An approach for calculation of turbulent transfer coefficient for momentum inside vegetation canopies

Abstract

A method for calculating the profile of turbulent transfer coefficient for momentum inside a vegetation canopy for use in land surface schemes is presented. It is done through the following steps. First, an equation for the turbulent transfer coefficient for momentum inside a vegetation canopy using the "sandwich" approach for its representation is derived. Second, it is examined analytically to determine whether its solution is always positive. Third, the equation for the turbulent transfer coefficient is solved numerically, using an iterative procedure for calculating the attenuation factor in the expression for the wind speed inside a vegetation canopy that is assumed to be a linear combination of an exponential function and a logarithmic function. The proposed method is tested using 1) the observations for the wind profiles in a Japanese larch plantation and a pine forest and 2) the outputs for surface fluxes and total soil water content obtained by the Land-Air Parameterization Scheme (LAPS) with the forcing data and observations in a soybean field at the Caumont site in France during the 1986 growing season. Also, a test is performed that compares the proposed method with the method for calculating the turbulent transfer coefficients for momentum inside a vegetation canopy commonly used in land surface schemes. © 2006 American Meteorological Society.