a study of mantle layering beneath the western pacific the reverberative interval of the seismogram defined as the portion following the surface wave train propagating along the minor arc and ending with the first body wave arrivals from the major arc provides an excellent window in which to observe subcritical reflections from mantle discontinuities on an sh polarized seismogram the intervals between scsn and sscsn wave groups zeroth order reverberations are approximately 15 min long and consist almost entirely of waves reflected one or more times from mantle discontinuities first and higher order reverberations we have developed signal enhancement and waveform inversion schemes to progressively extract information pertaining to mantle layering from the waveforms of zeroth and first order reverberations and have applied them to a data set of long period digital seismograms drawn from a number of tectonic regions in and around the western pacific the results place important constraints on the nature of the transition zone discontinuities measurements of the two way vertical shear wave travel time from the free surface to the 400 km and 650 km discontinuities 400 and 650 respectively yield estimates of transition zone travel time tz largely uncontaminated by outside heterogeneity variations in the path averaged estimates of tz are of the order of 5 4 s indicating significant lateral heterogeneity in the transition zone correlations of tz with 400 and lm travel time through the lower mantle are consistent with but do not require the thermal deflection of an exothermic phase transition near 400 km and an endothermic transition at 650 km with 12 km of long wavelength 500 5000 km topography on each the amount of topography estimated for the 650 km discontinuity is significantly less than predicted for a rigorously stratified mantle 100 km in a search for other mantle discontinuities we find evidence for a strong reflector possibly associated with the onset of partial melting in the upper mantle average depth of 86 km due to ambiguity inherent to the method this feature can also be interpreted as an impedance increase in the d region of the lower mantle 70 170 km above the core mantle boundary no evidence is found for a 220 km discontinuity or the d discontinuity proposed by lay and helmberger 1983 suggesting that if such features are present in the western pacific they are either small normal incidence sh reflection coefficient r 1 5 or intermittent or have lateral depth variations well in excess of 50 km

global gravity wave variances from aura mls characteristics and interpretation abstract the gravity wave gw resolving capabilities of 118 ghz saturated thermal radiances acquired throughout the stratosphere by the microwave limb sounder mls on the aura satellite are investigated and initial results presented because the saturated optically thick radiances resolve gw perturbations from a given altitude at different horizontal locations variances are evaluated at 12 pressure altitudes between 21 and 51 km using the 40 saturated radiances found at the bottom of each limb scan forward modeling simulations show that these variances are controlled mostly by gws with vertical wavelengths z 5 km and horizontal along track wavelengths of y 100 200 km the tilted cigar shaped three dimensional weighting functions yield highly selective responses to gws of high intrinsic frequency that propagate toward the instrument the latter property is used to infer the net meridional component of gw propagation by differencing the variances acquired from ascending a and descending d o

a coupled one dimensional viscoelastic plastic model for aquitard consolidation caused by hydraulic head variations in aquifers accurate and practical calculation of aquitard consolidation is required for a reliable analysis of land subsidence caused by groundwater overexploitation in a multilayered aquifer system because aquitards are generally more compressible than aquifers are this study proposes a coupled one dimensional viscoelastic plastic consolidation model that considers the combined effect of changes in soil parameters and body force to simulate aquitard consolidation caused by hydraulic head variations in neighbouring aquifers the proposed model uses variable total stress and simultaneously solves hydraulic head and vertical soil displacement the constitutive relation based on the voigt model with different elastic moduli of the spring in normally consolidated and overconsolidated soils is used to describe the viscoelastic plastic deformation mechanism of aquitards in addition the proposed model considers the combined effect of variations in hydraulic conductivity elastic moduli and body force on the calculation of aquitard consolidation three hypothetical scenarios with various hydraulic head variations in aquifers are used to examine the coupled one dimensional viscoelastic plastic consolidation model the results show that neglecting plasticity and viscosity of soil causes aquitard consolidation to be respectively underestimated and overestimated in addition ignoring body force variation underestimates aquitard consolidation whereas neglecting soil parameters variation overestimates aquitard consolidation two real case scenarios are also studied to further demonstrate the applicability of the coupled one dimensional viscoelastic plastic consolidation model copyright 2015 john wiley sons ltd

on the relation between gravity waves and wind speed in the lower stratosphere over the southern ocean abstractthe relationship between gravity wave momentum fluxes and local wind speed is investigated for oceanic regions at high southern latitudes during austral spring the motivation is to better describe the gravity wave field by identifying a simple relationship between gravity waves and the large scale flow the tools used to describe the gravity waves are probability density functions of the gravity wave momentum fluxes three independent datasets covering high latitudes in the southern hemisphere springtime are analyzed simulations with a mesoscale model analyses from the european centre for medium range weather forecasts and observations from superpressure balloons of the concordiasi campaign in 2010 a remarkably robust relation is found with stronger momentum fluxes much more likely in regions of strong winds the tails of the probability density functions are well described as lognormal the median momentum flux increases linearly with background wind speed for winds stronger than 50 m s 1

regional land subsidence simulation in su xi chang area and shanghai city china su xi chang area and shanghai city located in the south of yangtze delta china has subsided due to groundwater overpumping because of the regional scale of the groundwater exploitation cone of depression and land subsidence at present su xi chang area and shanghai city are treated as a single area for land subsidence study to avoid the uncertainty of boundary condition due to the regionalism the characteristics of aquifer system compaction are complex because of the difference in the types compositions and structures of the soils that the hydrostratigraphic units are composed of and in the histories of groundwater level change the hydrostratigraphic units have experienced considering the fact that different hydrostratigraphic units have different kinds of deformation and that an identical unit may also present different deformation characteristics such as elasticity elasto plasticity and visco elasto plasticity at different sites of the cone of depression or in different periods corresponding constitutive laws have been adopted this avoids the shortcomings of the previous research that the same constitutive law was adopted in all the hydrostratigraphic units during the entire time period a coupled flow and subsidence model which includes a three dimensional flow model with variable coefficients and a one dimensional vertical subsidence model is built according to the complicated hydrological condition in the region the simulation model is calibrated using observed data which include compression of individual strata from groups of extensometers and groundwater levels from observation wells from 1995 to 2002 the model reproduced that the primary subsidence layer in shanghai shifts from the shallow aquitard to the fourth confined aquifer because of the groundwater yield variations and the change of exploitation aquifers however the third aquitard was the primary subsidence layer in su xi chang area and the compaction deformation of the sandy aquifers was remarkable the simulation results could provide some reasonable advice about groundwater exploitation in the future

simulation of inertia gravity waves in a poleward breaking rossby wave abstract poleward breaking rossby waves often induce an upper level jet streak over northern europe dominant inertia gravity wave packets are observed downstream of this jet the physical processes of their generation and propagation in such a configuration are investigated with a mesoscale model the study is focused on an observational campaign from 17 to 19 december 1999 over northern germany different simulations with the fifth generation pennsylvania state university national center for atmospheric research psu ncar mesoscale model mm5 have been performed for a high resolution process study three domains were set up that encompass the evolution of rossby waves and that of inertia gravity waves to minimize the impact of model damping the horizontal and vertical resolution has been adjusted appropriately with a novel statistical approach the properties of inertia gravity wave packets have been estimated this method uses the horizontal divergence field and takes into account the spatial e

numerical evaluation of land subsidence induced by groundwater pumping in shanghai to predict the future behavior of land subsidence in shanghai due to pumping of groundwater a numerical model is established in the proposed model groundwater flow in three dimensional conditions and soil deformation in one dimen sional conditions are calculated the model takes into account the multi aquifer aquitard hydrogeological condition of the soft deposit of shanghai the variation of the coefficient of compressibility and coefficient of hydraulic conductivity of the soils with the consolidation process are simulated relationships among land subsidence groundwater withdrawal volume and groundwater level are analyzed comparison between the measured value and calculated value shows that the model simulates the measured value fairly well the future of land subsidence behavior due to groundwater withdrawal is predicted and discussed via consideration of the variation of the following parameters in the future 30 years net withdrawn volume of groundwater pumping layer and pumping region resume un modele numerique est propose afin de predire le comportement futur d un affaissement de sol cause par le pompage de l eau souterraine a shanghai dans le modele propose l ecoulement de l eau souterraine en trois dimensions et la deformation du sol en une dimension sont calcules le modele considere la condition hydrogeologique multi aquifere aquitard du depot mou de shanghai les variations du coefficient de compressibilite et du coefficient de conductivite hy draulique des sols lors du processus de consolidation sont simulees les relations entre l affaissement du sol le volume de retrait de l eau souterraine et le niveau phreatique sont analysees des comparaisons entre les valeurs mesurees et calculees montrent que le modele peut simuler les valeurs mesurees relativement bien le comportement futur du sol en affaissement cause par le retrait de l eau souterraine est predit et discute en considerant les variations pour les prochains 30 ans pour les parametres suivants le volume net d eau souterraine retire la couche de pompage et la region de pompage mots cles pompage de l eau souterraine affaissement du sol ecoulement de l eau souterraine en trois dimensions consoli dation en une dimension prediction traduit par la redaction

travel times of s and sks implications for three dimensional lower mantle structure beneath the central pacific the travel times of s and sks phases from deep focus fiji tonga events recorded in north america by canadian station network and world wide seismographic station network stations exhibit a strong azimuthal dependence the differential times of s sks exhibit relatively little scatter and are used to investigate three dimensional mantle models for the central pacific region s sks times are corrected for earth s ellipticity and residuals are computed with respect to the iasp91 reference model anomalously large s sks times ranging up to 9 s larger than iasp91 predictions for 100 suggest a slow lower mantle beneath the central pacific these results are compared to the predictions of three tomographic models mdlsh of tanimoto 1990 model sh12 wm13 of su et al 1992 and model sh 10c 17 of masters et al 1992 the three dimensional whole mantle models have been parameterized into 11 spherical shells qualitative agreement between the tomographic model predictions and observations is encouraging varying from fair to good however inconsistencies are present and suggest anomalies in the lower mantle of scale length smaller than the present 2000 km scale resolution of tomographic models laterally varying outer core structure is not necessary to explain the anomalies in this data set although such a scenario cannot be resolved with this data

gravity waves around the subtropical jet of the southern winter in an atmospheric general circulation model 1 gravity wave gw activities around the subtropical jet of the southern winter june are analyzed using atmospheric general circulation model outputs of t106l60 in order to clarify roles of gws in maintaining the zonal mean zonal wind dominant gws are characterized with periods of 10 24 hours relative to the ground and with horizontal and vertical wavelengths of about 600 700 km and 2 2 4 4 km respectively these gws propagate both upward and downward from the jet and westward relative to the mean zonal wind most of the upward propagating waves do not reach the upper stratosphere due to negative vertical wind shear of the zonal wind in the lower stratosphere dominant upward fluxes of easterly momentum due to the non stationary gws extend zonally along 30 s above the jet remarkable ep flux convergence due mostly to these gws is seen around 100 hpa at 30 s and explains up to 30 of the total ep flux convergence

inertia gravity waves revealed in radiosonde data at jang bogo station antarctica 74 37 s 164 13 e 2 potential sources and their relation to inertia gravity waves

fine structure of the 410 km discontinuity the april 14 1995 earthquake in western texas m w 5 7 produced a strong topside reflection off the 410 km discontinuity which was recorded on a multitude of seismic arrays throughout the southwestern united states data from 394 vertical short period and 24 broadband instruments provide dense coverage of this event from distances of 11 to 19 and provide a detailed look at the subcontinental 410 km structure the salient features of this data set are 1 the strong dependence on wavelength of the 410 km triplication range 2 the uniform amplitude ratio of the direct p and reflected p 410 phases on both short period and broadband recordings throughout the triplication and 3 the abrupt termination of the short period p 410 phase at 13 3 these features are best modeled by a composite discontinuity in which a sharp velocity jump of 3 is overlain by a linear velocity jump of 3 5 spread over 14 km the interference of energy turning in the diffuse and sharp portions of this discontinuity structure reproduces both the long and short period triplication range and the step like behavior of the p 410 short period amplitude which cannot be reproduced with either a simple linearly diffuse or a purely sharp discontinuity this composite structure produces a triplication range which depends on source frequency and has an apparent depth which depends on observation frequency additionally this is the structure expected from mineralogical arguments for the to olivine phase transition

a hybrid three dimensional computational model of groundwater solute transport in heterogeneous media 1 this study examines a new hybrid three dimensional computational solution for groundwater solute transport in a layered aquifer in this study the horizontal length scale of the computational domain referring to the nature geometry is assumed much larger than the vertical length scale thus the computation of solute transportation in the horizontal direction is more complex than the computation in the vertical direction using the dupuit forchheimer approximation of groundwater flow as a reference this study employs the vertical horizontal splitting vhs concept to divide the three dimensional solute transport equations into depth averaged two dimensional and vertical variation one dimensional equations the two dimensional equations are processed via the so called finite analytic method while the one dimensional equations are solved analytically the three dimensional solute transport is effectively reduced to a hybrid three dimensional model by combining the two dimensional computations and the one dimensional analytical solutions the resultant hybrid three dimensional method is capable of large computational time steps and large spatial grids and is thus suitable for simulating solute transport in large scale sites of layered aquifers with negligible spatial variation of both thickness and hydraulic properties within each layer where traditional numerical schemes fall short of satisfying the requirements of both accuracy and efficiency nevertheless the use of this method is necessarily restricted when 1 the site is extremely heterogeneous and thus cannot be treated as layers or 2 the flows in the aquifer and in the aquitard are highly three dimensional this method is verified by analytical solutions as well as by the numerical model mt3d

a study of the low frequency inertio gravity waves observed during the pyrenees experiment the purpose of this paper is to analyze and interpret the onset of some well characterized transient inertio gravity waves observed during the pyrex pyrenees experiment campaign the data used are the high resolution soundings launched every 6 hours on both sides of the ridge in agreement with other observations made during the field campaign certain among those soundings often show steady mountain waves it appears that those waves are often transients and are followed by well characterized inertio gravity waves propagating upward and downward from the level where the initial mountain waves are large to interpret those observations it is suggested that the observed inertio gravity waves result from the geostrophic adjustment of the large scale flow that follows the transit and eventually the breaking of the main mountain wave this hypothesis is supported by an analytical calculation of inertio gravity waves emission from a momentum deposit that lasts a finite time the spatial extent of this forcing are also finite and its maximum amplitude is a fraction of the measured mountain drag

mantle layering from scs reverberations 2 the transition zone this is the second paper in a four part sequence that examines the nature of mantle layering using the scsn phases and internal reflections observed within the reverberative interval of sh polarized seismograms mantle reflectivity profiles for 18 seismic corridors sampling portions of indonesia australia and the western and central pacific are constructed from low frequency 25 mhz scs reverberations i e scsn type phases reflected once from internal mantle discontinuities modeling the reflectivity profiles using synthetic seismograms yields precise path specific estimates of the travel times to the 410 km and 660 km discontinuities and their reflection coefficients the data are consistent with an olivine dominated model of the transition zone marked by two major phase transitions having average apparent depths of 414 2 km and 660 2 km and impedance contrasts of 0 046 0 010 and 0 072 0 010 respectively the interpath variations observed in the reverberation travel times imply that the topography on the two discontinuities is of the order of 20 km peak to peak and is negatively correlated consistent with an endothermic transition at 660 km whose clapeyron slope magnitude is comparable to that of the 410 km exothermic transition in the case of the 660 km discontinuity we have been able to supplement these long wavelength 1500 5000 km observations with an estimate of intrapath topography inferred from the frequency dependence of the 660 km reflection coefficient which gives peak to peak variations less than 40 km on scale lengths of 500 1500 km for the 660 km discontinuity the observed topography is significantly less than the dynamic topography expected for a simple compositional interface in regions of subduction however we do observed an intriguing negative correlation between the apparent depth and the reflection coefficient of the 660 km discontinuity which may involve small compositional variations plausible explanations for this correlation include heating of an initially cool chemical boundary layer gravitationally trapped above an endothermic phase transition loss of reflected energy due to local curvature or roughness of the reflector and or extreme topography occurring on a small compositional component to the discontinuity 40 of the total impedance contrast by stripping the 410 km and 660 km peaks from the composite path reflectivity profile we identify three minor reflectors at mean depths of 520 710 and 900 km the shallowest may mark the phase spinel phase transition the 710 km discontinuity can be attributed to the ilmenite gamet perovskite phase transition although changes in perovskite symmetry can potentially provide explanations for both the 710 km and 900 km features

a comparison of deterministic and stochastic approaches for regional scale inverse modeling on the mar del plata aquifer summary inversion of the spatial variability of transmissivity t in groundwater models can be handled using either stochastic or deterministic i e geology based zonation approaches while stochastic methods predominate in scientific literature they have never been formally compared to deterministic approaches preferred by practitioners for regional aquifer models we use both approaches to model groundwater flow and solute transport in the mar del plata aquifer where seawater intrusion is a major threat to freshwater resources the relative performance of the two approaches is evaluated in terms of i model fits to head and concentration data available for nearly a century ii geological plausibility of the estimated t fields and iii their ability to predict transport we also address the impact of conditioning the estimated fields on t data coming from either pumping tests interpreted with the theis method or specific capacity values from step drawdown tests we find that stochastic models based upon conditional estimation and simulation techniques identify some of the geological features river deposit channels and low transmissivity regions associated to quartzite outcrops and yield better fits to calibration data than the much simpler geology based deterministic model which cannot properly address model structure uncertainty however the latter demonstrates much greater robustness for predicting sea water intrusion and for incorporating concentrations as calibration data we attribute the poor performance and underestimated uncertainty of the stochastic simulations to estimation bias introduced by model errors qualitative geological information is extremely rich in identifying large scale variability patterns which are identified by stochastic models only in data rich areas and should be explicitly included in the calibration process

inertia gravity waves spontaneously generated by jets and fronts part i different baroclinic life cycles abstract the spontaneous generation of inertia gravity waves in idealized life cycles of baroclinic instability is investigated using the weather research and forecasting model two substantially different life cycles of baroclinic instability are obtained by varying the initial zonal jet the wave generation depends strongly on the details of the baroclinic wave s development in the life cycle dominated by cyclonic behavior the most conspicuous gravity waves are excited by the upper level jet and are broadly consistent with previous simulations of o sullivan and dunkerton in the life cycle that is dominated by anticyclonic behavior the most conspicuous gravity waves even in the stratosphere are excited by the surface fronts although the fronts are no stronger than in the cyclonic life cycle the anticyclonic life cycle also reveals waves in the lower stratosphere above the upper level trough of the baroclinic wave these waves have not been previously identified in idealized simulations the sensiti

a mesoscale gravity wave event observed during ccope iii wave environment and probable source mechanisms abstract synoptic and special mesoscale observations taken during the cooperative convective precipitation experiment ccope are used to describe the multiscale environment of a gravity wave event understand the wave environment interactions that led to the development of severe thunderstorms and asses possible wave generation mechanisms the storms formed sequentially as a packet of gravity waves propagated across a stationary thunderstorm outflow boundary convection developed most rapidly in that part of the mesonetwork in which existed the combination of relatively high parcel buoyant energy weak restraining inversion strong storm downdraft potential and substantial vertical wind shear associated with a mesoscale jet streak synoptic scale analysis reveals that the waves were excited north of a stationary front and within the right exit region of the jet streak as it approached a stationary ridge in the 300 mb height field strong indications of unbalanced flow were diagnosed within the gravit

global estimates of equatorial inertia gravity wave activity in the stratosphere inferred from era40 reanalysis 1 a new methodology is applied to era40 reanalysis in order to quantify large scale inertia gravity wave activity in the equatorial lower stratosphere both eastward and westward propagating waves are identified in the data set and a good agreement is found with previously published in situ observations global estimates of vertical fluxes of zonal momentum associated with such waves are obtained typical amplitudes of order 10 2 m2 s 2 suggest that the forcing of the quasi biennial oscillation by large scale inertia gravity waves is tantamount to that by kelvin waves this method can be used to document the space time variability of the wave activity in order to improve the wave drag parameterizations in climate models

rheology of the upper mantle a synthesis rheological properties of the upper mantle of the earth play an important role in the dynamics of the lithosphere and asthenosphere however such fundamental issues as the dominant mechanisms of flow have not been well resolved a synthesis of laboratory studies and geophysical and geological observations shows that transitions between diffusion and dislocation creep likely occur in the earth s upper mantle the hot and shallow upper mantle flows by dislocation creep whereas cold and shallow or deep upper mantle may flow by diffusion creep when the stress increases grain size is reduced and the upper mantle near the transition between these two regimes is weakened consequently deformation is localized and the upper mantle is decoupled mechanically near these depths

sh velocity and compositional models near the 660 km discontinuity beneath south america and northeast asia 1 we constrain sh wave velocity structures near the 660 km discontinuity beneath south america and northeast asia using triplicated phases near the discontinuity recorded in the epicentral distance range of 10 35 for three deep events we then explore mineralogical and compositional models appropriate for explaining the inferred seismic structures between the two regions sh velocity structures near the 660 km discontinuity are found to be different in the two regions beneath south america the velocity gradient above the 660 km discontinuity is larger than that of preliminary earth reference model prem while the velocity jump across the discontinuity is the same as prem beneath northeast asia the velocity gradient above the 660 km discontinuity is the same as that of prem while the velocity jump across the discontinuity is larger than prem both regions are characterized by a large velocity gradient extending about 80 km deep below the 660 km discontinuity the different velocity structures require different mineralogical models in the transition zone in the two regions the larger velocity gradient above the 660 km discontinuity beneath south america requires existence of the ilmenite phase in the bottom of transition zone while that beneath northeast asia can be explained by the temperature and pressure dependence of elastic properties of the major mantle mineral assemblages the observed large velocity gradients in the top of the lower mantle can be explained by gradual transformation of garnet to perovskite persisting to greater depths the velocity jump across the 660 km discontinuity beneath south america in the presence of the ilmenite phase in the bottom of the transition zone requires a bulk composition of more garnet than the pyrolite model while a larger velocity jump across the discontinuity beneath northeast asia requires a larger fraction of garnet transforming to perovskite across the discontinuity than what is required for explaining prem these different mineralogical models can be caused by different mantle temperature or composition especially the aluminum content in mantle composition the presence of garnet 80 km below the 660 km discontinuity in the two regions may be explained by a uniform composition in the lower mantle with an aluminum content of 3 4 the existence of ilmenite in the bottom of the transition zone beneath south america and the absence of ilmenite beneath northeast asia can be explained by either a difference in mantle temperature of about 100 c with that beneath south america being lower between the two regions assuming a uniform mantle composition or alternatively a difference in aluminum content of about 1 with that beneath south america being lower between the two regions without invoking a temperature difference between the two regions we also discuss conditions of mantle composition and temperature that double discontinuities may occur near the 660 km depth as well as the depth separation and velocity jumps of the double discontinuities for the inferred mantle temperature and composition beneath south america and northeast asia the maximum separation of the double discontinuities is 20 km and cannot be resolved by the sh wave data

mantle control of plate boundary deformation the seismic wavefield propagating along the recently instrumented pacific north american plate boundary california displays remarkable variation with regional shear waves arriving at coastal stations up to 20 seconds earlier than equidistant stations in eastern california broadband modeling of this data reveals that coastal paths sample fast upper mantle typical of miocene aged ocean plate 50 km thickness inland paths sample slower uppermost mantle with the seismic lithosphere or lid measuring less than 5 km thick characteristic of the basin and range extensional province the boundary in the uppermost mantle between these provinces is sharp expressing the juxtaposition of the stronger pacific plate with weaker continental north america the lid step coincides with regionally maximum dextral strain rates measured with gps suggesting the uppermost mantle modulates long term regional scale continental margin deformation and evolution

seismic structure of the upper mantle in a central pacific corridor the seismic structure of the tonga hawaii corridor has been investigated by combining two data sets revenaugh and jordan s reflectivity profile from scs reverberations which provides travel times to and impedance contrasts across the major mantle discontinuities and 1500 new observations of frequency dependent phase delays for the three component s ss and sss body waves and the r1 and g1 surface waves which constrain the velocity structure within this layered framework the shear waves turning in the upper mantle showed significant splitting of the sh and sv components indicative of shallow polarization anisotropy the data set was inverted in conjunction with attenuation and mineralogical constraints to obtain a complete spherically symmetric radially anisotropic structure the final model pa5 is characterized by a high velocity anisotropic lid bounded at 68 km depth by a large negative g discontinuity a low velocity anisotropic layer below g extending to a small l discontinuity at 166 km an isotropic steep gradient region between 166 km and 415 km and transition zone discontinuities at 415 507 and 651 km the depth of the radial anisotropy in pa5 is shallower than in most previous studies based on surface waves and higher modes the average value of radial shear anisotropy in the lid 3 7 is consistent with the magnitude expected from the spreading controlled models of olivine orientation while anisotropy in the low velocity zone which is required by our data set could be induced either by paleostrains that took place near the ridge crest or by shearing in the asthenosphere as a result of present day plate motions on the basis of recent work by hirth and kohlstedt we suggest that the g discontinuity is caused by a rapid increase in the water content of mantle minerals with depth marking the fossilized lower boundary of the melt separation zone active during crust formation the high gradient zone between 200 and 400 km is a characteristic feature of convecting oceanic upper mantle and is probably controlled by a steady decrease in the homologous temperature over this depth interval the average shear velocity gradient in the transition zone is lower than in most previous seismic models in better agreement with the predictions for a pyrolitic composition

model study of intermediate scale tropical inertia gravity waves and comparison to twp ice campaign observations abstracta 2 day inertia gravity wave igw was observed in high resolution radiosonde soundings of horizontal wind and temperature taken during the 2006 tropical warm pool international cloud experiment twp ice experiment in the darwin area the wave was observed in the stratosphere above darwin from 28 january to 5 february a similar wave event is observed in the european centre for medium range weather forecasts ecmwf operational data a comparison between the characteristics of the igw derived with the ecmwf data to the properties of the wave derived with the radiosonde data shows that the ecmwf data capture similar structure for this 2 day wave event but with a larger vertical wavelength a reverse ray tracing method is used to localize the source region using ecmwf data to define the atmospheric background conditions and wave properties observed in the soundings it is found that the 2 day wave event originated from deep convection in the indonesian region around 20 january the weather research

hydraulic response of highly compressible aquitards during consolidation the transient hydraulic behavior of highly compressible aquitards is investigated through numerical analysis and field studies variations in the hydraulic parameters of an aquitard during consolidation are accounted for by incorporating empirical relationships derived from standard consolidation tests into the one dimensional flow equation the resulting equation is highly nonlinear the hydraulic response of an aquitard with physical properties typical of the compressible clays of mexico city is evaluated with both standard linear analysis and with a nonlinear approach where the hydraulic parameters are stress dependent the results indicate that decreases in the hydraulic diffusivity of the aquitard due to consolidation lead to diminished leakage flux slower groundwater velocities and solute transport rates longer transient response periods and less land subsidence than would be predicted by classical linear theory evaluation of field data from a site near mexico city indicates that significant interpretive errors may arise if the stress dependence of the hydraulic parameters is ignored in these types of systems

coupling methodology and application of a fully integrated model for contaminant transport in the subsurface system summary an efficient integrated modeling approach is developed to simulate the contaminant transport in the subsurface system the unsaturated zone is divided into a number of horizontal sub areas according to the atmospheric boundary conditions land use types and hydrological conditions solute migration through the unsaturated zone of each sub area is assumed to be vertical and can be represented by the one dimensional advection dispersion equation which is then coupled to the three dimensional advection dispersion equation representing the subsequent groundwater transport the finite element method is adopted to discretize the vertical solute equation while the hybrid finite element and finite difference method is used to discretize the three dimensional saturated solute transport equation which is split into the horizontal and vertical equations based on the concept of the horizontal vertical splitting the unsaturated and saturated solute transport equations are combined into a unified matrix by the mass balance analysis for the adjacent nodes located at the one dimensional soil column and at the water table two hypothetical cases and two field cases are simulated to test the validity of the model with the results compared with those from hydrus 1d swms2d and the measured data the limitations of the model are discussed as well the analysis of the four cases demonstrates that the proposed model can calculate the water flow and solute transport reasonably even with complex boundary and variable topography conditions it also shows that the model is efficient to simulate the water flow and solute transport in regional scale areas with small computational costs however the model will lose accuracy when the lateral dispersion effect is dominant in the unsaturated zone

spinel elasticity and seismic structure of the transition zone of the mantle there is continuing debate about whether the upper mantle is chemically stratified and whether the seismic discontinuity at 400 km depth represents a chemical boundary a phase change of the mg fe 2sio4 component from the phase olivine to the p phase or a combination of both recent developments in high pressure synthesis1 2 and ultrasonic interferometry3 4 have made possible measurements of elastic wave velocities in small poly crystalline samples of high pressure phases by combining our new acoustic measurements on the spinel phase of mg2 sio4 with existing data for the and phases we present here velocity profiles for the m2sio4 component of the mantle where m represents mg or fe to depths of about 600 km we find it to be unlikely that any seismologically observable velocity discontinuity at about 520 km depth can be attributed to this component although the contrast in impedance the product of density and velocity might be sufficient for the transformation to be observed in long period seismic reflection studies at near normal incidence5 the velocity gradients in the transition zone particularly for shear waves are steeper than would be expected for simple adiabatic compression of likely mantle compositions suggesting that alternative explanations including chemical heterogeneity and anelastic relaxation need to be explored

upper mantle shear structure beneath the northwest atlantic ocean we have modeled the sh motion from earthquakes in the northwest atlantic ocean to derive an oceanic upper mantle shear velocity model the signals were recorded on long period wwssn and canadian network stations on the east coast of north america the travel times and waveforms of seismograms in the distance range 11 16 were used to constrain the lid structure these data indicate a fast 4 75 km s lid of about 100 km thickness in the older western atlantic from 16 to 28 the s waves pass through triplications due to velocity jumps near 400 and 660 km the branches from both discontinuities are visible in the s wave data these arrivals were modeled using synthetic seismograms to obtain accurate travel times the two triplications are also apparent in ss data from 30 to 50 the triplication curves derived from the s waves agree with the ss data given the lid structure the waveforms and travel times from the more distant data put tight constraints on the shear velocities at greater depths we find shear velocities from 200 to 400 km to be slow in relation to a shear model of the canadian shield derived by a similar technique indicating continent ocean heterogeneity to about 400 km

seismic imaging of upper mantle structure with new evidence for a 520 km discontinuity stacked images of long period seismic data reveal many phases some not previously observed which are caused by reflections and conversions at discontinuities in the earth s upper mantle these images support the existence of discontinuities at 410 520 and 660km depth but no evidence is found for a significant interface at 220 km

upper mantle q structure beneath the east pacific rise a model of q as a function of depth has been determined for the upper mantle beneath the east pacific rise the model is appropriate for shear waves with periods from roughly 15 to 30 s the amplitudes of multibounce sh phases which propagate within the upper mantle were used to constrain the q structure the multibounce phase amplitudes were measured with respect to the s wave amplitude for each seismogram the data consist of s ss sss and ssss waves for distances from 30 to 80 the sources are earthquakes which occurred on transform faults associated with the east pacific rise and the seismograms were recorded by world wide standard seismograph network and canadian seismic network stations in western north america mantle beneath oceanic crust less than 15 ma and tectonically active continental crust is sampled since the s wave data primarily sample the deep mantle the resulting upper mantle q model depends on the q structure assumed for the lower mantle we assumed a constant q of 312 for the mantle beneath 650 km depth with this assumption the upper mantle phase amplitudes require a q of about 70 in the upper 150 km of the mantle from 150 to 400 km depth q increases to 180 the q in the transition zone from 400 to 650 km depth was found to be 180 significantly lower than the lower mantle q the resulting q model is consistent with several surface wave studies of mantle attenuation beneath the pacific however our results predict a qscs 210 which is significantly higher than many direct measurements of scs attenuation indicate furthermore the large range in measured qscs is inconsistent with lateral q variations being confined to the upper mantle if the region we have studied represents the low q extreme of upper mantle we conclude that large lateral variations in q exist in the lower mantle

inertia gravity waves observed by the uk mst radar we present an analysis of eight years data from the uk mst radar at aberystwyth wales to determine the occurrence and properties of long period quasi monochromatic oscillations in the wind vector identified with inertia gravity waves wave perturbations were first isolated by filtering out background wind variation in the vertical then the continuity of the radar measurements was exploited to apply band pass filters in time to select quasi monochromatic oscillations with periods 4 8 hours or 12 24 hours by searching for altitude regions where the wind vector rotates systematically with height and fitting ellipses to such sections the properties of inertia gravity waves can be derived to guard against contamination by short intrinsic period mountain waves cases were discarded when the vertical velocity measured by the radar exceeded 15 cm s 1 results show that waves in the stratosphere are dominated by upward energy propagation clockwise rotation and those in the troposphere by downward propagation consistent with the dominant source for inertia gravity waves being at tropopause level long period waves 12 hours are observed 70 of the time in the lower stratosphere roughly twice as often as the shorter period waves and 10 20 of the time in the troposphere there is a winter maximum in occurrence in the troposphere and for the short period stratospheric waves however the dominant long period waves show little seasonal dependence likewise they show only a weak correlation with jet stream velocity or direction unlike the other categories which are preferentially associated with strong jet streams and propagate along the jet inertia gravity waves observed by the radar have typical amplitudes 1 2 m s 1 and vertical wavelength 2 km the intrinsic wave period estimated for non jet stream conditions is similar for the two band passed series pointing to the importance of doppler shifting in generating the observed oscillations copyright 2007 royal meteorological society

modeling compaction of multi layer aquifer system due to groundwater withdrawal abstract excessive groundwater extraction in a sedimentary environment can result in subsidence which not only deteriorates land and agricultural resources but also endangers public infrastructure subsidence can be contributed by compaction in different layers clarifying the causes and estimating the amount of compaction remain a challenge for a multi layer aquifer system with spatially and temporally varying pumping activities a distributed model that comprises an analytical quasi three dimensional groundwater model and a one dimensional deformation model is proposed to model the groundwater flow and deformation for a multi layer aquifer system using the analytical solution the groundwater level variation around a pumping well can be adequately modeled and then the compaction of soil layers can be calculated superposition allows the results to be extended to a system with multi well and or multi layer pumping the integrated model was applied to yuanchang in the center of the yunlin subsidence area taiwan data of groundwater level and compaction at aquifers 2 and 3 in dry season periods were used to explore the pumping effects on compaction the results show that single layer groundwater users are responsible for the large area compaction and that significant local compaction can be attributed to multi layer users constraining multi layer pumping activities and reducing the amount of groundwater exploitation are required to mitigate the subsidence in yunlin

comparison of gravity waves in the southern hemisphere derived from balloon observations and the ecmwf analyses abstractthe increase of spatial resolution allows the ecmwf operational model to explicitly resolve a significant portion of the atmospheric gravity wave gw field but the realism of the simulated gw field in the ecmwf analyses still needs to be precisely evaluated here the authors use data collected during the concordiasi stratospheric balloon campaign to assess the representation of gws in the ecmwf analyses over antarctica and the southern ocean in spring 2010 the authors first compare the balloonborne gw momentum fluxes with those in ecmwf analyses throughout the campaign and find a correct agreement of the geographical and seasonal patterns however the authors also note that ecmwf analyses generally underestimate the balloon fluxes by a factor of 5 which may be essentially due to the spatial truncation of the ecmwf model intermittency of wave activity in the analyses and observations are found comparable these results are confirmed on two case studies dealing with orographic and nonorographi

interbed storage changes and compaction in models of regional groundwater flow water released from permanent compaction of compressible fine grained interbeds within confined aquifers may be a significant source of pumped water permanent or inelastic compaction of the interbeds occurs when head declines from pumping cause the effective stress or grain to grain load to exceed the elastic limits of the interbeds as a result the grains in the interbeds rearrange and excess water is expelled the amount of inelastic compaction generally is proportional to the increase in effective stress and the decrease in head a common approach for the simulation of elastic and inelastic compaction in groundwater flow models is to assume that head changes in the aquifer result in instantaneous storage changes in the compressible interbeds a term is added to the groundwater flow equation to account for the storage changes changes in specific storage may be computed explicitly from the results at the previous time step in the finite difference formulation of the groundwater flow equation a better approach is to implicitly apportion storage changes between elastic and inelastic components within a time step if storage changes cannot be considered to occur instantaneously with change in head in the aquifer another approach is taken equations for horizontal flow in the aquifer are coupled with equations for vertical flow in the compressible interbeds to simulate flow in half a representative doubly draining interbed storage changes and compaction are calculated for the representative half thickness and are extrapolated to the entire thickness of all interbeds within each cell this approach was applied to an existing model of groundwater flow in the central valley of california the simulation demonstrates that solving coupled systems of equations is feasible for a regional flow model

a finite element linked model for analysis of solute transport in 3 d space of multilayer subsurface systems abstract the computational burden and instability of the fully 3 d saturated unsaturated unified approach can be lessened considerably by using the linked model of the quasi 3 d approach this approach is applicable to a multi layer subsurface system consisting of aquifers and aquitards in this approach 1 d vertical flow and solute transport is assumed in the vadose zone and aquitards and 2 d horizontal flow and quasi 3 d solute transport are assumed in the aquifers to simulate flow and transport in 3 d space in this paper the aquifers are sliced into sublayers in a aquifer with 2 d flow transport in the horizontal direction is assumed to be caused by advection and dispersion while transport in the vertical direction is assumed to be caused solely by dispersion as a mathematical simplicity the equations for vertical flow and transport in the vadose zone and confining layers and the equations for flow and transport in the aquifer are solved separately in two different solution packages during this time marching analysis the output in terms of source sink obtained from one solution package is coupled with the equations in the other solution package this linked model quasi 3 d approach was tested with other widely used numerical models and analytical solutions and was found stable and technically robust

gravity waves appearing in a high resolution gcm simulation global characteristics of gravity waves in the lower stratosphere are examined using a gcm with high resolution in both the horizontal t106 corresponding to about 120 km and the vertical 600 m the bottom boundary condition of the model is that of an aquaplanet with perpetual february sea surface temperature the simulated gravity waves are in good agreement with mesosphere stratosphere troposphere mst radar observations at a middle latitude on the gravity wave structure and on the frequency spectra as a function of height the frequency spectra of simulated wind and temperature fluctuations are also examined as a function of latitude large values of spectral density are observed at frequencies higher than the inertial frequency f in a weak wind region around 20 km which is consistent with the characteristics of internal gravity waves an isolated peak is observed near f for horizontal wind spectra at latitudes higher than 108 while the energy is distributed in a wide range of frequency at lower latitudes where f approaches zero further analysis is performed of those fluctuations having periods shorter than 24 h and those having vertical wavelengths smaller than 5 km these are frequently analyzed as gravity waves using observation data the distribution of energy and momentum fluxes in the latitude height section is examined the result indicates that short period waves mostly propagate upward and poleward from the equatorial region the wave energy reaches about 508 lat at the 27 km altitude a negative positive maximum of vertical flux of meridional momentum y9w9 is seen above the subtropical jet in the northern southern hemisphere for small vertical scale gravity waves this is consistent with the preferred equatorward propagation of the wave indicated by a statistical analysis based on mst radar observations the ratio of potential to kinetic energy maximizes over the equator and decreases poleward the eliassen palm flux divergence associated with gravity waves is decelerative above the subtropical jet albeit small

evolution of oceanic upper mantle structure abstract love and rayleigh wave phase velocities increase systematically with increasing age of oceanic lithosphere up to 150 ma the rates of increase differ between oceans and vary for different age intervals modeling of lithospheric age phase velocity relations indicates that the high velocity seismic lid thickens and the velocities in the sub lithospheric low velocity zone lvz increase with age at different rates between oceans the initial thickness of the lithosphere near mid ocean ridges as averaged by long period surface waves varies between 10 and 45 km and 100 ma lithosphere has thickness from 83 to 110 km for models with isotropic shear velocities hotspots in oceanic areas appear to modify oceanic lithosphere evolution producing deviations from average patterns with increasing age

low velocity zone atop the 410 km seismic discontinuity in the northwestern united states the seismic discontinuity at 410 km depth in the earth s mantle is generally attributed to the phase transition of mg fe 2sio 4 from the olivine to wadsleyite structure variation in the depth of this discontinuity is often taken as a proxy for mantle temperature owing to its response to thermal perturbations for example a cold anomaly would elevate the 410 km discontinuity because of its positive clapeyron slope whereas a warm anomaly would depress the discontinuity but trade offs between seismic wave speed heterogeneity and discontinuity topography often inhibit detailed analysis of these discontinuities and structure often appears very complicated here we simultaneously model seismic refracted waves and scattered waves from the 410 km discontinuity in the western united states to constrain structure in the region we find a low velocity zone with a shear wave velocity drop of 5 on top of the 410 km discontinuity beneath the northwestern united states extending from southwestern oregon to the northern basin and range province this low velocity zone has a thickness that varies from 20 to 90 km with rapid lateral variations its spatial extent coincides with both an anomalous composition of overlying volcanism and seismic receiver function observations observed above the region we interpret the low velocity zone as a compositional anomaly possibly due to a dense partial melt layer which may be linked to prior subduction of the farallon plate and back arc extension the existence of such a layer could be indicative of high water content in the earth s transition zone

global mantle tomography progress status in the past 10 years abstract we review the present status of global mantle tomography and discuss two main classes of models that have been developed in the past 10 years p velocity models based on large datasets of travel times from the international seismological centre bulletins often referred to as high resolution models and s velocity models based on a combination of surface wave and hand picked body wave travel times or waveforms referred to as long wavelength models we discuss their respective strengths and weaknesses as well as progress in the resolution of other physical parameters such as anisotropy anelasticity density and bulk sound velocity using tomographic approaches we present the view that future improvements in global seismic tomography require the utilization of the rich information contained in complete broadband seismic waveforms this is presently within our reach owing to theoretical progress as well as the increase in computational power in recent years

wave breaking and critical levels for propagating inertio gravity waves in the lower stratosphere this paper analyses and interprets the formation of mixed layers due to propagating inertio gravity waves observed during the fronts and atlantic storm track experiment the data used are high vertical resolution soundings launched from different sites located in the north atlantic sector in agreement with other studies attributing the origin of the inertio gravity waves to the adjustment of the jet stream near fronts the largest waves observed are often located in the vicinity of and above frontal bands the amplitude of these waves is large enough that they give rise to narrow mixed layers by a detailed analysis of the waves characteristics we can distinguish whether such a mixing is favoured by the presence of an inertia critical level where f or results from wave induced convective instability occurring far from critical levels here is the wave intrinsic frequency and f is the coriolis parameter these observations highlight the importance of inertio gravity waves in the vertical exchanges that occur in the stratosphere copyright 2002 royal meteorological society

identifying poromechanism and spatially varying parameters of aquifer compaction in choushui river alluvial fan taiwan abstract subsidence occurs in many alluvial depositional environments causing substantial socio economic losses thick aquifers with interbedding or lens structured clay can contribute significantly to compaction the poromechanism of aquifer compaction is usually complicated and its spatial variation is poorly understood inhibiting our ability to fully explain the region wide nature of groundwater exploitation induced land subsidence in this study we explore the poromechanism of aquifer deformation in the choushui river alluvial fan taiwan groundwater level and multi layer compaction data were collected for analyses elastic plastic and viscous characteristics all appear in the deformation data to various extents a visco elasto plastic vep model composed of a visco elastic set and a visco plastic set in series which are associated with different viscous dampers is proposed to model the deformation compared with existing models the proposed model is superior in terms of simulating compaction as well as its applicability and versatility the proposed vep model is applied to observation wells in the proximal middle and distal fans of the choushui river alluvial fan to explore the spatial variation in the poromechanical properties the results show that the young s modulus of the elastic spring increases with depth and with the distance from the distal fan to the proximal fan the young s modulus of the plastic element decreases with depth the system response factor of the visco plastic set decreases with depth and with the distance from the distal fan to the proximal fan aquifer recovery incapability increases with depth both the trend and dynamic fluctuations in compaction for the choushui river alluvial fan are well captured by the proposed vep model which is essential for assessing long term land and water resource management and evaluating potential short term threats to infrastructure caused by seasonal subsidence

upper mantle cross section from tonga to newfoundland a record section of long period u s and canadian observations of multibounce sh waves from a tonga event is used to study lateral variation in the upper mantle source to receiver distances range from 81 to 131 with triplication patterns apparent in s4 for the western north america stations and s5 for the more distant stations a corresponding synthetic section explaining the timing separation and waveform distortions for the various multiple s phases was derived by forward modeling initial trial models consisted of connecting existing pure path models assuming atl old atlantic as an analog for the old pacific tna for the western portion of the united states and sna for the shield portion of north america isovelocity depth contours were constructed to connect these models and corresponding synthetics were computed following a modified wkbj method lateral heterogeneity is found to exist in the upper 350 km of the pacific ocean region and can be modeled reasonably well with a high velocity lid vs 4 7 km s which thickens with increasing oceanic crustal age at the expense of the underlying low velocity zone velocities in the upper 200 km of the older southwest pacific are found to be up to 6 faster than those at comparable depths in the younger tectonic region near western north america the best fitting model indicates that the upper mantle structure of the old pacific is similar to that of the old atlantic although perhaps slightly slower

upper mantle compressional velocity structure beneath the northwest atlantic ocean a compressional velocity model for the northwest atlantic ocean is derived by modeling waveform and travel time data from long period and short period world wide standard seismograph network and canadian network station recordings a 90 km thick lid with a velocity of 8 1 km s at the top gradually increasing to 8 3 km s at the bottom is obtained by fitting the travel time data of first arrivals and waveform data of almost purely oceanic paths at distances of 8 20 triplication p waveform data constrain the structure below the lid a distinct but smooth low velocity zone is located at a depth of 170 km combining these results with the shear wave structure derived by grand and helmberger 1984a for the same region we suggest an olivine rich mineralogy in the upper 100 km and partial melting possibly extending as deep as 300 km based on low seismic velocities and high vp vs

can we resolve 3d density heterogeneity in the lower mantle we reexamine the possibility of resolving 3d density structure in the mantle by performing test inversions using a dataset of well constrained degree 2 splitting coefficients we show that degree 2 in vs and vp can be resolved and confirm that dlnvs dlnvp 2 5 at depths 2000km indicating a chemical component to large scale heterogeneity models with positively correlated with vs in the deepest mantle fit the data at least as well as those in which density and velocities are anti correlated however some rough bounds on dln dlnvs can be inferred models obtained from geodynamic considerations are acceptable in contrast to models with large negative 0 6 dln dlnvs throughout the lower mantle the most robust feature is a marked increase in dln dlnvs at the top of the lower mantle reaching a maximum around 1500 km

analysis of long term land subsidence near mexico city field investigations and predictive modeling the mexico city region has several flat plains formed on exceptionally porous 60 90 lacustrine deposits overlying a highly productive regional aquifer severe land subsidence due to consolidation of the lacustrine aquitard caused by aquifer exploitation has resulted in restrictions on pumping in the core of mexico city this has led to large increases in aquifer pumping in the outlying lacustrine plains where satellite communities are rapidly expanding the chalco basin is one of these lacustrine areas where pumping began in the 1950s and greatly increased in the 1980s the lacustrine sequence in the chalco area is significantly thicker than anywhere else in the basin of mexico averaging 100 m and reaching a maximum thickness of 300 m consequently this area is susceptible to the highest potential land subsidence effects as a result of groundwater extraction of anywhere in the basin land subsidence in the central part of the chalco basin has increased to 0 4 m yr since 1984 and by 1991 total subsidence had reached 8 m the rapid land subsidence in this area is causing the accumulation of meteoric waters during the rainy season resulting in extensive flooding of farmland this study first demonstrates a methodology for combining hydraulic data from a network of monitoring wells geotechnical data from core samples and a compilation of historical information on land surface elevation to quantify groundwater flow and land subsidence phenomena within the rapidly subsiding chalco basin then a one dimensional mathematical model is employed to develop predictions of future land subsidence under a range of pumping conditions the model permits the hydraulic properties of the aquitard to vary as transient functions of hydraulic head and porosity simulations suggest that under current pumping rates total land subsidence in the area of thickest lacustrine sediment will reach 15 m by the year 2010 if pumping is reduced to the extent that further decline in the potentiometric surface is prevented total maximum subsidence would be significantly less 10 m and the rate would nearly cease by 2010

sensitivity of mesoscale gravity waves to the baroclinicity of jet front systems abstract this study investigates the sensitivity of mesoscale gravity waves to the baroclinicity of the background jet front systems by simulating different life cycles of baroclinic waves with a high resolution mesoscale model four simulations are made starting from two dimensional baroclinic jets having different static stability and wind shear in order to obtain baroclinic waves with significantly different growth rates in all experiments vertically propagating mesoscale gravity waves are simulated in the exit region of upper tropospheric jet streaks a two dimensional spectral analysis demonstrates that these gravity waves have multiple components with different wave characteristics the short scale wave components that are preserved by a high pass filter with a cutoff wavelength of 200 km have horizontal wavelengths of 85 161 km and intrinsic frequencies of 3 11 times the coriolis parameter the medium scale waves that are preserved by a bandpass filter with 200 and 600 km cutoff wavelengths ha

multimode surface waveform tomography of the pacific ocean a closer look at the lithospheric cooling signature summary we present a regional surface waveform tomography of the pacific upper mantle obtained using an automated multimode surface waveform inversion technique on fundamental and higher mode rayleigh waves to constrain the vsv structure down to 400 km depth we have improved on previous implementations of this technique by robustly accounting for the effects of uncertainties in earthquake source parameters in the tomographic inversion we have furthermore improved path coverage in the south pacific region by including rayleigh wave observations from the french polynesian pacific lithosphere and upper mantle experiment deployment this improvement has led to imaging of vertical low velocity structures associated with hotspots within the south pacific super swell region we have produced an age dependent average cross section for the pacific ocean lithosphere and found that the increase in vsv with age is broadly compatible with a half space cooling model of oceanic lithosphere formation we cannot confirm evidence for a pacific wide reheating event our synthetic tests show that detailed interpretation of average vsv trends across the pacific ocean may be misleading unless lateral resolution and amplitude recovery are uniform across the region a condition that is difficult to achieve in such a large oceanic basin with current seismic stations

trans pacific upper mantle shear velocity structure 1 we use 50 tonga fiji events recorded at the broadband trinet array southern california to develop a pure path upper mantle shear velocity model across the pacific at the epicentral distances of 70 95 multibounce s waves up to s5 are observed including their triplicated branches which become particularly clear after stacking since these s wave multiples turn at various depths simultaneously modeling their differential traveltimes and waveforms provides strong constraints on the radial velocity structure we parameterize the velocity model according to a priori information from the previous oceanic models so that we can take a grid search approach to fully investigate possible interdependencies among the model parameters we construct synthetics with a reflectivity code and study both the sh and sv components by modeling the whole recordings from events at different depths with different mechanisms we are able to separate shallow low velocity zone lvz features from deeper structure our preferred model pac06 contains a fast lid vsh 4 78 km s 1 vsv 4 58 km s 1 with a thickness of 60 km the underlying lvz is prominent with the lowest velocities vsh 4 34 km s 1 and vsv 4 22 km s 1 occurring at a depth of 160 km these velocities are below the estimates of solid state lvz suggesting the presence of partial melt the anisotropy vsv vsh of pac06 extends to 300 km depth which is constrained by s5 turning at this depth besides the 406 km and 651 km discontinuities pac06 also has a small 1 velocity jump at 516 km we consider these main features of pac06 to be well determined since pac06 explains a large data set from various events therefore it is ideally suited for comparing with mineralogical models

comparison of a large scale inertia gravity wave as seen in the ecmwf analyses and from radiosondes 1 the location characteristics and evolution of a large scale inertia gravity wave that occurred in the lower stratosphere over the north of the british isles on february 6 1997 are studied numerous high resolution radiosondes were available at that time and in that region as part of the fastex database they reveal an intense large scale inertia gravity wave igw propagating upwards above the tropopause maps of the divergence of the horizontal wind on isentropic surfaces were obtained from the ecmwf analyses and showed a clear pattern of alternating bands of convergence and divergence at the lower stratospheric heights in the same geographical region and starting at the same time the comparison of the characteristics of this igw in the analyses and in the observations suggests that the ecmwf analyses can be used for qualitative indications regarding the locations most favorable to large scale igw generation and the corresponding orientation of the waves

adaptive explicit implicit quasi three dimensional finite element model of flow and subsidence in multiaquifer systems a quasi three dimensional finite element model is presented for the analysis of groundwater flow and land subsidence due to pumpage in multiaquifer systems in the model aquifers are simulated with the aid of two dimensional horizontal finite element grids each aquifer is connected to its neighbors above and below by one dimensional vertical finite element strings which allow leakage to take place across aquitards and aquicludes land subsidence is modeled by varying the void ratio of each vertical element according to a nonlinear version of terzaghi s one dimensional consolidation theory a major feature of the new method is its ability to solve the finite element equations explicitly in one part of the mesh and implicitly in another part depending on the ratio between the stability limit of each node and any given time step size since the hydraulic diffusivity of aquitards is usually very small compared to that of aquifers it is often possible to solve the finite element equations explicitly for most and sometimes all aquitard nodes this leads to a virtual decoupling of the aquifer equations during a given time step which results in a significant saving of computer time and storage

polar stratospheric ice cloud above spitsbergen 1 within the extremely cold and stable polar vortex of winter 2004 2005 a polar stratospheric ice cloud was observed from ny alesund spitsbergen on 26 january 2005 the observation of a cloud with backscatter ratios up to 23 and volume depolarization larger than 50 is unique in our 15 year ground based lidar data record simultaneous balloon borne water vapor measurements indicate the presence of mesoscale ice clouds nearby normally low horizontal wind speeds inside the inner vortex prevent vertical wave propagation however the rare coincidence of different meteorological processes occurring during a poleward breaking rossby wave event caused favorable conditions for the vertical propagation of mountain waves excited by the flow past spitsbergen detailed meteorological analysis shows that the ice particle formation processes on 26 january 2005 were most likely provoked by mesoscale stratospheric temperature anomalies leading to a local reduction in water vapor

inertia gravity wave generation by the tropospheric midlatitude jet as given by the fronts and atlantic storm track experiment radio soundings 1 generation of inertia gravity waves by the midlatitude tropospheric jet is studied on the basis of the data obtained from the radio soundings over the north atlantic during the fronts and atlantic storm track experiment campaign a sample of 224 radio soundings is used to analyze the wave activity as a function of the distance to the jet it is shown that radio soundings displaying the most intense gravity wave activity both in the stratosphere and in the troposphere are the ones closest to the jet axis thus the jet region is the dominant source of gravity waves in this region far from orography further examination allows for identification of two specific regions of the flow that are associated with intense gravity wave activity the vicinity of the maximum of the jet velocity and the regions of strong curvature of the jet the detailed case studies we provide suggest that geostrophic adjustment is the dynamical mechanism responsible for the generation of large amplitude inertia gravity waves in the regions of the strong curvature of the wind the generation of waves in the vicinity of the regions where the wind veers in the deep troughs of the geopotential appears to be systematic

gravity wave variations during the 2009 stratospheric sudden warming as revealed by ecmwf t799 and observations 1 ecmwf t799 is used to study gravity wave gw variations during the 2009 stratospheric sudden warming ssw in the arctic the magnitude and occurrence of gws correlate with the location and strength of the polar vortex that is strongly disturbed by planetary wave pw growth this location dependence on pw phase explains the observed gw variability during ssws during the development and the onset of ssw the zonal mean gw potential energy density gw ep increases on january 5 and 15 22 in association with the growth of pw wavenumber 1 and wavenumber 2 respectively as the initial prominent pw magnitude in the lower mesosphere progresses downward gw ep enhancement also seems to show a corresponding descent from january 5 22 gw ep peaks before the wind reversal occurrence and significantly weakens after the ssw these variations are confirmed by cosmic gps observations lidar data from antarctica are also used to validate gws as derived in ecmwf

evolution of long term land subsidence near mexico city review field investigations and predictive simulations 1 aquitard consolidation in the chalco plain is the most recent of a series of major land subsidence problems near mexico city caused by leaky aquifer pumping and involving a complex distribution of basalt flows within a lacustrine sequence this study first conducted a ground magnetic survey combined with lithologic logs to map the extension of basalts then it assessed the evolution of ground surface elevations and updated hydraulic heads in the aquifer and aquitard in order to verify the accuracy of previous simulations and develop new predictions on land subsidence employing a one dimensional nonlinear groundwater flow consolidation model results show the presence of shallow basalts that extend from sierra santa catarina into the chalco plain causing a differential consolidation that controls both the distribution of large scale fractures in the aquitard and the shape of a new lake cumulative land subsidence in the center of the chalco plain reached 13 m in 2006 thus closely matching previous numerical estimations since 1985 the ground surface decline has continued at a rate of 0 40 m yr while the potentiometric surface decline in the aquifer proceeds at an average rate of 1 5 m yr indicating that the flow system has not yet reached steady state conditions numerical predictions show that under current pumping rates where the aquitard is 300 m total land subsidence will reach 19 m by the year 2020 while where the aquitard is 140 m thick total land subsidence will reach 12 m and increase the risk of flooding and aquitard fracturing for nearby urban centers

modeling visco elastic plastic deformation of soil with modified merchant model eighty four to ninety eight percent of land subsidence in shanghai city is caused by the visco elastic plastic deformation of sediments numerical experiments are done on the sediments with visco elastic plastic deformation in shanghai to verify the modified merchant model mm model and land subsidence model based on the modified merchant ls mm model there are two advantages of the mm model and the ls mm model one is that only a few parameters are involved there are three parameters in the mm model and four parameters in the ls mm model the other one is that both models can describe elastic elastic plastic and visco elastic deformation in addition to visco elastic plastic deformation the corresponding models are developed by setting proper values of the three parameters of 1 and 2 the two advantages make the ls mm model flexible and applicable to the simulation of the large regional land subsidence with visco elastic plastic deformation and other different kinds of deformation the results can be improved by variable parameters especially specific storage

the pacific plume as seen by s scs and sks the forward modeling of s sks and scs s differential travel time residuals sensitive to structure beneath a localized region of the central pacific suggests the presence of two anomalous domains first a broad zone which becomes thinner as it extends into the mid mantle where the s velocity is reduced by 2 to 4 and which is deflected to the south east as it rises towards the surface adjacent to it a smaller domain where the s velocity is about 4 higher these strong velocity anomalies are likely the results of chemical heterogeneity that may involve subducted material and partial melting strong heterogeneity appears to extend at least locally well above d but the morphology of the anomalous domains is more reminiscent of localized rising or sinking currents rather than of a relatively uniform and thick geochemical reservoir

seismological structure of the upper mantle a regional comparison of seismic layering abstract we investigate seismic layering i e discontinuities regions of anomalous velocity gradients and anisotropy and its lateral variability in the upper mantle by comparing seismic models from three tectonic regions old 100 ma pacific plate younger 40 ma philippine sea plate and precambrian western australia these models were constructed by combining two data sets scs reflectivity profiles which provide travel times and impedance contrasts across mantle discontinuities and observations of frequency dependent travel times of three component turning s ss ss sss sss sa and surface r1 g1 waves which constrain the anisotropic velocity structure between discontinuities the models provide a better fit to observed seismograms from these regions than the current generation of global tomographic models the australian model is characterized by high shear velocities throughout the upper 350 km of the mantle with no low velocity zone lvz in the isotropically averaged shear velocities in contrast the oceanic models are characterized by a thin high velocity seismic lid underlain by a distinct lvz with a sharp boundary the g discontinuity separating them the g is significantly deeper beneath the western philippine sea plate than beneath the older pacific 89 and 68 km respectively implying that thermal cooling alone does not control the thickness of the lid we interpret this discontinuity as a compositional boundary marking the fossilized base of the melt separation zone msz active during sea floor spreading no discontinuity is detected at the base of the lvz in the oceanic models the s velocity gradient between 200 and 410 km depth is much steeper in the oceans than beneath australia this high oceanic gradient is probably controlled by a decrease in the homologous temperature over this depth interval the relative depths of the transition zone tz discontinuities are consistent with clapeyron slopes expected for an olivine dominated mineralogy the 660 km discontinuity displays variability in its amplitude that appears to correlate with its depth shallow and bright beneath the pacific deep and dim beneath australia and the philippine sea such behavior is possibly caused by the juxtaposition of the olivine and garnet components of the phase transition radial anisotropy extends through the upper 250 km of the mantle in the australia model and through the upper 160 km of the two oceanic models the magnitude of anisotropy is consistent with that expected for models of horizontally oriented olivine and the localization of anisotropy in the shallowest upper mantle implies that it reflects strain associated with past or present tectonic events

three dimensional s wave velocity structure in southern california 1 the three dimensional s wave velocity structure was constructed from rayleigh wave phase velocities measured using teleseismic trinet data the s wave velocity maps show some features that are much more distinct than previous tomographic results in southern california there is a clear seismic velocity contrast across the san andreas fault the north american plate side is systematically slower than the pacific plate side under the eastern california shear zone there are distinct slow velocity anomalies in the crust suggesting a close connection to lower viscosity crust previously concluded from observation of the post seismic deformation after the landers earthquake major upper mantle features include a fast velocity root under the transverse ranges which is the dominant feature in the upper mantle and a slow velocity anomaly under the salton trough our results support that the velocity contrast across the san andreas fault extends below the moho

the synoptic setting and possible energy sources for mesoscale wave disturbances abstract thirteen case studies of mesoscale wave disturbances characterized by either a singular wave of depression or wave packets with periods of 1 4 h horizontal wavelengths of 50 500 km and surface pressure perturbation amplitudes of 0 2 7 0 mb are reviewed to isolate common synoptic features for these cases and to shed light on possible energy sources for the waves a strong thermal inversion in the lower troposphere north of a frontal boundary and a jet streak propagating toward a ridge axis in the upper troposphere are commonly observed in all the cases in general the area of wave activity is bounded by the jet axis to the west or northwest a surface front to the southeast an inflection axis between the trough and ridge axes to the southwest and the ridge axis to the northeast the conditions specified by lindzen and tung as being necessary to form a wave duct which include the existence of the lower tropospheric inversion seem to be met in many of these cases this suggests that a du

whole mantle shear structure beneath the east pacific rise we model broadband seismograms containing triplicated s s 2 and s 3 along with scs to produce a pure path one dimensional model extending from the crust to the core mantle boundary beneath the east pacific rise we simultaneously model all body wave shapes and amplitudes thereby eliminating depth velocity ambiguities the data consist of western north american broadband recordings of east pacific rise epr affiliate transform events that form a continuous record section out to 82 and sample nearly the entire east pacific rise the best fitting synthetics contain attenuation and small changes in lithospheric thickness needed to correct for variation in bounce point ages the 660 km discontinuity is particularly well resolved and requires a steep gradient 4 extending down to 745 km we find no discernible variation in apparent depths of the 405 and 660 km discontinuities over ridge orthogonal distances on the order of 1000 km or 20 ma lithosphere body waveform comparisons indicate that we can resolve discontinuity depths to less than 10 km providing an upper limit to transition zone topography these depth estimates in conjunction with the fan shot nature of the ray paths lower the detection limit from s 2 precursor analysis of the lateral length scale over which short wavelength topographic variation could occur and indicate the sub epr transition zone and upper mantle are remarkably homogeneous the lower mantle beneath the east pacific rise is well modeled by prem with the greatest variation occurring in scs reflecting strong heterogeneity along the core mantle boundary together these observations require that the east pacific rise spreading ridge cannot be actively supplied from the local lower mantle and that tomographically imaged lateral variation beneath the ridge likely reflects lateral smearing of outlying velocity gradients dynamically the transition zone therefore appears vertically decoupled from the overlying east pacific rise spreading system

a strongly negative shear velocity gradient and lateral variability in the lowermost mantle beneath the pacific a new approach for constraining the seismic shear velocity structure above the core mantle boundary is introduced whereby sh sks differential travel times amplitude ratios of sv sks and sdiff waveshapes are simultaneously modeled this procedure is applied to the lower mantle beneath the central pacific using da ta from numerous deep focus southwest pacific earthquakes recorded in north america we analyze 90 broadband and 248 digitized analog recordings for this source receiver geometry sh sks times are highly variable and up to 10 s larger than standard reference model predictions indicating the presence of laterally varying low shear velocities in the study area the travel times however do not constrain the depth extent or velocity gradient of the low velocity region sv sks amplitude ratios and sh waveforms are sensitive to the radial shear velocity profile and when analyzed simultaneously with sh sks times rnveal up to 3 shear velocity reductions restricted to the lowermost 190 50 km of the mantle our preferred model for the central eastern pacific region ml has a strong negative gradient with 0 5 reduction in velocity relative to the preliminary reference earth model prem at 2700 km depth and 3 reduction at 2891 km depth and slight velocity reductions from 2000 to 2700 km depth 0 0 5 lower than prem significant small scale 100 500 km shear velocity heterogeneity 0 5 1 is required to explain scatter in the differential times and amplitude ratios