Surface energy balance measurements at a tropical site in West Africa during the transition from dry to wet season |
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Authors: | M Mauder O O Jegede E C Okogbue F Wimmer T Foken |
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Institution: | (1) Department of Micrometeorology, University of Bayreuth, Bayreuth, Germany;(2) Department of Physics, Obafemi Awolowo University, Ile-Ife, Nigeria;(3) Department of Meteorology, Federal University of Technology, Akure, Nigeria |
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Abstract: | Summary In one of the first micrometeorological experiments at a tropical site in West Africa, direct measurements of all surface
energy balance components were carried out. The experiment NIMEX-1 in Ile-Ife, Nigeria (7°33′ N, 4°33′ E), was conducted from
February 19, 2004 to March 9, 2004, during the transition from the dry to the wet season. Three typical weather situations
could be observed: firstly, monsoonal winds from the southwest blew over desiccated soils. Almost 100% of the available energy
at the surface was transformed into sensible heat flux. Secondly, after several thundershowers, monsoonal winds swept over
soils of increased water content, which led to a partitioning of the available energy corresponding to Bowen ratios between
0.3 and 0.5. Thirdly, harmattan winds advected dry dusty air from northern directions, which reduced the incoming shortwave
radiation. Again, Bowen ratios range from 0.3 to 0.5 during daytime, whereas latent heat fluxes are still high during the
night due to the advection of very dry air. No systematic non-closure of the surface energy balance could be found for the
NIMEX-1 dataset. Unlike other experiments in Europe, most of the ogives for the sensible and latent heat flux were found to
be convergent during NIMEX-1 in Ile-Ife. This can be attributed to the homogeneity of the surrounding bush, which lacks the
defined borders found in agriculturally cultivated landscapes. |
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