Scholarly works
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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 Assessing the Performance of Global Solar Radiation Empirical Models at a Sahelian Site, Sokoto, Nigeria(The Nigerian Association of Mathematical Physics, 2015) Otunla, T.A.; Kolehaje, O. T.In the region where solar radiation data are scarce, the next alternative method is to use solar radiation models to estimate the data needed for some applications such as simulation of crop performance and the design of solar energy conversion devices. In this paper, the validations of fifteen models for estimating monthly mean daily global solar radiation on the horizontal surfaces were conducted at a location in salielian region where there is great potential for solar energy utilization in electricity generation and irrigation. Evaluations of these models were carried out by using the Mean Bias Error (MBE), Root Mean Square Error (RMSE), Mean Percentage Error (MPE) and t-test. Three of these statistical performance indicators were combined to generate rank score for each model. Temperature based models made the rank of the best three during the wet season. On the annual scale and in the dry season, temperature variations and humidity were combined with sunshine duration to get the best rank of I to 3.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 Estimates of clear-sky solar irradiances over Nigeria(2019) Otunla, T.A.This study attempts to circumvent the problem of paucity of input data required in climatology mapping of clear-sky solar irradiance in Nigeria by computing beam normal (Ebn) and diffuse (Ed) irradiances using a high performance broadband radiative model in the country climate zones. Air temperature, relative humidity and global datasets of ozone thickness and angstrom turbidity were used as input parameters. The biases in the Ebn estimates with NASA datasets across Nigeria (11e25%) are of similar magnitudes with NASA observations with ground measurements. The estimates show persistent negative biases that increased from tropical savannah to semi-arid climate zones (_8 to _24%). The bias in the Ed estimates is only of similar magnitude with NASA in semi-arid climate zone (10%). The Ed estimates show persistent negative biases that increase from semi-arid to tropical savannah across Nigeria (_7 to _54%). Also, the estimates in each climate zone correspond to the expected climatology of water vapour, aerosol turbidity and absolute optical mass. Lastly, the response of Ebn to water vapour absorption and aerosol extinction signals is mostly active in monsoon zone while the response to the signals by Ed are active in all the zones.Item Estimation of Surface Energy Fluxes Using the Penman Monteith Method in a Tropical Station(2010) Adeniyi1, M.O.|; Otunla, T.A.The Penman Monteith (PM) model was applied in the estimation of sensible and latent heat fluxes on Nigerian Micrometeorological Experiment (Nimex_1) field at Obafemi Awolowo University, Ile-Ife, Nigeria, so as to validate its usage by comparing with direct eddy covariance measured fluxes. The resulting fluxes from the PM model were comparable to the measured eddy covariance ones. The root mean squared error (RMSE) ranging from 17.63 to 22.11Wm-2 and 38.72 to 76.08 Wm-2 was obtained for sensible and latent fluxes, respectively. The coefficient of determination for sensible and latent heat fluxes ranged from 0.83 to 0.90 and 0.78 to 0.90, respectively, with trend lines at the origin. The PM model gave a better estimation of sensible heat flux than the latent heat flux. The PM method was found to be rugged with respect to the choice of values for parameters of the correction advective term Fw which requires the inclusion of the relative humidity of the ground and the air near the surface. The resulting fluxes were not significantly dependent on the choice of the parameters, weather measured or assumed. The coefficient of determination between the two sets of computed fluxes were 1 for both sensible and latent heats. The RMSE ranged between 0.89 and 9.22 with the highest RMSE value on day of year (DOY) with the lowest soil moisture.Item Temperature variations and soil thermal properties at the Nigeria mesoscale experiment site, Ibadan, Nigeria(ECRTD-UK, 2019) Nwaokoro, E.; Nymphas, E. F.Soil temperature has been observed to depend on a number of factors, which also determine the surface temperature. In this study, soil temperature at the Nigeria Mesoscale Experiment (NIMEX) site, Ibadan (7.4398° N, 3.8930° E) was investigated and the soil thermal properties were estimated for the period of March, 2006 to January, 2007 using Kersten model. The rainy seasons had increased the soil moisture content and soil thermal properties while the dry seasons had low soil moisture content and soil thermal properties. The maximum temperature of 32.10° C at the 30cm depth was measured in November 2006 during the dry season and the minimum temperature 26.80° C was measured at 5cm depth in September 2016 during the wet/rainy season. Soil moisture, thermal conductivity, thermal diffusivity and volumetric heat capacity had their maximum value of 20.52m3m-3, 1.006 Wm-1K-1, 1.07*10-8m2s-1 and 0.91*108Jm- 3K-1 in September 2006 respectively. The minimum values for soil moisture, thermal conductivity and volumetric heat capacity occurred in January, 2007 with values of 15.75 m3m-3, 0.90 Wm-1K-1 and 0.91*108Jm-3K-1 respectively, and the minimum value of 0.85*10-8m2s-1 for thermal diffusivity occurred in July 2006.Item Simulating the influence of greenhouse gases on the climate of West Africa(2019) Adeniyi, M.O.; Nymphas, E.F.; Oladiran, E.O.The response of climate to perturbations in GHGs is location dependent. Six experiments: control (CTRL); double CH4; double CO2; double N2O; halved CFC11 and halved CFC12 were carried out to reveal the local area response to different GHGs levels in the atmosphere over West Africa. Double CH4, CO2 and N2O generally induce wetness but they also induce localized dryness at the hilly and mountainous areas of SW Ghana, Central Nigeria, Northern Cameroon and South-eastern Central African Republic. Increase in ground temperature is induced by double GHGs with intensified warming at the north by double CO2. However, patches of cooling are induced at the north. Changes in specific humidity induced by double CO2, CH4 and N2O are similar. Intensified tropical easterly jet is induced by double GHGs. A dipole anomaly of wind with positive at the lower latitude and negative at higher latitude is induced at the northern part of West Africa. Significant reduction in cloud water content is induced from 900 to 400 hPa and 0 and 15oN.Item Meteorological comfort indices to assess extreme warmness in southwest, Nigeria(2019) Aluko, T.O; Nymphas, E.F.; Bolaji, O.A.; Odubanjo, O.F.2015, 2016 and 2017 have been confirmed the three warmest years on record and the degree of warming during these three years has been exceptional. Extremes of heat and cold environmental conditions have been known to be very detrimental to the health and comfort of humans. The severity of these adverse effects is often local and varies from one place to another though they are happening on a global scale therefore Temperature variation, Heat Index (HI) temperature and Dew Point Temperature (DPT) ( Meteorological comfort indices) were used to assess the effect of this condition in southwest, Nigeria. Air temperature and Humidity data were collected from meteorological stations situated in the southwestern states selected for study and was processed using the rule of Thumb for DPT calculations as expressed by Lawrence (2005) and Steadman (1979) formula simplified by Rothfusz’ model (1990) for HI temperature. The data analysis was done using Microsoft Excel Package and Statistical Package for the Social Sciences (SPSS), the following results were obtained: Elevation may affect temperature yet during extreme warmness other factors can have a greater influence on temperature and meteorological comfort indices used to assess extreme warmness in southwest Nigeria from this study showed greater impacts thus: Heat Index Temperature has highest values in Lagos State, while Dew Point Temperature have highest values in Ogun state. None of these extreme warmness measuring variables seem to be solely in favour of state Location in terms of coordinates and elevation; this suggests more anthropogenic influence forming the characteristics of the states to geographic locations of the states however, between the start year of extreme warmness (2015) and 2017, HI temperature showed a significant increase while average DPT did not really change during the period of extreme warmness.Item Characteristics of worst hour rainfall rate for radio wave propagation modelling in Nigeria(springer, 2019) Osita I.; Nymphas E.F.Radio waves especially at the millimeter-wave band are known to be attenuated by rain. Radio engineers and designers need to be able to predict the time of the day when radio signal will be attenuated so as to provide measures to mitigate this effect. This is achieved by characterizing the rainfall intensity for a particular region of interest into worst month and worst hour of the day. This paper characterized rainfall in Nigeria into worst year, worst month, and worst hour. It is shown that for the period of study, 2008 and 2009 are the worst years, while September is the most frequent worst month in most of the stations. The evening time (LT) is the worst hours of the day in virtually all the stations.