Determination of Near-Surface Turbulent Fluxes at a Tropical Location: An Evaluation of Flux-Profile Technique

Abstract

Multilevel measurements of mean meteorological variables and turbulent fluxes of sensible and latent heat in the atmospheric surface layer (ASL) were undertaken at the experimental site located within the Teaching and Research Farm of Obafemi Awolowo University, Ile-Ife, Nigeria, between the 1st of June and 31st of July, 2016. Existing empirical flux-profile relationships under the framework of Monin-Obukhov similarity theory (MOST) were used to estimate the turbulent fluxes of sensible and latent heat. The performance of the flux-profile technique was then evaluated based on direct measurements of turbulent fluxes obtained from an eddy covariance system. The results showed that the sensible heat flux estimated from flux-profile relationships has a maximum value of 96.4 W/m2 (daytime mean value of 52.02 W/m2) in June while a peak value of 145.2 W/m2 (daytime mean value of 63.1 W/m2) was obtained from direct measurement. In July, a maximum value of 101.07 W/m2 was estimated as compared to 142.84 W/m2 that was obtained from direct measurement. The percentage error calculated for the period averaged values showed that the sensible heat flux was overestimated by up to 25%. The latent heat flux estimated gave a maximum value of 98.4W/m2 in June whereas a peak value of 310 W/m2 was obtained from the direct measurement. In July, a maximum value of 105.09 W/m2 was estimated as compared to 350 W/m2 recorded from direct measurements of the EC system. Negative Mean Bias Error, MBE values of -27.4 and − 18.6 W/m2 obtained for June and July respectively indicated the underestimation of latent heat flux by the flux-profile method.