Seasonal Variation of Surface Energy Budget In a Tropical Wet and Dry Climate Area of West Africa

The contiguous land area of West Africa basically experiences a monsoonal climate. In association with the north-south oscillation of the inter-tropical discontinuity (ITD) line at Ile-Ife, Nigeria (7.55^oN, 4.55^oE), a tropical wet and dry climate area, two contrasting seasons: dry (mostly, November – April) and wet (mostly, May – October) result. As a consequence of the seasonal weather changes, there is markedly contrasting surface energy budget of the turbulent convective heat fluxes (sensible, H_S and latent, H_LE) over the land area. In this study, the temporal variation (across the seasons) of the Bowen ratio (Bo = H_S/H_LE) obtained by using one year-long eddy covariance measurements (in-situ) of both the sensible and latent heat fluxes at an agricultural farm site located inside the campus of Obafemi Awolowo University in Ile-Ife has been investigated. Simultaneous measurements of net radiation and soil heat flux were made at the same site to determine the surface energy balance. Typically at the location, the maximum daytime value of H_S and H_LE is approximately 200 – 250 Wm^-2. The present results showed that during the dry season in Ile-Ife, when the measured soil volumetric water content, θ_v < 0.07 m³.m^-3, H_S > H_LE. Whereas in the wet season, usually when θ_v > 0.12 m³.m^-3, it is found that H_S < H_LE. As for the transition months in the area, March and November respectively, H_S ~ H_LE when θ_v ~ 0.1 m³.m^-3.