fluorescing macerals in south african coals abstract maceral microlithotype and fluorescing maceral content were analysed along with the vitrinite relative fluorescence measurements thirty samples from the south africa soutpansberg waterberg and main karoo basins were investigated these results were also compared with previously measured vitrinite reflectance values the application of fluorescence techniques has allowed the identification of much higher liptinite content about 5 as compared with the results of routine maceral analysis in white light results presented provide an explanation of this difference which is caused by difficulties in identifying fine liptodetrinite particles under illumination by the halogen lamp therefore detritic particles of uncertain affinity should be verified under fluorescing light during routine maceral analysis the presence and intensity of the fluorescing vitrinite in south african coals were also studied the occurrence of this component is connected with the rank of coal but could be also affected by the facies sample no b 35 and in situ coal oxidation sample no b 3 the relative fluorescence intensity of vitrinite depends on the rank of the coal but also on its degree of oxidation it seems also to be connected with the expulsion of oil which enhances its intensity the influence of the fluorescing macerals content on some coal properties was proved by the positive correlation between fluorescing vitrinite as well as sum of fluorescing macerals and calorific value 0 66 and 0 74 corr coeff respectively this proves the necessity of fluorescence application in routine maceral analysis carried out for coal quality evaluation

mesoscale physical and bio optical structure of the antarctic polar front near 170 w during austral spring as part of the u s joint global ocean flux study southern ocean program high resolution surveys of the antarctic polar front near 170 w were conducted during october november 1997 with a towed undulating system equipped with conductivity temperature depth and bio optical sensors transects along 170 w and two successive mapping surveys revealed zonal bands with sharp meridional gradients in east west velocity the polar front pf was characterized by a sea surface temperature drop from 1 6 to 1 6 c between 60 35 and 61 10 s with eastward velocities of 0 4 0 5 m s 1 in the core of the pf jet deep mixed layers 200 m were found within and north of the pf but mixed layers shoaled to 100 125 m south of the pf to the edge of loose ice at 62 3 s highest mixed layer chlorophyll concentrations 0 35 mg m 3 in late october along 170 w were to the south of the pf and associated with cold fresh water a large meander of the pf was observed with an alongfront wavelength of 175 km a cross front peak to peak amplitude of 100 km and an eastward phase propagation of 0 05 0 08 m s 1 all of which are consistent with its formation via hydrodynamic instability of the pf jet highest phytoplankton biomass was located just poleward of the center of the pf jet a high chlorophyll up to 1 1 mg m 3 50 by 50 km region was found downstream of the cyclonic bend associated with the meander a survey 7 5 days later revealed growth of this high biomass region so that chlorophyll was in excess of 0 8 mg m 3 over an 80 km cross front by at least 80 km alongfront region high biomass was observed to grow in place with respect to the meander rather than being displaced far downstream as would be expected from advection this pattern is consistent with meander driven upwelling of nutrients and or trace metals which in turn stimulates phytoplankton growth detailed cross sections of the pf reveal narrow 10 20 km wide bands or filaments of phytoplankton biomass that have temperature salinity properties distinct from surrounding water and are coherent for at least 120 km alongfront

simple climatic indices for the tropical atlantic ocean and some applications two indices related to the sea surface temperature sst variability in the tropical atlantic are proposed one index describes the sst averaged over the whole basin 30 n to 20 s 60 w to 15 e and the other illustrates a meridional dipole between the northern and southern hemispheres the computational method for obtaining these indices is intentionally kept simple the objective being to reproduce the signature of the main results previously provided from more complicated statistical analyses monthly time series for both indices are produced from 1964 up to the present time the whole basin index exhibits principally a sustained warming which has intensified since about 1975 and it has a significant periodicity close to that of the quasi biennial oscillation the dipole index exhibits a decadal scale variation and its building up seems to be related to other worldwide climatic changes as for instance el nino southern oscillation extreme episodes rainfall variabilities over the brazilian nordeste and african sahel

a relationship between the carbon and hydrogen content of coals and their vitrinite reflectance abstract an empirical relationship between carbon and hydrogen contents of coals and their measured vitrinite reflectances r v max henceforth r o determined from published data for 210 samples of australian coals from more than 60 different seams shows that r o depends upon both the carbon and hydrogen content via the equation r o 5 035 0 0804 c 0 184 h this equation allows prediction of the change in r o when the carbon and or hydrogen content vary the equi reflectance lines plotted on a seyler chart using this equation allow prediction of the variable suppression of r o caused by changes in hydrogen content

petrographic and reflectance analysis of solvent swelled and solvent extracted south african vitrinite rich and inertinite rich coals maceral transitions during solvent swelling and extraction of two south african coals similar in rank and age but different in maceral composition were evaluated inertinite rich highveld coal dominated by semifusinite and vitrinite rich waterberg coal were used maceral group analysis of solvent extracted and solvent swelled residues showed no changes in the maceral composition for both coals solvent extracted residues exhibited significant observable changes of some particles particle fracturing decrease in reflectance and rounding of particle edges inertinite rich coal exhibited extensive fracturing during solvent treatment random reflectance analyses of both coals showed that solvent treatment reduces reflectance values of both vitrinite and inertinite vitrinite reflectograms showed a shift from the dominant reflecting v types to lower reflecting v types the inertinite reflectograms exhibited an increase in the number of reflecting inertinite types i types with solvent treatment resulting in a broadening of the reflectograms the changes in reflectance between the original and solvent treated coal may be attributed to a combination of structural elemental or surface changes current data for these south african coals suggests a relationship between solvent extraction and mean random reflectance the higher the extraction yields the lower the mean random reflectance

the role of coal petrography in understanding the properties of south african coal abstract the variations in physical and chemical properties of coal can only be explained in terms of its petrographical composition and its rank by means of a trend computer programme quantitative relationships correlation coefficients 0 97 were established between the contents of total carbon and hydrogen daf of south african humic coals and their volatile matter and oxygen contents their calorific value all daf and their mean maximum reflectance of vitrinite rmax the inherent moisture content ash free the vitrinite content mineral matter free and the hardgrove and free swelling indices yielded only semiquantitative relationships correlation coefficients between 0 80 and 0 93 and high standard deviations when expressed in terms of total carbon and hydrogen contents daf these interrelationships are shown graphically by means of a seyler diagram modified for south african coal the relatively poor correlation in the case of vitrinite content is due to the presence of fairly large amounts of reactive semifusinite in most south african coals and for this reason it is necessary to distinguish between normal perhydrous and subhydrous coals depending on the relative difference between determined and inferred vitrinite contents due to the high content of low reflecting inertinite the modal reflectance of vitrinite is also regarded to a better rank parameter than the mean reflectance as the former is not affected by sporadic low or high values from the modified seyler diagram it is also possible to devise a grade type rank classification for south african coals where grade is given by the ash content moisture free basis this classification complements alpern s universal classification of solid fossil fuels the seyler diagram can also be used to delineate fields of the most useful application of south african coals based on the relevant coal properties

simulations of the atmospheric response to south atlantic sea surface temperature anomalies abstract the sensitivity of the atmospheric circulation to sea surface temperature sst anomalies in the tropical and subtropical south atlantic ocean is studied by means of simulations with an atmospheric general circulation model gcm two types of prescribed sst anomalies are used motivated by previous analyses of data the first occurs during austral summers in association with a strengthening of the south atlantic convergence zone sacz and consists of cold sst anomalies over the subtropical south atlantic the second is the leading seasonally varying empirical orthogonal function of sst consisting of warm basin scale anomalies with maximum amplitude in the subtropics during january march and at the equator in june an ensemble of about 10 seasonal simulations is made using each type of anomaly focusing on the january march period in the first case and the january june seasonal evolution in the second during january march both experiments yield a statistically significant baroclinic response o

organization of rainfall by an unstable jet with an application to african waves abstract african waves are believed to originate as shear instabilities although in certain cases rainfall is organized so that latent heating contributes to wave growth what determines whether the shear instability can organize rainfall is considered here in particular why african waves organize rainfall mainly during the late summer despite the regular occurrence of shear instability and rainfall throughout the season during gate moisture convergence by the waves was also largest toward the late summer it is assumed that an african wave will organize rainfall if it converges moisture as measured by the ascent at the top of the moist layer with sufficient amplitude the wave amplitude is specified at some level beneath the 600 mb african jet whose instability is a plausible source of the wave the ascent is calculated using the quasigeostrophic potential vorticity and thermodynamic equations and depends on the zonal wind separating the unstable jet from the top of the moist layer before turning

a physical basis for the interannual variability of rainfall in the sahel a major factor in rainfall variability over sahelian west africa is the latitudinal location of the tropical rainbelt when it is displaced abnormally far northward the sahel experiences a wet year an anomalous southward displacement results in drought in this paper we examine the question of what controls the location during the boreal summer hypothesizing that inertial instability plays a role an analysis of surface pressure and temperature fields wind fields divergence and vertical motion show that the criteria for inertial instability are satisfied in wet augusts but not in dry ones the key determinant appears to be the surface pressure gradient between the continent and the equatorial atlantic when this is large inertial instability results in the development of a low level westerly jet the presence of this jet enhances the horizontal and vertical shear and displaces the african easterly jet northwestward associated with this situation is strong vertical motion over the sahel and subsidence over the guinea coast producing dry conditions over the latter the result is a rainfall dipole one of two major modes of variability over west africa important factors include sea surface temperatures ssts in the equatorial atlantic and pressure in the south atlantic the first of these factors suggests a link with the atlantic nino mode of tropical atlantic variability while the second suggests a possible link with the pacific and the extratropical south atlantic overall our study relates the well known sst influence on sahel rainfall to atmospheric dynamics over the continent copyright 2007 royal meteorological society

decadal and interannual sst variability in the tropical atlantic ocean abstract the mechanisms regulating interannual and decadal variations of sea surface temperature sst in the tropical atlantic are examined observed variations of sea surface temperature are typically in the range of 0 3 0 5 c and are linked to fluctuations in rainfall on both the african and south american continents the authors use a numerical model to simulate the observed time series of sea surface temperature for the period 1960 1989 based on the results experiments are conducted to determine the relative importance of heat flux and momentum forcing two dominant timescales for variability of sst are identified a decadal timescale that is controlled by latent heat flux anomalies and is primarily responsible for sst anomalies off the equator and an equatorial mode with a timescale of 2 5 years that is dominated by dynamical processes the interhemispheric gradient of anomalous sst the sst dipole is primarily linked to the former process and thus results from the gradual strengthening and weak

the karoo basin of south africa type basin for the coal bearing deposits of southern africa abstract the coal bearing sediments and coal seams of the karoo basin southern africa are described and discussed the karoo basin is bounded on its southern margin by the cape fold belt onlaps onto the kaapvaal craton in the north and is classified as a foreland basin coal seams are present within the early permian vryheid formation and the triassic molteno formation the peats of the vryheid formation accumulated within swamps in a cool temperate climatic regime lower and upper delta plain back barrier and fluvial environments were associated with peat formation thick laterally extensive coal seams have preferentially accumulated in fluvial environments the coals are in general inertinite rich and high in ash however increasing vitrinite and decreasing ash contents within seams occur from west to east across the coalfields the triassic molteno coal seams accumulated with aerially restricted swamps in fluvial environments these molteno coals are thin laterally impersistent vitrinite rich and shaly and formed under a warm temperate climatic regime palaeoclimate depositional systems differential subsidence and basin tectonics influence to varying degrees the maceral content thickness and lateral extent of coal seams however the geographic position of peat forming swamps within a foreland basin coupled with basin tectonics and differential subsidence are envisaged as the primary controls on coal parameters the permian coals are situated in proximal positions on the passive margin of the foreland basin here subsidence was limited which enhanced oxidation of organic matter and hence the formation of inertinitic coals the coals in this tectonic setting are thick and laterally extensive the triassci coals are situated within the tectonically active foreland basin margin rapid subsidence and sedimentation rates occurred during peat formation which resulted in the preservation of thin laterally impersistent high ash vitrinite rich shaly coals

an investigation of interannual rainfall variability in africa abstract interannual variations in african rainfall are examined using rotated principal component analysis pca applied to anomalies from the annual mean as well as seasonal anomalies the rotated pca loading patterns suggest several preferred continental scale rainfall anomaly patterns the dominant features of year to year variations in african rainfall appear to be the high spatial coherence of rainfall anomalies over large portions of the continent in addition several dipole regions that is adjacent regions which tend to experience rainfall anomalies of opposite sign are found and discussed one dipole region the sub saharan region appears to have a relationship with a characteristic atlantic sea surface temperature anomaly pattern during boreal summer during austral summer the tendency for a large scale dipole pattern in southeast africa is apparent as is an association of this pattern with the warm and cold phases of the el nin southern oscillation enso phenomenon normalized rainfal

the burning of gondwana permian fires on the southern continent a palaeobotanical approach abstract fossil charcoal has widely been accepted as a direct indicator for the occurrence of palaeo wildfires in upper palaeozoic sediments of euramerica and cathaysia records of these remains are relatively common and regionally and stratigraphically more or less homogeneously distributed in terrestrial sequences on the other hand just a few records have been published for the permian of gondwana and only recently has it been demonstrated that macroscopic charcoals are also common here most permian macroscopic charcoal from gondwana is gymnospermous and has been reported from coal bearing strata macroscopic charcoal occurrences are spread out in different sequences and also in distinct stratigraphic intervals in the permian e g parana basin sakmarian artinskian of brazil karoo basin artinskian of south africa damodar basin lopingian of india and dead sea area changhsingian of jordan they range from peri glacial post glacial to warm temperate climatic systems throughout the permian macro and micro charcoal occurrences are compared to inertinite incidences to support the pyrogenic origin for these coal macerals and to provide an up to date overview on the known evidences of permian wildfires on gondwana in space and time

an analysis of west african dynamics using a linearized gcm abstract this study utilizes a linear primitive equation spherical model to study the development and propagation of easterly wave disturbances over west africa perturbations are started from an initial disturbance consisting of a barotropic vortex and the governing equations are integrated forward in time the perturbations are introduced into basic states corresponding to the observed dynamical and thermodynamical characteristics of two wet years in the sahel and two dry years the model simulations show consistent contrasts in wave activity between the wet and dry years the waves are markedly stronger in the wet years and show a barotropic structure throughout the troposphere the waves tend to extend throughout the troposphere to the level of the tropical easterly jet tej in the wet years but not in the dry years the upper tropospheric shear which is stronger in wet years appears to be a key factor in wave development this shear is dependent on the intensity of the tej suggesting that the t

mechanisms controlling variability of the interhemispheric sea surface temperature gradient in the tropical atlantic abstract the seasonal evolution of sea surface temperature sst fields in the tropical atlantic is explored for composites of extremely strong and weak northward sst gradients because these are known to control the basinwide pressure gradient latitude position of the intertopical convergence zone itcz and regional rainfall aimed at the origin and maintenance of anomalies in the interhemispheric sst gradient and using surface and subsurface marine observations differences in forcing of sst patterns from surface heat fluxes and entrainment are scaled by calendar monthly mixed layer depth and compared to the observed evolution of sst for years with a strong as compared to weak gradient in boreal winter a substantial portion of anomalous sst evolution from september to february can be attributed to departures in sst forcing by latent heat transfer in the north atlantic strengthened northeast trades associated with a stronger north atlantic high promote enhanced evaporative cooling while weakene

the role of inertial instability in determining the location and strength of near equatorial convection there are two major organized cloud configurations in the vicinity of the equator where there is a small cross equatorial surface pressure gradient convection is close to the equator and is generally tied to the location of the lowest sea level pressure slp and warmest sea surface temperature sst in agreement with arguments based upon simple thermodynamical considerations however when there is a substantial cross equatorial pressure gradient such as occurs in the monsoon regions organized convection appears off the equator in the summer hemisphere equatorward of the slp minimum and not necessarily collocated with the warmest ssts thus in this instance simple thermodynamical considerations alone cannot explain 2he location of the convection in this situation the zero absolute vorticity contour 0 also lies in the summer hemisphere therefore between the equator and the 0 contour is a region of locally anticyclonic absolute vorticity and an inertially unstable regime it is argued that the convection results from the low level divergence convergence doublet centred about the 0 contour which is the mitigating response to the inertial instability the associated latitude height secondary circulation should provide subsidence suppressed convection over the equator and rising motion enhanced convection to the north of the zero absolute vorticity contour signatures of the inertial instability predicted by theory are found in observations supporting the hypothesis wherever a strong cross equatorial pressure gradient exists the 0 contour bisects a maximum in the divergent wind field divergence is found equatorward of the zero contour and convergence on the poleward side latitude height cross sections show strong local meridional circulations with maximum rising motion on the poleward side of 0 as the regions where the rising motions occur are conditionally unstable there is deep convection and the vertical circulations extend throughout the troposphere it is noted that the intensity of the off equator convection is deeper and probably stronger than convection located at the equator this is probably because the convection associated with the inertial instability is more efficient necessary conditions for the location of near equatorial convection are listed arguments are presented whereby inertial instability is established as the cause rather than an effect of off equatorial convection these include an outline of the sequence of processes leading up to the convection the factors that limit the encroachment of the 0 contour into the summer hemisphere are discussed and an explanation for the existence of the low level westerly monsoon wind maximum is suggested the possible role played by the instability mechanism or the lack of it in coupled model simulations that produce seasonally migrating and or double itczs in the eastern pacific ocean is discussed finally it is proposed that the instability mechanism is important in the initiation of westward moving disturbances found in the eastern pacific and in determining active and break periods in the summer indian monsoon

structural characterization of vitrinite rich and inertinite rich permian aged south african bituminous coals abstract two south african coals of the same rank and age but different in maceral composition were subjected to extensive structural analyses inertinite rich highveld coal dominated by semifusinite and vitrinite rich waterberg coal were studied to determine structural differences and similarities the two coals had similar carbon content 84 dmmf and vitrinite reflectance mean maximum 0 71 for vitrinite rich vs 0 75 for inertinite rich but differed in hydrogen content 6 23 for vitrinite rich and 4 53 for inertinite rich the inertinite rich coal was more aromatic 86 for inertinite rich and 76 for vitrinite rich and more polycondensed indicated by a higher bridgehead carbon content the inertinite rich coal was structurally more ordered with a higher degree of crystalline stacking both coals had similar average aromatic cluster sizes 16 carbons for vitrinite rich and 18 carbons for inertinite rich and number of cluster attachments 6 attachments for vitrinite rich and 5 attachments for inertinite rich mass spectrometry showed that both coals consist of similar molecular weight distributions ranging to approximately 1700 m z with a maximum abundance of 450 m z for the vitrinite rich coal and 550 m z for the inertinite rich coal compared to the argonne premium coals the south african vitrinite rich waterberg coal was comparable to the coals in the high volatile bituminous range and inertinite rich highveld was closer to the medium to low volatile bituminous range both coals were surprisingly similar in bulk characterization although inertinite rich highveld coal was structurally more ordered hydrogen deficient and more aromatic

a gcm study of the teleconnections between the continental climate of africa and global sea surface temperature anomalies abstract in this case study the role of global sst anomaly forcing in promoting the extreme climatic conditions that prevailed in africa during the years of 1950 and 1973 is examined in 1950 abundant rainfall was observed over tropical africa particularly over the sahel and southern africa by contrast in 1973 this rainfall anomaly pattern was characterized by the opposite phase with most of the continent experiencing severe droughts the primary research vehicle in this investigation is the standard version of the ncar ccmi gcm with horizontal resolution of rhomboidal spectral truncation at wavenumber 15 r15 two separate 10 yr simulations based on the 1950 and 1973 observed sea surface temperature sst have been performed the empirical orthogonal functions method is employed to isolate the annual cycle harmonies in the data and also to remove statistical noise the filtered seasonal rainfall fields for the model and the observations are compared to investigate the response of the african contin

the grootegeluk formation in the waterberg coalfield south africa facies palaeoenvironment and thermal history evidence from organic and clastic matter the grootegeluk formation of the waterberg coalfield is about 70 m thick and consists of relatively thin coal beds interbedded with numerous mudstone and carbonaceous mudstone layers maceral analyses of the coal seams and the interbedded carbonaceous mudstones show that vitrinite is the dominant maceral up to 90 vol whereas inertinite liptinite and reactive semifusinite generally occur in minor proportions the vitrinite content increases upward in the formation with a concomitant decrease in inertinite including reactive semifusinite from around 60 inertinite at the base of the formation the upward increase in the vitrinite concentration is associated with an increase in the energy of the depositional environment which is also considered to have been instrumental in the enhanced preservation of the vitrinite the repetitive nature of the coal mudstone succession the lateral persistence of cycles and the maceral and ash proportions indicate that the formation may have resulted from a combination of allogenic controls tectonism and climate and authigenic controls environments of deposition the vitrinite reflectance rmax of the grootegeluk formation mean 0 72 and palynological evidence indicate that the grootegeluk formation was subjected to maximum post depositional temperatures of about 100 c the lower portion of the grootegeluk formation is dominated by kaolinite quartz and minor amounts of apatite and the upper parts by quartz kaolinite and minor amounts of montmorillonite illite and microcline the base of the grootegeluk formation is considered to have been relatively more distal and the upper portions more proximal to the source of the sediments at the base of the grootegeluk formation a 2 m thick tonstein zone occurs which is dominated by well crystallised kaolinite organic matter 40 wt siderite calcite and minor proportions of apatite the tonstein zone has mineralogical maceral and chemical characteristics distinctive from the other mudstones calcite lenses which occur predominantly in the upper half of the grootegeluk formation are interpreted as syndepositional early diagenetic globular pyrite and spherulitic siderite occur in the coals and organic rich mudstones of the grootegeluk formation fine grained granular siderite is present predominantly in the organic poor mudstones of the grootegeluk formation and the overlying beaufort group systematic changes in the mineralogy and major element chemistry make major element whole rock chemistry an ideal stratigraphic indicator tool for the grootegeluk formation the tonstein has anomalously high concentrations of the trace elements sc v cr mn ni cu ge se br rb sr y zr nb mo ba la ce nd pb th and u and low concentrations of s co as and zn which in addition to its mineralogical character and correlation throughout the basin make the tonstein an important chronostratigraphic marker for local and intrabasinal correlation the overlying beaufort group mudstones contain no organic matter however interpretation of the mineralogical and chemical data indicates that they were deposited with organic matter which was later degraded the mineralogy of the mudstones and the concentration of trace elements suggest that the sediments were deposited in fresh rather than in marine waters

circulation mechanisms related to northeast brazil rainfall anomalies this study explores the role of the upper ocean for circulation anomalies in the overlying atmosphere with focus on the late boreal winter and extreme climatic events in northeast brazil data sources comprise rainfall records in the nordeste surface ship observations of the sea surface temperature sst pressure and wind fields coads period 1948 1990 satellite observations of tropical convection hrc 1971 1988 and upper air analyses of the european centre for medium range weather forecasts ecmwf 1980 1991 all for the tropical atlantic sector interhemispheric sst gradients are most strongly associated with north south contrasts in pressure and the meridional wind component whereas the inverse sst pressure relations in situ are less close enhanced northward temperature increase in the tropical atlantic is accompanied by steeper meridional pressure gradient and accelerated southerly wind component which is representative of a northward displaced intertropical convergence zone itcz with the latter in turn leading to drought in northeast brazil interhemispheric contrasts in the 850 1000 mbar layer mean temperature are similar to those of sst and account for most of the meridional surface pressure gradient during wet as compared to dry years in northeast brazil the tropical north atlantic is cooler and the south atlantic warmer and accordingly the lower tropospheric thickness is reduced to the north but inflated to the south of the equator resulting in increased reduced surface pressure over the north south atlantic as well as reduced southerly surface wind stronger subsidence over the outer tropics of the northern hemisphere and intensified ascending motion and convective activity over the nordeste related to a southward displaced near equatorial convection belt the surface and upper air evidence thus indicates the ways in which the interhemispheric sst gradients exert a hydrostatic control on the lower tropospheric thickness pattern and thus force the south north surface pressure gradients and the surface meridional wind component and hence modulate the latitude position of the itcz and nordeste rainfall

the occurrence of potentially hazardous trace elements in five highveld coals south africa abstract permian coals of the southern hemisphere are generally considered to contain lower concentrations of sulfides halogens and trace elements when compared to northern hemisphere carboniferous coals few studies have considered the trace element content in south african coals and little or no work has been published for highveld coals of the nineteen coal fields in south africa the highveld coal field is one of the nine currently producing and is second largest in terms of production five run of mine samples and a high ash middlings product from the number 4 lower seam were analyzed totaling six sample sets fourteen trace elements as cd co cr cu hg mn mo ni pb sb se v and zn were selected for this study based on the global perception that these elements may be hazardous to human health and or the environment when they are released during coal utilization several sample preparation techniques were tested using certified reference materials sarms 18 19 and 20 to determine the most repeatable technique for these coals the samples were analyzed by icp aes and cvaa hg only microwave digestion proved to be generally unreliable despite the utilization of several different methods a slurry direct injection method into the icp aes provided good correlations with the reference material but requires further development to enhance the confidence level in this relatively unexplored technique samples prepared based on three astm standards for the determination of trace elements in coal provided repeatable results in most instances and were the preparation methods utilized for the highveld coals the trace element values determined for the highveld coals are generally in good agreement with values available in literature for south african coals with the exception of hg mn and cr hg values reported here are lower cr and mn higher results generally agree well with analyses on the same samples conducted by the united states geological survey when considering the global ranges for trace elements the highveld range values are within swaine s range boundaries with the exception of cr compared to the cited global average values for the fourteen trace elements determined the values obtained for the highveld coals generally fall below or well below these average values with the exception of cr and mn concentrations of cd and cu are lower compared to global average values and as mo pb se sb and zn can be considered low to very low arsenic is ten times lower compared to typical usa values concentrations of co and ni are similar to global averages with v and hg being very slightly higher the middlings samples reported higher concentrations of most elements related to the higher ash content of these samples of interest the chalcophile elements determined are all depleted in the highveld coals compared to global averages and the siderophile elements are enriched or comparable to global averages risk based health studies in the usa on coals with similar or higher hg and significantly higher as contents have not reported negative health effects and therefore it could be assumed that the mobilization of these trace elements from the five highveld coals are unlikely to cause human health problems work is ongoing to determine the modes of occurrence of these haps and to address the partitioning behaviors and speciation states of these elements during coal utilization

the influence of extractable organic matter on vitrinite reflectance suppression a survey of kerogen and coal types abstract the vitrinite reflectance suppression literature shows that while bitumen impregnation of the vitrinite group is often invoked as a significant contributor to suppression its existence is not often supported by petrological evidence this study examines bitumen impregnation as a factor in vitrinite suppression by comparing the vitrinite reflectance of source rock and coal samples before and after solvent extraction bitumen often defined as organic matter soluble or extractable in certain organic solvents should be removed by soxhlet method solvent extraction using chloroform removing the extractable bitumen should restore the suppressed reflectance to its true higher value however the solvent extracted samples averaged 0 014 r v less than that of the unextracted samples we conclude from these results and from other published data that reflectance suppression by bitumen impregnation in the vitrinite maceral group above the huminite stage of gelification is seemingly a rare phenomenon and whose effect on suppressing vitrinite reflectance is typically negligible

wind field coherence and its variations over west africa abstract the wind field coherence over west africa is investigated during two contrasted periods 1953 63 abnormally wet and 1963 75 abnormally dry in the sahel zonal and meridional components of the monthly mean wind are computed with radiosonde data relative to the 950 100 hpa layer a descriptive analysis reveals the main features of the west african atmospheric circulation and a correlation analysis points out their dynamical coherence the exiwnce of hadley type cells of northern and southern hemispheres are confirmed and a mutual interaction in the lower layers is depicted the functioning of a walker type cell defined by a coupling between the zonal components of the monsoonal flow and of the tropical easterly jet tej is shown during northern summer over the whole of west africa there is no correlation between the tej velocity and the african easterly jet aej velocity over the sahelian belt during the dry period the coherence of the cell circulations vanishes in concomitance with a

teleconnections between the tropical pacific and the sahel a greater understanding of equatorial teleconnections is a key aspect of research into seasonal prediction and future climate change for tropical regions here the impact of pacific sea surface temperature sst anomalies on rainfall fluctuations over the semi arid sahel is explored using a combination of observed and model data the first key topic of this study is the identification of those aspects of anomalous pacific sst variability that are most strongly linked to the sahel one of these also illuminated by earlier studies is similar to the classic el nino southern oscillation pattern in the central and east pacific which in its el nino phase increases the likelihood of sahel drought it is shown here that although a part of this link is indirect operating via atlantic ssts its main effect appears to be through a direct atmospheric teleconnection the other critical pattern of equal importance and revealed here by a novel analysis technique is the large scale zonal gradient of ssts from the west pacific to the east indian ocean if weakened this too enhances the likelihood of sahel drought atmospheric general circulation model experiments forced either by observed or idealized ssts are used to confirm these two influences on the sahel crucially their sahelian impact is substantially reinforced when both are present and additionally further empirical analysis shows them to be largely independent the second key topic is an investigation of the mechanisms for this pacific sahel teleconnection these appear to involve anomalous stationary equatorial waves with communication occurring in both the eastward and westward directions in el nino years for example a kelvin wave emanates across the atlantic from east pacific convective heating anomalies and an equatorial rossby wave appears over the indian ocean in response to the anomalous west pacific indian ocean sst gradients via convective heating anomalies over the indian ocean these interact over africa to enhance large scale subsidence over the sahel thus reducing seasonal rainfall totals interannual changes in propagating equatorial waves or in the residence of subseasonal regimes appear not to play a substantial role

observed decadal midlatitude and tropical atlantic climate variability two common indicators of atlantic climate variability viz the north atlantic oscillation nao and the cross intertropical convergence zone itcz sea surface temperature sst gradient are examined for their frequency characteristics and midlatitude tropical links sst anomalies north and south of the itcz are found to be uncorrelated on all time scales while the sea level pressure slp fluctuations associated with the nao display a coherent seesaw between iceland and the azores this out of phase relationship spans a broad range of time scales but is particularly strong in the 5 10 year period band strong broadband coherence between the nao and the tropical atlantic cross itcz sst difference is found in the 8 20 year period band suggesting a significant midlatitude tropical interaction moreover tropical atlantic ssts on both sides of the itcz separately exhibit significant coherence with the nao index and slp variability over iceland and the azores based on these findings we hypothesize that the tropical atlantic ta ocean atmosphere interaction is affecting north atlantic climate variability