use of a bounding surface model in predicting element tests and capacity in boundary value problems the paper examines the merit of a two surface plasticity model through an optimised calibration procedure and assesses the model performance in capturing the response at both element and system lev

review and test of reproducibility of subdecadal resolution palaeoenvironmental reconstructions from microfossil assemblages abstract very high even annual resolution quantitative palaeoenvironmental reconstructions have been generated from microfossil assemblage data using transfer functions evidence of the utility of some of these reconstructions is given by the high correlations between the reconstructions and instrumental records such performance is despite several ecological and taphonomic issues that can become more problematic at subdecadal resolution than at multidecadal resolution this paper explores these timescale dependent issues and tests the reproducibility of the several of published reconstructions it demonstrates that the previously reported exceptionally good performance of several published chironomid based reconstructions is not reproducible

large scale dynamics of the mesosphere and lower thermosphere an analysis using the extended canadian middle atmosphere model the extended canadian middle atmosphere model is used to investigate the large scale dynamics of the mesosphere and lower thermosphere mlt it is shown that the 4 day wave is substantially amplified in southern polar winter in the presence of instabilities arising from strong vertical shears in the mlt zonal mean zonal winds brought about by parameterized nonorographic gravity wave drag a weaker 4 day wave in northern polar winter is attributed to the weaker wind shears that result from weaker parameterized wave drag the 2 day wave also exhibits a strong dependence on zonal wind shears in agreement with previous modeling studies in the equatorial upper mesosphere the migrating diurnal tide provides most of the resolved westward wave forcing which varies semiannually in conjunction with the tide itself resolved forcing by eastward traveling disturbances is dominated by smaller scales nonmigrating tides and other planetary scale waves play only a minor role in the zonal mean zonal momentum budget in the tropics at these heights resolved waves are shown to play a significant role in the zonal mean meridional momentum budget in the mlt impacting significantly on gradient wind balance balance fails at low latitudes as a result of a strong reynolds stress associated with the migrating diurnal tide an effect which is most pronounced at equinox when the tide is strongest resolved and parameterized waves account for most of the imbalance at higher latitudes in summer this results in the gradient wind underestimating the actual eastward wind reversal by up to 40

high latitude lower thermospheric neutral winds at eiscat and sondrestrom during ltcs 1 the incoherent scatter radar located at sondre stromfjord greenland 67 n 51 w 74 5 and the eiscat incoherent scatter facility located in northern scandinavia 69 5 n 19 e 66 3 both obtained e and f region measurements during the first campaign of the lower thermosphere coupling study ltcs 1 september 21 25 1987 neutral winds deduced from these measurements have been analyzed for their mean flow and tidal components a number of the altitude profiles for the mean winds and the diurnal and semidiurnal wave components at the two radar locations show similar variations with height indicating that latitudinal rather than longitudinal effects are dominant in determining the observed wind field diurnal tidal amplitudes and phases are reasonably well represented by theoretical model results forbes 1982 the semidiurnal amplitudes and phases although somewhat consistent between the two radars are not well represented in equinox tidal model results forbes and vial this issue results from both radars indicate a vertical wavelength for the zonal semidiurnal oscillation of approximately 60 km during a period of impulsive magnetospheric forcing september 22 23 winds deduced from measurements at both radars show enhanced eastward flows near midnight accompanied by equatorward winds at sondrestrom comparison with the results of a national center for atmospheric research thermosphere ionosphere general circulation model tigcm simulation of the ltcs 1 interval shows generally better agreement with the observations at eiscat than at sondrestrom during the period of activity on september 22 23 the tigcm is reasonably successful at simulating the eastward surge near midnight in the eiscat but not in the sondrestrom observations and the equatorward flow after midnight in the sondrestrom results the observed winds in magnetic latitude and magnetic local time coordinates indicate the presence of anticyclonic divergent flow near dusk and cyclonic converging flow near dawn

tidal winds from the mesosphere lower thermosphere global radar network during the second ltcs campaign december 1988 winds and tides were measured by nine mlt mesosphere lower thermosphere radars with locations between 70 n and 78 s including an equatorial station at christmas island 2 n avery et al 1990 the mean winds were eastward westward in the northern southern hemisphere mesosphere consistent with midwinter circulations for the 12 hour semidiurnal tide observations and the model of forbes and vial 1989 were in generally good agreement in both cases northward components were closer to being in phase in the two hemispheres and winter wavelengths were shorter than those of the mid latitude summer major differences were large small amplitudes at 70 n for model observations and poor agreement of equatorial tidal profiles for the 24 hour diurnal tide the radar observations and model of forbes and hagan 1988 were in useful agreement in the summer hemisphere however the short long wavelengths at mid high latitudes of the model s winter hemisphere were not observed during ltcs lower thermosphere coupling study 2 nor in climatologies for december suggestions as to the reasons for this disparity are presented

effects of consolidation under a penetrating footing in carbonate silty clay abstractthe effects of consolidation under a footing are generally viewed as beneficial due to the resulting increased capacity consolidation may also be actively sought because it minimizes footing embedment which can be critical for the installation of mobile offshore jack ups because available leg length is limited however it can also set the platform footing up to subsequently punch through the strengthened zone with potentially serious consequences the problem is complex due to the three dimensional nature of consolidation further footing penetration leaves the soil above heavily remolded and generates large excess pore pressures below such that the soil state even prior to consolidation is significantly altered from its in situ conditions this study has taken an experimental approach to investigate the effects of consolidation around a footing penetrating into carbonate silty clay and following detailed discussion of the response offers a framework to predict the changes to the load pene

predicting peak resistance of spudcan penetrating sand overlying clay abstractaccurately predicting peak penetration resistance qpeak during spudcan installation into sand overlying clay is crucial to an offshore mobile jack up industry still suffering regular punch through failures this paper describes a series of spudcan penetration tests performed on medium loose sand overlying clay and compares the response to existing centrifuge data from tests performed on dense sand overlying clay together these data demonstrate that punch through is a potential problem for both dense and loose sand overlying clay soil stratigraphies using this experimental database a failure stress dependent model has been modified to account for the embedment depth and the depth of occurrence of qpeak is shown to be a function of the sand thickness hs the model then was recalibrated taking these findings into account for a larger range of material properties and ratios of sand thickness to spudcan diameter hs d finally the performance of the modified and recalibrated model is verified b

horizontal structure of the geomagnetic 2 day variation 1 principal component analysis was applied to 30 year geomagnetic field data of six observatories in low latitudes to extract the longitudinal structure of the geomagnetic 2 day variation it was revealed that characteristics of the 2 day variation agree well with those of the quasi 2 day wave observed in the middle atmosphere it propagates westward with a zonal wave number 3 and the monthly mean amplitude of the variation is largest in january and july in addition an investigation into the latitudinal profile of the variation clarified that the amplitude of the 2 day variation is largest in the equatorial region although it extends to the middle latitudes a previous result of spherical harmonics analysis of geomagnetic field data was reanalyzed to identify the global horizontal pattern of overhead currents responsible for the geomagnetic 2 day variation the results showed that the 2 day variation is attributed to westward propagating current vortices the foci of which are located along the equator all these features can be explained by a scenario in which there exists a 2 day wave in the ionosphere whose horizontal structure and temporal variation resemble those in the middle atmosphere and the wind drives electric fields and currents in the ionosphere through dynamo action

amplitude phase and period variations of the quasi 2 day wave in the mesosphere and lower thermosphere over london canada 43 n 81 w during 1993 and 1994 because there is as yet no conclusive evidence pointing to the source of the quasi 2 day wave further observations are required in order to resolve questions about the generating mechanism as well as to better understand the role of the wave in the middle atmosphere in this paper we investigate the period amplitude phase and vertical wavelength for the quasi 2 day wave in the mesosphere and lower thermosphere using the university of western ontario 2 mhz radar near london canada and in addition we look at possible coupling with atmospheric tides the results of the present study bring out certain new aspects of the quasi 2 day wave at midlatitude in the northern hemisphere that have not been previously reported in particular we show that the period of the quasi 2 day wave determined from our study is smaller 46 47 hours than the 51 to 52 h period generally suggested by other northern hemisphere results and our periods also showed variability as a function of time we also draw attention to the annual variability and especially highlight the occurrence of the wave in nonsummer months for example a brief occurrence in april is not uncommon our study also contributes additional midlatitude geographical data that should aid in developing a better picture of the quasi 2 day wave

effect of sleeves and skirts on mitigating spudcan punch through in sand overlying normally consolidated clay punch through failure of mobile jack up rigs is still a main concern for spudcan foundations using centrifuge model tests and numerical modelling this paper examines the mitigating effect of top

longitude structure of the ionosphere f region from topex poseidon and ground based data during january 20 30 1993 including the quasi 2 day oscillation the global structure of the f region ionosphere during january 20 30 1993 is examined with emphasis on longitudinal variations the database consists of total electron content tec measurements from the topex poseidon dual frequency altimeter experiment from 66 to 66 geographic latitude for prenoon and premidnight conditions and hourly f o f 2 and hmf 2 values from eight ionosonde stations between 42 and 26 geographic latitude in the pacific sector the 10 day averaged daytime tec data reveal latitude versus longitude structures whose salient features are captured within 10 tec units by the 1990 international reference ionosphere iri 90 and which can be explained by dynamically induced neutral composition changes due to a combination of solar and magnetically driven circulation systems the premidnight tec data at low latitudes reveal the double banded structure of the equatorial ionization anomaly with however pronounced variations in amplitude and position as a function of geomagnetic longitude none of these features which probably reflect some combination of electric field and neutral wind effects are captured by iri 90 time series analyses of the f 0 f 2 and hmf 2 data and space time fourier spectra of the tec data reveal the presence of a quasi 2 day qtd oscillation in the ionosphere which is associated with qtd wind and temperature oscillations in the mesosphere and lower thermosphere previously documented for this time period the satellite based qtd results are subject to significant caveats described herein nevertheless the topex poseidon tec data set clearly represents an important resource for global studies of ionospheric structure and plasmaneutral interactions

experimental investigation of spudcan penetration in multi layer clays with interbedded sand layers highly layered soils are prevalent in several areas of current offshore activity and in particular in emerging provinces and fields however no investigation has been carried out for spudcan penetration in stratified sediments with more than two layers this paper reports centrifuge modelling of spudcan foundations penetrating through 3 6 clay layers with interbedded stronger clay silica sand and carbonate sand layers the aim was to provide insight into the behaviour of spudcan foundations in stratified sediments comprising layers of different drainage conditions and mineralogy the motivation for this paper emanated directly from the future needs identified by the recent revised version of iso 19905 1 it was found that the downward soil deformation was extended into 3 4 underlying layers of sand and clay with thickness ratios t d less than 0 6 the limiting squeezing depth was 0 17 0 18d when approaching stiff clay moderate clay layers and 0 28d when approaching dense sand stiff clay layers these

first observations of mesospheric dynamics with a partial reflection radar in hawaii 22 n 160 w we present here an overview of the wind measurements made during the first year of operation of a partial reflection radar system in hawaii the system operates at 1 98 mhz and provides wind estimates between 60 and 100 km at 2 km intervals our wind observations reveal a zonal mean motion that has several features in common with the mesopause semiannual oscillation msao seen at more equatorial latitudes but which is influenced as well by the seasonal variations of the mesospheric jet structure at higher latitudes major features of the zonal mean wind structure include a downward progression of strong eastward and westward phases of the msao from january to july coinciding with the period during which the msao and the annual cycle of the zonal mean wind at higher latitudes are in phase this results in an eastward maximum of 60 ms 1 near 80 km during january and february which descends rapidly and a westward maximum of 50 ms near 85 km during march and april which descends much more slowly the second msao cycle is greatly suppressed relative to the first due to the reversal of the correlation between this and the annual cycle at higher latitudes from july to december mean eastward motions occur primarily above 85 km early in this cycle and throughout the height range at later times planetary wave activity is seen to contribute substantial variability during times of eastward mean flow and to have a smaller role when zonal mean motions are westward tidal and 2 day motions are found to be large and variable with the maximum 2 day amplitudes occurring during february and august the largest diurnal tides were observed during october and november march and april and july and august while the semi diurnal amplitudes exhibited a minimum from april to june

the tropical stratopause in the ukmo stratospheric analyses evidence for a 2 day wave and inertial circulations summary large scale atmospheric motions near the low latitude stratopause in the uk meteorological office stratospheric analyses during the northern hemisphere winter are investigated focusing in particular on the 2 day wave and inertial eddies the 2 day wave is a westward propagating planetary wave which appears recurrently in the summer subtropical upper stratosphere and mesosphere space time spectral analysis of the assimilated fields of temperature and winds and high resolution transport of water vapour reveal large amplitude breaking planetary waves in the summer subtropics principally a 2 day wave 3 and a wave 1 of a period near 7 days a region of anomalous zonal mean meridional gradient of potential vorticity also exists pointing to a barotropic instability mechanism for the origin of the 2 day wave by contrast the winter subtropics are characterized by mixing on less than planetary scales during the period considered occurring during the easterly phase of the stratospheric semi annual oscillation water vapour is mixed turbulently into gyres and drawn in narrow filaments out of the southern hemisphere the potential vorticity field displays vertically layered zonally asymmetric variations the behaviour of the model assimilated fields is supported by along track water vapour distribution observed by the microwave limb sounder aboard the upper atmosphere research satellite shows evidences for intermittent filamentary mixing in the northern subtropics and a 2 day wave signature in the summer subtropics based on these results a possible mechanism connecting the initiation of the austral 2 day wave events to strong planetary wave activity in the winter is proposed the winter planetary waves provide the background conditions for development of inertial instabilities at low latitudes of the winter hemisphere which in turn create conditions favourable for barotropic instability of the summer subtropical easterly jet

using a thin sand layer to ease spudcan extraction in clay difficulties are encountered in soft clay and silt sediments during extraction of the spudcan foundations of mobile jack up rigs this paper reports results from centrifuge model tests undertaken to provide a simple effective and practical means for easing spudcan extraction in soft normally consolidated and lightly overconsolidated clay the tests were carried out on model spudcans of two different geometries typically used in the field the spudcans were extracted from penetrations of 2 3 diameters and after an operation period of 19 months the measured pore pressure at the bottom face of the spudcan during extraction process provided insight into the development of suction at the interface between the spudcan base and the underlying soil the tests were carried out with and without a sand layer placed locally in between the spudcan and the mudline at the onset of penetration in the field a gravel layer can be placed by means of a flexible fall pipe system the presence of a sand layer with a

temporal modulation of the four peaked longitudinal structure of the equatorial ionosphere by the 2 day planetary wave 1 observations of electron densities by the constellation observing system for meteorology ionosphere and climate in august to october 2008 have shown a prominent four peaked longitudinal structure in the height of the f2 layer hmf2 in the equatorial ionosphere the development of this ionospheric structure in daytime is found to be consistent with the forcing by the eastward propagating nonmigrating diurnal tide with zonal wave number 3 de3 it is believed that tidal winds can modify the e region electric fields and subsequently produce variations in the ionosphere through the dynamo effect this study reveals that the amplitude of the hmf2 four peaked longitudinal structure is subject to a 2 day periodic modulation on certain intervals in the two month time period simultaneously wind measurements from the skiymet meteor radar at thumba 8 5 n 77 e india indicate corresponding 2 day planetary wave activity in the mesosphere and lower thermosphere mlt the 2 day planetary wave has both zonal and meridional wind components and it is the variability in the zonal component that most closely corresponds to f2 layer changes the zonal wind observations by the radar also show that the amplitude of the diurnal tide is modulated by the 2 day wave this study suggests that the identified 2 day variation of the hmf2 four peaked longitudinal structure in the equatorial ionosphere is caused by the interaction between the de3 tide and the 2 day planetary wave

sondrestrom incoherent scatter radar observations during the lower thermosphere coupling study september 21 26 1987 the incoherent scatter radar located at soendre stroemfjord greenland obtained e and f region measurements during the first lower thermosphere coupling study ltcs 1 september 21 26 1987 lower thermospheric neutral winds deduced from these measurements show that the neutral dynamics are influenced by both tidal oscillations and magnetospheric forcing during an interval which was relatively quiet geomagnetically september 23 24 a semidiurnal oscillation dominated the neutral motion the model equinox tidal amplitudes and phases of forbes 1982 for the diurnal tide are roughly in agreement with the observed diurnal oscillation for the first four days of the experiment vertical variations in the observed diurnal phases are consistent with the results of forbes and hagan 1988 and may provide evidence of dissipation of the propagating 1 1 tidal mode the semidiurnal motion observed during this period is not well represented by the recent theoretical results for the amplitude and phase of the semidiurnal tide forbes and vial this issue neutral winds obtained during a geomagnetically active interval september 25 26 displayed a flow pattern that was significantly distorted from that observed during the preceding relatively quiet interval although the changes in the zonal winds throughout this active interval were consistent with the directionmore of the ion drag force at 115 km and above the variations in the meridional winds suggest that other forces such as pressure gradients driven by joule heating need to be considered to explain the observations less

zonal wave numbers of the summertime 2 day planetary wave observed in the mesosphere by eos aura microwave limb sounder 1 recent observations and theoretical work suggest that the 2 day planetary wave in the summertime mesosphere is composed of multiple superposed zonal wave numbers here we use eos aura microwave limb sounder mls temperature data to determine the component zonal wave numbers of the 2 day wave in the mesosphere at latitudes of 70 s to 70 n from 2004 to 2009 we consider the effect of aliasing between different wave numbers and note that significant aliasing can occur and result in spurious signals particularly at high latitudes in winter the seasonal evolution of the different wave numbers is investigated and found to be very different between the northern and southern hemispheres in both hemispheres the wave is dominated by westward traveling waves of zonal wave number 3 and 4 w3 and w4 however in the southern hemisphere the wave is dominated by the w3 component but in the northern hemisphere the w3 component is smaller and the w4 component is often of similar or larger amplitude a small amplitude westward traveling zonal wave number 2 w2 wave is also evident in both hemispheres in the northern hemisphere the w2 amplitudes never exceed 3 k the w3 amplitudes can reach 3 5 k and the w4 can be the largest component reaching amplitudes of 4 k in the southern hemisphere the w2 amplitudes can reach up to 3 5 k the w3 amplitudes can be much larger reaching 12 k and the w4 amplitudes are smaller than in the northern hemisphere in 4 out of 5 years not exceeding 3 k the northern hemisphere w4 can reach large amplitudes in august when the w3 is small which means that the late summer northern hemisphere quasi 2 day wave is usually a w4 oscillation rather than the familiar w3 in contrast in the southern hemisphere the w3 is often larger than the w4 around the summer solstice and there are no episodes observed where the wave becomes dominated by the w4 for an extended period of time a high degree of interannual variability is evident particularly in the southern hemisphere where the w3 peak amplitudes vary from 12 k in january 2006 to 3 k in january 2009 the height latitude structure of the w4 suggests that this wave is a 4 0 rossby gravity wave

a 130 year micro and macrofossil record from regeneration peat in former peasant peat pits in the peel the netherlands a palaeoecological study with agricultural and climatological implications abstract two pollen diagrams a macrofossil diagram and a microfossil diagram from regeneration peat in old peat pits in the peel a former raised bog area in the southern part of the netherlands are presented the pollen diagrams reveal the local and regional flora and vegetation history these diagrams are correlated in a detailed way with historical data concerning the economic history of the region in the past two centuries especially with respect to developments in agriculture and afforestation as shown in acreage curves of a number of cultivated plants the changes in local bog vegetation as shown in the micro and macrofossil diagrams are attributed to climatic changes and to the impact of human activities in the direct surroundings of the core peat accumulation appeared to be 240 490 g m 2 yr 1 in the period studied

global observations of 2 day wave coupling to the diurnal tide in a high altitude forecast assimilation system we examine wave components in a high altitude forecast assimilation system that arise from nonlinear interaction between the diurnal tide and the westward traveling quasi 2 day wave the process yields a westward traveling sum wave with zonal wavenumber 4 and a period of 16 hours and an eastward traveling difference wave with zonal wavenumber 2 and a period of 2 days while the eastward 2 day wave has been reported in satellite temperatures the westward 16 hour wave lies outside the nyquist limits of resolution of twice daily local time satellite sampling hourly output from a high altitude forecast assimilation model is used to diagnose the nonlinear quadriad a steady state primitive equation model forced by tide 2 day wave advection is used to intepret the nonlinear wave products the westward 16 hour wave maximizes in the midlatitude winter mesosphere and behaves like an inertia gravity wave the nonlinearly generated component of the eastward 2 day wave maximizes at high latitudes in the lower thermosphere and only weakly penetrates to low latitudes the 16 hour and the eastward 2 day waves are of comparable amplitude and alias to the same apparent frequency when viewed from a satellite perspective

intraseasonal and interannual variability of the quasi 2 day wave in the northern hemisphere summer mesosphere this study uses global synoptic meteorological fields from a high altitude data assimilation system to investigate the quasi 2 day wave q2dw and migrating diurnal tide during the northern hemisphere nh summers of 2007 2009 by applying a two dimensional fast fourier transform to meridional wind and temperature fields we identify q2dw source regions and diagnose propagation of q2dw activity into the upper mesosphere and lower thermosphere we find that the q2dw in nh summer is composed primarily of westward propagating zonal wave number 3 and wave number 4 components that originate within baroclinically unstable regions along the equatorward flank of the summer midlatitude easterly jet the amplitude of the wave number 3 q2dw tends to peak in july while the amplitude of the wave number 4 q2dw tends to peak in late june and again in early august the seasonal mean q2dw amplitudes are largest in 2009 when the amplitude of the migrating diurnal tide in the upper mesosphere near 30 n was relatively weak however there is no evidence of rapid amplification of the q2dw via nonlinear interaction with the diurnal tide instead variations of q2dw amplitudes during nh summer appear to be linked to variations in the strength and location of the mesospheric easterly jet from one summer to the next with a stronger jet producing larger q2dw amplitudes linear instability model calculations based on the assimilated wind fields indicate that the fastest growing modes are zonal wave numbers 3 and 4 with periods near 2 days that originate in the vicinity of the easterly jet

predicting the resistance profile of a spudcan penetrating sand overlying clay assessment of the risk of punch through failure of spudcan foundations on sand overlying clay requires prediction of the full penetration resistance profile from touchdown and through punch through to equilibrium of the vertical resistance at depth in the underlying clay layer this study uses the coupled eulerian lagrangian approach a large deformation finite element analysis method to model the complete penetration resistance profile of a spudcan on sand overlying clay the sand is modeled using the mohr coulomb model while the clay is modeled using a modified tresca model to account for strain softening the numerical method is then used to simulate a series of spudcan penetration tests performed in a geotechnical centrifuge on medium dense sand overlying clay the punch through behavior observed in the experiments is replicated and the penetration resistance profiles from numerical analyses are generally a reasonable match to the experimental measure ments the influences of the sand layer height to foundation diameter ratio sand clay interface shear strength and strength gradient in clay on the penetration resistance profiles are explored in a complementary parametric study the penetration resistance in the underlying clay layer is well predicted using a simple linear expression for the bearing capacity factor for the spudcan and underlying sand plug this expression is combined with an existing failure stress dependent model for predicting peak resistance to form a simplified method for prediction of the full penetration resistance profile this new method provides estimates of the vertical penetration that the spudcan will run during the punch through event it is validated against both medium dense and dense sand centrifuge tests

evidence for a traveling two day wave in the middle atmosphere evidence is presented for the existence of a wave number 3 westward traveling 2 day oscillation in the temperature measurements made by the nimbus 5 scr and nimbus 6 pmr instruments the wave has largest amplitude in the mesosphere at low latitudes of the summer hemisphere and has a markedly asymmetrical meridional structure it is suggested that the wave may be a free wave similar to the 5 day wave identified in nimbus 5 scr data by rodgers 1976 the vertical structure shows little phase tilt and a slight indication of an increase in amplitude with height

mesosphere thermosphere tidal coupling during the september 21 25 1987 ltcs 1 campaign the thermosphere ge 90 km is dynamically coupled to the mesophere and lower atmospheric regions by gravity waves tides and planetary waves which propagate upward from below and often undergo dissipation in the 80 to 150 km region this paper focuses on the mesosphere thermosphere coupling due to the solar semidiurnal atmospheric tide during the first lower thermosphere coupling study ltcs campaign interval of september 21 25 1987 during this period determinations of semidiurnal eastward u and northward v velocity components and temperature delta t are available within the 80 to 150 km region from a total of 13 incoherent scatter meteor and spaced antenna radars a new method is developed and reported here for assimilating such data sets into a self consistent global empirical description of the tidal dynamics between 80 and 150 km using a set of numerically generated hough mode extension hme functions for u v and delta t corresponding to the 2 2 2 3 2 4 and 2 5 semidiurnal tidal modes a least squares fit to the radar data is performed the fit results in a single complex normalizing factor for each hme from which globally continuous and internally consistent semidiurnal oscillations in u v and delta t as well as vertical velocity and density canmore be derived the quality of fit to these data from various height regions including both northern and southern hemispheres establishes the internal consistency between these measurements as well as the applicability of the method to future data sets the resulting empirical model reproduces the data significantly better than recent theoretical models suggesting use of the method for deriving tidal boundary conditions for thermospheric general circulation models less

the mid holocene ulmus decline at diss mere norfolk uk a year by year pollen stratigraphy from annual laminations 3 m of annually laminated sediments were recovered from a small steep sided lake diss mere norfolk uk in an 8 cm section known to include the mid holocene elm decline the laminae were sampl

thermospheric extensions of the classical expansion functions for semidiurnal tides solutions to the thermospheric tidal equations are described that define the extensions into the thermosphere of normalized wind and temperature structures associated with the 2 2 2 3 2 4 and 2 5 semidiurnal propagating tidal modes sample figures are presented that illustrate the degree of alteration of vertical structures with latitude and the change in horizontal shapes with height corresponding to semidiurnal oscillations in northerly westerly and vertical velocity and temperature in the thermosphere additional figures and tables covering the 80 to 400 km altitude region for five levels of solar activity at 6 latitude increments are available on microfiche for potential users the structures can be used to extend meteor wind 80 100 km and partial reflection drift 60 100 km measurements to heights above 100 km for consistency checks with tidal winds and temperatures from thomson scatter measurements at possibly different latitudes or to simultaneously fit data covering these height regions for modeling purposes supplementary figures and tables are available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20002 document j82 003 1 00 payment must accompany order

on the coupling between the lower and the upper thermosphere during the first lower thermosphere coupling study simultaneous observations of the neutral winds and temperatures and electron densities in the upper and lower thermosphere are presented the measurements were made at arecibo and millstone hill during the first lower thermosphere coupling study ltcs 1 campaign in september 1987 the observations show a great deal of day to day variability possibly due to the geomagnetic activity which occurred during the period storm effects are discernible in the data at low altitudes near 120 km even at low latitudes near 18 n theoretical simulations of the period were attempted by the national center for atmospheric research thermosphere ionosphere general circulation model a novel development was the use in the model of lower boundary conditions representative of the upward propagating semidiurnal tides based on the ltcs 1 mesosphere lower thermosphere observations the upward propagating diurnal 1 1 mode was also included in the model simulations of the low and mid latitudes did not substantially improve with the use of lower boundary conditions derived from the measurements the model was also unable to reproduce the observations in both the lower and upper thermosphere this may be partially due to the effects of geomagnetic activity on the atmospheric fields since the observational period included two intervals of geomagnetic disturbances in the lower thermosphere resolution of the discrepancies between the data and model predictions may require the extension of the model to lower altitudes at present the model predictions in the lower thermosphere are strongly dependent on the lower boundary conditions the model predicts that diurnal waves are not negligible in analysis of lower thermosphere data indeed near 100 km at the model location of arecibo the diurnal wave amplitudes of the meridional winds were predicted to be greater than the semidiurnal investigation of the model predictions awaits the development of techniques to obtain observations of at least 24 hours duration in the lower thermosphere and the extension of the theoretical models to lower altitudes

dating raised bogs new aspects of ams 14c wiggle matching a reservoir effect and climatic change abstract high resolution ams dating of holocene raised bog deposits engbertsdijksvenen the netherlands shows natural 14c variations wiggles which can be matched with the dendrochronological calibration curve comparison of our results with other conventionally dated peat cores and the 14c record shows an unexpected and as yet unreported reservoir effect and a marked and sudden wetting of the bog surfaces coinciding with the advent of a sporer type solar minimum the homeric minimum the potential of ams dating to vastly improve the accuracy of holocene chronologies is demonstrated

the 2 day wave in the middle atmosphere observations and theory a recurrent global scale 2 day oscillation in the middle atmosphere is well documented in a variety of data sources meteor wind partial reflection satellite and rocketsonde the observed period is almost invariably near 2 1 days and the zonal structure has been established as a westward propagating wave number 3 mode observations also indicate that the meridional wind component maximizes near the equator and dominates the wind field at low latitudes these features suggest the disturbance s identification with the wave number 3 rossby gravity normal mode of a windless isothermal atmosphere such modes are found to exist largely independent of the mean fields the eigenperiods are only modestly altered by mean wind variations on the lowest three scale heights and the influence on the mode structure is local the vertical growth of amplitude is enhanced in regions of weak westerly wind relative to the wave and equatorward temperature gradient while the vertical growth rate is retarded and amplitudes may even decay in regions of strong westerlies or poleward temperature gradient in realistic mean fields the third rossby gravity mode has magnified responses very near 2 25 days in both equinox and solstice conditions the horizontal structure remains largely intact in the lowest levels however considerable asymmetry is introduced in the solstice upper stratosphere and mesosphere by the magnified vertical growth of amplitude in the summer hemisphere the latter results from the moderate easterlies and equatorward temperature gradient characteristic of the region as for the simple eigenstructure the meridional wind component in this region maximizes near the equator and dominates the wind field up to mid latitudes

coordinated incoherent scatter radar observations of the semidiurnal tide in the lower thermosphere the incoherent scatter radars at arecibo 18 3 degree n millstone hill 42 6 degree n and sondrestrom 67 degree n simultaneously observed the thermal structure and dynamics of the earth s lower thermosphere during the period september 21 25 1987 as part of the lower thermosphere coupling study plasma spectral measurements were used to derive ion temperatures and horizontal neutral wind velocities in the altitude region 90 140 km and semidiurnal harmonics were determined from the data sets the daily mean temperatures were found to be within 40 degree k at the three stations and the largest semidiurnal temperature amplitudes exceeding 70 degree k above 115 km were recorded at arecibo mean winds were about plus minus 30 m s at most altitudes shifting from eastward to westward directions at 115 km and the semidiurnal amplitudes were in the range 20 70 m s phase variations with height reveal reasonable consistency among the three stations within 3 4 hours and indicate an average vertical wavelength of 40 70 km however a strong variation is seen in the vertical structure in the 110 to 130 km region suggesting the presence of different tidal modes comparison with the most current tidal propagation model by forbes and vial this issue indicates that the model tends to underestimate the amplitudes for this time period particularlymore above 110 km by virtue of the latitudinal distribution of the three radars their coordinated observations of the lower thermosphere serve to constrain numerical models and improve their understanding of this important yet complex region of the atmosphere less

the quasi 2 day wave activities during 2007 austral summer period as revealed by whole atmosphere community climate model the quasi 2 day wave qtdw observed during 2007 austral summer period is well reproduced in an reanalysis produced by the data assimilation version of the whole atmosphere community climate model waccm data assimilation research testbed developed at national center for atmospheric research ncar it is found that the qtdw peaked 3 times from january to february but with different zonal wave numbers diagnostic analysis shows that the mean flow instabilities refractive index and critical layers of qtdws are fundamental for their propagation and amplification and thus the temporal variations of the background wind are responsible for the different wave number structures at different times the westward propagating wave number 2 mode w2 grew and maximized in the first half of january when the mean flow instabilities related to the summer easterly jet were enclosed by the critical layers of the westward propagating wave number 3 w3 and wave number 4 w4 modes this prevented w3 and w4 from approaching and extracting energy from the unstable region the w2 decayed rapidly thereafter due to the recession of critical layer and thus the lack of additional amplification by the mean flow instability the w3 peaked in late january when the instabilities were still encircled by the critical layer of w4 the attenuation of w3 afterward was also due to the disappearance of critical layer and thus the lack of overreflection finally the w4 peaked in late february when both the instability and critical layer were appropriate

coordinated global radar observations of tidal and planetary waves in the mesosphere and lower thermosphere during january 20 30 1993 a multi instrument global campaign involving incoherent scatter medium frequency and meteor wind radars was conducted during the period of january 20 30 1993 to study the dynamics of the mesosphere and lower thermosphere data obtained from 15 radar stations covering a wide latitude range have been used to determine the global distribution of planetary and tidal waves during this 10 day campaign spectral analysis of the neutral winds measured by the radars in the altitude range from 80 to 130 km indicates the existence of a strong 48 hour wave near 90 km at latitudes between 40 n and 40 s that is present up to 108 km at 18 n the semidiurnal tide is large at middle and high latitudes near 90 km and is predominant above 110 km while the diurnal tide is observed to be particularly important in the upper mesosphere near 40 latitude a least squares fit to the radar data is performed to obtain the amplitudes and phases of the tidal and 48 hour waves comparison with national center for atmospheric research thermosphere ionosphere mesosphere general circulation model shows that the predictions from the model agree reasonably well with the observed global morphology of tidal wave amplitudes

on modeling migrating solar tides recent updates and extensions to a steady state two dimensional linearized model of global scale atmospheric waves have facilitated improved calculations of the subset of those waves which are subharmonics of a solar day and propagate with the apparent motion of the sun the model improvements are briefly described and some updated predictions of the migrating solar diurnal component are highlighted the latter represent the first numerical modeling effort to examine the seasonal variability of the migrating diurnal harmonic as it propagates into the mesosphere and lower thermosphere

observations of the quasi two day wave in the middle and lower atmosphere over christmas island we present analyses of data collected at christmas island in the mesosphere and lower thermosphere using a meteor echo detection and collection system medac in addition to data collected in the troposphere and lower stratosphere using a clear air stratosphere troposphere st radar these data which provide 5 years of semicontinuous horizontal wind velocity estimates are analyzed to determine the temporal structure of the quasi two day wave in the middle and lower atmosphere our results show the presence of strong wave activity in the middle atmosphere during late january and early february as well as a secondary maxima in june august for each of the years we have data however the magnitude and duration of the wave events observed in late january and early february exhibit interannual variability

two day wave traveling westward with wave number 1 during the sudden stratospheric warming in january 2017 quasi two day wave qtdw propagating westward with wavenumber number 1 w1 in january 2017 is studied using global temperature observed by saber and wind observed by a meteor radar at fuke china 19 0on 109 8oe the amplitude of w1 significantly enhances during january 2017 when two stratospheric warming events occur the temperature perturbation of w1 reaches maximum amplitude of more than 6k at latitude 15o around 84 km and 95 km the structure of temperature w1 is symmetric with regard to the equator the temporal variation of w1 is consistent with the stationary planetary wave with wavenumber 2 spw2 but contrary to the qtdw propagating westward with wavenumber 3 w3 when spw2 is large during two sudden stratospheric warming events energy transfers from w3 to w1 two bursts of the two day wave in meridional wind observed by the meteor radar are just corresponding to the local maxima of w3 and w1 respectively we conclude that during january 2017 w1 is generated by the nonlinear interaction between spw2 and w3 spw2 which is modulated by the quasi 16 day perturbation in the stratosphere plays a key role in the energy transmission from w3 to w1 and it is responsible for the 16 day variation of w1

observations of the quasi 2 day wave from the high resolution doppler imager on uars a strong westward traveling oscillation with a period of 2 days and zonal wave number 3 is observed in the mesospheric and lower thermospheric winds from the high resolution doppler imager on the upper atmosphere research satellite the important events happen in january july and september october of which the occurrence in january is the strongest with an amplitude over 60ms 1 detailed analyses for the periods of january 1992 and january 1993 reveal a cause and effect relationship in the wave developing process at 95km the global structures of the wave amplitude and phase are also presented

bayesian prediction of peak resistance of a spudcan penetrating sand over clay assessing the potential for a punch through failure during spudcan installation in sand over clay is crucial for reducing risk in the operations of mobile jack up platforms typically in the offsh

short term variability in the migrating diurnal tide caused by interactions with the quasi 2 day wave 1 the migrating diurnal tide is one of the dominant dynamical features in the low latitudes of the earth s mesosphere and lower thermosphere mlt region representing the atmospheric response to the largest component of solar forcing ground based observations of the tide have resolved short term variations attributed to nonlinear interactions between the tide and planetary waves that are also in the region using the ncar thermosphere ionosphere mesosphere electrodynamics general circulation model time gcm we simulate a quasi 2 day wave qtdw event under late january conditions in this case sideband sum and difference child waves are resolved indicating that a nonlinear interaction is occurring between the qtdw and the tide the migrating diurnal tide in the mlt displays local amplitude decreases of 20 40 as well as a shortening of vertical wavelength by roughly 4 km examining the physical mechanisms driving the interaction nonlinear advection is found to result in amplification of the tide in some regions and damping in others manifesting as increased smoothing of the tidal structure when the qtdw is present in the mlt additionally the qtdw also enhances the easterly summer mean wind jet that can also account for changes in tidal amplitude and vertical wavelength we find that qtdw induced background atmosphere changes in time gcm can drive tidal variability at levels greater than nonlinear advection a possibility not previously considered

lower thermosphere coupling study comparison of observations with predictions of the university college london sheffield thermosphere ionosphere model during the first lower thermosphere coupling study ltcs september 21 25 1987 data were recorded from the incoherent scatter radar sites at eiscat millstone hill sondrestrom and arecibo these experimental facilities measured ionospheric parameters ne te ti and plasma velocity in the e and the f regions which have been used to determine the e region neutral wind and infer the neutral temperature in the height range 100 150 km propagating tides are clearly visible in some of the parameters and the latitude structure and phase variations with height indicate the presence of at least the 2 2 and 2 4 global tidal hough modes the influence of geomagnetic forcing is also clearly present at high latitudes the university college london sheffield university three dimensional coupled thermosphere ionosphere model has been used to simulate this period of observation by imposing tidal forcing at the lower boundary and magnetospheric forcing at high latitudes in an attempt to interpret and understand the experimental data model simulations are able to predict where the signature of a particular tidal mode is likely to be observed in the respective responses of the temperature and wind structure the numerical simulations predict the range of observed tidal amplitudes at mid and high latitudes providedmore the tidal forcing functions imposed near the lower boundary of the model are larger 400 m geopotential height variation than those inferred from linear tidal models less

bearing capacity of plane strain footings on layered soils a study has been carried out of the bearing capacity of sand layers overlying clay soils for the case where the thickness of the sand layer is comparable to the width of a rigid foundation placed on the soil surface a review of previous work is given and a discussion is presented of the dimensionless groups that govern the behaviour of this type of foundation a parametric study is carried out using both finite element and finite difference methods this study is based on the use of soil parameters obtained from an assessment of the range of values that might be expected to be appropriate for full scale structures the results of the parametric study are used to illustrate the mechanics of the system and also to develop charts that may be used directly in design in particular the results illustrate that the shear strength of the clay has an important influence on the mechanisms of load spread within the fill resume lion a roaliso une otude sur la capacito portante de couches de sable reposant sur des sols argileux pour le cas oo liopaisseur de la couche de sable est comparable la largeur diune fondation rigide posoe sur la surface du sol lion prosente une revue des travaux antorieurs et une discussion sur les groupes sans dimension qui rogissent le comportement de ce type de fondation une otude paramotrique est roalisoe en utilisant les mothodes tant des oloments finis que des difforences finies cette otude est fondoe sur liutilisation des paramtres de sols obtenus en partant de liovaluation de la plage des valeurs que lion pourrait siattendre trouver dans des structures pleine ochelle les rosultats de liotude paramotrique ont oto utilisos pour illustrer le mocanisme du systme et aussi pour dovelopper des abaques qui peuvent tre utilisoes directement dans la conception en particulier les rosultats illustrent que la rosistance au cisaillement de liargile a une influence importante sur les mocanismes de ropartition de la charge liintorieur du remblai mots clos capacito portante sols multicouches analyse numorique traduit par la rodaction

stability of a strip foundation on a sand embankment over mine tailings earthmoving equipment working on a progressively placed cover layer over mine tailings often experiences catastrophic rotational or punch through failure with potential for loss of the equipment and harm to the operator although the performance of foundations on a homogeneous sand or clay slope is routinely calculated and investigated comprehensive investigation of a thin stronger slope overlying a softer layer is scarce this paper reports the results of centrifuge model tests undertaken to provide insight into strip foundation behaviour during penetration with freedom in horizontal displacement and rotation adjacent to a sand embankment cover layer into a weaker clay layer representing mine tailings variables were the set back of the edge of the foundation from the crest of the slope the height of the slope relative to the foundation size and the normalised strength of the lower clay layer soil movement was captured continuously by a digital camera and subsequently quantified throu

the 6 5 day wave and its seasonal variability in the middle and upper atmosphere 1 the zonal wave number 1 planetary wave of period near 6 5 days is a robust feature in the mesosphere and lower thermosphere mlt region with prominent seasonal variability as revealed by ground based and satellite observations this wave and its seasonal variability are well reproduced in a recent one model year run of the national center for atmospheric research thermosphere ionosphere mesosphere electrodynamics general circulation model time gcm with its lower boundary specified according to the national centers for environmental prediction analysis year 1993 wavelet analysis of the model output shows that in the mlt region the wave maximizes before and after the equinoxes and minimizes at solstices the wave amplitudes at the equinoxes are smaller than the peaks before and after but are still larger than the wave amplitudes at solstices however at the lower boundary near 30 km the wave peaks are predominantly between fall and the following spring by examining the episodes of maximum and minimum wave amplitude and by conducting additional control experiments using the time gcm the structure of this planetary wave and the factors determining the wave characteristics and seasonal variability are studied in detail it is found that the wave source mean wind structure instability and the critical layers of the wave can all affect the wave response in the mlt region and can have a strong seasonal dependence before and after equinox the wave follows the waveguide and propagates from the stratosphere to the summer mesosphere mesopause where it may amplify due to baroclinic barotropic instability such instability is usually absent from the equinoctial atmosphere so that there is no wave amplification at equinox at solstice the wave decays significantly when propagating away from its winter source due to the strong eastward winter stratospheric jet in the summer side the westward jet is also strong and the meridional and vertical extension of the critical layer of the wave is large enough to enclose the instability in the summer mesosphere mesopause at middle to high latitudes the wave is thus reflected away and prevented from reaching and amplifying at the unstable region the seasonal variation of the quasi two day wave which has zonal phase speed similar to the 6 5 day wave is also studied using similar diagnostics it is further shown that within certain seasonal window periods the variability in the mlt especially the summer mlt may closely track the lower atmospheric variability associated with these waves

pollen percolation rates in euroamerican era cultural deposits in the northeastern united states abstract dimbleby s the palynology of archaeological sites new york academic press 1985 p 3 data from forested sites indicate that pollen percolates downward in soils at the rate of 1 cm in c 30 years data from archaeological sites and former agricultural fields in the northeastern united states suggest that pollen percolates downward at the faster rate of c 1 cm in 4 2 years in soils not sheltered by woodland this in turn suggests that the pollen sequences of former non forest soils preserved by rapid natural and cultural burial record much shorter periods of time than previously believed

vegetation history and environmental development since ca 6000 cal yr bp in and around ispani 2 kolkheti lowlands georgia abstract the kolkheti lowlands of western georgia have a unique vegetation and a rich cultural history palynological and macrofossil analysis accompanied by ams 14c dates of the deposits of the ispani 2 mire near kobuleti allow the reconstruction of regional vegetation environmental history and local peatland development within the context of black sea level and cultural changes comparison of two adjacent peatland cores confirms spatial differences in wetland development prior to 5400 cal yr bp the ispani basin was a floodplain of an active river system where overbank deposits with fluvially transported castanea pollen were deposited subsequently a lake or lagoon developed in which reeds expanded these were succeeded by herb rich open alder carrs after 1900 cal yr bp carpinus and fagus expanded on the dry grounds where formerly quercus was more abundant also castanea declined local reedbeds that burned regularly succeeded the alder carr after 1000 cal yr bp a percolation bog developed resulting in the formation of 4 m of loose porous and largely undecomposed sphagnum austinii peat with molinia roots the upper 50 cm of the analysed section show extensive human impact on the landscape during the 20th century

satellite observations of mean winds and tides in the lower thermosphere 1 aliasing and sampling issues 1 the canadian middle atmosphere model a general circulation model extending up to 200 km is used to analyze the impact of aliasing and data gaps on satellite observations of zonal mean winds and migrating tides in the lower thermosphere focus is placed on measurements from the wind imaging interferometer windii mock data sets are constructed by sampling daily zonal mean and migrating tides from the model like the satellite previously unverified assumptions that satellite observations of the zonal mean zonal winds and the meridional component of the diurnal tide winds are largely unaffected by aliasing are confirmed of the two the meridional component of the diurnal tide is more robust the amplitude of the zonal component of the diurnal tide is not strongly affected by aliasing tidal phase is nearly unaffected gaps in the windii data do not adversely affect the results provided sufficient local time coverage is available the analysis suggests that more subtle features in the windii observations such as the tidally driven cell like structures in the zonal mean meridional wind at low latitudes may be observable issues pertaining to the sampling interval and the use of daytime only data are also addressed sampling every second or third day provides nearly as good results as sampling every day and that using daytime only data results in substantial biases in the zonal mean zonal winds in the lower thermosphere the latter underscores the importance of the accurate removal of the migrating diurnal tide from climatologies generated from daytime only satellite data

lunar tidal winds at adelaide and saskatoon at 80 to 100 km heights 1985 1990 winds data from the two sites were analyzed for lunar tides in 2 year groups the variation with height of the phase and amplitude of the tide showed considerable variability from year to year yet in general seasonal variations at particular heights were similar to those determined previously phases of the tide at the two sites were compared in order to estimate whether the tide was symmetric or antisymmetric for this purpose it was found necessary to use only 1 year data sets the predominance of symmetric tides during solstice months and antisymmetric tides at the equinox came as a surprise yet the result is in broad agreement with phase relations of the lunar geomagnetic tide

in search of finiteness the limits of fine resolution palynology of sphagnum peat high resolution analysis of ombrogenous peats often reveals pollen frequencies that change markedly from one sample to the next indicating limited postdepositional mixing this raises the question whether with sufficiently thin samples seasonal differences in pollen deposition can be observed seasonal resolution in peat would provide a dating technique with an accuracy similar to that of other annually banded archives to study the limits of temporal resolution contiguous 0 5 mm thick slices of slightly humified sphagnum section cuspidata peat were palynologically analysed no seasonal patterns in the pollen stratigraphy could be observed this is ascribed to the mixing of pollen grains as a result of small scaled vertical water movements and to the horizontal mode of shoot layering in the sphagnum species the latter process may also be the cause of a smoothed annual signal because of the absence of seasonal differentiation the palynological distinction of annual peat layers is not feasible

the quasi two day wave observed in the equatorial middle atmosphere an oscillation with a period near 2 days is found in radar wind measurements made in the upper mesosphere and lower thermosphere at christmas island 2 n 157 w in the central pacific the oscillation is particularly strong in the meridional wind component and seems to be present almost continuously ir the 80 100 km height region although some intermittency is evident wave amplitudes are especially large about one month after the solstices in july august and in january february at times coincident with large 2 day wave events in the summer mesosphere at extratropical latitudes power spectral and complex demodulation techniques are used to study the amplitude and frequency variations of the oscillation as a function of height and time downward phase propagation is found consistent with upward energy propagation and with a vertical wavelength of about 70 km an unusual feature is a shift in wave period from near 50 hours in july august to 48 hours in january february when the largest amplitudes up to 45 m s 1 are observed a 16 hour oscillation is also found at times when the 2 day wave amplitudes are largest the observations are consistent with the 2 day wave being a manifestation of the 3 0 rossby gravity normal mode another weaker oscillation is also found in the meridional wind field at a period near 44 hours this oscillation may be due to the 2 0 normal mode

centrifuge model study of spudcan penetration in sand overlying clay a series of centrifuge model tests has been conducted to investigate the bearing resistance of spudcan foundations of offshore jack up rigs in sand overlying normally consolidated clay the spudcan bearing resistance profiles measured in most of the tests recorded a peak resistance at a shallow depth within the upper sand layer followed by an abrupt post peak reduction in resistance causing the spudcan to plunge into the underlying soft clay this phenomenon is commonly termed as spudcan punch through hazard which potentially leads to severe structural damage of jack up rigs in the field the centrifuge test results revealed that the ratio of upper sand layer thickness over spudcan diameter and the ratio of bearing resistance between the upper sand and underlying clay affect the development of spudcan bearing resistance the limitations of existing design methods which were derived for the ultimate bearing capacity of pre embedded shallow foundation to assess the spudcan bearing resistance depth prof

semidiurnal tidal climatology of the e region theoretical predictions of global monthly and seasonally averaged semidiurnal temperatures and winds between 80 and 150 km are presented and compared with seasonal means from measurements at the arecibo chatanika millstone hill and sondrestrom incoherent scatter radars the model values above 100 km are obtained by utilizing a set of tabulated hough mode extension functions to extrapolate the 2 2 2 3 2 4 and 2 5 propagating tidal modes at 100 km from a spectral model not valid in the e region due to the way molecular dissipation is parameterized to higher altitudes and by superimposing a component driven by in situ excitation important mainly above 140 km the monthly simulations demonstrate the close coupling that exists between seasonal and latitudinal structures and argue for an observational program emphasizing adequate seasonal and latitudinal coverage despite constraints imposed by the distributions of existing data with respect to month and year comparisons with the model reveal several trends that appear to be real 1 the model amplitudes are usually 20 50 smaller than those observed 2 vertical wavelengths are well predicted by the model but model phases generally lead the observations at middle and low latitudes by approximately 2 3 hours at all heights for both winds and temperatures 3 semidiurnal temperatures at middle and low latitudes in both the observations and model indicate significant seasonal changes in the phase of the temperature oscillation but not in the winds and 4 the seasonal trends in the model and observations are consistent with summer leading winter at millstone hill while the reverse is true at arecibo the sources of the absolute amplitude and phase discrepancies in the model which are probably connected with the adopted mean wind and thermal excitation specifications need to be investigated in addition a concerted effort must be made within the coupling energetics and dynamics of atmospheric regions cedar program to better delineate the seasonal latitudinal thermal structure and dynamics of the e region following the example of the extensive f region observational data base which has been accumulated over the last decade

subionospheric vlf signal perturbations possibly related to earthquakes a likely vlf subionospheric signal effect related to seismic activity was first reported by hayakawa et al 1996a b in association with the great kobe earthquake we have analyzed similar data during periods around 10 other great earthquakes magnitude m 6 in order to understand the main features of such an effect the following characteristics emerged from our analysis the effect appears as a transient oscillation with a 5 to 10 day period which is initiated a few days before a large earthquake and decays over a few days to weeks after it it is mainly related to crustal earthquakes it appears when resonant atmospheric oscillations with periods in a range of 5 11 days exist before the earthquake the seismic influence on the vlf signal is probably explained by the generation of long period gravity waves during the earthquake process and their intensification at heights of 70 90 km

14c ams wiggle matching of raised bog deposits and models of peat accumulation abstract high resolution accelerator mass spectrometer ams 14 c dates of selected plant macrofossils from the raised bog engbertsdijksvenen eastern netherlands show century scale wiggles analogous to the radiocarbon calibration curve we used three relative time scales viz based on depth mass and pollen concentration respectively to match the peat ams dates to the calibration curve this procedure is repeated for one conventionally dated core for each relative time scale realistic confidence intervals are calculated depth appears to be the best time scale for certain stratigraphical units of a core this justifies using depth for wiggle matching conventionally dated mire cores published by others even when 14 c errors are larger our evidence shows four major sources of 14 c variation for mire deposits compared to treerings 1 dating error due to sample composition this includes a reservoir effect demonstrated for many bulk peat samples 2 hiatuses causing a sudden leap of peat 14 c age 3 changing accumulation rates apparent from a break in the slope of the peat 14 c ages 4 sampling error these results shed doubt on the assumed continuities in theoretical peat accumulation models both mire stratigraphy and changing accumulation rates can be explained in qualitative hydrological terms more evidence for a previously discovered reservoir effect in bog deposits is presented though the physical biological mechanisms remain uncertain

extraction response of skirted foundations and a spudcan on sand over clay deposits this paper presents a comparison of extraction resistance between spudcan and skirted foundations in sand over clay deposits a series of centrifuge model tests was undertaken on a spudcan and two skirted foundations varying the length of the skirt relative to the foundation diameter the thickness of the sand layer was also varied to cover a range of practical interest it was found that the ultimate breakout forces of the spudcan and sealed skirted foundations in the sand over clay deposits are lower than that of a spudcan in a single layer clay deposit on the sand over clay deposits when the skirted foundations are sealed the breakout forces are 60 61 higher than that of the spudcan however when the skirted foundations are vented this difference becomes minimal regardless of the skirt length and the effective sand layer thickness beneath the foundation with the height of the sand plug left in the clay layer being similar to the thickness of the sand layer

atmospheric tide 2 the solar and lunar semidiurnal components solar and lunar semidiurnal wind and temperature oscillations from the surface to 400 km are simulated for average solar activity conditions utilizing the numerical tidal model described in part 1 hough mode decomposition of the solstitial solar semidiurnal tide excited by h2o and o3 insolation absorption below 80 km indicates that it is characterized by a predominance of 2 2 below 60 km about equal contributions of 2 2 2 3 and 2 4 between 70 and 90 km mostly 2 4 with some 2 5 and 2 2 between 90 and 120 km and a predominance of 2 2 above 140 km with secondary contributions from 2 3 and 2 5 the solstitial lunar semidiurnal tide is characterized by a predominance of 2 2 below 70 km 2 4 with secondary contributions from 2 2 2 3 and 2 5 between 80 and 110 km and by 2 2 with a fairly strong secondary contribution from 2 3 above 120 km similar descriptions for both the solar and lunar oscillations apply at equinox except that the asymmetric 2 3 and 2 5 modes are absent relative to the solar component lunar temperature and wind amplitudes are sufficiently large 20 in the lower and upper thermosphere to account for some of the observed variability previously attributed to the solar tide amplitudes of the 2 4 and 2 5 modes above 100 km are significantly affected by mesospheric eddy diffusion coefficients in excess of 2 106 cm s 1 the total solar semidiurnal exospheric temperature oscillation for average solar conditions ranges from 10 20 k poleward of 40 n to 40 60 k equatorward of 30 n and has its origin in three sources of excitation all of comparable importance 1 euv solar radiation absorption in the lower thermosphere 100 200 km 2 in situ momentum coupling due to the interaction of diurnal winds and diurnally varying ion drag and 3 tides propagating upwards from below 100 km in addition the calculations are compared with rocket meteor radar partial reflection thomson scatter and satellite data to evaluate the consistency of the model with observations

all age depth models are wrong but how badly the uncertainty and error associated with fitted age depth models were investigated by fitting a range of models to sets of simulated radiocarbon dates based on varved sediments and comparing the modelled relationship with the varve timescale with large numbers of dates cubic smooth splines out perform other models with few dates no model reliably provides a good fit to reality and calculated confidence intervals are over optimistic c 2003 elsevier ltd all rights reserved

numerical investigation of bearing capacity due to spudcan penetration in sand overlying clay numerical studies were carried out to investigate the bearing capacity of spudcan foundations of offshore jack up rigs in sand overlying normally consolidated clay by using the coupled eulerian lag

can rapidly accumulating holocene peat profiles provide sub decadal resolution proxy climate data to test the potential for developing sub decadal resolution records of ombrotrophic bog surface wetness bsw selected abrupt climate events were identified in cores from four sites in north west europe and time slices over each event were investigated at 2 5 mm resolution using peat humification testate amoeba and plant macrofossil analyses age depth models based on radiocarbon spheroidal carbonaceous particle and tephra dates were applied and the error in these models was used to determine the effective temporal sampling resolution which in most cases was sub decadal fine resolution results revealed some inconsistencies in the co variability of individual proxies and there was a lack of correspondence between some results from adjacent cores however we found evidence of abrupt shifts in bsw occurring over ca 5 20 years indicating a more rapid proxy response than identified in previous research to maximize potential temporal resolution and produce reliable sub decadal bsw data in future research we recommended that peat based studies should obtain the best possible chronological control focus on sites with high species diversity and rapid accumulation rates and perform replicate coring or use open peat sections where the stratigraphy can be clearly seen to assess intra site differences in microtopography site specific factors should be a primary consideration in the selection of sites for future fine resolution research

improved prediction of spudcan penetration resistance by an observation optimized model abstractthe prediction models of penetration resistances of spudcan footings on sand overlying clay have been established by extensive centrifuge tests and large deformation numerical simulations

improving the time control of the subboreal subatlantic transition in a czech peat sequence by 14c wiggle matching to achieve an optimal time control for a late subboreal to early subatlantic peat sequence from pancavska louka in the czech republic different strategies are applied to convert a series of radiocarbon dates into a calendar time scale the methods of selection and preparation of the samples for ams 14c dating are presented the results of calibrating single radiocarbon dates are compared with a 14c wiggle match strategy as the accumulation rate of the peat was not constant the concentrations of arboreal pollen are used to estimate the accumulation rate changes and to correct for these changes the resulting time control represents the best solution for this peat sequence with the methods currently available

two day wave structure and mean flow interactions observed by radar and high resolution doppler imager data obtained with four mf and meteor radars at equatorial and subtropical sites and with the high resolution doppler imager hrdi instrument aboard the uars satellite were used to examine the structure wave mean flow interactions and potential sources of the 2 day wave in the middle atmosphere during three southern hemisphere summers the three wave events were highly transient having typical durations of 20 to 30 days and exhibiting modulation at shorter periods temporal variations were found to exhibit good correlations between radar and hrdi data radar and hrdi data were used to estimate those components of the eliassen palm flux that could be assessed with these data meridional fluxes of momentum and heat were computed using hrdi data and agree reasonably with the momentum fluxes computed from radar data at discrete locations these fluxes were found to exhibit consistent latitudinal structures each year suggesting systematic wave excitation and wave mean flow interactions meridional momentum flux gradients were seen to be anticorrelated with zonal wind accelerations in a manner consistent with wave forcing of the large scale circulation the apparent wave mean flow interactions suggest that the 2 day wave could be a transient response to baroclinic instability of the summer hemisphere mesospheric jet a calculation of the meridional gradient of quasi geostrophic potential vorticity using hrdi winds and the cospar international reference atmosphere cira 1986 temperatures exhibits a region of instability in the lower and middle mesosphere extending into subtropical latitudes and provides additional evidence of a possible source of this motion via baroclinic instability of the summer hemisphere jet structure

revealing the bearing capacity mechanisms of a penetrating spudcan through sand overlying clay the safe and economic use of mobile jack up structures is still hindered by limited understanding of the installation of their large conical spudcan footings in layered sand over clay sites this paper addresses this by detailing experimentally observed bearing failure modes induced during the penetration of a spudcan through a layer of sand into underlying normally consolidated clay digital images were captured continuously by installing a half spudcan against a transparent window and analysed using a particle image velocimetry technique coupled with close range photogrammetry correction as the experiments were performed in a geotechnical centrifuge the observed mechanisms occurred in stress conditions of similar magnitude to the offshore case the experimental evidence provides a failure modes at different spudcan penetration depths b the transitional failure mechanism at the event of peak bearing resistance and c the changes in overall failure mechanism due to varying geometric and streng

dynamics of the equatorial mesosphere first results with a new generation partial reflection radar the first observations of mesospheric winds made between january august 1990 with an mf partial reflection radar located on christmas island 2 n 157 w in the central pacific are described the mean zonal winds are in general westward but show clear evidence for a wave driven circulation power spectral studies indicate that waves are present over a wide range of periods ultra fast kelvin waves are especially evident in january march with peak amplitudes 20 ms 1 and intrinsic phase speeds of 150 ms 1 indicated the kelvin waves are estimated to contribute an eastward acceleration of up to 10 ms 1 day 1 gravity wave amplitudes are also found to be almost as large as those observed at mid latitude sites which suggests that convection is a major source of gravity wave activity

assessing the punch through hazard of a spudcan on sand overlying clay a complete analytical method to describe the full load penetration resistance profile of a mobile jack up spudcan footing penetrating a sand over clay stratigraphy is described it is based on both large deformation finite element analyses and geotechnical centrifuge experiments the coupled eulerian lagrangian cel approach is used to accommodate the large deformations of a spudcan footing penetrating sand overlying clay modified mohr coulomb and tresca models describe the sand and clay behaviour with modifications accounting for the effects of strain softening on the response of the soil the cel results are shown to match centrifuge tests well allowing the numerical study to be extended parametrically and with confidence to cover the range of layer geometries sand relative densities and footing shapes that are of practical interest to offshore jack ups the results are used to a assess the performance of an existing model to predict the peak resistance in the sand layer extending its range of

tidal signatures in temperature data from crista 1 mission temperature measurements in the stratosphere and mesosphere were taken during the first cryogenic infrared spectrometers and telescopes for the atmosphere crista 1 mission using co2 emissions these measurements range from 13 to close to 100 km and individual temperature measurements have a precision of 1 k the crista orbit was circular at an inclination of 57 so local time variations during the 7 day mission were small for a given latitude and orbit leg zonal averages of the data show significant structure in the vertical and as a function of latitude temperature differences between the zonal mean data from the ascending and descending portions of the orbit are of the form expected from the diurnal tide the maximum zonal mean difference is 20 k and occurs over the equator at an altitude of 75 km zonal variations in the temperature difference indicate that the tidal amplitude is not uniform at all longitudes at the equator the maximum amplitude 30 k appears over the african sector and the minimum 10 k over the pacific sector this variation is most likely a nonmigrating wavenumber 2 diurnal tide although other less plausible possibilities exist to facilitate comparisons with model results the temperature variations are converted to equivalent vertical displacements assuming the tidal motions are adiabatic such an approach is appropriate in the mesosphere where diurnal variations due to radiative effects are small and reduces the dependence of the measured temperature amplitude on the background temperature profile equivalent vertical displacements are also calculated using results from the global scale wave model for the most part the model results and observations are in excellent qualitative and good quantitative agreement from the tropopause to the mesopause however the observed vertical wavelength is smaller and its amplitude in terms of equivalent displacement is smaller in the upper mesosphere than that in the model the decrease in amplitude is consistent with that expected from the transition from equinox to solstice conditions

geotechnical model tests of bearing capacity problems in a centrifuge the paper introduces the centrifuge research activities undertaken by the soil mechanics group at the tokyo institute of technology during the past ten years and focuses on the bearing capacity of shallow foundations in dense sand a series of experiments was conducted to explain de beer s scale effect and to investigate the effect of the roughness of the footing base the anisotropy in dense sand the embedment of footings and the effect of slopes near footings measurements of deformations were attempted during loading tests using an automatic tracking device developed by the group and radiographs were used to detect slip lines progressive failure was found to be more marked for wider footings which is considered to be the main cause of the scale effect the smaller bearing capacity factors occur for wider footings it is shown that strong anisotropy in dense sand is also responsible for the scale effect a smooth footing made by lubricating the base with a greased membrane yielded two symmetrical w

a numerical simulation of the two day wave near the stratopause abstract the middle atmosphere version of the national center for atmospheric research community climate model 2 maccm2 mechanistic model is used to simulate several aspects of the observed two day wave near the stratopause and its possible connection with inertial instability model experiments show that for a prescribed initial wind condition with strong horizontal wind variation in the tropics inertial instability can trigger the two day wave an increase in horizontal wind curvature fostered by inertial instability circulation barotropically destabilizes the easterly jet in low summer latitudes and allows first the growth of the wavenumber 4 and then the wavenumber 3 component of the two day wave near the stratopause the two day wave eliassen palm flux is directed equatorward away from the wave s critical line source and westerly momentum is transported into the easterly jet core by the wave while much of the wavenumber 4 energy is confined near the stratopause the wavenumber 3 energy can prop

bearing capacity on sand overlying clay soils a simplified conceptual model the derivation of a new conceptual model for predicting the peak penetration resistance of circular footings installed vertically into sand overlying soft clay is presented in this paper based on visualisation experiments and finite element analyses a failure mechanism of a frustum of sand being forced into the underlying clay with the outer angle reflecting the dilation in the sand is assumed the analytical basis of the new conceptual model follows the approach for silo analysis and takes into account the stress level and dilatant response of the sand a comprehensive analysis of the performance of the new model and other existing analytical methods in retrospectively predicting the peak resistance of a database of 49 geotechnical centrifuge tests is provided significant improvements over existing punching shear and load spread models are shown as a result of incorporating the strength properties of the sand in a consistent manner the new model has application to the offshore mobile jack up

local impact of palaeolithic man on the environment during the end of the last glacial in the netherlands abstract comparison of palynological data from lake deposits and soils from locations along a transect approaching the remains of a palaeolithic settlement in the younger dryas stadial shows four cycles in the vegetation from open pine forest to open ground vegetation and back to open pine forest this outcome is discussed in terms of the impact of man on the vegetation in the later part of the weichselian lateglacial

pollen and macrofossils attributable to fagopyrum in western eurasia prior to the late medieval an intercontinental mystery abstract the widespread perception that buckwheat fagopyrum esculentum and f tataricum did not occur in western eurasia prior to the late medieval is challenged by numerous pollen finds we traced some 240 localities from the area with pollen or macrofossils attributed to fagopyrum in often much earlier time slices this paper evaluates various explanations for these finds within the context of palaecological methods vegetation history and cultural development the clear morphological characteristics make large scale misidentification of the pollen unlikely although some records are suspect contamination is improbable for the vast majority of the pollen diagrams also long distance transport of pollen of fagopyrum snowdenii or oxygonum from africa seems unlikely as the pollen rain of that continent hardly contains that pollen the option that fagopyrum was present in western eurasia already much earlier than the late medieval must therefore be seriously considered cultivated species may have reached the area by trade between the mediterranean and eastern chinese realms which was regular since 2000 bce as the low pollen values argue against large scale cultivation the taxon may merely have occurred as a weed or its pollen was transported with other products and subsequently re emitted the pervasive notion that buckwheat was cultivated on large scale by the scythians in the ukrainian realm since 800 bce is highly ambiguous and probably wrong there are some indications that wild fagopyrum or a related taxon may have occurred widespread in eurasia during the pleistocene glaciations and the early middle holocene i e predating 2000 bce

simultaneous observations of the july 1996 2 day wave event using the super dual auroral radar network and the high resolution doppler imager simultaneous observations of a 2 day wave using the super dual auroral radar network superdarn and the upper atmospheric research satellite based uars high resolution doppler imager hrdi are presented recent comparisons of superdarn data with data from the saskatoon mf radar hall et al 1997 demonstrate that superdarn data at ranges close to the radar is most likely due to scatter from meteor trails and can be used to trace neutral winds in the meteor region this study exploits this near range scatter to observe the winds during july 1996 during the study period a clear 2 day wave event was observed in both the radar data and in the hrdi data comparisons between the two data sets show similarities and distinct differences both instruments observed a wave of similar amplitude in the same time interval both instruments indicated a westward propagating wave with zonal wave number 3 hrdi observed the wave to form and diminish at earlier times than superdarn observed in addition there were distinct differences between the winds observed by hrdi at the radar longitudes and the winds observed by the radars many of the differences may be explained by the latitude difference between the radars and the northern most latitude observed by hrdi

undrained bearing capacity factors for conical footings on clay introduction the bearing capacity of circular foundations on undrained clay is of fundamental importance in many geotechnical problems in particular there are a number of designs of offshore foundations where the foundation can be treated approximately as a large circular footing for instance some gravity bases the spudcan foundations of jack up units and the more recently developed caisson foundations in most cases the footing is not placed at the ground surface and it is important to take into account the depth of embedment furthermore the base of a spudcan is generally not flat but approximates a shallow cone for foundations on soft clays the effect of the increase of strength of the soil with depth needs to be taken into account and this is particularly important for large foundations the purpose of this note is to present calculations of bearing capacity factors for shallow circular foundations accounting for embedment cone angle rate of increase of strength with depth and surface roughness of the foundation the results have widespread application particularly in the offshore industry the soil is assumed to be rigid plastic with yield determined by the tresca condition with an undrained strength su the method of characteristics is used for the bearing capacity calculation as described by shield 1955 eason shield 1960 houlsby 1982 and houlsby wroth 1982a for application to undrained axisymmetric problems some previous results have been published for this problem using similar numerical techniques e g houlsby wroth 1982b salencon matar 1982 houlsby wroth 1983 tani craig 1995 martin 2001 but the study presented here involves a much more comprehensive coverage of the parameters where comparisons can be made with the previous solutions the factors differ by up to about 0 5 which gives some indication of the level of accuracy attainable with this numerical technique exceptionally the rough footing results given by tani craig 1995 are higher by up to about 5 but this may be due to a problem with their numerical integration procedures see martin randolph 2001

the two day wave in eos mls temperature and wind measurements during 2004 2005 winter 1 two day wave observations during january march 2005 are reported using the recently launched microwave limb sounder mls aboard nasa s earth observing system aura mission wave induced disturbances in temperature water vapor carbon monoxide and mls line of sight wind appear in early january peak near the end of january and persist until late february temperature and wind amplitudes as large as 9 k and 50 m s are observed near 90 km the wave disturbance is initially confined in the mid to low summer latitudes where the climatological summer easterly jet exhibits strong shear the wave then develops features akin to the third rossby gravity global normal mode with a weak temperature disturbance in the winter hemisphere anti symmetric about the equator and wind disturbance over the equator strong wind perturbation episode around 17 23 january 2005 in the mid latitude southern hemisphere coincides with a particularly intense solar proton event