interpretations of observed climatological patterns in stratospheric gravity wave variance observational analyses of gravity waves in the stratosphere have revealed various climatological patterns in gravity wave activity seasonal geographical and vertical variations have all been observed in this work a linear model of gravity wave propagation is applied to investigate the underlying causes of some of the observed patterns a collection of monochromatic gravity waves that represent a broad spectrum of wavenumbers and frequencies is input at 6 km altitude in the model propagation of the waves through realistic background atmospheric wind and stability fields is treated with linear ray theory and a simple saturation condition to limit amplitudes to stable values the wave spectrum at the 6 km source height is specified to be constant at all latitudes longitudes and times so the variability that appears at higher altitudes is due entirely to background atmosphere variations before the model results are compared to the observations the spectrum of waves is filtered in a way that mimics the limitations of each of the observation techniques the filtering is described in terms of vertical wavelength and is referred to as the observational filter in a vertically varying background wind gravity waves are doppler shifted in intrinsic frequency and refracted to different vertical wavelengths as they propagate vertically through the atmosphere the observational filter and the wave refraction effects can thus couple in interesting ways that have not been explicitly considered in previous work the model shows that this coupling can give rise to geographical seasonal and vertical variations in gravity wave observations without any variations in the spectrum or amplitude of gravity wave sources in the troposphere thus careful consideration of both the background wind profile and observational filter can greatly affect the interpretation of the observed climatological patterns in gravity wave activity

diatom inferred salinity in palaeolakes an indirect tracer of climate change lakes in arid and semi arid regions respond to climatic change through shifts in lake water volume and ionic concentration because diatom distribution is highly correlated with lake hydrochemistry diatoms can be used to infer changes in salinity and brine composition and thus to infer past climates here we critically examine the use of diatom inferred salinity as a climate proxy with examples taken from both modern waterbodies and sedimentary profiles sediment records may contain assemblages mixed from periods or sites of differing hydrochemistries because of the high degree of spatial and temporal heterogeneity in saline systems dissolution and diagenesis in saline brines may further complicate interpretation of sedimentary assemblages furthermore threshold effects salinity regulation via groundwater seepage antecedent conditions and other aspects of local hydrology may modify the relationship between salinity change and climatic forcing these complexities necessitate critical examination of the ecology and taphonomy of sedimentary assemblages as well as evaluation of potential non linearities in the salinity climate relationship through comparison of diatom inferred salinity with other proxy records of hydrochemical change historical documents where they exist and with other regional lake systems

acoustic detection of buried objects in 3 d fluid saturated porous media numerical modeling acoustic waves can be a viable tool for the detection and identification of land mines unexplored ordnance uxo and other buried objects design of acoustic instruments and interpretation and processing of acoustic measurements call for accurate numerical models to simulate acoustic wave propagation in a heterogeneous soil with buried objects compared with the traditional seismic exploration high attenuation is unfortunately ubiquitous for shallow surface acoustic measurements because of the loose soil and the fluid in its pore space to adequately model such acoustic attenuation we propose a comprehensive multidimensional finite difference time domain fdtd model to simulate the acoustic wave interactions with land mines and soils based on the biot theory for poroelastic media for the truncation of the computational domain we use the perfectly matched layer pml the method is validated by comparison with analytical solutions unlike the pure elastic wave model this efficient pml fdtd model for poroelastic media incorporates the interactions of waves and the fluid saturated pore space several typical land mine detection measurements are simulated to illustrate the application

persistent millennial scale climatic variability over the past 25 000 years in southern africa abstract 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 5 ka hiatus high resolution oxygen and carbon stable isotope data suggest that postglacial warming was first initiated 17 ka was interrupted by cooling probably associated with the antarctic cold reversal and was followed by strong warming after 13 5 ka the early holocene experienced warm evaporative conditions with fewer c4 grasses cooling is evident from 6 to 2 5 ka followed by warming between 1 5 and 2 5 ka and briefly at ad 1200 maximum holocene cooling occurred at ad 1700 the new stalagmite largely confirms results from shorter holocene stalagmites reported earlier the strongest variability superimposed on more general trends has a quasi periodicity between 2 5 and 4 0 ka also present are weaker 1 0 ka and 100 year oscillations the latter probably solar induced given similarities to the antarctic records the proximate driving force producing millennial and centennial scale changes in the makapansgat record is postulated to be atmospheric circulation changes associated with change in the southern hemisphere circumpolar westerly wind vortex

gravity wave and orographic wave activity observed around the antarctic and arctic stratospheric vortices by the cosmic gps ro satellite constellation 1 polar stratospheric gravity wave activity is studied using data from the constellation observing system for meteorology ionosphere and climate cosmic global positioning system radio occultation gps ro waves with vertical wavelengths of 2 to 15 km are considered the temperature variance 2 is used as a measure of wave activity and is studied on isentropic surfaces large intermittent orographic wave activity is identified during austral spring 2007 above the patagonian andes and the antarctic peninsula where 2 in the stratosphere increases by up to a factor of 5 for periods of 5 days to a few weeks the 2 are also investigated in equivalent latitudes to allow a direct comparison with the changing vortex structure the october 2007 2 inside the antarctic vortex boundary region at 400 600 k is one and a half times that outside the vortex this region of enhanced 2 descends in time and is not observed during the decay of the arctic vortex during the boreal winter of 2006 2007 orographic wave activity is observed above scandinavia and greenland an analysis of the 400 k and the 450 k levels in both hemispheres shows a strong relationship between enhanced 2 and the location of the vortex edge suggesting that the waves observed are propagating poleward and are guided to higher altitudes by the vortex the line of sight of the occultations shows a preference for north south alignment indicating that cosmic favors the detection of orographic waves above the north south oriented mountain ranges considered here

elastic waves interacting with buried land mines a study using the fdtd method a three dimensional 3 d finite difference model for elastic waves in the ground has been developed and implemented the model has been created to supplement the development of a sensor that uses elastic waves to detect buried land mines the model is used to investigate the propagation characteristics of elastic waves in the ground and to explore the interaction of elastic waves with buried land mines when elastic waves interact with a buried mine a strong resonance occurs at the mine location the resonance can be used to enhance the mine s signature and to distinguish the mine from clutter results presented in this paper explain the features of elastic wave propagation in the ground and show the interaction of elastic waves with both an anti personnel mine and an anti tank mine

compressional head waves in attenuative formations forward modeling and inversion we develop a method of forward modeling and inverting formation attenuation data from sonic compressional head waves in a fluid filled borehole using a branch cut integration bci technique to calculate individual acoustic arrivals we validate this approach with a real axis integration rai method that does not separate the individual arrivals we show that the straightforward application of the original bci method for lossless media gives erroneous results for attenuative formations with a choice of the riemann sheets satisfying the radiation condition the new bci method gives correct results for most lossy and lossless formations however modeling very slow formations needs to include the contribution of a leaky pole near the vertical branch cut with a constant q assumption we develop a simple processing scheme to extract the formation compressional q factor from the p head wave arrivals we used experimental data from laboratory scale borehole measurements to invert for the compressional q val

climatology of polar mesospheric clouds abstract the ultraviolet spectrometer on board the solar mesophere explorer satellite has measured solar radiation scattered from a diffuse and patchy layer of material near the summer polar mesopause we call this scattering layer polar mesospheric clouds pmc and present here a first climatology of this phenomenon covering three years six summer seasons we address these general questions how bright are pmc and how frequently do they occur in space and time are there year to year or hemisphere to hemisphere differences in pmc seasons we find that the brightest pmc are found right where they occur most frequently above 70 c 75 c in latitude and in a season of 60 to 80 days duration centered about the peak which occurs about 20 days after the summer solstice this holds true for both hemispheres we find variability on time waves from day to day to year to year averaging over large time and space scales does however reveal a basic underlying symmetry a major finding is that for three years six

global estimates of gravity wave parameters from gps radio occultation temperature data 1 gravity waves gws play critical roles in the global circulation and the temperature and constituent structures in the middle atmosphere they also play significant roles in the dynamics and transport and mixing processes in the upper troposphere and lower stratosphere and can affect tropospheric weather despite significant advances in our understanding of gws and their effects in different regions of the atmosphere in the past few decades observational constraints on gw parameters including momentum flux and propagation direction are still sorely lacking global positioning system gps radio occultation ro technique provides global all weather high vertical resolution temperature profiles in the stratosphere and troposphere the unprecedentedly large number of combined temperature soundings from the constellation observing system for meteorology ionosphere and climate and challenging minisatellite payload gps ro missions allows us to obtain gw perturbations by removing the gravest zonal modes using the wavelet method for each day we extended the gw analysis method of alexander et al 2008 to three dimensions to estimate the complete set of gw parameters including momentum flux and horizontal propagation direction from the gw temperature perturbations thus derived to demonstrate the effectiveness of the analysis we showed global estimates of gw temperature amplitudes vertical and horizontal wavelengths intrinsic frequency and vertical flux of horizontal momentum in the altitude range of 17 5 22 5 km during december 2006 to february 2007 consistent with many previous studies gw temperature amplitudes are a maximum in the tropics and are generally larger over land likely reflecting convection and topography as main gw sources gw vertical wavelengths are a minimum at equator likely due to wave refraction whereas gw horizontal wavelengths are generally longer in the tropics most of the waves captured in the analysis of the gps data are low intrinsic frequency inertia gws and the estimated intrinsic frequencies scaled by the coriolis parameter also show a strong maximum at equator enhanced wave fluxes are linked to convection topography and storm tracks among others as preliminary tests of the analysis in deriving horizontal propagation directions we compared the gps estimates with the corresponding estimates from the u s high vertical resolution radiosonde data using the conventional stokes parameters method and we also conducted a separate analysis of the gps data over the southern andes in south america we also showed the first global estimates of gw propagation directions from the gps data finally the sensitivity of the analysis to the temporal and spatial dimensions of the longitude latitude time cells and the uncertainties of the analysis and possible ways to reduce these uncertainties are discussed

a climatological study of short period gravity waves and ripples at davis station antarctica 68 s 78 e during the austral winter february october period 1999 2013 a scanning radiometer deployed at davis station antarctica 68 s 78 e has been recording infrared 1 10 1 65 m images of a small region 24 km 24 km of the zenith night sky once per minute each austral winter night since february 1999 these images have been processed to extract information on the passage of gravity waves gws horizontal wavelength h 15 km and ripples h 15 km over the observing station phase speeds periods horizontal wavelengths and predominant propagation directions have been deduced observed speeds were found to be highly correlated with horizontal wavelengths as has been reported in previous studies reverse ray tracing of the detected gws only enabled us to identify four distinct groups on average only 15 of waves detected can be traced back to the troposphere and a large proportion 45 were not successfully reverse traced substantially below the airglow layer two smaller groups were found to reach a termination condition for reverse ray tracing at altitudes near 50 km and 75 km of those that reached the termination altitude in the troposphere 10 km most of the end points fell within a radius of 300 km of the station with a very pronounced concentration of wave initiation to the north west at approximately of the observing point the predominant direction of propagation was southward and they were observed throughout the year recent reports suggest the interaction of planetary waves with the background wind field as a potential source for these waves

incorporating full attenuation mechanisms of poroelastic media for realistic subsurface sensing porous materials are ubiquitous in the subsurface formations of the earth where acoustic and seismic waves are used for remote sensing however it is not well understood how the dissipation and the dispersion of poroelastic waves are caused by the viscoelastic and viscous properties of the constituents such as solid grains and pore fluid and by the viscoelastic dissipation of the solid frame as well as the viscodynamic coupling of the pore fluid to the solid frame due to its global and local flows relative to the solid grains such attenuation mechanisms have seldom been incorporated in subsurface sensing simulations although they can be very important to applications in this paper we propose a complete attenuation model including both full stiffness and viscodynamic dissipation for poroelastic media in seismic wave simulations completely based on a generalized zener model the effects associated with physical dissipation and frequency dependent dispersion are accurately simulated by a finite difference time domain algorithm verifications with analytical solutions show the accuracy efficiency and flexibility of our method numerical results demonstrate that the attenuation of biot s model in the sediment of the seafloor has significant effects on acoustic wave scattering from complex geologic structures

holocene climatic variability indicated by a multi proxy record from southern africa s highest wetland the eastern lesotho highlands experience climate patterns distinct from those of surrounding lower altitude regions representing a niche environment with a unique biodiversity leading to well adapted but restricted vegetation this study explores changes in the holocene composition of diatoms and pollen at southern africa s highest altitude wetland mafadi 3390 m a s l the palaeoenvironmental record for mafadi wetland indicates fluctuations between cold wet conditions prevalent between 8140 and 7580 cal yr bp and between 5500 and 1100 cal yr bp and warmer drier periods between 7520 and 6680 cal yr bp and between 6160 and 5700 cal yr bp marked climatic variability is noted from 1100 cal yr bp with colder conditions at 150 kyr bp notably the first of these cold periods occurs soon after the northern hemisphere 8 2 kyr event while a second period of notably cold conditions occurs around 1100 cal yr bp variability exists between the moisture reconstructions presented in this study and those from adjacent lower altitude sites which is hypothesised to reflect variations in the strength and extent of the westerlies throughout the holocene

a statistical study of gravity waves in the polar regions based on operational radiosonde data gravity waves in the lower polar stratosphere are examined using operational radiosonde observations gathered from 33 stations over a period of 10 years both the potential and kinetic energies of the gravity waves vary annually and reach maxima in winter in the arctic and in spring in the antarctic in the antarctic spring a region of large gravity wave energy propagates downward following the movement of a zone of high static stability associated with southern hemispheric warming moreover the enhanced energy region and the high stability zone coincide in the horizontal plane and move gradually from 135 e 50 s to 45 w 70 s over the south pole the vertical and horizontal directions of wave propagation are examined using hodograph analysis in the vertical most gravity waves transfer energy upward in the arctic while the percentage of downward energy propagation is relatively high in winter and spring in the antarctic horizontally gravity waves propagate westward relative to the mean wind in the arctic while in the antarctic the dominant direction varies from station to station the correlation between gravity wave energy in the lower stratosphere and the mean wind is also examined in the arctic gravity wave energy is highly correlated with the surface wind though in the antarctic it correlates with the stratospheric wind these results suggest that gravity waves observed in the arctic are forced by topography whereas in antarctica some sources may exist in the stratosphere one such source candidate is likely to be the polar night jet

a paleohydrologic reinterpretation of the homeb silts kuiseb river central namib desert namibia and paleoclimatic implications abstract slack water deposits are usually fine grained fine sand and coarse silt flood sediments deposited in areas of the floodplain that are sheltered from high velocity flood flows slack water deposits have been recognized by many investigators in a wide variety of physiographic and climatic settings late quaternary slack water deposits have not been described from the extremely arid namib desert of southwestern africa fine grained flood sediments in the kuiseb valley near homeb accumulated between 23 000 and 19 000 14c years bp have been interpreted by previous workers as i sediments deposited behind dune dams ii river endpoint accumulations and iii flood deposits of an aggrading river controlled either by a base level change in the lower reaches or a change in the hydrological regime in the catchment area furthermore the so called homeb silts could document more arid climatic conditions in the kuiseb catchment area during the last glacial maximum lgm our research shows that the homeb silts are slack water deposits and that in many valleys of the namib desert slack water sediments are observed most commonly at the junctions of major rivers and minor tributaries in bedrock canyon settings here we present evidence that these slack water deposits accumulated as a result of more humid conditions and or more intense precipitation events in the upper reaches of the river they do not document climatic changes in the desert itself as postulated by many researchers

coastal paleo environment and sea level change at macassa bay southern mozambique since c 6600 cal bp changes in holocene coastal paleo environment and sea level variations have been recorded in estuary sediments from macassa bay southern mozambique methods include analysis of fossil diatoms sediment stratigraphy mineral magnetic properties stable carbon and nitrogen isotope composition and carbon and nitrogen content the chronology based on six ams c 14 dates suggests a basal age of the sediment core of c 6600 cal bp calibrated years before present the multi proxy dataset implies two phases when the site was experiencing marine conditions and tentative sea level high stands 1 between c 6600 6300 cal bp which is contemporary with the last phase of the global transgression and the holocene climatic optimum and 2 between c 4700 1000 cal bp a period when sea level curves from the region suggest occasional minor sea level high stands between these phases c 6300 4700 cal bp the environment within the macassa bay estuary was less influenced by marine processes and studied proxies indicate a freshwater phase associated with relatively low sea levels after c 1000 cal bp a terrestrial environment prevailed at the site probably as a result of a combined effect of sea level lowering and high accumulation of organic peat within the estuary c 2011 elsevier ltd and inqua all rights reserved

a gravity wave climatology for antarctica compiled from challenging minisatellite payload global positioning system champ gps radio occultations 1 the seasonal geographical and altitudinal dependence of gravity wave activity in the lower stratosphere over antarctica is presented gravity wave activity is estimated by calculating potential energy ep from radio occultation profiles obtained by the challenging minisatellite payload global positioning system champ gps experiment significant seasonal variation of wave activity is observed smaller wave activity in summer is attributed to waves with small phase velocities experiencing critical level filtering at other times of the year when wave activity is large less filtering occurs and the strong background wind is likely to cause doppler shifting of waves to longer vertical wavelengths which can reach larger amplitudes before saturating relationships between gravity wave activity and geographic location indicate that topography is a strong source for wave activity especially over the antarctic peninsula however wind rotation in this area was found to reduce the wave energy in summer at certain altitudes a strong enhancement of wave energy is observed at the edge of the polar vortex again reduced critical level filtering and doppler shifting in the area of the jet are likely to be major causes for this finding possible limitations to this study due to observational filtering are discussed

lidar observations of stratospheric gravity waves from 2011 to 2015 at mcmurdo 77 84 s 166 69 e antarctica 1 vertical wavelengths periods and frequency and vertical wave number spectra five years of atmospheric temperature data collected with an fe boltzmann lidar by the university of colorado group from 2011 to 2015 at arrival heights are used to characterize the vertical wavelengths periods vertical phase speeds frequency spectra and vertical wave number spectra of stratospheric gravity waves from 30 to 50 km altitudes over 1000 dominant gravity wave events are identified from the data the seasonal spectral distributions of vertical wavelengths periods and vertical phase speeds in summer winter and spring fall are found obeying a lognormal distribution both the downward and upward phase progression gravity waves are observed by the lidar and the fractions of gravity waves with downward phase progression increase from summer 59 to winter 70

rapid climate shifts in the southern african interior throughout the mid to late holocene a detailed climate proxy record based on 18o 13o 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 holocene prior to 5200 years ago was humid and warm a fundamental transition occurred 3200 years ago leading to drier and cooler conditions that culminated at 1750 ad comparisons with ice core records suggest synchronous changes implicating rapid global teleconnections

wave propagation in heterogeneous porous media a velocity stress finite difference method a particle velocity stress finite difference method is developed for the simulation of wave propagation in 2 d heterogeneous poroelastic media instead of the prevailing second order differential equations we consider a first order hyperbolic system that is equivalent to biot s equations the vector of unknowns in this system consists of the solid and fluid particle velocity components the solid stress components and the fluid pressure a maccormack finite difference scheme that is fourth order accurate in space and second order accurate in time forms the basis of the numerical solutions for biot s hyperbolic system an original analytic solution for a p wave line source in a uniform poroelastic medium is derived for the purposes of source implementation and algorithm testing in simulations with a two layer model additional slow compressional incident transmitted and reflected phases are recorded when the damping coefficient is small this slow compressional wave is highly attenuated in porous media saturated by a viscous fluid from the simulation we also verified that the attenuation mechanism introduced in biot s theory is of secondary importance for fast compressional and rotational waves the existence of seismically observable differences caused by the presence of pores has been examined through synthetic experiments that indicate that amplitude variation with offset may be observed on receivers and could be diagnostic of the matrix and fluid parameters this method was applied in simulating seismic wave propagation over an expanded steam heated zone in cold lake alberta in an area of enhanced oil recovery eor processing the results indicate that a seismic surface survey can be used to monitor thermal fronts

a multi proxy analysis of late quaternary palaeoenvironments sekhokong range eastern lesotho the eastern lesotho highlands host an array of periglacial and glacial geomorphic features their analysis has provided past climate interpretations predominantly for cold periods yet no multi proxy temporally continuous palaeoenvironmental records exist this study presents a palaeoenvironmental reconstruction based on sedimentary characteristics fossil pollen and diatoms from an alpine wetland located in the sekhokong mountain range the record commences in the late pleistocene with a wet period from 16 450 to 14 440 cal a bp interrupted by dry conditions from 16 350 to 15 870 cal a bp from 14 150 to 8560 cal a bp drier conditions are inferred slowly transitioning to warmer wetter conditions warmer dry conditions are inferred for 8560 7430 cal a bp followed by cold wet conditions from 7280 to 6560 cal a bp a dry warmer period occurs from 6560 to 3640 cal a bp indicated by pollen diatom and sedimentary records followed by cool wet conditions from 3400 to 1200 cal a bp the period from 1110 cal a bp to the present is characterized by progressive drying pronounced cold events are detected from the diatom record moisture records appear relatively specific to the topographic setting of sekhokong near the great escarpment edge probably driven by orographically constrained synoptic controls

inertia gravity waves in antarctica a case study using simultaneous lidar and radar measurements at mcmurdo scott base 77 8 s 166 7 e 1 this study presents the first coincident observation of inertia gravity waves igws by lidar and radar in the antarctic mesopause region this is also the first known observation of two simultaneous igws at the same location an fe boltzmann lidar at arrival heights 77 8 s 166 7 e provides high resolution temperature data and a co located mf radar provides wind data on 29 june 2011 coherent wave structures are observed in both the fe lidar temperature and mf radar winds two dominant waves are determined from the temperature data with apparent periods of 7 7 0 2 and 5 0 0 1 h and vertical wavelengths of 22 2 and 23 2 km respectively the simultaneous measurements of temperature and wind allow the intrinsic wave properties to be derived from hodograph analyses unambiguously the analysis shows that the longer period wave propagates northward with an azimuth of 11 5 clockwise from north this wave has a horizontal wavelength of h 2 2 0 2 103 km and an intrinsic period of i 7 9 0 3 h the intrinsic horizontal phase speed cih for this wave is 80 4 m s while the horizontal and vertical group velocities cgh and cgz are 48 3 m s and 0 5 0 1 m s respectively the shorter period wave has i 4 5 0 3 h and 100 4 with h 1 1 0 1 103 km and cih 68 5 m s its group velocities are cgh 58 5 m s and cgz 1 1 0 1 m s therefore both waves propagate with very shallow elevation angles from the horizon 0 6 0 1 and 1 1 0 1 for the longer and shorter period waves respectively but originate from different sources our analysis suggests that the longer period igw most likely originates from the stratosphere in a region of unbalanced flow

late quaternary sea level change in south africa abstract a late quaternary sea level curve for south africa is presented on the basis of new and published data from a range of sea level indicators and a variety of locations available evidence suggests that sea level in south africa broadly follows that described from the caribbean but that deviations occur during sea level highstands during the last interglaciation oxygen isotope stage 5 and the late holocene coastal emergence produced higher sea levels in south africa than those identified in the caribbean during the same time intervals this is tentatively ascribed to predicted lithospheric deformation in continental margin settings

polar mesosphere and lower thermosphere dynamics 1 mean wind and gravity wave climatologies 1 mean wind and gravity wave climatologies are presented for the polar mesosphere and lower thermosphere mlt the data were derived using mf radars at davis 69 s 78 e and syowa 69 s 40 e in the antarctic and poker flat 65 n 147 w and andenes 69 n 16 e in the arctic the dynamics of the antarctic mlt are found to be significantly different from the arctic mlt summer maxima in both the westward and equatorward winds occur closer to the solstice in the antarctic than in the arctic the greater symmetry around the solstice suggests radiative effects may play a greater role in controlling the state of the antarctic mlt than in the arctic where dynamical effects appear to be more important gravity wave observations also suggest that wave drag may be greater in the arctic than in the antarctic the equatorward flow near the mesopause persists later in summer in the arctic than in the antarctic as do observations of polar mesospheric clouds and polar mesospheric summer echoes all three phenomena begin at about the same time in each hemisphere but end later in the arctic than in the antarctic it is proposed that the magnitude of the meridional winds can be used as a proxy for gravity wave driving and the consequent adiabatic cooling in the mlt seasonal variations in gravity wave activity are predominately combinations of annual and semiannual components significant hemispheric differences are observed for both the timing and magnitude of these seasonal variations

energy enhancements of gravity waves in the antarctic lower stratosphere associated with variations in the polar vortex and tropospheric disturbances 1 gravity waves in the antarctic lower stratosphere are examined using original operational radiosonde data obtained at syowa station 69 0 s 39 6 e with fine vertical resolution in the lower stratosphere the temporal variation in gravity wave energy depends on height in the height region of 13 15 km just above the tropopause the seasonal variation in gravity wave energy is not evident the wave energy is rather enhanced when the absolute value of potential vorticity in the upper troposphere becomes small over syowa station this fact implies that tropospheric disturbances affect the dynamical processes of gravity waves there however the gravity wave energy in the height region of 15 25 km shows clear seasonal variation having a maximum in spring the time variation in gravity wave energy is examined in detail in terms of the polar vortex by using the equivalent latitude coordinate energy enhancements occur when the edge of the polar vortex approaches syowa station and the enhancements are especially large when the polar vortex breaks down in spring these results suggest that height variation in the background atmosphere leads to the difference of wave characteristics between the two height regions the enhancements of wave energy are partly explained as modification of the wave structure by the background wind speed and the static stability but it is also likely that enhancements of wave activity contribute to the energy enhancement at the edge of the polar vortex in spring

a study of multiple tropopause structures caused by inertia gravity waves in the antarctic abstractmultiple tropopauses mts defined by the world meteorological organization are frequently detected from autumn to spring at syowa station 69 0 s 39 6 e the dynamical mechanism of mt events was examined by observations of the first mesosphere stratosphere troposphere mst radar in the antarctic the program of the antarctic syowa mst incoherent scatter is radar pansy and of radiosondes on 8 11 april 2013 the mt structure above the first tropopause is composed of strong temperature fluctuations by a detailed analysis of observed three dimensional wind and temperature fluctuation components it is shown that the phase and amplitude relations between these components are consistent with the theoretical characteristics of linear inertia gravity waves igws numerical simulations were performed by using a nonhydrostatic model the simulated mt structures and igw parameters agree well with the observation in the analysis using the numerical simulation data it is seen that igws were generate

detecting overlapping gravity waves using the s transform 1 we discuss an adaptation to the widely used stockwell transform based method for the detection of gravity waves to allow the detection of multiple overlapping waves this adjusted method is applied to data from the high resolution dynamics limb sounder for the period of may 2006 and is found to change the measured distribution of gravity wave momentum flux on a global scale an overall 68 increase in measured momentum flux is observed for the 20 30km altitude range with significant regional variability the largest absolute increase is over india the southern ocean and the antarctic peninsula regions previously known to exhibit high levels of momentum flux a strong relative increase is observed north of the equator particularly in the tropics analysis of the wavelength distribution of detected gravity waves shows that the majority of this increase is due to the detection of small vertical and horizontal scale waves which were presumably previously masked by higher amplitude events in the same profile

numerical modeling of the excitation propagation and dissipation of primary and secondary gravity waves during wintertime at mcmurdo station in the antarctic

historical climatic record from flood sediments deposited in the interior of spiralka cave czech republic abstract magnetic susceptibility was measured on more than four hundred samples collected from a 5 m high section of fine grained sediments deposited during flood events in the interior of spiralka cave spiralka cave is located in the northeastern portion of the moravian karst czech republic in the upper 1 5 m of this profile mineral magnetic fe arm sirm s ratio t and other non magnetic measurements heavy mineral concentration loss on ignition and particle grain size indicate that variations are controlled by the concentration of magnetite and by magnetic grain size i e increased magnetic susceptibility results from increased concentration of coarse grained magnetite a positive correlation with ti and zr concentrations in this part of the profile with our magnetic susceptibility record is a detrital signal responding to changing environmental conditions in the catchment area furthermore a comparison of our susceptibility record to the record of winter temperature anomalies constructed from both instrumental and historical records collected at the klementinum observatory in prague shows a remarkable correlation the most probable explanation of these correlations is that during years with warmer winters positive winter temperature anomalies and less snow cover the floods were less intensive but probably had access to larger tracts of cultivated land as agriculture tended to expand during these warmer periods cultivation of the land provided flood waters with greater access to coarser grained magnetite like materials exposed by tilling of soils lower in the profile interpreting the environmental significance of magnetic susceptibility variations is more complex as remobilization of iron has occurred nevertheless the magnetic susceptibility record when coupled with non magnetic measurements can be shown to correlate to known environmental conditions present in central europe during the deposition of the lower portion of the profile

the separated polar winter stratopause a gravity wave driven climatological feature abstract an examination of satellite derived temperatures reveals that the winter polar stratopause is usually elevated and warmer than the adjacent midlatitude stratopause this separated stratopause occurs in both hemispheres but is more pronounced and persistent in the southern winter it descends with time towards spring and exhibits week to week variability observational diagnostics and results from a two dimensional 2 d model suggest that gravity wave driving can account for this separated polar stratopause by driving a meridional circulation with downwelling over the winter pole in the model the solar heating pattern induces stronger winter westerlies than summer easterlies which leads to a stronger gravity wave driven circulation in the winter hemisphere spherical geometry and the high latitude location of the winter westerly jet combine to yield a concentrated region of downwelling model results suggest that descent of the temperature maximum with time is probably caused by wave mean f

rayleigh raman lidar observations of gravity wave activity from 15 to 70 km altitude over syowa 69 s 40 e the antarctic the potential energy of gravity waves gws per unit mass ep at altitudes of 15 70 km has been examined from temperature profiles obtained by a rayleigh raman rr lidar at syowa station 69 s 40 e from may 2011 to october 2013 with the exception of the summer months the gws with ground based wave periods longer than 2 h and vertical wavelengths between 1 8 and 16 km were extracted from the temperature profiles ep was larger in winter than in spring and fall although in 2012 at altitudes below 30 km ep was larger in spring than in winter and fall ep increased with a mean scale height of 11 3 km ep profiles showed a local maximum at an altitude of 20 km and a minimum at 25 km in almost every month which has not been reported by previous studies observed by radiosondes the values of ep in october of 2012 were smaller at 35 60 km and larger at 20 35 km than those in october of 2011 and 2013 this difference in the ep profile is most probably caused by different seasonal variations of zonal winds the larger and smaller ep values seem to be observed both below and above the altitude at which the zonal wind speed reached 0 m s 1 this result suggests that wind filtering of gravity waves with small phase speeds is significantly important in early spring

global estimates of gravity wave momentum flux from high resolution dynamics limb sounder observations analyzed to derive global properties of gravity waves we describe a wavelet analysis technique that determines covarying wave temperature amplitude in adjacent temperature profile pairs the wave vertical wavelength as a function of height and the horizontal wave number along the line joining each profile pair the analysis allows a local estimate of the magnitude of gravity wave momentum flux as a function of geographic location and height on a daily basis we examine global distributions of these gravity wave properties in the monthly mean and on an individual day and we also show sample instantaneous wave events observed by hirdls the results are discussed in terms of previous satellite and radiosonde observational analyses and middle atmosphere general circulation model studies that parameterize gravity wave effects on the mean flow the high vertical and horizontal resolution afforded by the hirdls measurements allows the analysis of a wider range of wave vertical and horizontal wavelengths than previous studies and begins to show individual wave events associated with mountains and convection in high detail mountain wave observations show clear propagation to altitudes in the mesosphere

holocene uplift derived from relative sea level records along the coast of western kobe japan abstract mid to late holocene sea level observations have been obtained from tamatsu and tarumi in western kobe japan in this tectonically active area we evaluate the local tectonic effect during the holocene by comparison between observations and predictions of sea level variations for the purpose of this study we analysed the diatom assemblages and carried out sulphur analysis of sediments these were used along with radiocarbon dates to derive relative sea level variations for the sites a rate of tectonic uplift of between 0 1 and 0 3 mm per year corrected for the prediction fits well with relative sea level rsl index points of tamatsu at 6415 5320 cal bp depending on the altitude of the rsl index point at about 5700 cal bp the best estimate of the rate of tectonic uplift for tamatsu is calculated as 0 11 0 25 mm yr over the period concerned a rate of tectonic uplift between 0 3 and 0 5 mm per year is derived for tarumi at about 7300 and 3835 3365 cal bp these values may explain the height distributions of the late pleistocene marine terraces along the coast of the western kobe providing a first approximation for rates of local crustal movements during the late quarternary

paleo environment and flooding of the limpopo river plain mozambique between c ad 1200 2000 multi proxy analysis was performed on a radiocarbon dated core collected from a relic oxbow lake in the limpopo river plain mozambique with the aim to reconstruct paleo environment and past flooding of the lower river system over the past c 800 years an additional objective was to evaluate and investigate the potential use of different proxies as recorders of paleo flooding events and paleo environmental variability within the floodplain the proxies applied in this study were mineral magnetic properties grain size distribution organic carbon content and diatom microfossil assemblages we found that sediment grain size and mineral magnetic properties of the minerogenic fraction were the most sensitive proxies in terms of detecting signals from high intensity river discharge events in the 800 year long sequence variations in sand content magnetic susceptibility and saturation isothermal remnant magnetization suggest at least four major flooding events at the site during the reconstructed period in the mid 1200 late 1300 mid 1500 ad and during the last century the diatom proxy reflects the development of the site from an open oxbow lake to a mainly terrestrial area the diatom assemblage indicates that open lake conditions prevailed at the site between c ad 1200 1400 with periodic inundation by marine water most likely due to late holocene sea level changes from c ad 1400 and onwards diatoms were rarely deposited at the site which indicates drier conditions this was a result of soil formation and gradual in filling of the lake a process which possibly was accentuated by a regionally dry climate situation our study shows that oxbow lakes and the proxies used here have great potential for reconstructing flooding events a knowledge that is crucial for potential prediction and mitigation of flooding events in mozambique in the future although chronological uncertainties limit comparisons to other paleo environmental records it seems that the flooding events recorded at our site occurred both during regionally wet and dry periods our data infer however that flooding was probably more clearly recorded during the lake stages than during infilled stage probably as the terrestrial environment was more exposed to erosion c 2014 elsevier b v all rights reserved less

does strong tropospheric forcing cause large amplitude mesospheric gravity waves a deepwave case study the deepwave deep propagating wave experiment campaign was designed for an airborne and ground based exploration of gravity waves from their tropospheric sources up to their dissipation at high altitudes it was performed in and around new zealand from 24 may till 27 july 2014 being the first comprehensive field campaign of this kind a variety of airborne instruments was deployed onboard the research aircraft nsf ncar gulfstream v gv and the dlr falcon additionally ground based measurements were conducted at different sites across the southern island of new zealand including the dlr rayleigh lidar located at lauder 45 04 s 169 68 e we focus on the intensive observing period iop 10 on the 4 july 2014 when strong wsw winds of about 40 m s at 700 hpa provided intense forcing conditions for mountain waves at tropopause level the horizontal wind exceeded 50 m s and favored the vertical propagation of gravity waves into the stratosphere the dlr rayleigh lidar measured temperature fluctuations with peak to peak amplitudes of about 20 k in the mesosphere 60 km to 80 km msl over a period of more than 10 hours two research flights were conducted by the dlr falcon falcon flight 04 and 05 during this period with straight transects mt aspiring 2a over new zealand s alps at three different flight levels around the tropopause approx 11 km msl these research flights were coordinated with the gv research flight 16 where the largest mountain wave amplitudes at flight level approx 13 km msl were measured during deepwave additionally a first analysis of falcon s in situ flight level data revealed amplitudes in the vertical wind larger than 4 m s at all altitudes in the vicinity of the highest peaks of the southern alps here we present a comprehensive picture of the gravity wave characteristics and propagation properties during this interesting gravity wave event we use the airborne observations combined with a comprehensive set of ground based measurements consisting of 13 radiosoundings 1 5 hourly interval together with the dlr rayleigh lidar to cover the altitude range from the troposphere to the mesosphere high resolution 1 hourly ecmwf analyses and forecasts are used to estimate the propagation conditions of the excited mountain waves the goal of our investigation is to find out whether the large amplitude mesospheric gravity waves are caused by the strong tropospheric forcing

rainfall variability and vegetation dynamics of the lower limpopo valley southern africa 500 ad to present abstract the long term responses of vegetation to climate variability are of relevance for predicting present and future vegetation change and have implications for the management of savanna and riparian ecosystems this paper explores the links between regional rainfall hydrology and vegetation dynamics in the savannas and riverine forests of the lower limpopo valley southern africa from 800 ad to the present reviewing palaeoecological data fossil pollen spores diatoms and lithology from several hydrological systems in kruger national park knp south africa and limpopo national park pnl mozambique the pnl knp records show that riverine arboreal taxa expanded during wetter periods including 800 1400 ad and after 1800 ad between 1400 and 1800 ad grasses savanna taxa and generalist taxa were favored over riparian taxa a change that is linked with the onset of dry spells in the region corresponding to the so called little ice age the most extreme drought events around 1700 ad resulted in a marked decline of riparian forest taxa near lake mapimbi knp in contrast many water scarce sequences away from the riverine environment such as radio pan mafayeni pan malahlapanga pan and lake makwadzi show stable grassland vegetation throughout the last 1200 years the results demonstrate the resilience of the grassland savanna ecosystems to projected climate change with warmer and overall drier climate the riverine forests are predicted to be more vulnerable especially as more extreme weather events are projected

influence of heterogeneous soils and clutter on the performance of ground penetrating radar for landmine detection ground penetrating radar gpr has been studied for landmine detection and identification since this application employs higher frequencies as compared to conventional largescale gpr measurements the gpr performance is greatly influenced by soil properties and their spatial heterogeneity in order to study the influence of soil heterogeneity on gpr performance three types of soil were investigated from the soil heterogeneity gpr clutter was modeled with the aim of assessing the difficulty encountered in successful gpr performance a handheld dual sensor system that combines a metal detector and gpr was tested in these three test soils and its performance for identifying buried objects was evaluated the gpr performance obtained from the test showed a clear correlation with the modeled gpr clutter hence the present study illustrates that clutter plays a major role in the detection of small objects in heterogeneous soil by gpr

lidar observations of persistent gravity waves with periods of 3 10 h in the antarctic middle and upper atmosphere at mcmurdo 77 83 s 166 67 e persistent dominant and large amplitude gravity waves with 3 10 h periods and vertical wavelengths 20 30 km are observed in temperatures from the stratosphere to lower thermosphere with an fe boltzmann lidar at mcmurdo antarctica these waves exhibit characteristics of inertia gravity waves in case studies yet they are extremely persistent and have been present during every lidar observation we characterize these 3 10 h waves in the mesosphere and lower thermosphere using lidar temperature data in june from 2011 to 2015 a new method is applied to identify the major wave events from every lidar run longer than 12 h a continuous 65 h lidar run on 28 30 june 2014 exhibits a 7 5 h wave spanning 60 h and 6 5 h and 3 4 h waves spanning 40 and 45 h respectively over the course of 5 years 323 h of data in june reveal that the major wave periods occur in several groups centered from 3 5 to 7 5 h with vertical phase speeds of 0 8 2 m s these 3 10 h waves possess more than half of the spectral energy for 93 of the time a rigorous prewhitening postcoloring technique is introduced for frequency power spectra investigation the resulting spectral slopes are unusually steep 2 7 below 100 km but gradually become shallower with increasing altitude reaching about 1 6 at 110 km two dimensional fast fourier transform spectra confirm that these waves have a uniform dominant vertical wavelength of 20 30 km across periods of 3 5 10 h these statistical features shed light on the wave source and pave the way for future research

seasonal variations of gravity wave activity in the lower stratosphere over an antarctic peninsula station an 8 year series of 965 high resolution radiosonde soundings over rothera 67 degrees s 68 degrees w on the antarctic peninsula are used to study gravity wave characteristics in the lower stratosphere the gravity wave energy is shown to have a seasonal variation with peaks at the equinoxes the largest peak is around the spring equinox during the winter months and extending into the spring there is both an enhancement in the downward propagating wave activity and a reduction in the amount of critical level filtering of upward propagating mountain waves the horizontal propagation directions of the gravity waves were determined using hodographs it was found that there is a predisposition toward northward and westward propagating waves above rothera this is in agreement with previous observations of gravity wave momentum flux in the wintertime mesosphere over rothera these results are consistent with a scenario whereby the stratospheric gravity wavefield above rothera is determined by a combination of wind flow over topography generating waves from below and sources such as the edge of the polar stratospheric vortex generating waves from above especially during winter and spring

generation of mesoscale gravity waves in upper tropospheric jet front systems abstract multiply nested mesoscale numerical simulations with horizontal resolution up to 3 3 km are performed to study the generation of mesoscale gravity waves during the life cycle of idealized baroclinic jet front systems long lived vertically propagating mesoscale gravity waves with horizontal wavelengths 100 200 km are simulated originating from the exit region of the upper tropospheric jet streak in a manner consistent with past observational studies the residual of the nonlinear balance equation is found to be a useful index in diagnosing flow imbalance and predicting wave generation the imbalance diagnosis and model simulations suggest that balance adjustment as a generalization of geostrophic adjustment is likely responsible for generating these mesoscale gravity waves it is hypothesized that through balance adjustment the continuous generation of flow imbalance from the developing baroclinic wave will lead to the continuous radiation of gravity waves

rayleigh lidar observations of reduced gravity wave activity during the formation of an elevated stratopause in 2004 at chatanika alaska 65 n 147 w 1 we report rayleigh lidar measurements of nightly temperature profiles in the 40 80 km altitude region and 15 min relative density profiles in the 40 50 km altitude region at poker flat research range chatanika alaska 65 n 147 w in december january and february over three winters 2002 2003 2003 2004 and 2004 2005 we characterize the gravity wave activity in terms of the measurements of buoyancy period and relative density fluctuations and estimate the potential energy density and growth of potential energy density with altitude we use satellite and reanalysis data to analyze the synoptic structure of the stratospheric vortex and the aleutian anticyclone the planetary wave activity and the mean winds these three winters have a major stratospheric warming in 2002 2003 an extreme warming event in 2003 2004 resulting in an elevated stratopause and no warming in 2004 2005 the gravity wave activity shows significant interannual variability with an average potential energy density of 2 1 j kg in 2002 2003 1 1 j kg in 2003 2004 and 5 7 j kg in 2004 2005 we find a positive correlation of 0 74 between the gravity wave activity in the upper stratosphere and the winds in the lower stratosphere where the winds are lightest the reduction in gravity wave activity in 2002 2003 relative to 2004 2005 reflects the influence of the aleutian anticyclone that is present over chatanika in 2002 2003 but absent in 2004 2005 the occurrence of lower gravity wave activity in 2003 2004 when the aleutian anticyclone is present less often than in 2002 2003 supports recent modeling studies that indicate that the elevated stratopause is formed due to a reduction of gravity waves propagating upward into the mesosphere

rayleigh lidar observations of gravity wave activity in the winter upper stratosphere and lower mesosphere above davis antarctica 69 s 78 e 1 gravity wave activity in the upper stratosphere and lower mesosphere uslm is investigated using temperature data retrieved from a rayleigh lidar at davis antarctica 69 s 78 e during the 2007 and 2008 winters the temporal and height variabilities of waves with ground based periods greater than 2 h and vertical wavelengths between 4 km and 20 km are analyzed stratospheric gravity wave potential energy per unit mass shows a weaker correlation with stratospheric winds at davis than that reported in the arctic gravity waves dissipate above 40 km during winter while there is no dissipation in the autumn mesosphere a separate analysis of gravity waves with ground based periods of 2 6 h revealed lower dissipation in the winter mesosphere the seasonal cycle of gravity wave activity is evident throughout the uslm with peak activity observed during winter the gravity wave potential energy and vertical wavenumber power spectral density at davis are similar to that recorded at other high latitude sites

rayleigh lidar observations of thermal structure and gravity wave activity in the high arctic during a stratospheric warming abstract during february and march 1993 rayleigh lidar observations of temperature structure and gravity wave activity were carried out in the high canadian arctic at eureka northwest territories 80 n 86 w a sudden warming was observed first in the upper stratosphere during late february and then at lower levels in early march the warming appeared to be part of a disturbance of the entire middle atmosphere with temperature changes in the mesosphere and lower stratosphere being opposite in sign to those in the upper stratosphere shorter time and length scale temperature fluctuations observed in the upper stratosphere are interpreted as being a result of atmospheric gravity waves the wave amplitudes are shown to be capable of inducing convective instability the rms perturbation and available potential energy density show substantial vertical and day to day variability in regions of conservative and dissipative growth rates vertical growth of the potential energy spectral density is seen to ceas

relief peels in the study of palaeoflood slack water sediments abstract the use of slack water sediments as palaeostage indicators in palaeoflood hydrological analysis requires detailed sedimentological description conventional descriptions have relied mainly on field descriptions of slack water profiles however this method often fails to reveal important detail by employing the well established technique of relief peels modified for use in slack water sediment studies the problem of insufficient data recovery from slack water deposits was successfully overcome during a palaeoflood hydrological investigation of south african rivers the use of relief peels showed that this technique is a useful and in some cases indispensable aid in the description and interpretation of palaeoflood deposits for example relief peels have shown that slack water sediments are for the most part not massive exhibiting mainly flat lamination this indicates that slack water sedimentation was characterised by moderate rates of deposition rather than sudden or rapid rates relief peels have also shown that the base of tributary back flooded slack water sediments often contain intraformational rip up clasts this indicates that reworking of the existing slack water sediments is a common process during tributary back flooding the technique was particularly effective in enhancing sedimentary structure and in differentiating between interpalaeoflood non palaeoflood and intraflood pulses relief peels can also be stored permanently as a surface sample of the slack water sequence to be retrieved for later study

the sediment stratigraphy of a flood event an example from the sabie river south africa abstract the geomorphic effects of river floods in various climatic settings worldwide have been extensively described but there is little information on sedimentary processes during and immediately following flood peaks here we reconstruct sedimentary processes and patterns of the 2012 flood on the sabie river in kruger national park south africa from the preserved geomorphic and sedimentary signature of this event based on a combination of geomorphic and sedimentary evidence the maximal and waning flow stages of the flood event are identified shown by cut and fill and fining up sequences within aggradational bars and organic horizons which may be buried that correspond to the period of flood peak recession the presence of organic horizons suggests a strongly seasonal flow regime typical of semi arid south african rivers it also provides an exemplar of a flood event stratigraphy that is usually poorly preserved in the geologic record

reconstruction of multi century flood histories from oxbow lake sediments peace athabasca delta canada floods caused by ice jams on the peace river are considered to be important for maintaining hydro ecological conditions of perched basins in the peace athabasca delta pad canada a highly productive and internationally recognized northern boreal ecosystem concerns over the potential linkages between regulation of the peace river in 1968 for hydroelectric production and low peace river discharge between 1968 and 1971 during the filling of the hydroelectric reservoir absence of a major ice jam flood event between 1975 and 1995 and low water levels in perched basins during the 1980s and early 1990s have sparked numerous environmental studies largely aimed at restoring water levels in the pad lack of sufficient long term hydrological records however has limited the ability to objectively assess the importance of anthropogenic factors versus natural climatic forcing in regulating hydro ecological conditions of the pad here we report results of a paleolimnological study on laminated sediments from two oxbow lakes in the pad which are located adjacent to major flood distributaries of the peace river sediment core magnetic susceptibility measurements supported by results from several other physical and geochemical analyses as well as stratigraphic correspondence with recorded high water events on the peace river provide proxy records of flood history spanning the past 180 and 300 years in these two basins results indicate that inferred flood frequency has been highly variable over the past 300 years but in decline for many decades beginning as early as the late nineteenth century well before peace river regulation additionally several multi decadal intervals without a major flood have occurred during the past 300 years while climate related mechanisms responsible for this variability in flood frequency remain to be determined as does quantifying the relative roles of river regulation and climate variability on hydro ecological conditions in the pad since 1968 these results suggest that ecosystem management strategies for the pad need to explicitly account for natural variations in flood recurrence intervals copyright 2006 john wiley sons ltd

vertical accretion sand proxies of gaged floods along the upper little tennessee river blue ridge mountains usa abstract understanding environmental hazards presented by river flooding has been enhanced by paleoflood analysis which uses sedimentary records to document floods beyond historical records bottomland overbank deposits e g natural levees floodbasins meander scars low terraces have the potential as continuous paleoflood archives of flood frequency and magnitude but they have been under utilized because of uncertainty about their ability to derive flood magnitude estimates the purpose of this paper is to provide a case study that illuminates tremendous potential of bottomland overbank sediments as reliable proxies of both flood frequency and magnitude methods involve correlation of particle size measurements of the coarse tail of overbank deposits 0 25 mm sand from three separate sites with historical flood discharge records for the upper little tennessee river in the blue ridge mountains of the southeastern united states results show that essentially all floods larger than a 20 probability event can be detected by the coarse tail of particle size distributions especially if the temporal resolution of sampling is annual or sub annual coarser temporal resolution 1 0 to 2 5 year sample intervals provides an adequate record of large floods but is unable to discriminate individual floods separated by only one to three years measurements of 0 25 mm sand that are normalized against a smoothed trend line through the down column data produce highly significant correlations r 2 values of 0 50 to 0 60 with p values of 0 004 to

siliceous microfossils and mineral magnetic characteristics in a sediment core from lake manitoba canada a remnant of glacial lake agassiz a 14 2 m long core was recovered from the southern lake manitoba basin the sediment consisting mainly of silty clay was studied for siliceous microfossil content and mineral magnetics 14 new ac

late holocene sea level changes and paleoclimate recorded in lake lungue southern mozambique abstract we report on late holocene paleoenvironmental and sea level changes in southern mozambique based on analysis of diatom stratigraphy mineral magnetic susceptibility saturation isothermal remnant magnetization sirm and organic carbon content in a sediment core from lake lungue located ca 30 km north of xai xai city in the limpopo river floodplain eleven radiocarbon dates performed on terrestrial shells allowed establishment of an age depth model high content of brackish marine taxa especially diploneis suborbicularis and navicula yarrensis suggests that the lake lungue basin was part of the indian ocean coastal zone between ca 740 and 910 ce suggesting higher relative sea level during this phase a similar diatom distribution in older parts of the sequence of unknown age indicates that the site was connected to the indian ocean also at some stage prior to 740 ce between ca 910 and 1130 ce the basin was under a combined effect of sporadic marine water influx and limpopo river actions a freshwater lake was established sometime between 1130 and 1360 ce when the basin became less affected by marine influences due to lower sea levels instead the lake system was more influenced by limpopo river meandering dynamics and flooding events and eventually isolated into a more or less independent lake ecosystem where diatom diversity most likely responded to lake levels fluctuations driven by shifts in relative humidity and rainfall amounts within the floodplain and also from upstream sources during this phase high abundance of freshwater planktonic species i e aulacoseira granulata and a ambigua indicates high lake levels and wetter conditions dated to ca 1360 1560 ce from 1560 ce until present the lake has been subject to drier conditions and higher evaporation as indicated by lower lake levels reported by a decline in freshwater planktonic taxa and increase in brackish taxa e g amphora robusta

11 years of rayleigh lidar observations of gravity wave activity above the southern tip of south america gravity wave gw activity is analyzed using temperature t data retrieved from a rayleigh lidar at rio gallegos argentina 51 6 s 69 3 w gw characteristics are derived from 302 nights of observations providing more than 1018 h of high resolution lidar data between 20 km and 56 km height from august 2005 to december 2015 t measurements are performed by a differential absorption lidar dial instrument this lidar was the southernmost outside antarctica until the end of 2017 rio gallegos is an exceptional place to observe large amplitude gw every lidar measurement is classified according to its relative position to the polar vortex the lidar measurements are compared with collocated sounding of the atmosphere using broadband emission radiometry saber and global positioning system radio occultation gps ro data the different instruments show different windows of the gw spectrum providing complementary observations in general the geometric mean of the specific gw potential energy pe is larger during winter and spring than during summer and autumn the largest geometric mean of pe is found inside the vortex and decreases monotonically at its edge outside it and when there is no vortex the same behavior is observed with satellite data on average it can be seen that lidar observations provide larger pe values than limb sounding measurements from a morlet continuous wavelet transform analysis 3 distinct modes are captured from saber and from gps ro data at the upper and lower stratosphere respectively in particular a systematic 3 5 4 years oscillation possibly related to el nino southern oscillation is observed

lidar observations of gravity wave activity in the middle atmosphere over davis 69 s 78 e antarctica a 16 month series of lidar measurements in the stratosphere and mesosphere lower thermosphere mlt region over davis station 69 s 78 e in antarctica is used to study gravity waves the unprecedentedly large number of observations totaling 2310 h allows us to investigate seasonal variations in gravity wave activity in great detail in the stratosphere the gravity wave potential energy density gwped is shown to have a large seasonal variation with a double peak in winter and minimum in summer we find conservative wave propagation to occur between 29 and 41 km altitude in winter as well as in summer whereas smaller energy growth rates were observed in spring and autumn these results are consistent with selective critical level filtering of gravity waves in the lower stratosphere in the mlt region the gwped is found to have a semiannual oscillation with maxima in winter and summer the structure of the winter peak is identical to that in the stratosphere suggesting that the gravity wave flux reaching the mlt region is controlled by the wind field near the tropopause level

the mid holocene sea level highstand at bogenfels pan on the southwest coast of namibia the radiocarbon ages of mollusc shells from the bogenfels pan on the hyper arid southern coast of namibia provide constraints on the holocene evolution of sea level and in particular the mid holocene highstand the bogenfels pan was flooded to depths of 3 m above mean sea level amsl to form a large subtidal lagoon from 7300 to 6500 calibrated radiocarbon years before present cal yr bp the mollusc assemblage of the wave sheltered lagoon includes nassarius plicatellus lutraria lutraria and the bivalves solen capensis and gastrana matadoa both of which no longer live along the wave dominated southern namibian coast the radiocarbon ages of mollusc shell from a gravely beach deposit exposed in a diamond exploration trench indicate that sea level fell to near or 1 m below its present day position between 6500 and 4900 cal yr bp the rapid emergence of the pan between 6500 and 4900 cal yr bp exceeds that predicted by glacio isostatic models and may indicate a 3 m eustatic lowering of sea level the beach deposits at bogenfels indicate that sea level rose to 1 m amsl between 4800 and 4600 cal yr bp and then fell briefly between 4600 and 4200 cal yr bp before returning to 1 m amsl since 4200 cal yr bp sea level has remained within one meter of the present day level and the beach at bogenfels has prograded seaward from the delayed arrival of sand by longshore drift from the orange river a 6200 cal yr bp coastal midden and a 600 cal yr bp midden 1 7 km from the coast indicate sporadic human utilization of the area the results of this study are consistent with previous studies and help to refine the holocene sea level record for southern africa