Analysis of geodetic and model simulated data to describe non-stationary moisture fluctuations over Southern Africa

Recent advances in space geodetic techniques such as Very Long Baseline Interferometry, Global Navigation Satellite Services, Satellite Laser Ranging and advanced numerical weather prediction model simulations, provide huge tropospheric data sets with improved spatial temporal resolution. These data sets exhibit unique fluctuations that have a spatial-temporal structure which are thought to mimic the complex behaviour of the atmosphere. As a result, the analysis of non-stationary structure in the tropospheric parameters derived from geodetic and numerical model simulations could be used to probe the extent of universality in the dynamics of the atmosphere, with applications in space geodesy. In order to identify the physical causes of variability of tropospheric parameters, parametric and nonparametric data analyses strategies which are investigated and reported in this thesis, are used to inform on the geophysical signals embedded in the data structure. In the first task of this research work, it is shown that the fluctuations of atmospheric water vapour over southern Africa are non-linear and non-stationary. Secondly, the tropospheric data sets are transformed to stationarity and the stochastic behaviour of water vapour fluctuations are assessed by use of an automatic algorithm that estimates the model parameters. By using a data adaptive modelling algorithm, an autoregressive-movingaverage model was found to sufficiently characterise the derived stationary water vapour fluctuations. Furthermore, the non-linear and non-stationary properties of tropospheric delay due to water vapour were investigated by use of robust and tractable non-linear approaches such as detrended fluctuation analysis, independent component analysis, wavelet transform and empirical mode decomposition. The use of non-linear approaches to data analysis is objective and tractable because they allow data to speak for themselves during analysis and also because of the non-linear components embedded in the atmosphere system. In the thesis, we establish that the non-linear and non-stationary properties in the tropospheric data sets (i.e., tropospheric delay due to water vapour and delay gradients) could be triggered from strongly non-linear stochastic processes that have a local signature (e.g. local immediate topography, weather and associated systems) and/or exogenous. In addition, we explore and report on the presence of scaling properties (and therefore memory) in tropospheric parameters. This self-similar behaviour exhibit spatial-temporal dependence and could be associated with geophysical processes that drive atmosphere dynamics. Satellite Laser Ranging data are very sensitive to atmospheric conditions, which causes a delay of the laser pulse, hence an apparent range increase. A test for non-linearity is applied within specialised software for these data; it is found that the range residuals (i.e., the observed minus computed residuals) are improved when possible non-linearity of the locally measured meteorological parameters as applied to a range delay model are considered.Thesis (PhD)--University of Pretoria, 2011.Geography, Geoinformatics and MeteorologyPhDUnrestricte

Investigating the effect of tide parameterization and gravity field models on SLR solutions

Satellite laser ranging (SLR) as a proven geodetic technique provides a wide and significant contribution to scientific studies of the Earth/Atmosphere/Ocean systems. In particular, modelling of the Earth and pole tides plays a very important role when analyzing SLR data. The accuracy of the determined satellite orbits is highly dependent on the models used for dynamic orbit determination. Gravity field models, which are represented by a series of spherical harmonic coefficients, have an impact on the satellite orbit and its precision. In addition, different empirical model parameterization used during SLR data analysis also has significant influence on the computed spherical harmonics, satellite orbits and their accuracies. In this contribution we investigate the impact of different SLR parameterizations on gravity field models used for precise satellite orbit determination. Data from satellites LAGEOS 1 and 2 were analysed using four different parameterization schemes namely: IERS1, IERS2 and IERS3 Earth tide models and pole tides. These are compatible Earth tide modelsofdifferentcomplexity derived fromIERS2010,astandard modeloftheInternational Earth Rotation and Reference Systems Service (IERS) and the standard IERS2010 pole tide model, and they aim to study their impacts on SLR solutions. The results indicate that the combination of IERS3, which is the most complex Earth tide model and the standard IERS2010 pole tide model, has a significant influence on the accuracy of gravity field models in precise orbit determination. In particular almost all the evaluated models give the smallest RMS values when IERS3 and pole tides are jointly selected in the analysis software during SLR data analysis, which indicates that the most complex models are also the most accurate. This work therefore validates the currently accepted IERS2010 Earth tide and pole tide models.http://link.springer.comjournal/403282015-12-3

Satellite laser ranging measurements in South Africa : contributions to earth system sciences

This contribution reassesses progress in the development of satellite laser ranging (SLR) technology and its scientific and societal applications in South Africa. We first highlight the current global SLR tracking stations within the framework of the International Laser Ranging Service (ILRS) and the artificial satellites currently being tracked by these stations. In particular, the present work focuses on analysing SLR measurements at Hartebeesthoek Radio Astronomy Observatory (HartRAO), South Africa, based on the MOBLAS-6 SLR configuration. Generally, there is a weak geometry of ILRS stations in the southern hemisphere and the SLR tracking station at HartRAO is the only active ILRS station operating on the African continent. The SLR-derived products – such as station positions and velocities, satellite orbits, components of earth’s gravity field and their temporal variations, earth orientation parameters – are collected, merged, achieved and distributed by the ILRS under the Crustal Dynamic Data Information System. These products are used in various research fields such as detection and monitoring of tectonic plate motion, crustal deformation, earth rotation, polar motion, and the establishment and monitoring of International Terrestrial Reference Frames, as well as modelling of the spatio-temporal variations of the earth’s gravity field. The MOBLAS-6 tracking station is collocated with other geodetic techniques such as very long baseline interferometry and Global Navigation Satellite Systems, thus making this observatory a fiducial geodetic location. Some applications of the SLR data products are described within the context of earth system science.http://www.sajs.co.za/am201

Appraising the effects of atmospheric aerosols and ground particulates concentrations on GPS-derived PWV estimates

Please read abstract in the article.The University of Pretoria postgraduate bursary and the Ahmadu Bello University , Zaria research grant to the first author.http://www.elsevier.com/locate/atmosenv2019-11-01hj2018Geography, Geoinformatics and Meteorolog

Appraising city-scale pollution monitoring capabilities of multi-satellite datasets using portable pollutant monitors

The retrieval characteristics for a city-scale satellite experiment was explored over a Nigerian city. The study evaluated carbon monoxide and aerosol contents in the city atmosphere. We utilized the MSA Altair 5× gas detector and CW-HAT200 particulate counter to investigate the city-scale monitoring capabilities of satellite pollution observing instruments; atmospheric infrared sounder (AIRS), measurement of pollution in the troposphere (MOPITT), moderate resolution imaging spectroradiometer (MODIS), multi-angle imaging spectroradiometer (MISR) and ozone monitoring instrument (OMI). To achieve this, we employed the Kriging interpolation technique to collocate the satellite pollutant estimations over 19 ground sample sites for the period of 2015–2016. The portable pollutant devices were validated using the WHO air filter sampling model. To determine the city-scale performance of the satellite datasets, performance indicators: correlation coefficient, model efficiency, reliability index and root mean square error, were adopted as measures. The comparative analysis revealed that MOPITT carbon monoxide (CO) and MODIS aerosol optical depth (AOD) estimates are the appropriate satellite measurements for ground equivalents in Zaria, Nigeria. Our findings were within the acceptable limits of similar studies that utilized reference stations. In conclusion, this study offers direction to Nigeria's air quality policy organizers about available alternative air pollution measurements for mitigating air quality effects within its limited resource environment.The University of Pretoria postgraduate bursary and the Ahmadu Bello University, Zaria research grant to the first author.http://www.elsevier.com/locate/atmosenv2019-04-01hj2018Geography, Geoinformatics and Meteorolog

Spatial distribution of temporal precipitation contrasts in South Africa

The focus of the present study was to investigate the spatial-temporal variability and trends of precipitation concentration across South Africa using the Tropical Rainfall Measuring Mission (TRMM) 3B42 version 7 satellite precipitation data sets spanning 1998–2015. In the analysis, the precipitation concentration index (PCI) was used to infer the variability of temporal precipitation contrasts and the spatial distributions at annual, seasonal and supra-seasonal timescales. The results indicate that precipitation concentration across South Africa exhibits noticeable spatial-temporal variability. In terms of PCI classification criteria, the precipitation distribution ranges from relatively uniform (mainly in the central and southern interior of South Africa) to highly irregular (especially to the northeastern and western parts of South Africa) at annual timescales. At seasonal timescales, the precipitation distribution is uniform during December–February season, moderate during March–May and September–November seasons while during the June–August season, the precipitation distribution is highly irregular. Furthermore, during the 1998–2015 period, there exists a spatial and temporal pattern of PCI trends which are generally statistically insignificant. The PCI analysis results reported in this study are essential because they provide valuable information on the longterm total variability in the precipitation records across South Africa. In particular, this study contributes towards evaluating the spatial contrasts or concentration of the different accumulated amounts of the received precipitation. Results from this study have important scientific and practical applications in hydrological hazard risks (floods and droughts) and soil erosion monitoring. SIGNIFICANCE : • Precipitation concentration exhibits spatial-temporal variability. • At an annual timescale, precipitation concentration is highly irregular in most parts of the country. • Precipitation concentration distribution varies across seasons.http://www.sajs.co.zaam2019Geography, Geoinformatics and Meteorolog

Hydrometeorological research in South Africa : a review

Water resources, particularly in arid and semi-arid regions of the world are of great concern, as they are closely linked to the wellbeing of humankind. Sophisticated hydrological prediction tools are required to assess climatic and hydrometeorological conditions, as they impact the sustainability of water resources as well as water availability. Research and data collection activities from multi-hydrometeorological sensors (e.g., gauges, radars, satellites) form the basis for quantifying the impact of extreme episodes along the hydrologic phases that manifest in terms of the magnitude, duration and frequency of floods, droughts and other hydrometeorological hazards that affect water resources management. A number of hydrometeorological research activities have been reported in the literature by various researchers and research groups globally. This contribution presents (a) a review of the hydrometeorology resource landscape in South Africa; (b) an analysis of the hydrometeorology services and products in South Africa; (c) a review of the hydrometeorological research that has been conducted in South Africa for the last four decades; and (d) highlights on some of the challenges facing the sustained advancement of research in hydrometeorology in South Africa.http://www.mdpi.com/journal/wateram201

The hydrometeorology of the Kariba catchment area based on the probability distributions

In this paper, monthly, maximum seasonal, and maximum annual hydrometeorological (i.e., evaporation, lake water levels, and rainfall) data series from the Kariba catchment area of the Zambezi River basin, Zimbabwe, have been analyzed in order to determine appropriate probability distribution models of the underlying climatology from which the data were generated. In total, 16 probability distributions were considered and the Kolmogorov–Sminorv (KS), Anderson–Darling (AD), and chi-square (x2) goodness-of-fit (GoF) tests were used to evaluate the best-fit probability distribution model for each hydrometeorological data series. A ranking metric that uses the test statistic from the three GoF tests was formulated and used to select the most appropriate probability distribution model capable of reproducing the statistics of the hydrometeorological data series. Results showed that, for each hydrometeorological data series, the best-fit probability distribution models were different for the different time scales, corroborating those reported in the literature. The evaporation data series was best fit by the Pearson system, the Lake Kariba water levels series was best fit by theWeibull family of probability distributions, and the rainfall series was best fit by the Weibull and the generalized Pareto probability distributions. This contribution has potential applications in such areas as simulation of precipitation concentration and distribution and water resources management, particularly in the Kariba catchment area and the larger Zambezi River basin, which is characterized by (i) nonuniform distribution of a network of hydrometeorological stations, (ii) significant data gaps in the existing observations, and (iii) apparent inherent impacts caused by climatic extreme events and their corresponding variability.http://www2.ametsoc.org/ams/index.cfm/publications/journals/earth-interactions/2015-10-31hb201

A literature review of the impacts of heat stress on human health across Africa

Heat stress-related illness attributed to the changing climate, particularly the more frequent extreme high temperatures, is becoming a theme of public concern, especially in the most vulnerable regions, such as the African continent. Knowledge of the existing research directions and gaps on heat stress and human health is vital for informing future strategic research foci capable of influencing policy development, planning, adaptation, and mitigation efforts. In this regard, a bibliometric analysis was conducted, with an emphasis on Africa, to assess regional research contributions to heat stress impacts on human health. The goals of the study were to review publication growth and patterns of the scientific publications and to identify key players (especially collaborating institutions and countries) and the evolution of research themes on the African continent, while paying attention to global trends and emergent hot topics and methodology of heat stress research. Using the Web of Science (WoS) and Scopus core collection databases, a structured keyword search was undertaken, which yielded 463 and 58 research publications from around the world and Africa, respectively. The retrieved scientific documents, published between 1968 and 2020, were analyzed and visualized using a bibliometric analysis technique and the VOSviewer software tool. The results indicate low statistics and slow scientific growth in publication output, with the highest peak having been reached in 2018, resulting in 13 scientific publications. While global research collaborations are successfully reflected in the literature, there is a considerable gap in understanding heat stress and related collaborations between African countries and international institutions. The review study has identified key opportunities that can benefit Africa through the expansion of the scope of heat stress and human health research on the continent. These opportunities can be achieved by closing the following research gaps: (1) vulnerability assessments within demographic classes, such as the elderly, (2) personal exposure and associated risks, (3) Urban Heat Island (UHI) evaluation for urban environments, and (4) heat adaptation research, which will enable informed and targeted preventive actions that will limit future heat health impacts. The authors opine that the pursuit of such studies will be most impactful if the current knowledge gaps are bridged through transdisciplinary research supported by local, regional, and international collaborators.The Water Research Commission of South Africa.https://www.mdpi.com/journal/sustainabilitydm2022Geography, Geoinformatics and Meteorolog

Leafminer agromyzid pest distribution over Limpopo province under changing climate

The objective of the study was to assess the impact of climate change on the spatial distribution of leafminer agromyzid pest over Limpopo province, South Africa. In the study the Conformal Cubic Atmospheric Model (CCAM) simulated climate scenarios; (a) the current climatology (1981-2010), (b) projected near future climatology (2041-2070) and (c) the projected distant future climatology (2071-2100) was used. In particular, the linkage between the model simulated temperature and the pest population parameters (that is, the intrinsic rate of increase (rm), net reproduction (ro), mean generation time (tg)) was modeled by empirical functions based on laboratory temperature measurements. The empirical functions (derived from the correlation between temperature and rm, o as well as tg) are used to simulate spatial distribution of leafminer agromyzid pest under changing climate. The present analysis illustrates that leafminer agromyzid pest and climatic factors exhibit a non-linear relationship best described by polynomial function of order two while in general, the influence of climate change on the spatial distribution of leafminer agromyzid pest over Limpopo province is noticeable. This work contributes towards our understanding of the impact of climate change on the population dynamics of leafminer agromyzid pest and hence impacts on tomato production in Limpopo province, South Africa.Canon Collinshttp://www.academicjournals.org/AJARam201