Constructing wind profiles in forests from limited measurements of wind and vegetation structure.

Abstract

The aim of the advection initiative ADVEX within CarboEurope-IP CEIP was the evaluation of the importance of advection on three coniferous sites. A prerequisite and crucial point for calculating the advective terms of the CO2 balance are the assumptions for the construction of wind fields. Wind measurements have to be interpolated and extrapolated over complex control volumes. Here the plant area density is identified as a key variable. During ADVEX campaigns the rectangular control volumes were marked by four towers at the corners, each carrying four sonic anemometers over the volume height (up to 30 m). A fourth experiment was designed at the CEIP forest site Tharandter Wald to investigate the error made by interpolation between only four measurement levels. 13 sonic anemometers on one tower over the height of 42 m (canopy height is 30m) were installed. In addition profiles of the plant area density were measured to derive plant specific parameterisation of the wind profiles. Profiles of velocity moments and nondimensional wind speed gradients are discussed as basic characteristics of the wind field. A new parameterization scheme for a modified mixing length approach is developed. The model was validated with the high resolved data and applied to calculate horizontal advection for the ADVEX sites. Beside an improvement of the interpolation routine it provides the opportunity to calculate wind profiles having measurements only at two levels, one above and one in the canopy.