African Stations Research Articles

Seasonal Autoregressive Integrated Moving Average Modelling and Forecasting of Monthly Rainfall in Selected African Stations

Seasonal Autoregressive Integrated Moving Average Modelling and Forecasting of Monthly Rainfall in Selected African Stations

Comparative Analysis of Trigonometric and Polynomial Models in Meteorological Parameter Prediction for Sub-Saharan West African Stations

Comparative Analysis of Trigonometric and Polynomial Models in Meteorological Parameter Prediction for Sub-Saharan West African Stations

Harmattan Dust Characteristics using Fourier Transform-Infrared and Gas Chromatography-Mass Spectrometry Method of Selected Sub-Saharan Region in African Stations

Harmattan Dust Characteristics using Fourier Transform-Infrared and Gas Chromatography-Mass Spectrometry Method of Selected Sub-Saharan Region in African Stations

ANALYSIS OF AEROSOLS IN WEST AFRICA: MODELLING AND RADIATIVE FORCING

We studied the aerosol properties in Cinzana and Ilorin in West Africa using data of aerosols’ properties over the period 2000–2015 from MODIS (Moderate resolution Imaging Spectroradiometer). There has been limited report on the comparison between this two West African Stations. The time series modelling, prediction of aerosol parameters and the estimation of aerosol radiative forcing (ARF) were focused on. Statistical Package for the Social Sciences (SPSS) software was used for the modelling the monthly averaged measurements of aerosol optical depth at 550 nm (τ550), Angstrom exponent at 470 – 660 nm (α470-660), cloud fraction (Ncloud), fine mode fraction (FMF) and single scattering albedo at 470 nm (ωo) data over the two stations while the ARF values were calculated. The generated time series models are all good fit and the values are biased, both negatively and positively. The ARF of the two stations’ aerosol data shows value between 0.0 and -750.0 W/m2 for Ilorin and -10.0 to -200. 0 W/m2, which results mainly in cooling. Although there is a difference between ARF values in the two stations, both stations demonstrated clear seasonal variation with the rainy season having the least negative aerosol forcing. The results suggest that the aerosols are predominantly mineral dust, but those in Cinzana have more absorbing properties than those in Ilorin. Overall, the research shows that the modelled parameters can be utilized in lieu of the measured data and that the solar radiation received in this region has been attenuated at various degrees

Sensitivity and Consistency Analysis of BDS-3 GEO Satellite Orbit Maneuver Detection

In this study, 22 maneuvering events of C59 and C60 geostationary equatorial orbit (GEO) satellites of the BeiDou global navigation satellite system (BDS-3) in 2021 were detected and analyzed based on a time-differenced carrier phase velocity measurement algorithm combined with a broadcast ephemeris and station data. We set different empirical thresholds to analyze the effect of threshold selection on the maneuvering detection sensitivity. The sensitivity and consistency of this algorithm for GEO satellite maneuvering detection were analyzed by combining BDS-3 with other Global navigation satellite systems (GNSS) and selecting different geographic stations. The results demonstrate that changing the threshold significantly affects the maneuvering detection of C60, with the optimal maneuvering thresholds of C59 and C60 being 0.045 and 0.02, respectively. A combination of BDS-3 and GPS with equal weights was identified to be most suitable for maneuvering detection of GEO satellites. For any specific maneuver, the difference between the maneuvering time detection of C59 by stations at different geographical locations was no more than 1 min. During the maneuvering detection of C60, the start time of maneuvering detected by African stations was 4.26–8.61 min earlier than that detected by the Chinese and Australian stations, and the end time of maneuvering detected by the African stations was consistent with that detected by the Chinese and Australian stations.

Validation of the models of the ionospheric equivalent slab thickness using data from African stations

Recently, the equivalent slab thickness τ of the ionosphere has attracted great attention. This is due to its role in determining the critical frequency foF2 from the data of the total electron content TEC, which is important in obtaining the characteristics of the high frequency HF radio waves propagation, especially during disturbances, when vertical sounding data may be absent. Currently, a global Neustrelitz equivalent Slab Thickness Model NSTM model has been developed, for the use of which it is sufficient to have 12 coefficients and an index of solar activity. On the other hand, empirical models, in particular the IRI-Plas model, in which TEC and the maximum density NmF2 are calculated, are also global and can provide values of τ on a global scale. These models can complement each other, but both need to be testing. Preliminary comparison of the NSTM model with the NGM model whose values were calculated as the quotient of values TEC(NTCM-GL) and NmF2(NPDM) has shown better performance for the τ(NSTM) model. In this paper, τ is compared for the NSTM and IRI-Plas models using the Grahamstown station data for 2001–2010. It is shown that both models reflect the diurnal and seasonal variations of the observational τ. To quantify the correspondence between the model and observational values of τ, standard metrics were used: the mean absolute error (MAE), the root mean-square-error (RMSE), the normalized root-mean-square error (NRMSE). The MAE values were 87.6 km for the NSTM model and 64.7 km for the IRI-Plas model in 2001. The corresponding values in 2007 were 70.2 km and 58 km. The RMSE values were 109.1 km for the NSTM model and 80 km for the IRI-Plas model in 2001. For low solar activity conditions, the RMSE values are 87.0 km and 73.1 km (that is, the values for IRI-Plas are also smaller than for NSTM). The NRMSE values are 25.2 % and 18.4 %, respectively, under high solar activity, and 21.2 % and 18.0 % under low solar activity. The greatest RMSE of the model values concern morning and evening hours: they can reach 180 km for the NSTM model and 120 km for the IRI-Plas model.

Modeling and Forecasting Selected Meteorological Parameters for the Environmental Awareness in Sub-Sahel West Africa Stations

The monthly air temperature, rainfall, air pressure, and wind speed direction for the environmental time series recorded between January 1, 1980 and December 31, 2020 in six African stations from different climatic zones were modeled and forecasted. In the forecasting, Augmented Dickey Fuller test, ARIMA models, Auto correlation Function (ACF) and Partial Autocorrelation Function (PACF) were used. Result showed that in most of the fitted models, the Moving Average terms both seasonal and non- seasonal were also significant (p<0.05) indicating that the previous day value of the stochastic term also had a significant effect on the present value of meteorological parameters in the environment. It was observed that in all the fitted models except for wind direction in Conakry and rainfall in Abidjan have all their Autoregressive term of order 1 significant (p<0.05) which implies that previous day value of these meteorological parameter had a significant effect on the present day value of the parameters. Therefore, the forecast model indicates that maximum temperature are expected in February, March, April, and June while minimum temperatures in January, August, December. Although, the selected models cannot forecast the precise air temperature, this can also provide information that can be of help to create tactics for appropriate preparation of farming which can be used as tools for effective envi­ronmental preparation and policymaking.

Pattern of F2-layer peak electron density across African Ionosonde locations and response to solar activity

The diurnal, longitudinal, and latitudinal characteristics of the F2-layer peak electron density (NmF2) at six African stations comprising mid- and equatorial latitudes was investigated. The study covers years of low- (F10.7 = 82.2sfu) and high- (198.6sfu) solar activities. The results revealed that the NmF2 noontime-bite-out was prevalent only in the equatorial latitude. There is latitudinal (geographic) influence on the NmF2 pre-noon and post-noon peak magnitudes at the equatorial locations irrespective of solar activity. The pattern of the NmF2 amplitude during some selected specific time showed that the noontime-12LT, sunset-18LT and midnight-00LT observations are latitudinally inclined, whereas that of the sunrise-06LT is longitudinally-based for both conditions of solar events. Generally, there is a semi-annual asymmetry in the NmF2 monthly pattern with peaks in the equinoctial months. This asymmetry is significant at equatorial latitudes at daytime (06LT/12LT) and nighttime (18LT/00LT) but absent at nighttime of mid-latitudes. The asymmetry feature at the equatorial stations finds its explanation in the ionization anomaly being triggered by the fountain effect mechanism. The NmF2/F10.7 pair correlation (r) presents highest value at 06LT at all equatorial stations for both conditions of solar activity. Generally, r is higher during LSA than during HSA, and finds its explanation in the rate of ionized neutral species and ionospheric electrodynamics. The equatorial noontime bite-out amplitude (bite-outamp) is highest in equinoxes and is latitudinally inclined. We obtained a higher bite-out intensity at the equatorial stations during the HSA than the LSA period by a factor of ≈ 41 %. The importance of thermospheric neutral winds in the large-scale distribution of plasmas was emphasized.

Effects of full and partial halo geomagnetic storms on an East African low latitude station

Effects of full and partial halo geomagnetic storms on an East African low latitude station

Variability of Equatorial Electrojet (EEJ) at EIA regions

The EEJ is a worldwide solar-driven wind that results in the solar quiet (Sq) current system in the E region of the earth’s ionosphere. The variability of some features such as EEJ, are very important in understanding the complex nature of the ionosphere, especially the low-latitude ionosphere. The magnetometer data from stations located near the equator and outside the edge of the electrojet strip for Africa and India stations were used to estimate and investigate the variability of EEJ in African and Indian Low-Latitudes. The stations are Addis Ababa, Ethiopia (geographic lat/long: 9.03oN/38.76oE) and at Mbour, Senegal for African region (geographic lat/long 14.392oN/343.042oE) and Hyderabad, India (geographic lat/long: 17.413oN/78.555oE) and Beijing Ming Tombs, China for Indian region (geographic lat/long: 40.3oN/116.2oE). The data in XYZ orientation was used to estimate the EEJ strength. The result shows that EEJ exhibits diurnal and seasonal variations and that its variability is stronger in African station than in Indian station, so also is the occurrence of counter electrojet (CEJ).

Organisational politics on job satisfaction: An empirical study of police officials in a selected police service station

Background: The phenomenon of organisational politics is widely recognised in organisations, and it can have a significant impact on job satisfaction. A negative organisational variable, organisational politics alters the organisational environment, culture and behaviour. The study of organisational politics is proliferating and is now a popular research topic. In terms of job satisfaction, this can be divided into two different categories: hygiene and motivation. The purpose of this study is to explore how organisational politics affect motivational and hygiene factors in relation to job satisfaction.Aim: This study aimed to investigate the relationship between organisational politics and job satisfaction amongst police officials in a selected South African police service station in the Limpopo province.Setting: An empirical investigation was undertaken using a sample of 114 police officers drawn using the random sampling technique.Methods: A quantitative methodology, using self-administered surveys consisted of the Perception of Politics Scale (POPS) and Job Satisfaction Questionnaire (JSQ) was employed to collect data. The data were analysed using the Statistical Package for the Social Sciences (SPSS), version 24. Inferential statistics in the form of Pearson correlation analysis was used to test for relationships between the independent variable (organisational politics) and the dependant variable (job satisfaction).Results: The findings of the study revealed that organisational politics has a significant negative relationship with job satisfaction.Conclusion: It is recommended that police management should attempt to deal with perceptions of organisational politics and job satisfaction adequately.

Site or regional design wind speeds?

Estimates of high return period design wind speeds are required to achieve an acceptable probability of failure. These can be found by fitting an appropriate distribution to observed data but is complicated by spatial variation of the wind climate, therefore it is unclear which data are relevant at a particular location. We aim to frame this problem in terms of model selection and the bias variance trade-off. Existing models for incorporating site versus regionally averaged statistics are expressed in terms of key parameters, which allow the errors associated with each model to be derived. It is found that using a characteristic wind speed in codification combines the site statistics (low bias) with regionally averaged statistics (low variance). The return period of the characteristic wind speed is shown to act as a parameter controlling the relative weighting of these models. This insight is used to develop an optimal (minimum mean square error) estimator of the design wind speed, which is shown to vary based on both the available quantity of data at a particular site and how well this data corresponds to the regional average. Some practical advantages of this optimal model are then demonstrated at several South African stations.

The “tribal drum” and Literary Radio: The Postcolonial Poetics of the Transcription Centre’s Africa Abroad

On June 1, 1963, J. P. Clark’s poem “Agbor Dancer” was recorded for the London-based Transcription Centre’s program Africa Abroad, an English-language radio magazine program distributed for broadcast on multiple African stations. Africa Abroad producer Lewis Nkosi praised the poem and recorded it in its entirety in his review of the anthology Poems from Black Africa, edited by

Investigation of anomalous propagation conditions in Central and West African stations using high-resolution GPS radiosonde observations

A comprehensive study on the anomalous propagation (AP) conditions occurring over the central and west African stations was made from 2 years (January 2005–December 2006) high-resolution data measured by GPS (Global Positioning System) radio survey observations. Through data quality control and diagnostic analysis, the probability of AP occurrence and characteristic quantities of the three typical anomalous propagation conditions were given. The sub-refraction, super-refraction and ducting cases were investigated statistically using the vertical profile of modified refractivity gradient. Strong diurnal variation in the percentage occurrence of the AP had its peak during the wet months, while the dry months had the lowest values. From 0600 to 1800 local time (LT) at day (1800–0600 LT at night), the total percentage occurrence of super-refraction, sub-refraction and ducting were 82.5% (78.5%), 11% (15.5%) and 6.5% (6%), respectively. Besides statistical results, local meteorological conditions prevailing over central and west Africa have also been discussed.

Review: Design norms for soil and water conservation structures in the sugar industry of South Africa

This paper contains a critical review of the norms employed in the design of soil and water conservation structures in the South African sugar industry and highlights research needs in order to update them. Sugarcane in South Africa is grown on wide-ranging soils, sometimes in non-ideal climates and on steep topographies where soils are vulnerable to erosion. A consequence of unsustainable soil loss is reduction in field production capacity. Sugarcane fields are protected against erosion through, inter alia, the use of engineered waterways, contour banks and spill-over roads. The South African Sugarcane Research Institute (SASRI), previously known as the South African Sugar Experiment Station (SASEX), developed a nomograph to easily compute the maximum width of field panels based on soil type, tillage method, replant method, surface structures to control runoff, surface cover and slope. This was followed by guidelines and norms for the design of soil and water conservation structures. However, the nomograph was developed based on an acceptable soil loss of 20 t·ha−1·yr−1, yet soil formation rates in South Africa range between 0.25 and 0.38 t·ha−1·yr−1. Comparisons between design norms in the National Soil Conservation Manual and norms used in the sugar industry clearly show discrepancies that need to be investigated. The design of soil conservation structures includes the design of both contour bank spacing and hydraulic capacity. The sustainable soil loss method is recommended in the design of contour spacing and it determines contour spacing based on evaluation of site-specific sheet and rill erosion potential of the planned contour spacing while the hydraulic design employs Manning’s equation. Considering that increases in both design rainfall and design floods are anticipated in South Africa, it is necessary to incorporate these projections in the design of soil and water conservation structures. Many soil loss models exist, of which empirical models are the most robust and provide stable performances. The majority of empirical models are lumped models which estimate average annual soil loss. The Modified Universal Soil Loss Equation (MUSLE) estimates event-based erosion and, given that the majority of soil erosion occurs during a few extreme events annually, the design norms should be updated using the MUSLE.

Mineralogical, chemical, and petrographic properties of selected South African power stations’ feed coals and their corresponding density separated fractions using float-sink and reflux classification methods

ABSTRACTThree South African feed coal samples for the combustion process were beneficiated to produce carbon-rich and mineral-rich fractions. The mineralogical, petrographical, and chemical properties of these feed coals and their density separated fractions were investigated using XRD, XRF, QEMSCAN, Electron microprobe, and petrography analyses. This work was conducted with the goal of better understanding the processes and operational problems which could possibly occur during coal utilization, with particular focus on the included and excluded mineral matter transformational behavior at elevated temperatures. The conventional float-sink and reflux classification methods used were shown to successfully eliminate liberated minerals and produced maceral-rich float fractions (98%) macerals. The main differences between the feed coals were related to the mode of occurrence of mineral matter. An integration of these different analytical techniques allowed for better determination of the concentrations of mineral matter responsible for industrial ash-related problems. In this paper, we propose that blends of the different density fractions will reduce or minimize clinker and slag formation as well as the abrasive nature of the clinkers or slags. Possible blends to minimise clinker and slag formation include the float and sink fractions of the feed coals in varying proportions based on the specific mineralogical, petrographical and chemical data.

Stochastic Inversion of Geomagnetic Observatory Data Including Rigorous Treatment of the Ocean Induction Effect With Implications for Transition Zone Water Content and Thermal Structure

AbstractIn this paper we estimate and invert local electromagnetic (EM) sounding data for 1‐D conductivity profiles in the presence of nonuniform oceans and continents to most rigorously account for the ocean induction effect that is known to strongly influence coastal observatories. We consider a new set of high‐quality time series of geomagnetic observatory data, including hitherto unused data from island observatories installed over the last decade. The EM sounding data are inverted in the period range 3–85 days using stochastic optimization and model exploration techniques to provide estimates of model range and uncertainty. The inverted conductivity profiles are best constrained in the depth range 400–1,400 km and reveal significant lateral variations between 400 km and 1,000 km depth. To interpret the inverted conductivity anomalies in terms of water content and temperature, we combine laboratory‐measured electrical conductivity of mantle minerals with phase equilibrium computations. Based on this procedure, relatively low temperatures (1200–1350°C) are observed in the transition zone (TZ) underneath stations located in Southern Australia, Southern Europe, Northern Africa, and North America. In contrast, higher temperatures (1400–1500°C) are inferred beneath observatories on islands, Northeast Asia, and central Australia. TZ water content beneath European and African stations is ∼0.05–0.1 wt %, whereas higher water contents (∼0.5–1 wt %) are inferred underneath North America, Asia, and Southern Australia. Comparison of the inverted water contents with laboratory‐constrained water storage capacities suggests the presence of melt in or around the TZ underneath four geomagnetic observatories in North America and Northeast Asia.

A critical review of health risk assessments of exposure to emissions from coal-fired power stations in South Africa

Emissions from coal-fired power stations increase the incidence of respiratory, cardiovascular and cardiopulmonary diseases and contribute to premature deaths. Wildly varying estimates of the magnitude of these health impacts have been published, however. This paper investigates the reasons for the large discrepancies calculated in five comprehensive health risk assessments of South African coal-fired power station emissions. We review the approaches and input data used by the studies. We also evaluate the exposure-response functions (which relate the pollution concentration to which the population is exposed, to the increase in health risk) used by each study and pay specific attention to whether the exposure-response functions are relevant to the South African context. Health risks are under-estimated in studies that only consider impacts in industrialised areas, or assume high counterfactual concentrations. Health risks are probably over-estimated, however, in other studies which use linear or exponential exposure-response functions that are not applicable in areas where exposure levels are much higher (such as solid fuel-using communities). A more accurate estimate of health effects would be obtained by applying integrated exposure-response functions to quantify health risks at actual exposure levels, and then apportioning the health effects relative to the contribution made by each source to total exposure levels. A fair assessment of the health risk of South Africa’s older coal-fired power stations should also weigh the health costs of the emissions against the health benefits of electricity use in lower income households.

Longitudinal variation of equatorial electrojet and the occurrence of its counter electrojet

Abstract. We examined the longitudinal variability of the equatorial electrojet (EEJ) and the occurrence of its counter electrojet (CEJ) using the available records of the horizontal component H of the geomagnetic field simultaneously recorded in the year 2009 (mean annual sunspot number Rz = 3.1) along the magnetic equator in the South American, African, and Philippine sectors. Our results indicate that the EEJ undergoes variability from one longitudinal representative station to another, with the strongest EEJ of about 192.5 nT at the South American axis at Huancayo and a minimum peak of 40.7 nT at Ilorin in western Africa. Obtained longitudinal inequality in the EEJ was explicable in terms of the effects of local winds, dynamics of migratory tides, propagating diurnal tide, and meridional winds. The African stations of Ilorin and Addis Ababa registered the greatest % of CEJ occurrence. Huancayo in South America, with the strongest electrojet strength, was found to have the least occurrence of the CEJ. It is suggested that activities that support strong EEJ inhibits the occurrence of the CEJ. Percentage of occurrence of the CEJ varied with seasons across the longitudes. The order of seasonal variation of morning occurrence does not tally with the evening occurrence order at any station. A semiannual equinoctial maximum in percentage of morning occurrence of the CEJ was obtained at Huancayo and Addis Ababa. Only Addis Ababa recorded equal equinoctial maxima in percentage of evening occurrence of the CEJ. The seasonal distribution of the occurrences of the CEJ at different time regimes implies a seasonal variability of causative mechanisms responsible for the occurrence of the CEJ.

Ionospheric F2-layer Perturbations Observed After the M8.8 Chile Earthquake on February 27, 2010, at Long Distance from the Epicenter

The F2-layer critical frequency (foF2) data from several ionosondes are employed to study the long-distance effect of the M8.8 Chile Earthquake of February 27, 2010, on the F2 layer. Significant perturbations of the peak F2-layer electron density have been observed following the earthquake at two South African stations, Hermanus and Madimbo, which are located at great circle distances of ~8,000 and ~10,000 km from the earthquake epicenter, respectively. Simplified estimates demonstrate that the observed ionospheric perturbations can be caused by a long-period acoustic gravity wave produced in the F-region by the earthquake.