sedimentation in the lakes and marshes ahwar of the tigris euphrates delta southern mesopotamia the fluvial plains of lower mesopotamia crossed by the tigris and euphrates rivers are occupied by fresh brackish water lakes and extensive reed marshes dominated by phragmites sp and typha sp together locally called ahwar allochthonous sediment is mostly supplied by the tigris and euphrates seasonal floodwaters and by winds which bring aeolian dust from the north west and sand during storms from the western deserts in summer other contributions to the sediment budget are made by in situ biological activity and by biochemical chemical processes within the sediments the sediments are dominantly silts with silt comprising more than 60 of the sediment the remainder of the sediment consists of varying quantities of clay and sand clay is more abundant in the lower parts of most of the analysed cores 30 80 cm in length indicating a change in sediment supply and or sedimentary environment well developed stratification is found only on the river levees and in some clay rich lake and marsh sediments the remainder of the sediments are generally poorly stratified with irregular stratification and considerable bioturbation mineralogically the sediments consist mainly of calcite quartz dolomite and feldspar particularly albite aragonite is present as a result of in situ production by macrofauna the clay fraction 2 n consists of smectite illite smectite illite palygorskite kaolinite and chlorite the total organic carbon toc content is usually 5 except for some peaty surface layers of the freshwater lakes and marshes where toc may rise to 10 20 the sediments have a relatively high calcium carbonate content 20 80 the highest values only being found in mollusc rich horizons the sediments contain high amounts of ca mg and sr and are generally low in al ti k and v values for fe co pb zn and mn are close to the average for mudstones whereas cu and p are relatively low the high ni and cr contents of the sediments are related to high contents in the source material of the major rivers and aeolian deposits multivariate statistical analysis shows that elemental components of surface and source materials correlate well with other sedimentary properties aragonitic molluscs of various species dominate the macrofauna but a microfauna of foraminifers ostracods and diatoms is also present in the sediments

the impact of the eruptions of mount pinatubo and cerro hudson on antarctic aerosol levels during the 1991 austral spring at the beginning of 1991 austral spring volcanic aerosols from mt pinatubo and cerro hudson were present in the polar stratosphere of the southern hemisphere satellite observations of aerosol extinction were used to identify and track the movement of these aerosols in the vicinity of the antarctic vortex during august through november 1991 a layer of mature mt pinatubo aerosols was identified near 21 km and a layer of fresh cerro hudson aerosols was identified near 12 km this altitude separation of the mt pinatubo and cerro hudson aerosols was observed throughout the period below 15 km the polar stratosphere was subject to episodes of strong wave activity which transported the cerro hudson aerosols poleward and after the middle of september they became a persistent feature beneath the vortex above 15 km signatures of mt pinatubo aerosols were observed near the vortex boundary but significant portions of the vortex interior remained free of any detectable intrusions of mt pinatubo aerosols until the final warming in mid november 13 refs 4 figs

uv induced mass independent sulfur isotope fractionation in stratospheric volcanic sulfate 1 sulfuric acid aerosols produced in the stratosphere following massive volcanic eruptions possess a mass independent sulfur isotopic signature acquired when volcanic so2 experiences uv photooxidation the volcanic data are consistent with laboratory so2 photooxidation experiments using uv light at 248 nm maximum absorption of ozone whereas sulfur isotopic anomalies previously observed in archean samples are consistent with photodissociation at 190 220 nm a mechanism of so2 photooxidation occurring in the early stage of a stratospheric volcanic plume in the range of 220 320 nm weak band absorption of so2 is also proposed since mass independent sulfur isotope anomalies in stratospheric volcanic sulfate appear to depend on the exposure of so2 to uv radiation their measurements might therefore offer the possibility to determine the degree of uv penetration in the ozone absorption window for the present and past atmospheres they can also be used to determine the stratospheric or tropospheric nature of volcanic eruptions preserved in glaciological records offering the possibility to reassess the climatic impact of past volcanic eruptions

dilatancy induced p waves as evidence for nonlinear soil behavior a much discussed topic in seismology deals with how and under which loading conditions soil shows nonlinear behavior and how this can be verified from seismograms seismologists have been seriously searching for signatures of nonlinear soil response to earthquakes for about two decades a mechanism explaining the dispersion in the p wave spectra due to the interaction between compressional p and shear s waves is presented shear waves in granular materials induce longitudinal dilatancy waves so called waves with approximately double frequency this can be explained with dilatancy and contractancy which is characteristic of granulates under shear deformations the predicted dispersion is observed in laboratory experiments and verified by comparing accelerograms from hard rock and soil stations from the vrancea region romania the arrival time difference between waves and s waves may theoretically be indicative of the thickness of nonsaturated granular layers these results modeled with nonlinear constitutive relations of the rate type show a specific type of nonlinearity in granular sediments also for earthquakes of moderate magnitudes

methods and some results of investigations of the scattering properties in the crust and mantle abstract results derived from analyses of mainly forward scattered seismic waves are reported major findings are that the strongest scattering originates in the crust and upper and lower mantle while the central parts of the mantle appear relatively homogeneous in the upper mantle the extent of the heterogeneities exhibits regional variations interestingly scattering observations do not appear to be time invariant in certain regions thus being indicative of active evolutionary processes

problems of nonlinear seismology abstract experimental seismic activations in situ undertaken during recent years reveal the character of three different types of nonlinear effect these are wave velocity temporal changes due to temporal changes of the stress field seismic wave interactions during comparatively small deformations 1 2 10 12 strong influence of the slow changes of the stress field and seismic vibrations on the seismic activity of the real geological media i e parameters of the seismic emission process new opportunities for detailed investigation of nonlinear effects are provided by the use of seismic vibrators that generate sinusoidal signals as well as by highly sensitive narrow frequency band recording channels these two tools open up broad new possibilities for investigation of nonlinear effects in a large variety of geological conditions and wave propagation situations these results change our opinion that nonlinear effects play a remarkable role only for strong wave propagation even very weak but detectable nonlinear effects can be used for purposes of investigating media structure and geodynamical processes for seismic prospecting and for the monitoring of oil and gas exploration

textural characteristics of dust fallout and potential effect on public health in kuwait city and suburbs the textural and mineralogical characteristics of the dust fallout along with the potential effect on human health were investigated at 12 locations in kuwait city and suburbs during march 2006 february 2007 mineralogically the dust comprises mostly calcite and quartz with grain size ranging from 1 to 25 m chemically elements such as ca fe mg and al are the dominant ones with the highest amount of average percentage concentration 12 89 for ca results showed that humans in the 12 sites are being exposed to different ranges of average percentage concentrations of minerals such as calcite 15 00 51 80 quartz 26 40 66 9 albite 6 30 17 30 dolomite 1 20 10 20 and gypsum 0 00 6 4 where site k3 recorded the lowest average concentrations for calcite dolomite and gypsum and the highest for quartz and albite the elements ca fe mg al k zn na cr and cd recorded ranges of 5 845 12 890 0 946 3 141 0 752 2 513 0 545 2 261 0 059 0 307 0 004 0 792 0 003 0 018 0 001 0 005 and 0 0004 respectively inhalation of such concentrations of calcite particles may cause coughing sneezing and nasal irritation and in cases of chronic exposure to excessive oral doses of calcite may produce alkalosis and hypercalcemia quartz can have potentially serious respiratory effects following long term exposure 1 year or more which is the case here in our study comparing with international and local standards it is highly likely that harmful and hazardous effects on the human body are being experienced by long term exposure to dust fallout in kuwait

a reinterpretation of the data from the nasa stratosphere troposphere exchange project data obtained during the nasa stratosphere troposphere exchange project step mid latitude field experiment displayed laminae of ozone water and condensation nuclei in the stratosphere in association with a mid latitude stratosphere troposphere folding event danielsen et al 1991 constructed cross sections of these observations and interpreted these quasi horizontal laminae as evidence of ultra low frequency gravity waves we use a new technique to show that these laminae could have resulted from differential advection rather than transport by ultra low frequency gravity waves this new technique uses reverse domain filling back trajectories on multiple isentropic surfaces in conjunction with modified potential vorticity to reveal the qualitative details of the constituent laminae

evidence from sulfate mass independent oxygen isotopic compositions of dramatic changes in atmospheric oxidation following massive volcanic eruptions 1 oxygen isotopic ratio measurements 17o and 18o of background and volcanic sulfate preserved in south pole snow and ice were used to investigate the impact on the oxidation state of the atmosphere by explosive volcanic eruptions by comparing different paleovolcanic events we observe a difference in the so2 oxidation pathway between moderate tens of teragrams tg of so2 and massive hundreds of tg eruptions both isotopic data and numerical simulations suggest the shutdown of stratospheric oh chemistry and the opening of unaccounted oxidation channels for so2 such as the reaction with o 3p atoms when hundreds of tg of so2 are injected into the stratosphere it is very likely that oxidation rates and pathways and concentrations of most traces gases are also dramatically affected with potentially important implications for climate forcing

a simulation of the cerro hudson so2 cloud an isentropic trajectory model is used to simulate the evolution of the southern hemisphere so2 cloud associated with the eruption of cerro hudson by matching the parcel trajectories with total ozone mapping spectrometer so2 retrievals the principal stratospheric injection region is determined to be between 11 and 16 km in altitude this region is characterized by weak wind shears and is located just poleward of the subtropical jet in the outer fringe of the stratospheric polar vortex the lack of wind shear in the injection region explains the slow zonal dispersal of the so2 cloud which was still clearly observed 19 days after the eruption the trajectory model simulation of the so2 cloud shows good agreement with observations for 7 days after the eruption using the potential vorticity and potential temperature estimates of the initial eruption cloud the cloud position relative to the polar night jet is shown to be nearly fixed up to september 2 1991 which was as long as the cloud was observed this result suggests that the lower stratospheric polar and mid latitude regions are nearly isolated from each other during the late august period

lithospheric studies based on holographic principles earth holography was applied to norwegian seismic array norsar earthquake p wave recordings simulation of the norsar sensor configuration indicates that a satisfactory reconstruction of the essential features of an embedded body is feasible with a depth resolution which seems to be better than that attained using more traditional time and amplitude inversion schemes the earth holography concept was tested using norsar recordings of three deep earthquakes at teleseismic distances the results indicate lithospheric heterogeneous bodies with a significant vertical extent the most pronounced scattering features of these inhomogeneities are located at depths around 100 148 and 212 km

dust transport and the question of desert loess formation although contemporary dust storms are frequent in arid and semi arid areas desert loess deposits are poorly developed much of the world s loess occurs in mid latitude areas which experienced glaciation during the pleistocene ocean core evidence indicates that dust transport from sub tropical deserts increased during cold stages of the pleistocene but loess formed only on certain desert margins for reasons which have not been fully explained this paper re examines the mechanisms of dust transport and deposition and the circumstances leading to the accumulation of thick loess typical loess is composed mainly of medium silt grains which are transported in short term suspension a few metres above the ground significant thicknesses of loess form only when dust is trapped within a limited area often relatively close to the source dust particles finer than 20 m are transported mainly in long term suspension over a greater height range and may be widely dispersed the availability of silt and the frequency magnitude and direction of dust transporting winds are important factors governing the potential for loess formation but the existence of a suitable dust trap is particularly important traps may be formed by topographic obstacles areas of moist ground or vegetated surfaces vegetation adjacent to glacial outwash plains and braided meltwater streams trapped dust in mid latitudes during the pleistocene dust blown during glacial periods from certain deserts notably in sinai soviet central asia and china accumulated as loess in neighbouring semi arid regions on the margins of other deserts loess formation was inhibited partly by the absence of vegetation traps during most of the holocene net dust deposition rates in all desert marginal areas have been too low for significant loess accumulation this is mainly due to a reduction in silt availability and a tendency towards landscape stability reported dust storm frequencies during the past 50 years over estimate the longer term holocene dust flux due to the effects of human activities much modern dust owes its origin to erosion of cultivated soils in semi arid areas and is finer than typical loess

simulations of tephra dispersal from the 1991 explosive eruptions of hudson volcano chile abstract the 1991 explosive eruptions of hudson volcano in southern chile produced 2 7 km 3 dense rock equivalent of basalt and trachyandesite tephra during the period august 8 15 the initial basaltic phase phase i august 8 9 produced a maximum column height of 12 km above sea level asl and tephra fallout was directed to the north and northeast by the prevailing winds the paroxysmal trachyandesitic phase phase ii august 12 15 involved at least three separate events with a maximum 18 km high asl eruption column inferred from satellite temperature data during the initial 24 h of this phase the plume was advected almost directly south before swinging towards the east as the wind changed direction the plume was ultimately directed to the southeast and stayed relatively fixed at this bearing for the remainder of the eruption these temporal variations in the main dispersal direction during the earlier stages of the phase ii eruption produced a much wider overall deposit than would be expected from a plume with a relatively fixed transport direction e g latter stages of phase ii the lagrangian ash tracking model puff was utilized to simulate the 1991 explosive eruptions and was able to successfully reproduce the aerial distribution and temporal evolution of the plumes the optimal agreement between the observed and simulated plumes occurs when the highest concentration of ash particles coincides with the tropopause a height that is typically lower than the maximum observed column heights for the 1991 eruptions gravitational settling of the laterally spreading umbrella region e g pinatubo 1991 may result in the concentration of ash at this level this may account for differences in column height estimates between ground or satellite based and lithic based models the plume associated with the paroxysmal phase august 12 15 1991 produced a multilayered deposit composed of alternating layers of fine ash and pumice lapilli the highly stratified nature of the fall deposit is likely the result of multiple eruptive events coupled with a time varying wind field a strongly changing wind direction that occurred during the earlier stages of the paroxysmal eruption could have produced variations in the dominant grain size being deposited between fine ash and pumice lapilli during individual eruptive sequences

circumpolar transport of a volcanic cloud from hekla iceland 1 hekla volcano iceland erupted on 17 august 1980 and emplaced a sulfur dioxide so2 cloud into the north polar stratosphere at a maximum altitude of 15 km the so2 is tracked using satellite data from the ultraviolet uv nimbus 7 total ozone mapping spectrometer n7 toms and the infrared ir high resolution infrared radiation sounder hirs 2 on the noaa tiros operational vertical sounder tovs platform the eruption emitted 0 5 0 7 tg of so2 which later split into three distinct clouds one of which circled the north pole at the perimeter of an atypically persistent arctic cyclone for six days impacting airspace on three continents separate clouds drifted across eastern russia alaska and canada maximum so2 columns derived from toms and hirs 2 accurately define the volcanic cloud s path and fit trajectories produced by the noaa hybrid single particle lagrangian integrated trajectory hysplit model providing confidence in the model when combined with the so2 measurements trajectory altitudes derived from hysplit provide robust estimates of the altitudes of the so2 clouds 8 15 km which would be elusive using either the satellite data or the trajectory model in isolation near coincident spectrally discrete uv and ir retrievals are compared in the volcanic cloud and indicate good agreement between toms and hirs 2 so2 columns for pixels with similar viewing geometry hekla eruptions which follow a pattern of early explosive venting of volcanic gases with significant stratospheric injection could play a role in promoting arctic ozone loss depending on the phase of the north atlantic oscillation during the eruption

estimation of dust fallout rates in the northern arabian gulf the penetration of dust clouds over a sea surface is modelled as a sediment transport diffusion problem the model is used to determine the steady state concentration field of two dimensional dust clouds during offishore dust storms the rates of dust deposition into the sea can then be calculated from the obtained concentration fields the model was applied to offshore dust storms blowing over the arabian gulf yielding estimated dust sedimentation rates of 0 8 mm yr 1 this is substantially higher by several orders of magnitude than dust fallout estimates in most seas of the world the calculated fallout rates are in line with the results of existing field measurements

wideband nonlinear time reversal seismo acoustic method for landmine detection acoustic and seismic waves provide a method to localize compliant mines by vibrating the top plate and a thin soil layer above the mine this vibration is mostly linear but also includes a small nonlinear deviation the main goal of this paper is to introduce a method of processing that uses phase inversion to observe nonlinear effects in a wide frequency band the method extracts a nonlinear part of surface velocity from two similar broadcast signals of opposite sign by summing and canceling the linear components and leaving the nonlinear components this phase inversion method is combined with time reversal focusing to provide increased seismic vibration and enhance the nonlinear effect the experiments used six loudspeakers in a wood box placed over sand in which inert landmines were buried the nonlinear surface velocity of the sand with a mine compared to the sand without a mine was greater as compared to a linear technique

quantifying the pinatubo volcanic signal in south polar snow recent snow and firn core samples from south pole contain increased sulfate so42 concentrations during 1992 1994 as a result of the june 1991 pinatubo eruption and the august 1991 cerro hudson eruption in chile traces of pinatubo tephra volcanic ash were identified in the 1993 and 1994 snow layers supporting the conclusion that increased so42 in 1993 1994 is from the pinatubo eruption although the pinatubo eruption preceded hudson its so42 signal in south polar snow follows and is resolved from that of hudson the deposition of the pinatubo so42 aerosol was delayed due to the long transport to the high southern latitudes and its initial existence at high altitudes in the antarctic atmosphere multi year multi site sampling demonstrates that the volcanic signals are well preserved and spatially consistent measurements on 2 firn cores show that the south pole so so42 flux from pinatubo is 10 9 1 2 kg km 2 over 2 2 years while the hudson flux is 3 2 0 6 kg km 2 in 1 1 years these results when combined with satellite determined pinatubo sulfur dioxide so2 emission make it possible to link quantitatively the atmospheric aerosol mass loading from a low latitude volcanic eruption to its signal in polar ice cores

complexities in eolian and marine interactions processes and eustatic controls on erg development abstract the interplay between eolian and marine realms includes process interactions cycles of transgression and regression and possible inland effects of marine coastal events process interactions are geologically common and most obvious where eolian and marine environments are adjacent these interactions include sediment exchange between the two environments the supply of marine ions to the erg for surface and near surface cementation and the control directly or indirectly of marine events on the sediment budget of an erg regression accompanied by erg progradation over marine deposits occurs with both onshore and offshore winds marine transgression of ergs varies from producing a planar marine scoured surface to a planar deflation surface that precedes the transgression to varying degrees of paleotopographic dune preservation and a variety of transitional facies the extent of paleotopographic dune preservation is largely a function of the energy level of the transgressing marine realm the rate of the transgression and potential for early dune cementation general correlations between ergs and global eustatic sea level and coastal onlap curves occur for coastal and near coastal cyclic erg sequences eustatic control of inland ergs exists to the extent that sea level controls in large measure the extent of the basin exposed to subaerial processes i e regional base level and probably to a lesser extent the sediment supply to the erg direct correlation of inland erg events to coastal onlap curves is dubious at present but an indirect relationship may exist

atmospheric summer circulation and coastal upwelling in the arabian sea during the holocene and the last glaciation accumulation rates of biogenic and lithogenic components were studied in 39 turbidite free well dated sediment cores from the northern indian ocean to define the proportions of fluvial and eolian input and to reconstruct quaternary patterns of coastal upwelling the majority of dust deposited in the western arabian sea during the holocene about 100 106 t yr 1 is advected from arabia by northwesterly winds which overlie the low level southwest monsoon the glacial increase in dust flux to 160 106 t yr 1 culminated in the northern arabian sea most probably due to i entrainment of dust rich in chlorite dolomite and lithogenic carbonate in the then dry persian gulf and ii a southward shift of the mean position of the southwest monsoon during glacial summer this shift is recorded in reduced accumulation rates of biogenic opal and increased rates of marine carbonate off somalia and oman both the terrigenous and biogenic sediment records show that the northwesterly winds and the southwest monsoon persisted over the last 27 000 yr as well as the asian continental summer heat low however the glacial seasonal time span of the southwest monsoon season was much reduced most likely because of a delay in the seasonal onset of the southwest monsoon

neogene sediments and modern depositional environments of the zagros foreland basin system a sedimentological investigation of the neogene deposits of the zagros foreland basin in sw iran reveals a continuous and largely gradational passage from supratidal and sabkha sediments at the base represented by the gachsaran formation to carbonates and marine marls mishan formation with basal guri carbonate member followed by coastal plain and meandering river deposits agha jari formation and finally to braided river gravel sheets bakhtyari formation this vertical succession is interpreted to represent the southward migration of foreland basin depozones from distal foredeep and foredeep to distal wedge top and proximal wedge top respectively as the zagros fold thrust belt migrated progressively southward towards the arabian foreland this vertical succession bears a striking similarity to modern depositional environments and sedimentary deposits observed in the zagros region today where one passes from mainly braided rivers in the zagros mountains to meandering rivers close to the coast to shallow marine clastic sediments along the northern part of the persian gulf and finally to carbonate ramp and sabkha deposits along the southeastern coast of the persian gulf this link between the neogene succession and the modern day depositional environments strongly suggests that the major neogene formations of the zagros foreland basin are strongly diachronous as shown recently by others and have active modern day equivalents

aeolian processes and sand encroachment problems in kuwait abstract the surface of kuwait is carved in a calcretized clastic sequence of miocene pleistocene age mostly covered by a thin blanket of recent aeolian deposits fast rate of development and increase of human activities contributed to denudation of the vegetative cover and exposure of dry loose sediments to wind action at present kuwait is intensively subjected to aeolian actions manifested by frequent occurrences of sand and dust storms this dictated the need for regional understanding of the magnitude of the aeolian processes their behavior with man made establishments and their long and short term impacts a comparison between the nature and distribution of recent surface sediments in kuwait in 1979 and 1990 shows significant changes that reflect the work of aeolian processes during this period the direct impact of the enhancement of aeolian action is represented by the increase in the rate of sediment transport transportation of fine grained particles in suspension frequently occurs during dust storms usually initiated in southern iraq the particles migrate over kuwait as thick dust clouds and finally settle in the northern part of the arabian gulf bedload transport of sand or saltation frequently occurs during summer whenever wind speed reaches 5 4 m s the average annual sand drift rate in kuwait is about 20 m 3 m width 1 yr 1 the majority of the drift occurring during the period may august to the southeast bedform transport or sand dune movement is also recognized in kuwait sand dunes mostly occur as small barchans of about 3 m height the measured rate of movement of these barchans varies with height a barchan of average height usually moves about 20 m in nine monthes january august the remarkable high rate of sand transport and the increase in development activities in the desert areas are responsible for the enhancement of the sand encroachment problems in kuwait almost all installations roads and farms are significantly affected by the accumulation of considerable amounts of aeolian sand these problems have pronounced adverse environmental and economic impacts

sulfur isotope evidence of little or no stratospheric impact by the 1783 laki volcanic eruption 1 historic records and research have suggested that the 1783 1784 eruption of the laki fissure volcano in iceland impacted northern hemisphere climate significantly probably as a result of the direct injection of volcanic materials into the stratosphere where the volcanic aerosols would linger for years to cause surface cooling across the northern hemisphere however recent modeling work indicates the laki climatic impact was limited to the northern hemisphere and only in the second half of 1783 we measured sulfur 33 isotope excess 33s in volcanic sulfate of historical eruptions including laki found in summit greenland ice cores no 33s excess is found in sulfate of apparently tropospheric eruptions while sulfate of stratospheric eruptions is characterized by significant 33s excess and a positive to negative change in 33s during its gradual removal from the atmosphere because the same characteristics have been previously found in volcanic sulfate in antarctica snow the results from greenland indicate similar global processes of stratospheric chemical conversion of so2 to sulfate the isotopic composition of laki sulfate is essentially normal and shows no characteristics of sulfate produced by stratospheric photochemical reactions this clearly indicates that the laki plume did not reach altitudes of the stratospheric ozone layer further the short aerosol residence time 6 months suggests that the bulk of the laki plume and subsequent aerosols were probably confined to the middle and upper troposphere these conclusions support the hypothesis of d arrigo and colleagues that the unusually cold winter of 1783 1784 was not caused by laki

volcanic perturbation of the atmosphere in both polar regions 1991 1994 long term measurements by sunphotometers of the spectral dependence of aerosol optical depth are reported for several sites in the arctic and antarctic for the period january 1991 through december 1994 in the antarctic a pronounced increase of atmospheric turbidity was observed at the end of september 1991 the observed wavelength dependence in aerosol optical depth indicated that the increase was due to the presence of fresh and therefore small stratospheric aerosol particles associated with the eruption of cerro hudson in august 1991 after the breakdown of the polar vortex in mid november 1991 we measured a second significant increase of the aerosol optical depth at this time the 1 0 m aerosol optical depth was approximately 0 12 or about 10 times background levels this second incrcase is shown to be the result of the influx of mount pinatubo aerosols a similar perturbation of the aerosol optical depth was observed in the arctic with the return of sunlight in march 1992 however the increased loading of the arctic stratosphere by the pinatubo aerosols was already evident at high northern latitudes in satellite measurements at the end of 1991 stratospheric aerosol and gas experiment ii stratospheric 1 0 m optical depth measurements show that meridional transport of pinatubo aerosol from equatorial to middle and higher latitudes is greatest in the winter spring hemisphere this observation explains the observed seasonal trend of aerosol optical depth during the posteruption a significant decrease of the perturbation by mount pinatubo aerosol was observed in both polar regions by the end of 1994 the measured 1 0 m aerosol optical depths at this time were only 0 04 these values exceed the background level by about 0 01 0 02 therefore the aerosol optical depth values are still slightly higher than during undisturbed conditions in addition we show that the occurrence of volcanic aerosols caused changes in the spectral dependence of the aerosol optical depth in the arctic and the antarctic these variations including the changes in the aerosol size distribution derived from the aerosol optical depth are discussed in comparison to undisturbed conditions

dry fall of fine dust on sea the transport and fallout of dust during the advance of offshore dust cloud over water surface is studied some important issues concerning this problem are re examined particularly the effect of water surface presence on the concentration field and deposition rates of dust the analysis will show that an inner or surface layer may exist near the water surface where surface retention or absorption processes are dominating and that large dust concentration gradients will be sustained there a logarithmic concentration profile is shown to exist extending from the surface roughness height throughout the surface layer thickness which will be shown to be dependent upon the wind strength and the dust particles sedimentation velocity the surface layer structure will not be dependent upon the particular profile assumed by the initial dust concentration at the land sea boundary and the analysis will show that the dust fallout rates due to both sedimentation and surface absorption effects combined can be significantly larger than those commonly obtained by considering sedimentation effects alone the theory can be used in assessing both the magnitude and the extent of aeolian sediments contribution to marine environment which exist adjacent to large desert area

monochromatic components of the seismic noise in the norsar area summary monochromatic components of the seismic noise have been detected in the norsar area the most prominent are near 2 08 hz and 2 78 hz the geographical distribution and the variation with time is studied and also the particle motion and wave propagation a source for the 2 78 hz peak has been found at a hydroelectric power plant but the sources for the other spectral peaks are still unknown

eolian input into the late ordovician postglacial soom shale south africa the soom shale member of the cedarberg formation south africa is a key early paleozoic lagerstatte that directly overlies glacigenic deposits of the late ordovician glacial maximum it was deposited on the gondwanan craton during deglacial transgression we show that it contains a substantial coarse silt to fine sand component that occurs in discrete laminae intimately associated with plankton derived organic material we interpret this component as loess sourced from glacially derived debris and blown into the sea either directly or across seasonal sea ice as happens today on the mcmurdo ice shelf antarctica falling through the water column this material likely stimulated production of phytoplankton which then sank as sediment loaded aggregates in marked sedimentary partitioning these silt and or organic laminae alternate with fine organic poor mud laminae that likely represent river derived nepheloid plumes and that sporadically thicken into centimeter scale mud turbidites sustained eolian input directly into the surface water may have been key to maintaining the high productivity of the soom sea and then via eutrophication and anoxia to the exceptional preservation of its biota

measurements of polar vortex air in the midlatitudes the stratospheric photochemistry aerosols and dynamics expedition spade was conducted in the spring of 1993 from moffett field california nasa ames research center utilizing the nasa high altitude er 2 aircraft these northern midlatitude aircraft flights showed laminae containing high ozone concentrations traceable to the april 1993 polar vortex breakup and corroborated by laminae of other trace gases such as cfcs ch4 n2o and co2 these laminae are clearly traceable as polar vortex breakup fragments using rossby ertel s potential vorticity and isentropic trajectory calculations laminae in stratospheric ozone profiles are commonly observed in the northern hemisphere from fall to spring and are hypothesized to originate from very low frequency transverse waves and or via rossby wave breaking on the basis of these results the ozone laminae observed during spade were a result of rossby wave breaking during the breakdown of the polar vortex in addition it is shown that conventional once per day meteorological analyses were adequate for representing the transport of this material into the lower stratosphere midlatitudes over the course of the spring vortex breakup

volcanic eruptions prediction hazard assessment remote sensing and societal implications in volcanology the period 1991 1994 was very busy with many active volcanoes keeping pace with the higher than average frequency of eruptions about 60 70 per year recorded during the late 1970 s to the late 1980 s simkin 1993 some large and violent eruptions occurred in well populated areas but these passed without the higher death tolls caused by eruptions in the previous decade a reflection perhaps of increased volcanic hazard awareness improved prediction and monitoring and better communication between volcanologists and public officials peterson and tilling 1993 the loss of human life was limited to a little over 1000 with perhaps 750 of these attributable to the mount pinatubo eruption on luzon in the philippines many were killed by post eruption phenomena such as mudflows and by disease in the displaced populations this large eruption which had a world wide atmospheric impact dominates the picture of volcanism in the early 1990 s however significant eruptions also occurred at hudson unzen spurr redoubt hekla mayon galeras rabaul kliuchevskoi etna the most voluminous lava outpourings this century and many other volcanoes here we assess the current state of volcano monitoring and hazard awareness against a backdrop of the eruptions of the past four years and take a look at future developments stressing new techniques in the field of remote sensing

denitrification mechanism of the polar winter stratosphere by major volcanic eruptions the uptake of hno3 by volcanic sulfuric acid droplets is investigated using a one dimensional sulfate aerosol model and recent laboratory data hno3 uptake by volcanic sulfate particles coupled with the sedimentation of the particles may lead to irreversible transfer of hno3 from higher to lower altitudes in the polar stratosphere during winter this denitrification mechanism is found to be strongly dependent on the sulfate aerosol loading and temperature model calculations suggest that anomalously large volcanic eruptions have caused a severe denitrification of the arctic winter lower stratosphere there is conflicting evidence for this mechanism in ice core nitrate records

particles in the great pinatubo volcanic cloud of june 1991 the role of ice 1 pinatubo s 15 june 1991 eruption was earth s largest of the last 25 years and it formed a substantial volcanic cloud we present results of analysis of satellite based infrared remote sensing using advanced very high resolution radiometer avhrr and tiros operational vertical sounder high resolution infrared radiation sounder 2 tovs hirs 2 sensors during the first few days of atmospheric residence of the pinatubo volcanic cloud as it drifted from the philippines toward africa an so2 rich upper 25 km portion drifted westward slightly faster than an ash rich lower 22 km part though uncertainty exists due to difficulty in precisely locating the ash cloud the pinatubo clouds contained particles of ice ash and sulfate which could be sensed with infrared satellite data multispectral ir data from hirs 2 were most useful for sensing the pinatubo clouds because substantial amounts of both ice and ash were present ice and ash particles had peak masses of about 80 and 50 mt respectively within the first day of atmospheric residence and declined very rapidly to values that were 10 mt within 3 days ice and ash declined at a similar rate and it seems likely that ice and ash formed mixed aggregates which enhanced fallout sulfate particles were detected in the volcanic cloud by ir satellites very soon after eruption and their masses increased systematically at a rate consistent with their formation from so2 which was slowly decreasing in mass during the same period the initially detected sulfate mass was 4 mt equivalent to 3 mt so2 and after 5 days was 12 16 mt equivalent to 9 12 mt so2

trace a trajectory intercomparison 2 isentropic and kinematic methods kinematic and isentropic trajectories are compared quantitatively during a single 5 day period october 13 18 1992 when several flights for the transport and atmospheric chemistry near the equator atlantic trace a experiment were conducted off the west coast of africa european centre for medium range weather forecasts ecmwf data are used to compute the 5 day backward trajectories arriving at locations over the south atlantic ocean and nearby parts of south america and southern africa two versions of kinematic trajectories are examined one version employs vertical motions supplied with the ecmwf data these trajectories often differ greatly from those based on the isentropic assumption the kinematic trajectories usually undergo considerably greater vertical displacements than their isentropic counterparts however most diabatic rates are consistent with those of synoptic scale systems ratios of acetylene to carbon monoxide are related to backward trajectories at various locations along a trace a flight a second version of kinematic trajectories employs vertical motions diagnosed from ecmwf horizontal wind components using the continuity equation these vertical motions are stronger than those supplied with the ecmwf data causing many of the trajectories to have larger vertical displacements and considerably different paths than the original kinematic versions many of these kinematic trajectories undergo diabatic rates that exceed generally accepted values on the synoptic scale this occurs in part because the diagnosed vertical motions are inconsistent with the ecmwf data the research indicates that the kinematic procedure yields realistic 5 day backward trajectories when the three dimensional wind data are available from a numerical model or other dynamically consistent data set such as provided by ecmwf

using horizontal transport characteristics to infer an emission height time series of volcanic so2 from omi column measurements observed far from the volcano using observations fromthe november 2006 eruption of nyamuragira back trajectories are run and statisticalanalyses are computed based on the distance of closest approach to the volcano thesestatistical analyses provide information about the emission height time series of so

the structure of the polar vortex reconstruction of the airborne antarctic ozone experiment and airborne arctic stratosphere expedition aircraft constituent observations radiative heating rate computations and trajectory calculations are used to generate comparative pictures of the 1987 southern hemisphere sh late winter and 1989 northern hemisphere nh mid winter lower stratospheric polar vortices overall both polar vortices define a region of highly isolated air where the exchange of trace gases occurs principally at the vortex edge through erosional wave activity aircraft measurement showed that 1 between 50 and 100 mbar horizontally stratified long lived tracers such as n20 are displaced downward 2 3 km on the cyclonic poleward side of the jet with the meridional tracer gradient sharpest at the jet core 2 eddy mixing rates computed using parcel ensemble statistics are an order of magnitude or more lower on the cyclonic side of the jet compared to those on the anticyclonic side 3 poleward zonal mean meridional flow on the anticyclonic side of the jet terminates in a descent zone at the jet core despite the similarities between the sh and nh winter vortices there are important differences during the aircraft campaign periods the sh vortex jet core was located roughly 8 o 10 o equatorward of its nh counterpart after pole centering as a result of the arger size of the sh vortex the dynamical heating associated with the jet core descent zone is displaced further from the pole the sh polar vortex can therefore approach radiative equilibrium temperatures over a comparatively larger area than the nh vortex the subsequent widespread formation of polar stratospheric clouds within the much colder sh vortex core gives rise to the interhemispheric differences in the reconstructed h20 noy c10 and 03 species which are affected by polar stratospheric clouds