Scholarly works
Permanent URI for this collectionhttps://repository.ui.edu.ng/handle/123456789/420
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Item Assessment of Soil Thermal Properties in a Tropical Environment: Ile Ife and Ibadan(Journal of Faculty of Science, University of Ibadan, Ibadan, Nigeria., 2011) Otunla T.A.; Oladiran E.O.Soil thermal properties are crucial parameters that affect soil heat flux. Time series of soil temperature, soil moisture content, and rainfall and soil heat flux were measured at two tropical locations in West Africa during the transition from dry to wet season, and at the peak of rainy season in July. The data were analyzed to estimate soil thermal diffusivity, thermal inertia and volumetric heat capacity. The thermal properties were clearly related to soil moisture (and thus rainfall) throughout the measurement period. The modeled soil heat flux using the soil thermal properties compared favorably with the measured soil heat flux.Item Simple and Reliable methods of Estimating Ground Heat Flux at a Tropical location in Nigeria(2019) Otunla, T.A.; Oladiran, E. O.Ground heat flux (Go) plays an important role in the partitioning of energy budget at earth’s surface. The estimates of G0 are required as part of boundary conditions by all general circulation models. In this work, reliability of four simple and computationally cheap models was tested against a more complex and reliable model as the reference. The simple models selected for investigation are: Simple measurement (SM), Percentage of net radiation (PR), Universal function of net radiation (UR), and Linear function of net radiation (LR) models. Force restore model (FR) was used as the reference model. The data of soil temperature measured at the surface and 0.05 m depth, soil heat flux, measured at 0.05m, and net radiation were obtained from Nigerian Micrometeorological Experiment, Ile Ife. Force restore model was first calibrated with direct measurements for soil heat flux at 0.05 m depth with satisfactory result before it was employed to generate reference G0 estimates. Estimates of SM, PR, UR and LR were compared with FR using simple statistics of coefficient of determination (R2), slope, intercept, root mean square error (RMSE) and mean bias error (MBE). The SM model reproduced the day-time and night-time variations of G0 better than all the models that parameterized G0 as a function of net radiation (R2, slope, intercept, RMSE and MBE values of 0.85, 0.87, 3.43W/m2, 32.69, W/m2, -3.70 W/m2 respectively). This model however requires measurement of both soil heat flux and temperature. The LR model generated the best estimates of Go out of all the models that utilized net radiation measurements (R2, slope, intercept, RMSE and MBE values are 0.60, 0.58,4.55 W/m2, 53.81 W/m2 and 3.60 W/m2 respectively) while UR model is the worst. The LR model, though depend only on one measurement, requires site-specific calibrations and can therefore be deployed for gap filling where SM model cannot be used. "Item Impact of Soil Heat Flux Attenuation on Surface Energy Balance Closure(2012) Otunla, T.A.; Oluwafemi, S.M.In surface energy balance (SEB) measurements, ground heat flux (G) is either reconstructed from soil temperatures using analytical method or from the combination of calorimetric method with soil heat flux measured at 0.05 cm depth or more. Soil heat flux signal attenuation is known to increase with depth. This work intends to investigate the impact of this attenuation, which arises from the placement depths of soil temperature and heat flux plates sensors on SEB closure. Ground heat flux was reconstructed from soil heat flux and temperature measurements at two separate depths of 0.05 and 0.10 cm using calorimetric and analytical methods. The two data sets of G were combined with other SEB components to quantify the impact of placement depth of the soil sensors on SEB closure as a change in residual of SEB measurements (ΔRes). For the calorimetric method, the lowest value of ΔRes in the morning hours was -10W/m2 and the peak value during the daytime was +43W/m2. The values of ΔRes fluctuate between ±20 W/m2 in the morning hours and ±42W/m2 during the daytime for the analytical method but with a greater tendency towards positive ΔRes. Thus, SEB closure decreased with the increasing placement depth of the soil sensors, especially during the daytime. The implication of all these results is an irrecoverable signal loss in the soil heat flux as the placement depth of the sensors increases especially during the daytime.Item Impact of the total solar eclipse of 29 March 2006 on the surface energy fluxes at Ibadan,Nigeria(2012) Nymphas,E.F.; Otunla,T.A.; Adeniyi,M.O.; Oladiran, E.O.This paper document the impact of the total solar eclipse (97.4%) of 29 March 2006 on the surface energy fluxes at Ibadan, Nigeria (longitude4.561E, latitude7.551N), a tropical location. The surface energy (determined by the BREB method) was found to be grossly affected by the eclipse. The latent heat and net radiation (Rn) lagged the sensible heat by 11 min in totality. The sensible heat lagged the latent heat and Rn by 6 min before it start to increase after the totality phase of the eclipse while global radiation (Rg) lagged Rn by 7 min. The sensible heat reversed sign reaching a value of _1.02 Wm_2 during the total phase of the eclipse while the latent heat dropped by 89.7%. All the radiation fluxes (global radiation, Rg, net radiation Rn, temperature and soil heat flux) measured during the eclipse event were significantly affected by the sudden ‘cutoff’of the solar irradiation.There was a 95% decrease in Rg, while Rn dropped from 354.3Wm_2 to _11.7 Wm_2.