Muritala Ayoola - Academia.edu (original) (raw)

Papers by Muritala Ayoola

Modeling Earth Systems and Environment

The diurnal and seasonal variations of heat flux and the moisture content in the soil at a site f... more The diurnal and seasonal variations of heat flux and the moisture content in the soil at a site for the Nigeria Mesoscale Experiment (NIMEX) in the University of Ibadan, Nigeria (7.38 0 N and 3.93 0 E), had been investigated. The study also investigated effects of the atmospheric phenomena on magnitudes of the surface layer parameters. The month of May to August (wet months) had the least soil moisture of about 19% which was beyond the maximum obtained in the dry months. The frequency of this was above 10, and there was a record of soil moisture content above 22% in the month of June when the mean rainfall amount approached 22 mm. The frequency of soil moisture, which was less than 17%, was as high as 16, particularly in the month of November (the peak of the dry month). The month of October was peculiar with the frequency as high as 14 and soil moisture content well above 20%. This was because of the unusual heavy rainfall in the month of October, 2006. The substantial difference r...

Scientific Data

As part of the Dynamics-Aerosol-Chemistry-Cloud Interactions in West Africa (DACCIWA) project, ex... more As part of the Dynamics-Aerosol-Chemistry-Cloud Interactions in West Africa (DACCIWA) project, extensive in-situ measurements of the southern West African atmospheric boundary layer (ABL) have been performed at three supersites Kumasi (Ghana), Savè (Benin) and Ile-Ife (Nigeria) during the 2016 monsoon period (June and July). The measurements were designed to provide data for advancing our understanding of the relevant processes governing the formation, persistence and dissolution of nocturnal low-level stratus clouds and their influence on the daytime ABL in southern West Africa. An extensive low-level cloud deck often forms during the night and persists long into the following day strongly influencing the ABL diurnal cycle. Although the clouds are of a high significance for the regional climate, the dearth of observations in this region has hindered process understanding. Here, an overview of the measurements ranging from near-surface observations, cloud characteristics, aerosol an...

Ife Journal of Science, 2020

In this study, the performances of two types of Radiation Energy Balance Systems (REBS) net radio... more In this study, the performances of two types of Radiation Energy Balance Systems (REBS) net radiometers, a domed (model Q-7.1) and domeless (model NR-LITE) against a reference, four-component net radiometer (model NR01), are evaluated during the conduct of Nigeria Micrometeorological Experiment (NIMEX) held between May 27 and June 12, 2013 at a tropical location in Ile-Ife, Nigeria. During the daytime, net radiation measurements made by NR-LITE and Q-7.1 showed good agreements with NR01, with coefficient of determination for both > 0.90. The values of the mean and standard deviation for daytime net radiation as measured by NR01, NR-LITE and Q-7.1 were 257.7 ± 174.7 W m2 , 179.6 ± 129.3 W m2 and 240.6 ± 153.1 W m2 , respectively. At nighttime, NR-LITE net radiometer responded to longwave radiation better than Q-7.1. Adjustments made by linear regression of NR-LITE and Q-7.1 datasets with NR01 produced better fit. Though costs of the two REBS type net radiometers are comparativel...

Meteorology and Atmospheric Physics, 2021

Three static stability indices (K-index, KI; Lifted-index, LI; and Total Totals index, TTI) and t... more Three static stability indices (K-index, KI; Lifted-index, LI; and Total Totals index, TTI) and three related thermodynamic parameters (First and second Adedokun indices; ADED1 and ADED2 as well as the available potential energy; CAPE) were estimated to predict instability condition and precipitation over Nigeria. ERA5 reanalysis datasets of daily air temperature and specific humidity at multiple pressure levels from 1979 to 2018 were used for the prediction while the computed seasonal averages of the static stability indices (SSIs) and thermodynamic parameters (TPs) were validated with the precipitation data. It was revealed that SSIs and TPs produced ranges of values that were fairly good predictive of atmospheric convection and instability conditions over different climatic zones. They adequately captured seasonal variations in atmospheric instability conditions and migration and pulsation of the south-westerly and the north-easterly wind systems. Significant decreasing trends in annual SSIs, PTs, and precipitation were obtained over Sahel. Furthermore, fairly strong and significant positive correlations (0.66 ≤ r ≤ 0.87) were obtained between precipitation and SSIs in the north i.e. Sahel and Savannah. Fluctuation in precipitation was explained by 26–70% variations in LI, 13–19% in ADED1, and 27–36% variations in KI, particularly in the north. In conclusion, diminishing trends of the LI, KI, and ADED1 during the 40-year study period were adduced to reduced precipitation. The study has application in improved weather forecast of convection systems and precipitation in West Africa at large.

2020 International Conference in Mathematics, Computer Engineering and Computer Science (ICMCECS), 2020

The study of the Earth’s atmosphere and the space environment is important because of the role pl... more The study of the Earth’s atmosphere and the space environment is important because of the role played by the medium in the activities that affect the Earth and its inhabitants directly or indirectly. A robust capability to monitor, model and predict the happenings in the atmospheric space through deployment of both space- and ground-based observational systems for data acquisition, is key to result-oriented scientific research in atmospheric and space sciences. In this paper, we highlight the importance of regional deployment of observational facilities for data acquisition to complement current observational tools. We briefly review the capabilities of very low frequency (VLF) radio waves (in monitoring and studying changes in the atmosphere and ionosphere), and also present data obtained from our newly deployed VLF radio waves receiver at Anchor University, Lagos (AUL). We show that the diurnal signature characterised by VLF radio signal reflected in the data of three of four prop...

SN Applied Sciences, 2020

This study investigates impacts of cloudiness on surface radiation budget and temperature from 19... more This study investigates impacts of cloudiness on surface radiation budget and temperature from 1983 to 2018 in Nigeria, West Africa. The National Aeronautics and Space Administration meteorological datasets were used to achieve this objective. Net radiation (R) increased latitudinally from the coast to the inland areas. The least value of R was obtained in wet season which coincided with the period when cloud cover was at its optimal. We obtained significant decreasing trends (− 0.110 to − 0.536 Wm −2 year −1) in R but significant increasing trends in cloud cover in most parts of the region. Under clear-sky conditions, however, significant increasing trends (0.256-0.807 Wm −2 year −1) in R were obtained. Annual mean temperature showed significant upward trends under all-sky (0.009-0.059 °C year −1) and clear-sky (0.019-0.072 °C year −1) conditions. Furthermore, significant negative correlations (− 0.70 ≤ r ≤ − 0.95) were obtained between monthly values of cloud cover and R over the country. However, r values for cloud cover and temperature were positive over Sahel (r ~ 0.65) but negative over Guinea (r ~ 0.45); both significant at p < 0.05. Changes in R were accounted for by 21 to 26% variations in cloud cover, while fluctuation in temperature was explained by about 14% variation in cloud cover over Sahel region at p < 0.05. Our results revealed that the surface radiation budget was significantly perturbed by variations in cloudiness which resulted in net cloud-radiative cooling (− 30 Wm −2) over Guinea but warming over Savannah (25 Wm −2) and Sahel (50 Wm −2) zones.

Asian Journal of Applied Sciences, 2020

This study evaluates the performance of some evapotranspiration models at Ile – Ife (7o 33’ N, 4o... more This study evaluates the performance of some evapotranspiration models at Ile – Ife (7o 33’ N, 4o 33’ E) Nigeria. This was to identify suitable evapotranspiration (ET) models at the study site and to provide useful information for standardizing evapotranspiration estimations at a tropical location. Meteorological parameters (wind speed, relative humidity, temperature, solar radiation, soil heat flux, and net radiation) were routinely measured at the Obafemi Awolowo University (OAU) Meteorological Station located within the Teaching and Research Farm of the campus for a period of a month (1st – 29th July 2014). Nine standardized models for the estimation of ET; Penman-Monteith (FAO-56 PM), Priestly-Taylor (PT), Makkink (MAKK), Jensen-Haise (JH), Hargreaves-Samani (HS), Ivanov (IVA), Modified Romanenko (MROM), FAO-24 Radiation (FAO-24 RAD) and Turc (TURC) models were employed. The ET values obtained from these models were then compared to the estimated values obtained from the FAO-56 ...

Journal of Atmospheric and Solar-Terrestrial Physics, 2020

Abstract This study analysed NCEP/NCAR reanalysis datasets of wind speed components at multiple p... more Abstract This study analysed NCEP/NCAR reanalysis datasets of wind speed components at multiple pressure levels from 1956 to 2015 with a view to examining seasonal variations in wind shears in relation to convective precipitation over West Africa. It also estimated the West African Monsoon (WAM) wind shear index and related it to the WAM dynamics during different seasons (December to February: DJF; March to May: MAM, June to August: JJA; September to November: SON). The computed wind shear indices were compared with those derived from higher-resolution datasets of ERA5. Results revealed very similar spatial and seasonal distributions of wind patterns and significant positive correlations (0.75 ≤ r ≤ 0.99; p ≤ 0.05) between NCEP and ERA5 over West African onshore region. We obtained both positive and negative trends in wind shears (−0.001 to −0.05 units per year) and precipitation (−1.5 to −3.5 mm per year) over the entire study period and region. However, the trends were found to be statistically insignificant at 95% confidence level. The WAM wind shear index (WAMI) effectively captured the northward migration of the monsoon system over West Africa with peak values in JJA season. We established significant and strong associations between wind shear indices and precipitation climatology of the Climate Research Unit. The deep layer shear (0–6 km above ground level) and WAMI gave significant and positive correlation (0.75 ≤ r ≤ 0.95) with convective precipitation while fluctuation in precipitation was explained by 50–75% variations in these indices over most parts of the monsoon region. We concluded that convective precipitation was significantly influenced by seasonal variations in wind shears over West Africa.

Theoretical and Applied Climatology, 2019

In this paper, diurnal and seasonal variability of sensible heat ( H ) and latent heat ( LE ) flu... more In this paper, diurnal and seasonal variability of sensible heat ( H ) and latent heat ( LE ) fluxes have been investigated at an agricultural site in tropical wet and dry climate, Ile-Ife, Nigeria. Half-hourly averaged flux data for two complete years (2017–2018) of eddy covariance measurements at the study site was used to determine the seasonal trend of Bowen ratio ( Bo ). In wet season (April–October), diurnal range for both fluxes, H and LE , was 75.3 W m −2 and 177.0 W m −2 , respectively. Conversely, in dry season (December–February), the range for H and LE was 182.0 W m −2 and 89.9 W m −2 respectively. For wet season, the daily mean value of H was 19.7 ± 27.2 W m −2 and LE was 52.1 ± 63.5 W m −2 , while for dry season, H and LE were 44.0 ± 66.4 W m −2 and 26.6 ± 33.7 W m −2 respectively. A reversal of relative magnitudes of both fluxes was observed, such that the values of H were larger in dry season ( Bo > 1) but lower in wet season ( Bo < 1). There is a lag of about 1 h between H and LE .

Modeling Earth Systems and Environment, 2017

An Eddy Covariance (EC) system was set up to measure vertical transport of water vapour fluxes ov... more An Eddy Covariance (EC) system was set up to measure vertical transport of water vapour fluxes over a grass covered surface at a site located within Obafemi Awolowo university campus (7°33′N, 4°35′E) southwestern Nigeria between 31st of May and 14th of June, 2013. The EC measurement was used as a benchmark to evaluate the performances of four evapotranspiration models (the standardized FAO-56 Penman–Monteith (PM), Priestly-Taylor (PT), Makkink (MK) and Turc) which were employed to estimate evapotranspiration in the study area. The ET estimates from the models showed similar diurnal variation with the direct measurement from EC technique with daytime mean (mm/day) ranging between 0.79 and 2.37 for EC, 1.02–3.75 for PM, 1.58–5.46 for PT, 1.13–4.02 for MK and 1.21–4.27 for Turc. Based on regression analysis and standard error of estimates (SEE), the performances of the models ranked from PM (R = 0.96, slope, b = 0.687, SEE = 0.049), MK (R = 0.97, b = 0.569, SEE = 0.395), Turc (R = 0.97, b = 0.539, SEE = 0.553) to PT (R = 0.97, b = 0.386, SEE = 1.32). Recalibration of models coefficients using least square method showed significant improvement in their estimates and thus, the models were found very reliable for predicting ET which is a relevant parameter for irrigation scheduling.

Ife Journal of Science, 2019

International Journal of Environment and Climate Change, 2019

Meteorological data including air temperature and wind speed which were collected from DACCIWA me... more Meteorological data including air temperature and wind speed which were collected from DACCIWA measurement site at a tropical agricultural field site in Ile-Ife (7.55oE, 4.56oE), south-western Nigeria have been used to classify boundary layer stability regimes using gradient Richardson number. Three categories were considered to deduce the pattern of stability conditions namely stable, unstable and neutral conditions for 3-hourly intervals at 0.00, 03.00, 06.00, 09.00, 12.00, 15.00, 18.00 and 21.00 hours from 15th June to 31st July 2016. The data were sampled every 1sec and stored subsequently as 10 minutes averages for all the measured parameters. The data was further reduced to 30 minutes averages for easy analysis and manipulation in the calculation of gradient Richardson number used for boundary layer stability regime characterization. The results showed that the month of June 2016 had prevalence of stable regime from 0:00 – 6:00 am and 6:00 pm; 9:00 am was predominantly neutral...

Earth Systems and Environment, 2019

This study investigated the potential effects of prevailing local atmospheric conditions on dispe... more This study investigated the potential effects of prevailing local atmospheric conditions on dispersion pattern of point source emissions from a Scrap-Iron and Steel Smelting Factory, Ile-Ife, Nigeria. The American Meteorological Society/Environmental Protection Agency Regulatory Model (AERMOD) was adopted to predict the atmospheric dispersion of particulate matter (PM) emissions around the source. The PM estimates at two experimental points (M1 and M2) around the source were compared with the observations. The model simulations suggested that the PM was mostly dispersed by the dominant southwesterly wind such that the plume moved towards the northeast with variations in their spatial distributions across the seasons. Under low wind speeds and humid conditions, there was accumulation of the pollutants within the periphery of the point source. The simulated pollutant concentrations compared fairly well with the observations for both fine PM, i.e., PM2.5 (mean error = − 6441 µg m−3, kappa coefficient, κ = 0.31 at M1 and mean error = − 16,608 µg m−3, κ = 0.41 at M2) and the coarse, i.e., PM2.5–10 (mean error = − 5506 µg m−3, κ = 0.27 at M1 and mean error = − 4174 µg m−3, κ = 0.36 at M2). A hypothetical increase in stack height enhanced effective plume rise which resulted in a decrease in atmospheric pollutant concentration. The study has implication in industrial air pollution reduction.