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Subject: search.filters.subject.Solar radiation

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    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.
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    Estimation of daily solar radiation at equatorial region of West Africa using a more generalized Angström‑based broadband hybrid model
    (2020) Otunla, T.A.
    A well-calibrated simple and economical viable Ȧngström–Prescott model has long been accepted to be more accurate than other surface meteorological data-based models. The major limitation is that it is site dependent. This study exploited the appropriateness of a more generalized Ȧngström-based broadband hybrid model in the estimation of solar radiation at seven stations in equatorial region of West Africa. This model features parametric equations that explicitly and accurately account for clear-sky damping processes in the atmosphere. It empirically estimates cloudy sky radiation extinctions using relative sunshine duration. A new cloud transmittance calibration curve that followed the cloud cover patterns of the region of study was also tried. The result indicated that the new cloud transmittance could be unique to equatorial region of West Africa. The performance of the hybrid model, after modification using the new cloud transmittance equation, was tested using mean bias error and root mean squared error. The performance was found to be comparable to the site-dependent, locally calibrated, Ȧngström–Prescott model at the calibration stations, and even better at validation stations. The same performance test comparisons with the original version of the hybrid model, and four other site-independent models: globally calibrated, FAO-recommended Ȧngström–Prescott models, Hay and Gopinathan models indicated the modified version of the hybrid model as better
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    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.