2D Electrical Resistivity Tomography (ERT) Survey using the Multi-Electrode Gradient Array at the Bosumtwi Impact Crater, Ghana

The 10.5 km diameter Bosuntwi impact crater in Ghana is occupied by a lake of about 8.5 km in diameter. The multi-electrode gradient array has been used to carry out 2D electrical resistivity tomography (ERT) survey at different locations around the crater. The 2 m take-out cable of the ABEM LUND Resistivity Imaging System was modified to function as a 5 m take-out. 2D electrical resistivity survey was carried out along six (6) radial profiles running from the shore of the lake towards the crater rim. The least-square inversion technique was used to invert the topographically corrected data. The area extending from the lake shore towards the crater rim contains essentially three formations: the low resistivity regions from the shore of the lake towards uphill with resistivities < 64 W.m representing the lake sediments; the moderately high resistivity regions with values between 128 and 200 W.m interpreted as impact related breccias such as dikes, allochthonous or parautochthonous depending on their geometries; lastly, the model clearly differentiates the resistive basement metamorphic rocks of resistivities > 128 W.m from the lake sediments and the breccias due to their geometry and lateral extent. The ERT models allowed us to locate faults and fractures and also the thickness of the post impact lake sediments and the breccias. The results showed that the cables take-outs of the multi-core cable can be modified to suit the requirements of a particular survey thus highlighting the utility of this technique in impact cratering studies and geo-electrical imaging studies in general. Keywords: impact crater, target rock, electrical resistivity tomography (ERT), multi-electrode gradient array, roll-along techniqu

Groundwater Exploration using 1D and 2D Electrical Resistivity Methods

Integrated geophysical techniques involving 2D electrical resistivity imaging (ERI) and vertical electrical sounding (VES) were used to delineate groundwater potential zones for borehole siting in the Pru District of the Brong Ahafo Region of Ghana. The ABEM Terrameter LS was employed in the survey. A total of fifteen (15) 400 m - ERT profiles and thirty-one (31) VES points were investigated using the Schlumberger protocol. The Res1DINV and Res2DINV inversion software were used for data analysis. The 2D ERI images showed a lot of fractures within the subsurface of the study area. The results of the VES generally revealed either three or four subsurface geological layers at the selected points. The second and third layers were found to possess relatively low-to-moderate resistivity values indicative of potential aquifer zones. The resistivity of the fourth layer indicated the presence of slightly-fractured to fresh bedrock. The borehole logs depict four sequences: brownish or lateritic sandy clay overlying highly weathered sandstone which is underlain by moderately weathered sandstone and highly fractured sandstone basement. Keywords: Electrical resistivity tomography, vertical electrical sounding, groundwater, aquifer, geological layer and hydrogeology

West Africa's moist convective environment as observed by the Atmospheric Infrared Sounder (AIRS)

Knowledge of the seasonal positioning of the Intertropical Discontinuity (ITD) is critical to understanding seasonal moist convective processes and associated rainfall over West Africa. This study constitutes a new analysis of the seasonality of moist convection over West Africa, relative to the ITD, based on NASA's Atmospheric Infrared Sounder (AIRS) measurements from 2003 to 2018. Results show that AIRS resolves the seasonal march of the ITD, including its inherent diurnal-scale variations. AIRS captures the north–south daytime skin temperature dipole around the ITD, with greater relative temperatures to the north, especially during March–August. In the vicinity of the nighttime ITD, AIRS profiles indicate increased instability that is characteristic of nocturnal thunderstorm propagation. For seven Ghana weather stations, we show that AIRS positive moisture and equivalent potential temperature anomalies coincide with observed thunderstorm days. On these thunderstorm days, the mean latitude of the AIRS-derived ITD is displaced 3°, 0.2°, and 2° north of its DJF, MAM, and SON climatological positions, respectively, and 1.2° south in JJA. Among four common thunderstorm initiation indices considered, the K-index is determined to be most skillful. The findings of this study contribute to the Global Challenges Research Fund, African Science for Weather Information and Forecasting Techniques project's mission to build local tropical weather forecasting capacity and capabilities in West Africa

Verification of satellite and model products against a dense rain gauge network for a severe flooding event in Kumasi, Ghana

Floods as a result of severe storms cause significant impacts on lives and properties. Therefore, timely and accurate forecasts of the storms will reduce the associated risks. In this study, we look at the characteristics of a storm on 28 June, 2018 in Kumasi from a rain gauge network and satellite data, and reanalysis data. The storm claimed at least 8 lives and displaced 293 people in Kumasi, Ghana. The ability of satellite and reanalysis data to capture the temporal variations of the storm was assessed using a high temporal resolution (accumulation per minute) rain gauge data. We employed the observation data from the Dynamics–Aerosol–Chemistry–Cloud Interactions in West Africa (DACCIWA) rain gauges to assess the storm's onset, duration, and cessation. Subsequently, the performance of the ERA5 reanalysis and Global Precipitation Measurement (GPM) satellite precipitation estimates in capturing the rainfall is assessed. Both GPM and the ERA5 had difficulty reproducing the hourly pattern of the rain. However, the GPM produced variability that is similar to the observed. Generally, the region of maximum rainfall was located in the southern parts of the study domain in ERA5, while GPM placed it in the northern parts. The study contributes a verification measure to improve weather forecasting in Ghana as part of the objectives of the GCRF African Science for Weather Information and Forecasting Techniques (SWIFT) project

Advancing human nutrition without degrading land resources through modeling cropping systems in the Ethiopian highlands

Food shortage in sub-Saharan Africa is generally considered a function of limited access to food, with little thought to nutritional quality. Analyzing household production of nutrients across farming systems could be valuable in guiding the improvement of those systems. An optimization model was employed to analyze the scenario of human nutrition and cropland allocation in enset (Enset ventricosum)/root crop-based and cereal-based systems of the Ethiopian Highlands. The type and amount of nutrients produced in each system were analyzed, and an optimization model was used to analyze which cropping strategies might improve the nutritional quality of the household using existing resources. Both production systems were in food deficit, in terms of quantity and quality of nutrients, except for iron. The energy supply of resource-poor households in the enset/root crop-based system was only 75% of the recommended daily dietary allowance (RDA) of the World Health Organization (WHO), whereas resource-rich farmers were able to meet their energy, protein, zinc, and thiamine demands. Extremely high deficiency was found in zinc, calcium, vitamin A, and vitamin C, which provided only 26.5%, 34%, 1.78%, and 12%, of the RDA, respectively. The RDA could be satisfied if the land area occupied by enset, kale, and beans were expanded by about 20%, 10%, and 40%, respectively, at the expense of maize and sweet potato. The cereal-based system also had critical nutrient deficits in calcium, vitamin A, and vitamin C, which provided 30%, 2.5%, and 2% of the RDA, respectively. In the cereal system, the RDA could be fully satisfied by reducing cropland allocated to barley by about 50% and expanding the land area occupied by faba beans, kale, and enset. A shift from the cereal/root crop-dominated system to a perennial-enset dominated system would decrease soil erosion by improving the crop factor by about 45%. This shift would also have a very strong positive impact on soil fertility management. However, any policy suggestions for change in cropland allocation should be done through negotiations with households, communities, and district stakeholders

Underrepresentation of Local Researchers in Geophysical Studies at the Bosumtwi Impact Crater: Insights from A Systematic Review

Impact cratering is an important aspect of planetary evolution. Geophysics plays a complementary role in identifying impact craters on Earth given the non-unique geological characteristics associated with such craters. The Bosumtwi impact crater in Ghana represents one of the world's most well-preserved and young mid-sized impact craters, and this study aims to evaluate the current state of geophysical research conducted in this area. The Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) technique was employed for data collection and analysis, which involved identifying and screening relevant sources of data. Results indicated that the maximum number of publications (14) on the Bosumtwi impact crater was recorded in 2007, with 15% of these articles being affiliated with Ghanaian institutions. Furthermore, only two articles reported funding from Ghana. The major geophysical methods applied in studies of the Bosumtwi impact crater include various techniques that have confirmed the presence of shock-metamorphosed rocks. Although geophysical methods cannot provide unambiguous evidence for an impact origin of the Bosumtwi crater, they did provide additional constraints in establishing its impact origin. This study highlights the lack of local financial support for research in Ghana and African countries in general, with the underrepresentation of Ghanaian geophysical researchers being a concerning outcome. The absence of hazard studies such as the creation of unstable cliffs and the long-term effects of the meteorite impact on inhabitants of the Bosumtwi impact crater is particularly significant. Further research is necessary to fully understand the implications of this underrepresentation. Moreover, this study highlights the importance of research at the Bosumtwi impact crater for achieving the UN Sustainable Development Goals

The African SWIFT project: growing science capability to bring about a revolution in weather prediction

Africa is poised for a revolution in the quality and relevance of weather predictions, with potential for great benefits in terms of human and economic security. This revolution will be driven by recent international progress in nowcasting, numerical weather prediction, theoretical tropical dynamics and forecast communication, but will depend on suitable scientific investment being made. The commercial sector has recognized this opportunity and new forecast products are being made available to African stakeholders. At this time, it is vital that robust scientific methods are used to develop and evaluate the new generation of forecasts. The GCRF African SWIFT project represents an international effort to advance scientific solutions across the fields of nowcasting, synoptic and short-range severe weather prediction, subseasonal-to-seasonal (S2S) prediction, user engagement and forecast evaluation. This paper describes the opportunities facing African meteorology and the ways in which SWIFT is meeting those opportunities and identifying priority next steps. Delivery and maintenance of weather forecasting systems exploiting these new solutions requires a trained body of scientists with skills in research and training; modelling and operational prediction; communications and leadership. By supporting partnerships between academia and operational agencies in four African partner countries, the SWIFT project is helping to build capacity and capability in African forecasting science. A highlight of SWIFT is the coordination of three weather-forecasting “Testbeds” – the first of their kind in Africa – which have been used to bring new evaluation tools, research insights, user perspectives and communications pathways into a semi-operational forecasting environment