P. D. Tyson's research while affiliated with University of KwaZulu-Natal and other places

Publications (98)

Article
Acoustic radar observations are discussed and shown to provide useful information relating to the nature and diurnal variation of the lower boundary layer of the atmosphere over Johanesburg. Particular phenomena considered include inversion formation and dissipation. development of fumigation conditions and the occurrence of daytime thermal convect...
Article
Spectra of velocity fluctuations in mountain winds observed in two Transvaal valleys of very different geometry show that surges with periods the order of 1 hour, and to a lesser extent those with periods 8–20 mins., contribute most to the total turbulent energy of the stable mountain wind. Vertical velocity fluctuations, particularly the upward, a...
Article
The onset of the valley wind in valleys around Pietermaritzburg is shown to produce distinctive changes in the spatial variation of the wind field which are conducive to the occurrence of dynamic air pollution fumigations.
Article
Radiosonde data for the years 1969-1972 have been processed to determine surface inversion conditions over Southern Africa. Results are presented to show the actual and probable frequency of occurrence, depth and strength of surface inversions at midnight, early morning and midday for the year as a whole and for summer, autumn, winter and spring.
Article
Changing world patterns of climate are reviewed for pre–Pleistocene to recent times. with increasing emphasis being placed on the changes that have taken place in the last centuries and decades. Changes in South African climate over the last century are discussed in the context of world changes. Approaches to modelling future climatic fluctuations...
Article
The coincidence of that part of South Africa experiencing a quasi 20-year-old oscillation in total annual rainfall and the summer rainfall region is demonstrated. Space mean time series (or the region arc synthesised and shown to peak around 1921, 1940 and 1958 with minima around 1911, 1930, 1949 and 1967. The average range of the oscillation is sh...
Article
It is hypothesised that during extreme dry years rainfall over the interior of southern Africa will increase due to an equatorward shift of the circumpolar westerlies. Examination of extreme wet and dry years during the wet spell of the 1970s and the dry spell of the 1980s shows that this was the case. Cloud cover, rainfall and the degree of regula...
Article
The use of the terms plain-mountain and mountain-plain wind to describe regional movements of air towards and away from the Drakensberg mountains of Natal by day and by night is cumbersome and not conducive to common usage. Instead it is suggested that the umzansi and minza be adopted to describe the plain-mountain and mountain-plain winds respecti...
Article
Hourly wind speeds at eighteen stations have been used to determine regional and seasonal diurnal and inter-diurnal wind variabilities in southern Africa. From the ratio of the diurnal/inter-diurnal variabilities the degree to which diurnal boundary layer processes dominate the near-ground windfield has been established and mapped in generalised fo...
Article
The mountain wind in the Bushmans valley of the Drakensberg is shown to have distinctive spatial and temporal characteristics. The onset of the wind occurs as a pronounced surge of cool air. Thereafter surging continues as regular fluctuations in turbulent energy occur throughout the 12- to 15-hour period of the mountain wind. Horizontal velocity s...
Article
Diurnal and seasonal oscillations of the atmospheric boundary layer over the central Namib Desert on the west coast of southern Africa are examined. Both the vertical and horizontal structure of the thermo-topographic airflow are contrasted with similar wind systems occurring over Natal on the east coast of the subcontinent. Thermo-topographic airf...
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Full-text available
Data from stalagmites in the Makapansgat Valley, South Africa, document regional climatic change in southern Africa in the Late Pleistocene and Holocene. A new TIMS U-series dated stalagmite indicates speleothem growth from 24.4 to 12.7 ka and from 10.2 to 0 ka, interrupted by a 2.5ka hiatus. High-resolution oxygen and carbon stable isotope data su...
Article
Data from stalagmites in the Makapansgat Valley, South Africa, document regional climatic change in southern Africa. A new TIMS U-series dated stalagmite indicates speleothem growth from 24.4-12.7 ka and from 10.2-0 ka, interrupted by a 2.5 ka hiatus. The record has an extremely good chronology for the Holocene and a some-what less secure, but none...
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Wavelet analysis has been used to determine changes in the variability of southern Africa climate over the last three millennia. The structure of the variability in a 3000-year δ¹⁸O record has been compared with that in tree ring data for the last 600 years and both to the variability in annual rainfall and runoff during the 20th century. Preferred...
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Climates of equatorial East Africa and subtropical Southern Africa have varied inversely over long periods of time. The high-resolution δ 18O stalagmite record from Cold Air Cave in the Makapansgat valley in South Africa and a similar resolution lake-level record for Lake Naivasha in Kenya have been in anti-phase for much of the last thousand years...
Article
Unravelling the skein of global change effects in southern Africa is a non-trivial task. It is made all the more interesting since Africa is the birthplace of humanity. Southern Africa preserves an impressive five-million-year record of human-environmental interaction. From the evolutionary cradle onwards, environmental change has profoundly affect...
Article
The phrase, ‘the future of the past,’ is in many ways the epitome of Earth System science and global change. For the natural component of the system, the statement is to a large extent true; for anthropogenically induced change, it is true only for the Anthropocene—the latest era in Earth’s history in which the influence of humanity has come to riv...
Chapter
Regional syntheses have been carried out for four regions of the developing world: Southern Africa, South Asia, East Asia and Southeast Asia. Understanding the Earth System requires that the two-way linkages between regions and the global system be well understood and predictable. In each of the regions considered, distinctive manifestations of glo...
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Full-text available
A detailed climate proxy record based on delta18O, delta13C, and grey index of a well-dated stalagmite from Cold Air Cave in the Makapansgat Valley of north-eastern South Africa suggests that regional precipitation, temperatures and vegetation oscillated markedly and rapidly over the last ~6500 years on centennial and multi-decadal scales. The mid-...
Article
A multi-tiered forecast procedure is employed to simulate real-time operational seasonal forecasts of categorized (below-normal, near-normal and above-normal) streamflow at the inlets of twelve dams of the Vaal and upper Tugela river catchments in South Africa. Forecasts are made for the December to February (DJF) season over an 8-year independent...
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In the last few decades, a great deal of work has been carried out on the nature of the oceanic circulation around southern Africa. Attempts have been made to determine regional ocean-atmosphere interactions and the effect of changing sea-surface temperature fields on weather and climate. At the same time, the marine biology and ecosystems of coast...
Article
Attention is focused on temperature and rainfall changes occurring over the subcontinent of southern Africa, on atmospheric circula- tion and transport of aerosols and trace gases in the vertical and horizontal, and on repeated recirculation of atmospheric constitu- ents over the region. It is shown that most air, and whatever is contained therein,...
Article
Over the last 400 000 years, the pattern of climatic change in the southern African sector of the southern hemisphere is shown to have followed in broad outline that defined by the Vostock ice-core sequence. Regional-local differences are apparent in the inshore ocean sediment core record taken from the continental shelf off Namibia and probably re...
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Full-text available
Understanding the earth system requires that the two-way linkages between regions and the global system be well understood and predictable. Most studies of global change are undertaken thematically across limited disciplinary boundaries; few are attempted holistically across many disciplines within regions. The regional approach offers many advanta...
Article
A preliminary 3000-year palaeotemperature series is presented for South Africa. The series has been derived using the correlation in recent times between the colour variation in annual growth layers of a stalagmite taken from a cave in the Makapansgat Valley and an area-averaged regional annual maximum temperature series. A statistical transfer fun...
Article
Sea-surface temperature (SST) variations of the oceans surrounding southern Africa are associated with seasonal rainfall variability, especially during austral summer when the tropical atmospheric circulation is dominant over the region. Because of instabilities in the linear association between summer rainfall over southern Africa and SSTs of the...
Article
Ambient SO2 concentrations and atmospheric deposition of sulphur resulting from emissions on the industrialised highveld region of South Africa are estimated using the multi-scale atmospheric transport and chemistry (MATCH) modelling system, developed at the Swedish Meteorological and Hydrological Institute (SMHI), and compared with an inferential...
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Aeolian transport of iron-bearing fine dust is shown to take place from southern Africa to the central South Indian Ocean area in a pathway leading towards Australasia. Deposition of dust to the ocean takes place by subsidence of transport trajectories to the surface in the region of the centre of the South Indian Anticyclone and over the area of t...
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The Little Ice Age in South Africa, from around AD 1300 to 1800, and medieval warming, from before 1000 to around 1300, are shown to be distinctive features of the regional climate of the last millennium. The proxy climate record has been constituted from oxygen and carbon isotope and colour density data obtained from a well-dated stalagmite derive...
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Seasonal flooding in the Okavango Delta is influenced equally by local rainfall and inflow from the catchment to the north. Local rainfall is convective, modulated by the semi- permanent anticyclone over southern Africa and easterly waves, and is subject to the well-documented 18-year oscillation of the subcontinental interior. The catchment is mor...
Article
A review of climatic change in southern Africa over the last half million years is presented. The foundation for the synthesis is the use of continuous and near-continuous data series derived from deep-sea ocean sediment cores, terrestrial sediment cores, and stalagmites in South African caves. These are supplemented by non-continuous data from a v...
Article
Speleothems have been identified as being useful tools for reconstructing long continuous palaeoclimatic records. A stalagmite sample was taken from a Cold Air Cave (24°S 29°11′E; 1500 m above sea level) in the Makpansgat valley, South Africa, in order to investigate the possibility of using it to reconstruct climatic changes in southern Africa. Th...
Article
The climatic history over South Africa during the past few centuries is modelled by mathematical inversion of perturbations in temperature profiles measured in boreholes drilled in solid rock. Preliminary investigation reveals that 19th and 20th century rapid warming of the ground surface commenced about 170 years ago and that on average surface te...
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Full-text available
High-resolution stable isotope variations and growth structure analyses of the last three millennia of a 6600-year stalagmite record at Cold Air Cave, Makapansgat Valley, South Africa, are presented. Growth layers, which are measurable over the last 250 years, are shown to be annual. The correlation between the width of growth layers and precipitat...
Article
South Africa is the most industrialised country in southern Africa with approximately 1.1 Tg of sulphur emitted from anthropogenic activities per annum. Complex circulation patterns and highly stable vertical atmospheric conditions promote the accumulation of pollutants below 700 hPa or 3000 m asl. A remote site in the Eastern Cape of South Africa,...
Article
A model of climate change over southern Africa is presented. It includes both latitudinal changes in and in situ intensification of major atmospheric circulation features of the southern African sector of the southern hemisphere. Longitudinal changes in the position of the African cloud band and the position of the southern African trough of planet...
Article
Long-range and inter-hemispheric transport of atmospheric aerosols over equatorial Africa has received little attention so far. Most aerosol studies in the region have focussed on emissions from rain forest and savanna (both natural and biomass burning) and were carried out in the framework of programs such as DECAFE (Dynamique et Chimie Atmospheri...
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While sufficient to control the vertical transport of aerosols and trace gases to the troposphere, inversion of temperature are not necessary for vertical mixing to be inhibited. In this paper the notion that absolutely stable layers are both necessary and sufficient to determine the nature of the mixing process is explored. Layers of absolutely st...
Article
The southern African haze layer is a ubiquitous subcontinental-scale feature of the lower atmosphere that extends to a depth of ∼5 km(∼500 hPa level) on non rain days, particularly in winter. Aerosols derived from biomass burning are commonly thought to contribute substantially to the total background aerosol loading within the layer. It is shown t...
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Southern hemisphere and South African regional air temperature anomalies for the period 1860-1996 are compared to borehole-derived surface rock-temperature anomalies to assess the extent to which surface rock temperatures reflect possible global warming in South Africa. The warming of the southern hemisphere since the mid-nineteenth century is evid...
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The role of water and airborne sediments and nutrients is examined in the nearly closed system of the Okavango Delta. The total annual sediment load carried by the Okavango River into the delta is estimated at 620 000 tonnes. Annual deposition on the delta from the atmosphere under anticyclonic conditions only is estimated at 250 000 tonnes. Nutrie...
Article
A pall of aerosols and trace gases frequently occurs over southern Africa to a depth of ∼500 hPa, blanketing vast areas, particularly in the austral winter and spring. Large-scale offshore transport of these aerosols and trace gases in extremely large plumes from interior continental areas of the subcontinent to the Indian and Atlantic Oceans is a...
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A climatology of air transport to and from Kenya has been developed using kinematic trajectory modeling. Significant months for trajectory analysis have been determined from a classification of synoptic circulation fields. Five-point back and forward trajectory clusters to and from Kenya reveal that the transport corridors to Kenya are clearly boun...
Article
The detection of periods of elevated industrial pollutants at a remote site along a pathway of maximum subcontinental scale transport just below 700 hPa absolutely stable layer was studied. Long-term time-resolved particulate matter samplers (an open faced stacked filter unit (SFU) and an open faced single stage filter unit (SSFU)) were commissione...
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Kinematic trajectory modelling is used in a preliminary examination of inter-regional transport of air within the Southern Hemisphere. In particular, the westerly zonal transport of air in the lower troposphere from southern Africa and Australia to New Zealand is determined for January and July, using both forward and backward trajectories originat...
Article
Given the uncertainties associated with GCM modelling of aerosol effects on regional precipitation, a simple model is used to make a preliminary assessment of the influence of aerosols on rainfall in the Lake Tanganyika region of tropical southern Africa. No attempt will be made to consider the effects of changing carbon dioxide and moisture conten...
Article
Twentieth century changes in the terminal position of the Franz Josef Glacier on the west coast of New Zealand are compared with an area-averaged mean annual rainfall series for the summer rainfall region of South Africa. Distinctive teleconnections are evident in an out-of-phase relationship between the two series, each of which exhibits an oscill...
Article
Copyright: 1997 Bureau Scientific Publications Tropical-temperate troughs and their associated cloud bands have been modelled over southern Africa using the Regional Atmospheric Modelling System (RAMS). The correspondence between simulated fields and observational data for both the dry, (1980) and the wet (1981) late summer case studies has been ex...
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Vertically integrated back and forward trajectories for the 300-200, 700-500 and surface-800 hPa levels are calculated using Pretoria as point of origin for the Southern Africa Fire-Atmosphere Research Initiative (SAFARI) period September-October 1992. The transport fields are then combined to show both horizontal and vertical transport of air to a...
Article
Atmospheric transport of airborne material over and out of a region has important consequences for global change. In this article, recent developments concerning the transport of air, aerosols and trace gases in the troposphere over southern Africa will be examined. Regional circulation patterns affecting horizontal advection of aerosols and trace...
Chapter
Atmospheric transports of fire-generated products are scale-dependent phenomena. The occurrence of fires in time and space is also related to atmospheric scales of motion. Large scales of motion (>1000 km), such as the semi-permanent subtropical anticyclones, may control rainfall and rainfall in turn influences the water balance and the probability...
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Kinematic air parcel trajectory analysis is used to determine patterns of horizontal air transport in 2000 km × 2000 km areas over southern Africa. From these, composite zonal and meridional transport fields are derived for the subcontinent to estimate the extent to which recirculation of air and aerosols may take place in the lower troposphere bet...
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Tropospheric air trajectories that occurred during the Southern African Fire-Atmosphere Research Initiative (SAFARI) in August-October 1992 are described in terms of a circulation classification scheme and the vertical stability of the atmosphere. Three major and frequently occurring stable discontinuities are found to control vertical transport of...
Article
Changes in seasonally averaged surface air temperature, mean sea-level pressure and rainfall predicted by a representative range of current equilibrium climate models linked to mixed-layer oceans and fully coupled ocean-atmosphere models are compared. All fully coupled and mixed-layer models predict increased temperatures under enhanced greenhouse...
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Full-text available
Two episodes of long-range aerosol transport (4000 km) from southern Africa into the central tropical South Atlantic are documented. Stable nitrogen isotope analysis, multi-elemental analysis, and meteorological observations on local and regional scales are used to describe the observed surface aerosol chemistry during these transport episodes. The...
Article
The thermodynamic structure of the atmosphere over South Africa is examined to determine the occurrence and persistence of stable discontinuities that govern the horizontal and vertical transport of aerosols and trace gases in the troposphere over the region. Absolutely stable layers in which the lapse rate of temperature is less than the saturated...
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An air transport climatology is derived for subtropical southern Africa (Africa south of 15°S) by classifying daily synoptic situations into predominant circulation types. The annual variation of these provides the basis for determining month-by-month transport. Percentage zonal transport in easterly and westerly directions, levels of transport, an...
Article
Back and forward kinematic trajectory modelling has been undertaken for rain and no-rain days over the central interior of South Africa in mid-summer. No-rain days (rain days) are shown to be characterised by dry (moist) south-westerly (northerly to north-easterly) flow originating over the South Atlantic (tropical Indian) Ocean. Air parcels for tr...
Article
Models of southern African palaeoclimate implicate surface atmospheric circulation anoma lies as forcing large-scale changes during the Late Quaternary. The available proxy data are insufficient to test the models since they provide information about temperature and rainfall rather than surface circulation. A conceptual model is proposed which link...
Article
Inter-seasonal and inter-annual variations of low-level tropospheric water vapour transport over southern Africa and adjacent oceans have been examined using the ECMWF III-B global analysis data set. Velocity potential and stream function analyses have been used to investigate differences between the large-scale circulation fields and the sources a...
Article
Until recently, relatively little was known of the exact nature of climatic change in southern Africa over the past two millennia. New research based on oxygen isotope analyses of cave speleothems and mollusc remains in shell middens, together with foraminifera studies of inshore marine deposits, palynological and micromammalian research and earlie...
Article
Correlations between solar activity and southern African rainfall, stratified according to the phase of the Quasi-Biennial Oscillation (QBO), reveal significant zero and 3-month lag associations in both the summer and the winter rainfall regions. The solar-rainfall associations are significant for in-season rainfall only when the QBO is in its east...
Article
A brief review of climatic changes over the last 800 000 years in southern Africa is presented. The greatest emphasis is placed on those changes occurring during the Holocene and the period of meteorological record. Twentieth-century rainfall variations and their spatial manifestations are examined, and scenarios of possible future conditions are p...
Article
A present-day climatic model is presented in which extended wet spells of near-decadal duration and dry spells of similar length are explained on the basis of surface and upper tropospheric circulation variations. Wet spells are shown to be the result of increased tropical atmospheric disturbances and tropical-temperate interaction, and to be linke...
Article
Differences in annual geopotential heights at the 850 and 500 mb levels between 16 pairs of stations have been submitted to principal component analysis to identify the most important statistically uncorrelated pressure patterns accounting for the variance of the annual pressure field over South Africa and adjacent oceans. By correlating component...
Article
Observations of the atmospheric temperature structure over Johannesburg have revealed the existence of both well-developed and suppressed heat plumes. Suppressed plumes appear to be associated with the incidence in a stable atmosphere of positive wind shear and well-developed katabatic flow away from the city. A localised cool region in the atmosph...
Article
Observations are presented suggesting the significance of sea breezes in producing distinctive diurnal boundary layer oscillations over Christchurch. Sea breeze effects are shown to be an all-year phenomenon reaching their maxima in summer. The interaction of onshore wind components with south-westerly gradient winds (even under cloudy conditions)...
Article
Variations in rainfall over southern Africa are explained in terms of variations in pressure and circulation patterns. The extended wet spells of the quasi 18-year oscillation in rainfall that have affected the subcontinent are shown to have occurred in association with increased pressures in the region where the subtropical ridge of the first zona...
Article
An energy balance model is presented and tested against surface temperature fields observed over Christchurch under clear winter conditions. The fit between observed and simulated fields is shown to be close by night and slightly less so by day. Using the model the spatial variation of net radiation, sensible, latent and substrate heat fluxes withi...
Article
Short-term changes in the general circulation of the atmosphere, which may lead to prolonged periods of drought, are catalysts for producing accelerated desertification. In southern Africa the northeastward thrust of desertification from the western and central arid and semi-arid areas (the Karoo) has long been recognised, but up til 1970 research...
Article
Acoustic sounder data show that over the Highveld of South Africa nocturnal inversions do not dissipate beneath an absolutely stable layer with a constant upper surface height. Instead. penetrative convection and entrainment lift and weaken the echo envelope of the surface inversion so that it slopes upwards with time. Final dissipation is shown to...
Article
Annual rainfall anomalies over Africa south of 22 are shown to have exhibited a striking degree of organisation in both time and space during the period of meteorological record. Since the beginning of the twentieth century eight regularly alternating wet and dry spells of nine to ten years duration are shown to have occurred in association with a...
Article
Frequencies of wind for eight speed classes and sixteen directions are presented for three static stability classes, viz. lapse rates exceeding the dry adiabatic, between the dry adiabatic and isothermal and for inversion conditions. For each of nine aerological stations in southern Africa stability wind roses have been constructed to show the clim...
Chapter
That desert and semi-desert conditions are encroaching towards the northern and eastern parts of South Africa, and that Karoo vegetation is replacing grassland and in turn is being replaced by dryland woody species has been suggested by many research workers (Phillips 1938, Acocks 1953, Shantz & Turner 1958, Donaldson & Kelk 1970). Various reasons...
Article
Radiosonde data for the years 1969–1972 have been processed to determine non-surface inversion conditions over Southern Africa. Results are presented to show, first, the spatial and point characteristics of mean non-surface inversions by season and by month, and secondly, the nature of inversion occurrence within six layers of the lower atmosphere.
Article
By fitting a trigonometrical regression model to a regionally averaged time series for the period 1910–72, and by extrapolation to the year 2000, an estimate of future extended wet and dry spells has been made for the summer rainfall region of South Africa. It is suggested that the periods 1972–81 and 1991–2000 will experience above normal rainfall...
Article
By fitting a trigonometrical regression model to a regionally averaged time series for the period 1910-72, and by extrapolation to the year 2000, an estimate of future extended wet and dry spells has been made for the summer rainfall region of South Africa. It is suggested that the periods 1972-81 and 1991-2000 will experience above normal rainfall...
Article
Analysis of time series for 157 stations with records covering the period 1910–1972 and for fewer stations with records extending back to 1880 suggests that the commonly held view that South Africa, as a whole, is undergoing progressive desiccation must be questioned. Instead the data suggest the specific regional occurrence of weak (but nonetheles...