous studies over flat terrain, the velocity and temperature spectra above and inside the forest canopy appear to shift toward higher frequencies. The turbulence is approximately isotropic in the inertial subrange within the forest canopy, and is anisotropic above the forest canopy. The turbulent kinetic energy and heat energy dissipation rates above and inside the forest canopy are much larger than those obtained by Kaimal and Hogstrom over grassland and grazing land. The distinct features in the results of the present experiment may be attributed to the dynamic forcing caused by the rough surface of the forest canopy. Keywords: Dissipation rates, Forest canopy, Local isotropy, Spectra, Turbulent kinetic energy. 1. Introduction Recently, studies of turbulent transfer above and inside forests have received in- creasing attention. Because forests occupy a significant portion of Earth’s land ⋆ Project supported by the National Natural Science Foundation of China (Grant No. 49575251) and State Key Laboratory of Atmosphere Physics and Chemistry. ⋆⋆ E-mail: Lshuhua@ibmstone.pku.edu.cn Boundary-Layer Meteorology 98: 83–102, 2001. © 2001 Kluwer Academic Publishers. Printed in the Netherlands.