Integral turbulence characteristics over a clear woodland forest in northern Benin (West Africa)

Abstract

This study aims at investigating whether the Integral Turbulence Characteristics (ITC) obey the Monin-Obukhov Similarity Theory (MOST) above a forest site in a Sudanian climate, and at identifying the appropriate ITC models for this ecosystem. Data were collected from a 18 m tower equipped with an Eddy Covariance system, above the clear forest close to Bellefoungou's village, Northwest of Benin, West Africa. The turbulence intensity parameters calculated for five years and half, were analyzed according to wind speed, stability conditions and seasons. From their relationships with the stability parameter, data driven models were then obtained by the nonlinear least squares. The results showed that, all similarity functions follow MOST with a 1/3 power law whatever the stratification of the atmosphere during all the seasons excepted the temperature which had a parabolic shape in near neutral condition (−0.05 < ζ < 0.1). A seasonal dependence of all ITCs was evidenced under stable conditions. We also showed that the heat transfer is relatively more efficient than H2O transfer under both stability conditions. The established temperature and CO2 similarity models are found to be closer, and for some given stratification conditions, to those already existing in literature. But a noteworthy finding is that the models often used to assign a quality criterion to turbulent fluxes showed an overestimation relatively to those established ‘locally’ for u and w through all atmospheric stratification.