Keywords
turbulence inside the tall sparse vegetation, turbulent transfer coefficient, mixing length, land surface schemes, environmental modelling
Start Date
1-7-2004 12:00 AM
Abstract
The sparse tall grass significantly affects the heat and moisture exchange in the lower atmosphere through the turbulent transfer coefficient inside its environment. Common approaches for calculation of turbulent transfer coefficient inside the tall grass environment are based on the assumption that it depends either on wind speed or mixing length inside the canopy. In this paper we suggested a new approach for calculating the turbulent transfer coefficient inside the sparse tall vegetation. In that sense we first derived an equation for the turbulent transfer coefficient inside the sparse tall grass using the “sandwich” approach for representation of vegetation, then we examined analytically whether its solution is always positive. Next, we solved the equation numerically using an iterative procedure for calculating the attenuation factor in the expression for the wind speed inside the canopy assumed to be a linear combination of an exponential and a logarithmic function. The proposed calculation of turbulent transfer coefficient is tested using the Land-Air Parameterization Scheme (LAPS). Model outputs of air temperature inside the canopy for 11-13 July 2002 are compared with micrometeorological measurements inside a sunflower field at the Rimski Sancevi experimental site (Serbia).
An Approach for Calculating the Turbulent Transfer Coefficient Inside the Sparse Tall Vegetation
The sparse tall grass significantly affects the heat and moisture exchange in the lower atmosphere through the turbulent transfer coefficient inside its environment. Common approaches for calculation of turbulent transfer coefficient inside the tall grass environment are based on the assumption that it depends either on wind speed or mixing length inside the canopy. In this paper we suggested a new approach for calculating the turbulent transfer coefficient inside the sparse tall vegetation. In that sense we first derived an equation for the turbulent transfer coefficient inside the sparse tall grass using the “sandwich” approach for representation of vegetation, then we examined analytically whether its solution is always positive. Next, we solved the equation numerically using an iterative procedure for calculating the attenuation factor in the expression for the wind speed inside the canopy assumed to be a linear combination of an exponential and a logarithmic function. The proposed calculation of turbulent transfer coefficient is tested using the Land-Air Parameterization Scheme (LAPS). Model outputs of air temperature inside the canopy for 11-13 July 2002 are compared with micrometeorological measurements inside a sunflower field at the Rimski Sancevi experimental site (Serbia).
