Determination of near-surface turbulent fluxes at a tropical location: an evaluation of flux-profile technique

Abstract

An experimental site at Obafemi Awolowo University's Teaching and Research Farm, in Ile-Ife, Nigeria, was used to conduct multilevel measurements of meteorological parameters, and turbulent fluxes of sensible and latent heat in the atmospheric surface layer (ASL) between June 1 and July 31, 2016. The framework provided by Monin-Obukhov Similarity Theory (MOST) for estimating the turbulent fluxes of sensible and latent heat through existing empirical flux-profile relationships was employed. The objective of this study was to evaluate the performance of the flux-profile technique based on direct measurements of turbulent fluxes obtained from an eddy covariance (EC) system set up at the same location. The results showed that the diurnal patterns of both sensible and latent heat fluxes estimated from flux-profile technique compared relatively well with the direct measurements of the EC system. Nighttime estimations under stably stratified conditions of the atmosphere strongly correlated (R = 0.98) with the directly measured values. However, during the daytime convective conditions, there were some consistent discrepancies in the performance of the flux-profile technique with errors in some of the estimated fluxes well within the uncertainty range of the EC measurements. For sensible heat flux estimates; the coefficient of determination, R2 (0.71), the mean biased error, MBE (15.1 W/m2) and the percentage error determined for the period averaged values of the daytime estimates indicated that the sensible heat flux was only overestimated by up to 20%. On the other hand, a negative MBE 2 2 (-28.2 W/m2), weak coefficient of determination, R2(0.58)and negative percentage error obtained for the period averaged values of the latent heat flux indicated there is an underestimation of up to 45%. It can be concluded the flux-profile relationships can be employed within certain limits of confidence interval at tropical locations especially for the estimation of sensible heat flux.