FACULTY OF SCIENCE
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Item Characteristics of total solar radiation in an urban tropical environment(2012) Adeniyi M. O.,; Nymphas E. F.; Oladiran, E. O.The maximum total solar radiation in Ibadan (7.38° N, 3.93° E), Nigeria occurred around 13 and 14h local time (LT) and it varied from an average value of 584.3±10.9 Wm-2 in the wet season (April to October) to 642.5±10.8 Wm-2 in the dry season (November to March) throughout the period of 1997 to 2001. Maximum total solar radiation had two peaks, one in March/April/May with value 750.3±41 Wm-2 and the other in October/November with value 633.1±63.5 Wm-2. The minimum was in July/August with the value 404.8±54 Wm-2. Diurnal total solar radiation had a similar variation with mean day total solar radiation; the latter had its maxima and minimum values to be 564.7±19, 488±36 and 308.4±40 respectively. The annual trend of solar radiation was positive throughout the period considered, which revealed global brightening. The values of total solar radiation observed in Ibadan compared well with those obtained at Ife (7.55° N, 4.56° E) a nearby tropical station. A time lag of about 3 h between the peak of the diurnal temperature and solar radiation was observed. During the month of July or August as the case may be, there was little or no time lag between the time of maximum total solar radiation and maximum diurnal temperature. Significant intra-annual solar radiation cycles (at 0.05 significant level) of 360 to 370 days (1 per year); 180 to 200 days (2 per year), 90 to 121 days (3 per year), 45 to 70days (5 per year); 20 to 35 days (10 per year), 4 to 16 days (20 per year) were obtained for all the years (1997 to 2001).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.Item Estimation of bare soil surface temperature from air temperature and soil depth temperature in a tropical station(2011) Adeniyi, M.O.; Nymphas,E.F.Soil surface temperature has critical influence on climate, agricultural and hydrological activities since it serves as a good indicator of the energy budget of the earth’s surface. Two empirical models for estimating soil surface temperature from air temperature and soil depth temperature were developed. The coefficient of determination (R2) of soil surface temperature from the air temperature model ranged from 0.92 - 0.99, while the mean absolute error (MAE) and root mean squared error (RMSE) ranged from 0.5 - 2.48 and 0.77 - 2.630C respectively. For the soil depth model, the R2 value ranged from 0.75 - 0.96, MAE ranged between 1.05 and 4.94, while RMSE ranged from 1.28 - 5.25. Both models performed well on days of year (DOYs), under similar prevailing weather conditions during the model training period.Item On the environmental effects on a point discharger(2011) Nymphas E.F.; Oladiran E. O.The environmental effect on a point discharger has been investigated. It was found that the magnitude of point-discharge current (Ip) measured from a discharger is strongly affected by the presence of other dischargers, particularly when they are very close to the discharger through which Ip is measured. The starting potential depends on the tip clearance of the central discharger rather than the separation of the points. At higher tip clearances the compound discharger exhibits a stepped-leader like process. Atmospheric contaminants also affect the magnitude of Ip.Item Behavior of multiple lightning dischargers under a tropical thundercloud(2010) Nymphas. E.F.; Adeniyi, M.O.; Oladiran, E.O.Lightning discharges on ground depend on the electrostatic charges, nature of vegetation, topography and dynamics of the turbulent layer. In designing lightning protectors, one major consideration is the highest point in the surrounding that lightning is directed. The effects of ambient dischargers on lightning protectors were investigated. to determine both the discharge behavior and performance. The starting potential of the discharger configuration increased with clearance of tip of the central discharger from surrounding dischargers, instead of increasing with the average spacing between dischargers. The point of strike of lightning discharge depended on the line of least stress rather than the height clearance from the cloud: which determined the charge structure and dynamics of the cloud particulatesItem Food security measures during uncertain climatic conditions in Nigeria(2009) Adeniyi M.O.; Ogunsola O.E.; Nymphas E.F; Oladiran, E.O.Food security is a function of a few variables such as technological input, capital, government policies and environmental (climate) factors. Good control of all these dependent variables except the last, and the thorough understanding of the last can take the nation to food security level. Possible ways of controlling the first three variables (technological input, capital, government policies) are suggested. To have thorough understanding of the climate factors, time series analysis of climate variables precisely temperature and precipitation data in twelve locations covering the various climatic belts of Nigeria were carried out. Nigeria rainfall has a usual zonal pattern and the vast majority of precipitation falls within a well-defined period. The coastal stations received more rainfall than the inland locations. The northern locations received less rainfall than southern locations. The onset period for the northern stations is May/June while the cessation period is September/October. The southern stations have April as their onset month while October is their cessation month. The southern stations have two peaks of rainfall in June/July and September. A period when rainfall ceases within the wet season exists in the south, and is referred to as ‘August break’. The northern stations have only one peak, which is in August. Annual trend of precipitation is positive in most of the southern stations while it is negative in most northern stations. At the ninety-nine percent confidence limits, all the stations have mean annual rainfall close to or within the limits except during El Nino Southern Oscillation (ENSO) years. Harmonic analysis reveals 3 to 4 and 7-8 years inter-annual cycle of precipitation which correspond to the warm and cold ENSO cycle. Temperature has a bimodal variation through the twelve months in a year. The two maxima occur in March/April/May and October/November while the minimum is in July/August. Annual temperature trend is positive (small slope) in some stations while it is negative in some not necessarily depending on the position.Item Analysis of data on net longwave, shortwave, and global radiation during a transition period in a tropical station in southwestern Nigeria(2009) Ogolo, E.O. Ph.D,; Falodun,S.E.; Oluyanmo,S.S.; Nymphas, E.This paper examines the distribution of the surface radiation balance components measured during the Nigerian Micrometeorological Experiment (NIMEX-1), a field study conducted to measure surface heat fluxes in the boundary layer during the transition period which marks the end of dry season and the onset of wet season (February 15 and March 10, 2004) in the southwestern part of Nigeria. Regression equations were obtained using the daily average values and hourly mean values between net shortwave and net longwave radiation, respectively, with the global radiation. Higher correlations with low standard error of measurement were obtained for daily mean values than the hourly mean. It was also observed that the peak values of each type of radiation during the period occurred, on average, two hours after noon when it was expected to occur.Item Micrometeorological measurements in Nigeria during the total solar eclipse of 29 March, 2006(2009) Nymphas, E.F.; Adeniyi, M,O.; Ayoola, M.A.; Oladiran, E.O.The total solar eclipse of 29 March, 2006 which was visible at Ibadan (7.55°N, 4.56°E), south-western Nigeria was utilized to document atmospheric surface-layer effects of the eclipse for the first time in Nigeria. The meteorological parameters measured are global radiation, net radiation, wind speed (at different heights), atmospheric pressure and soil temperature (5,10 and 30cm), moisture and heat flux and rainfall. The results revealed remarkable dynamic atmospheric effects. The observations showed that the incoming solar radiation, net radiation and air temperature were significantly affected. There was an upsurge of wind speed just before the first contact of the eclipse followed by a very sharp decrease in wind speed due to the cooling and stabilization of the atmospheric boundary layer. The atmospheric pressure lags the eclipse maximum by 1 h 30 min, while the soil temperature at 5 and 10cm remain constant during the maximum phase of the eclipse.Item The characteristics of positive ground discharges of tropical thunderstorms at Ibadan, Nigeria(2006) Oladiran. E.O.; Nymphas, F.F.; Akpan U. F.; Israelsson, SPositive ground lightning discharges were continuously recorded over a period of three years at Ibadan to supplement earlier composite records from 1987 by adapting the earlier design of Oladiran. et al (1988a) using the shape of the radiation field signatures and the frequency components of positive discharges (Oladiran and Israelsson. 1990). We recorded 92% discrimination between negative and positive ground flashes. The positive ground flashes were recorded at VLF and 17.3kHz, 3Db attenuation and yielded an average 13 and 11.6% ratios for (+CG)/(-CG) respectively. Compared to our results of 1988, the flash-rate characteristics for positive ground flashes are not significantly different from those of negative ground flashes and it does not show any seasonal preference. This leads to the conclusion that the occurrence of positive and negative ground flashes depends only on the cloud charge structure. Its dynamics and the ground conditions.Item Lightning signature as an index for the determination of the beginning of the Planting season in Nigeria(2004) Nymphas, F..F.; Adeniyi. M.O.; Ogolo, E.O.; Oladiran, L.O.The discharge characteristics of a Franklin rod and a compound discharger with an insolated central point and surrounding points (a modified Franklin rod) has been investigated in the Laboratory and in the open atmosphere with a view to determine their effectiveness as lightning protectors. Analysis of the data showed that the compound discharger is about two and half times more effective as lightning protectors as compared to a typical Franklin rod with multiple ends. An aperiodic relationship between in (At V.. :/AVf) and m (dn/dt) has been observed instead of the speculated linear relationship. Investigation of the environment effects reveals that point- discharge current measurement from a point in a built discharge is an under-estimate.