the two dimensional dynamics of west african squall lines the two dimensional dynamics of multicell and unicell squall lines are examined using a numerical model both types feature a convective jump updraught with extensive deep rearward extending anvils the multicell case contains travelling convection cells and is unsteady but persistent whereas the unicell case is quasi steady in the multicell case an extensive density current is produced by the evaporation and drag of rain falling from a succession of convection cells which travel rearwards relative to the density current head the circulation within the density current is complex and consists of three mutually interactive branches a rotor a cold downdraught and a subsidence region in the unicell case a density current is not produced and the updraught is forced by a propagating wave of elevation generated as an interaction between the updraught water loading and evaporation in a very localized area the squall line structure is compared with other models and it is shown that certain propagating two dimensional tropical and mid latitude squall lines are dynamically similar their detailed structure being controlled by the inflow wind profile the multicell case is compared with a quasi two dimensional west african squall line which occurred on 22 june 1981 during the convection profonde tropicale copt 81 experiment performed in the northern part of the ivory coast good agreement is found between the model and the observations and hence the dynamics of the observed squall line is quantified the unicell case in which a density current and conventional downdraughts are absent has yet to be identified in atmospheric observations

detailed crustal thickness variations beneath the illinois basin area implications for crustal evolution of the midcontinent we present high resolution imaging results of crustal and upper mantle velocity discontinuities across the illinois basin area using both common conversion point stacking and plane wave migration methods applied to p wave receiver functions from the earthscope oiink ozark illinois indiana and kentucky experiment the images reveal unusually thick crust up to 62 km throughout the central and southeastern illinois basin area a significant moho gradient underlies the nw trending ste genevieve fault zone which delineates the boundary between the illinois basin and ozark dome relatively thinner crust 45 km underlies most of the precambrian highlands surrounding the illinois basin and beneath the rift related structures of the reelfoot rift and the rough creek graben we consider four hypotheses to explain the presence of thick crust under the central and southeastern illinois basin crustal thickening may have been produced 1 prior to its accretion to north america around 1 55 ga and is an inherited characteristic of this crustal province 2 by underthrusting or shortening during proterozoic convergent margin tectonics around 1 55 1 35 ga 3 by late precambrian magmatic underplating at the base of older crust associated with the creation of the eastern granite rhyolite province around 1 3 ga and 4 through crustal relamination during an episode of proterozoic flat slab subduction beneath the illinois basin possibly associated with the grenville orogeny

structure and evolution of the 22 february 1993 toga coare squall line organization mechanisms inferred from numerical simulation abstract mechanisms responsible for meso and convective scale organization within a large tropical squall line that occurred on 22 february 1993 during the tropical ocean global atmosphere coupled ocean atmosphere response experiment are investigated using a three dimensional numerical cloud model the squall line occurred in an environment typical of fast moving tropical squall lines characterized by moderate convective available potential energy and moderate to strong vertical shear beneath a low level jet with weak reverse vertical shear above a well simulated aspect of the observed squall line is the evolution of a portion of its leading convective zone from a quasi linear to a three dimensional bow shaped structure over a 2 h period this transition is accompanied by the development of both a prominent mesoscale vortex along the northern edge of the 40 60 km long bow shaped feature and elongated bands of weaker reflectivity situated rearward and oriented transverse to the leading edge within enha

improving understanding of near term barrier island evolution through multi decadal assessment of morphologic change abstract observed morphodynamic changes over multiple decades were coupled with storm driven run up characteristics at fire island new york to explore the influence of wave processes relative to the impacts of other coastal change drivers on the near term evolution of the barrier island historical topography was generated from digital stereo photogrammetry and compared with more recent lidar surveys to quantify near term decadal morphodynamic changes to the beach and primary dune system between the years 1969 1999 and 2009 notably increased profile volumes were observed along the entirety of the island in 1999 and likely provide the eolian source for the steady dune crest progradation observed over the relatively quiescent decade that followed persistent patterns of erosion and accretion over 10 30 and 40 year intervals are attributable to variations in island morphology human activity and variations in offshore bathymetry and island orientation that influence the wave energy reaching the coast areas of documented long term historical inlet formation and extensive bayside marsh development show substantial landward translation of the dune beach profile over the near term period of this study correlations among areas predicted to overwash observed elevation changes of the dune crestline and observed instances of overwash in undeveloped segments of the barrier island verify that overwash locations can be accurately predicted in undeveloped segments of coast in fact an assessment of 2012 aerial imagery collected after hurricane sandy confirms that overwash occurred at the majority of near term locations persistently predicted to overwash in addition to the storm wave climate factors related to variations within the geologic framework which in turn influence island orientation offshore slope and sediment supply impact island behavior on near term timescales

sharpness of upper mantle discontinuities determined from high frequency reflections an understanding of the nature of seismic discontinuities in the earth s upper mantle is important for understanding mantle processes in particular the amplitude and sharpness of these discontinuities are critical for assessing models of upper mantle phase changes and chemical layering so far seismic studies aimed at determining the thickness and lateral variability of upper mantle discontinuities have yielded equivocal results particularly for the discontinuity at 410km depth1 2 here we present short period 0 8 2 0 s recordings of upper mantle precursors to the seismic phase p p pkppkp from two south american earthquakes recorded by the 700 station short period array in california our results show that the 410 and 660 km discontinuities beneath the indian ocean are locally simple and sharp corresponding to transi tion zones of 4 km or less these observations pose problems for mineral physics models3 5 which predict a transitional thickness greater than 6 km for the peridotite to spinel phase transition in contrast to the results of long period studies6 7 we observe no short period arrivals from near 520 km depth

three dimensional prestack plane wave migration of teleseismic p to s converted phases 1 theory 1 we present the theoretical foundations for a prestack migration technique to image teleseismic p to s converted phases the method builds on teleseismic p wave deconvolution pseudostation stacking neal and pavlis 1999 and on the idea of using a plane wave decomposition for imaging as introduced by treitel et al 1982 deconvolution operators are constructed by pseudostation stacking of the array aligned to the incident p wave arrival times to produce a space variable deconvolution operator the resulting data are then muted to remove the deconvolved direct p wave pulse and pseudostation stacked over a grid of feasible slowness vectors the pseudostation stack interpolates the wave field onto a regular grid along earth s surface producing a series one per slowness vector of uniformly sampled three dimensional data cubes two space variables and time the plane wave components can be propagated downward using a form of approximate ray tracing with a three dimensional earth model this yields a series of distorted cubes topologically equivalent to the original uniformly sampled data cubes these data volumes are summed as a weighted stack with the weights derived from an integration formula for inverse scattering based on the generalized radon transform this allows an image of the subsurface to be constructed on an event by event basis beneath the array we apply this technique to data from the lodore array that was deployed in northwestern colorado the results suggest the presence of a major lithospheric scale discontinuity defined by a south dipping boundary

shear parallel moist convection over the tropical ocean a case study from 18 february 1993 toga coare abstract this paper describes a newly observed form of shear parallel rainbands that were observed on 18 february 1993 in tropical ocean global atmosphere coupled ocean atmosphere response experiment using the ncar eldora airborne doppler radar interesting features of these rainbands included their rapidly changing and highly cellular nature their complicated and layered kinematic structure and the effects of the rainbands on the tropical environment in their lower levels the rainbands consisted of east west elongated clusters of small convective cells aligned with the z 0 5 km shear vector strong low level convergence inflow from the north and enhanced westerly winds extended from the surface up to 5 km much of this air was vented out of the storm at midlevels exiting to the north in the 0 c stable layer at z 5 7 km this midlevel outflow fed an area of widespread stratiform precipitation lying to the north of the rainband the cold pool outflow emanating from this area of precipitation t

geomorphic and stratigraphic analysis of fire island new york abstract barrier islands along the east coast of the united states are believed to be migrating landward in response to sea level rise modes and rates of displacement of fire island along the south shore of long island n y were investigated through geomorphic and stratigraphic analyses inlet processes are principally responsible for bayshore sediment accretion and hence landward displacement while overwash has contributed to increasing the island s elevation portions of marsh areas covered by washover deposits were often raised above the tidal level permitting colonization by barrier flat vegetation photographic analysis showed that only the 1938 hurricane resulted in bayshore accretion by washover a small amount at one locality most of the bayside marshes formed on relict flood tidal delta shoals former inlet sites are characterized by typical geomorphic features including relict inlet ridges indentation of the bay shoreline wide marsh plains and relict flood tidal delta islands in the bay historical records and relict inlet features indicate that as much as 85 of the area has been affected by inlet activity the geomorphic and vegetative data supported by the stratigraphic interpretations showed that the western section of fire island n y is migrating landward more slowly than the eastern section of the barrier chain this trend is probably due to hurricane tracks and to an increased sediment supply to the western part barrier migration is occurring continuously over geologic time but considered on a short term basis displacement is sporadic and related to inlet processes over the past 1000 years fire island has experienced shoreface erosion as well as bayshore erosion and submergence

a mathematical model of spit growth and barrier elongation application to fire island inlet usa and badreveln spit sweden a mathematical model of spit growth and barrier elongation adjacent to an inlet of arbitrary width supplied by sediment coming from longshore sediment transport was developed based on the spit growth model proposed by kraus 1999 the fundamental governing equation is the conservation equation for sand where the width of the spit is assumed constant during growth the portion of the longshore sediment transport feeding the spit has been estimated based on the ratio between the depth of the inlet channel and the depth of active longshore transport sediment transport from the channel due to the inlet flow as well as other sinks of sand e g dredging are taken into account measured data on spit elongation at fire island inlet united states and at badreveln spit sweden were used to validate the model the simulated results agree well with the measured data at both study sites where spit growth at fire island was restricted by the inlet flow and the growth at badreveln spit was unrestricted the model calculation for fire island inlet indicates that the dredging to maintain channel navigation is the major reason for the stable period observed from 1954 to 1994 at the fire island barrier the average annual net longshore transport rate at the eastern side of the fire island inlet obtained in this study was about 220 000 m 3 yr of which approximately 165 000 m 3 yr 75 of the net longshore transport is deposited in the inlet feeding the spit growth whereas the remaining portion 25 is bypassed downdrift through the ebb shoal complex c 2011 elsevier ltd all rights reserved less

seismic scattering at the top of the mantle transition zone abstract we document strong seismic scattering from around the top of the mantle transition zone in all available high resolution explosion seismic profiles from siberia and north america this seismic reflectivity from around the 410 km discontinuity indicates the presence of pronounced heterogeneity in the depth interval between 320 and 450 km in the earth s mantle we model the seismic observations by heterogeneity in the form of random seismic scatterers with typical scale lengths of kilometre size 10 40 km by 2 10 km in a 100 140 km thick depth interval the observed heterogeneity may be explained by changes in the depths to the spinel transformations caused by an unexpectedly high iron content at the top of the mantle transition zone the phase transformation of pyroxenes into the garnet mineral majorite probably also contributes to the reflectivity mainly below a depth of 400 km whereas we find it unlikely that the presence of water or partial melt is the main cause of the observed strong seismic reflectivity subducted oceanic slabs that equilibrated at the top of the transition zone may also contribute to the observed reflectivity if this is the main cause of the reflectivity a substantial amount of young oceanic lithosphere has been subducted under siberia and north america during their geologic evolution subducted slabs may have initiated metamorphic reactions in the original mantle rocks

accelerated relative sea level rise and rapid coastal erosion testing a causal relationship for the louisiana barrier islands abstract the role of relative sea level rise as a cause for the rapid erosion of louisiana s barrier island coast is investigated through a numerical implementation of a modified bruun rule that accounts for the low percentage of sand sized sediment in the eroding louisiana shoreface shore normal profiles from 150 km of coastline west of the mississippi delta are derived from bathymetric surveys conducted during the 1880s 1930s and 1980s an rms difference criterion is employed to test whether an equilibrium profile form is maintained between survey years only about half the studied profiles meet the equilibrium criterion this represents a significant limitation on the potential applicability of the bruun rule the profiles meeting the equilibrium criterion along with measured rates of relative sea level rise are used to hindcast shoreline retreat rates at 37 locations within the study area modeled and observed shoreline retreat rates show no significant correlation thus in terms of the bruun approach relative sea level rise has no power for hindcasting and presumably forecasting rates of coastal erosion for the louisiana barrier islands

thermodynamic analytic fields from doppler radar data by means of the mandop analysis the paper is devoted to scale interaction studies it presents a new approach for retrieving mesoscale and convective scale thermodynamic fields from doppler radar data in order to diagnose processes involved in these interactions thermodynamic fields are retrieved analytically using the analytic form of the three dimensional wind field obtained by the mandop analysis in the non dissipative and stationary first order anelastic approximation of the equation of motion applications on simulated data and experimental data from the toga coare show the capability of this new method to retrieve the pressure and temperature fields at various scales of motion and in particular at mesoscale this new analysis will be used intensively on doppler radar data collected during the fronts and atlantic storm tracks experiment in order to diagnose the multiscale interaction processes associated with frontal wave and or secondary cyclogenesis

shear wave splitting and the pattern of mantle flow beneath eastern oregon a r t i c l e i n f o article history the tectonic and geologic setting of eastern oregon includes the volcanically active high lava plains hlp province and the accreted terrains of the blue and wallowa mountains and is bounded by the columbia river ood basalts to the north basin and range extension to the south the cascade arc to the west and stable north america to the east several models have been proposed to explain the tectonic evolution of eastern oregon and in particular the voluminous volcanic activity in the hlp but a consensus on which model fully describes the complex range of processes remains elusive measurements of the seismic anisotropy that results from active mantle ow beneath the region can provide a crucial test of such models to constrain this anisotropy here we present new sks splitting results obtained at approximately 200 broadband seismic stations in eastern oregon and the surrounding region data come from the usarray transportable array ta and two temporary experiments carried out in the hlp and in the wallowa mountains our splitting data set includes 2900 individual splitting measurements from sks phases recorded between 2006 and 2008 stations in eastern oregon exhibit signi cant shear wave splitting with average delay times at individual stations between 0 8 s and 2 7 s in the hlp nearly all observed fast directions are approximately e w while to the north in the blue and wallowa mountains there is more variability in the splitting patterns the average delay time observed at stations located in the heart of the hlp province is 2 s well above the global average of 1 s for continental regions we infer from the large split times and homogeneous fast directions that there must be signi cant active ow in a roughly e w direction in the asthenosphere beneath the hlp this inferred ow eld places a strong constraint on models that seek to explain the young tectonomagmatic activity in the region in the wallowa region the anisotropic signature is more complicated and there may be a signi cant contribution from fossil fabrics in the crust or mantle lithosphere

experiments in migration processing of ss precursor data to image upper mantle discontinuity structure long period ss precursors result from underside reflections off upper mantle discontinuities by grouping and stacking global seismic data by ss bounce point location it is possible to map lateral variations in depths to the 410 and 660 km discontinuities a process analogous to common midpoint cmp stacking in reflection seismology because this method assumes horizontal reflectors energy arriving from dipping or intermittent reflectors may not be correctly imaged to address this possibility we experiment with techniques based on migration processing of shallow seismic reflection data the problem is complicated by the uneven distribution of sources and receivers for the ss precursor observations but the data are sufficiently dense beneath the northwest pacific ocean that reasonably good coverage can be obtained for this region we parameterize the model as a grid of point scatterers in latitude longitude and depth from the surface to 1000 km depth and compute travel times from each grid point to the source and receiver locations these times are used to construct a matrix equation that yields predicted ss precursor waveforms from the assumed scatterers to recover the model we experiment with both simple back projection and full inversions using a conjugate gradient method tests on noise free synthetic data generated using the same source receiver distribution as the actual data suggest that detailed resolution of discontinuity structure is possible at horizontal scales much smaller than the fresnel zone however the real data do not produce coherent results unless some degree of horizontal smoothing is imposed at least partially defeating the purpose of this approach results for the northwest pacific find structure on the 410 and 660 km discontinuities and hints of intermittent reflectors at other depths random resampling tests however suggest that most of these features are not reliably resolved with the exception of a depression on the 660 km discontinuity seen in the northwest pacific our experiments show that it is unlikely that small scale structure on the 660 km discontinuity near subducting slabs causes significant bias in maps of the large scale 660 km topography derived from long period ss precursor observations

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

observations of mesoscale circulations within extratropical cyclones over the north atlantic ocean during erica abstract pseudo dual doppler analyses of two mesoscale circulations 20 40 km in horizontal dimensions that formed along a warm front within a rapidly deepening extratropical cyclone over the ocean are presented the circulations were analyzed using airborne doppler radar during erica experiment on rapidly intensifying cyclones over the atlantic iop intensive observing period 4 and are believed to be a type of frontal instability that has not been addressed in past theoretical studies of frontal waves and cyclones these features may be the shallow circulations that have been documented to play a role in cyclogenesis when they become coupled with an upper level baroclinic wave the present case is compared and contrasted with the only other well analyzed event during erica iop 5 a retrieval of the perturbation pressure and buoyancy fields using the kinematic wind fields is performed in order to facilitate the interpretation of the dynamic structure of these vortices in addition a set of equations

test of a convective wake parameterization in the single column version of ccm3 abstract a convective wake parameterization incorporated into the single column scm version of the ncar community climate model ccm3 is tested using observational data from 12 squall line cases to determine whether it can successfully reproduce convectively driven wakes in a global climate model the key spatial thermodynamic and kinematic properties of the modeled versus the observed wakes are examined as these features determine the effects of the wakes on surface fluxes and the initiation of convection effects that should be simulated correctly in general circulation models if deep convection and the resulting earth atmosphere energy exchanges are to be adequately represented results from these simulations indicate that while the scm convective wake scheme combination generally produced long lasting squall wake systems the wakes were often too shallow too warm and too moist these differences occurred despite the ability of ccm3 s standard cumulus parameterization to provide the wake scheme

protecting natural landforms and habitats by nourishing an eroding estuarine beach an important issue facing coastal managers is how natural coastal habitats can be protected against wave erosion by human action an assessment is made of attempts to protect a rare maritime forest on the bay side of a barrier island at fire island new york usa using artificial beach fill the sediment deficit is caused by human attempts to stabilize the island by restricting inlet formation overwash and dune migration and it is exacerbated by a nearby marina bulkhead a total of 1099 m3 of sand dredged from the navigation channel was placed near the bulkhead loss of fill was 5 54 7 87 m3 m 1 in the first 6 months the fill was gone 18 months after placement sediment moving out of the fill area caused almost 4 m of shoreline advance 40 m downdrift after 6 months gain of 3 28 m3 m 1 followed by retreat of about 5 m at that location over the next 12 months loss of 5 51 m3 m 1 these results reveal how small changes in volume of microtidal estuarine beaches can cause great shoreline displacement rates the amount of fill from maintenance dredging is insufficient to replenish erosion losses placing additional fill sediment on the bayside to create artificial washover fans can mimic natural landforms and overcome loss of sediment inputs caused by stabilizing the ocean shore mechanical placement may be preferable to natural processes which would deliver sediment across the island and through pre existing stable habitat eliminating some of the features that take long to form

low energy sandy beaches in marine and estuarine environments a review this review was undertaken to identify locations where low energy beaches may occur and their diagnostic forms and process controls including waves tides and water levels examples are drawn from the sheltered coastline of western australia near perth and fetch limited estuarine environments on the northeast coast of the united states we suggest that the term low energy be used in locations where 1 non storm significant wave heights are minimal e g 0 25 m 2 significant wave heights during strong onshore winds are low e g 0 50 m 3 beachface widths are narrow e g 20 m in microtidal environments and 4 morphologic features include those inherited from higher energy events micro topographic features can persist in the swash zone of low energy beaches under non storm wave conditions there is little evidence of cyclic cross shore sediment exchange bars excepting transverse forms located seaward of low still water level do not appear to be part of the sediment exchange system with the foreshore developing a better definition of the term low energy requires understanding the occurrence and duration of morphological characteristics and the type magnitude and frequency of hydrodynamic controls that are responsible for these characteristics efforts also should be directed toward 1 discriminating between processes generated within basins in true fetch limited environments and processes generated outside basins that affect sheltered environments 2 identifying the relative contributions of tide and surge related water level fluctuations on low energy beach shape and 3 estimating thresholds for beach change

heterogeneous distribution of water in the mantle transition zone inferred from wavefield imaging abstract the amount of water in the earth s deep mantle is critical for the evolution of the earth mineral physics studies revealed that the mantle transition zone can store several times the volume of water in an ocean however the actual water distribution in the transition zone remains enigmatic we used the highest resolution images produced of scatterers in the north american transition zone derived from teleseismic data recorded by the earthscope transportable array we find that the transition zone is filled with previously unrecognized small scale heterogeneities that produce pervasive negative polarity signals simulations demonstrated the images can be explained by low velocity bodies shaped as distributed blobs or near vertical structures we suggest these low velocity bodies may be heterogeneously distributed water enriched subducted harzburgites produced through long term accumulation

restoring sediment to compensate for human induced erosion of an estuarine shore abstract shoreline erosion is often exacerbated by reduction of sediment inputs because of interference with sediment transport by human structures we evaluate use of sediment dredged from a navigation channel to establish a feeder beach adjacent to a bulkhead as a solution for addressing erosion of landforms and habitats on sandy estuarine shores the objectives are to determine how beach volume position and shape within and downdrift of the fill area change and whether the volumes supplied by dredging match sediment losses caused by human actions the fill was placed along a 75 m length of shoreline adjacent to a marina in great south bay at fire island new york usa changes in beach shape and volume were determined from topographic surveys conducted before and after fill and at half year intervals for 18 months the quantity of fill was 1747 m3 maximum shoreline advance due to fill emplacement was 20 7 m the maximum volume placed at any transect was 28 6 m3 m 1 of shoreline length erosion of the fill occurred rapidly with landward migration of a conspicuous scarp the edge of the upland 18 months after the fill was placed was up to 4 6 m farther landward than prior to the fill movement of sediment alongshore downdrift of the fill occurred as wave like pulses extending the active foreshore bayward causing accretion of the inner low tide terrace burying saltmarsh peat outcrops on the foreshore and creating a higher and wider overwash platform over portions of the saltmarshes landforms downdrift of the fill area underwent successive stages including erosion pre nourishment accretion stability with throughput of sediment and then erosion beach nourishment compensates for human induced sediment losses the volume of sediment added from maintenance dredging can slow the rate of erosion but may not prevent long term shoreline retreat restoration and maintenance of coastal landforms and habitats to specific target states at a given location is difficult but augmenting longshore sediment inputs can allow those locations to undergo cycles of erosion and accretion creating a variety of landforms and habitats where only erosional forms existed previously alternatively nourishment could occur more frequently and in smaller volumes to reduce fluctuations in accretion erosion cycles

four year performance and associated controlling factors of several beach nourishment projects along three adjacent barrier islands west central florida usa abstract to quantify the performance of several beach nourishment projects on three adjacent barrier islands located in west central florida a total of 5200 beach and nearshore profiles spaced at 300 m were surveyed monthly to bi monthly from 2006 to 2010 beach nourishment performance at annual temporal and kilometer spatial scales within the microtidal low wave energy barrier island coast is most significantly influenced by the interruption of longshore sediment transport by complex tidal inlet processes the inlet processes directly influencing adjacent beach nourishment performance include longshore transport interruption resulting from divergence induced by wave refraction over an ebb tidal shoal flood tidal currents along the beach and total littoral blockage by structured inlets secondary factors controlling the nourishment performance include project length and width shoreline orientation and antecedent geology a morphologic indicator of a large longshore transport gradient within the study area is the absence of a nearshore sandbar these non barred beaches are characterized by persistent shoreline erosion the presence of a sandbar indicates the dominance of cross shore processes with bar migration in response to wave condition variations and a relatively stable shoreline the entirety of a barrier island system should be considered when evaluating the performance of a nourishment

mantle discontinuity structure beneath the colorado rocky mountains and high plains analysis of mantle discontinuity structure using converted p to s pas phases beneath colorado from the program for array seismic studies of the continental lithosphere passcal rocky mountain front rmf experiment reveals significant topography at the 410 and 660 km depth discontinuities and corresponding transition zone thickness variations a stack of all radial receiver functions resolves the 410 and 660 km discontinuities at average depths of 419 and 677 km respectively imaging of lateral variations in mantle discontinuity structure is accomplished by geographically binning the pds conversion points and then stacking the receiver functions in each bin to form spatial images analogous to common depth point stacking corrections for lateral velocity heterogeneity are calculated using the local s wave tomographic model of lee and grand 1996 and a constant lnvs lnvp scaling of 1 3 this scaling value is determined from the relative scaling between teleseismic p and s wave travel time residuals measured from the rocky mountain front deployment mantle discontinuity images using 150 km square bins show 20 km of 410 km discontinuity topography 30 km of 660 km discontinuity topography and up to 40 km of transition zone thickness variation features of the discontinuity structure include a 20 km depression of the 660 km discontinuity beneath western colorado and a gradual 10 km dip of the 410 km discontinuity beneath the high plains the thickening of the transition zone beneath southwest colorado is consistent with the presence of the subducted farallon slab in this region as imaged by van der lee and nolet 1997 in general our results show that the transition zone discontinuity structure is more complex than that predicted by the simple model of olivine phase boundaries modulated by vertically coherent thermal anomalies

burrowing inhibition by fine textured beach fill implications for recovery of beach ecosystems abstract beach nourishment is often considered the most environmentally sound method of maintaining eroding shorelines however the ecological consequences are poorly understood fill activities cause intense disturbance and high mortality and have the potential to alter the diversity abundance and distribution of intertidal macroinvertebrates for months to years ecological recovery following fill activities depends on successful recolonization and recruitment of the entire sandy intertidal community the use of incompatible sediments as fill material can strongly affect ecosystem recovery we hypothesized that burrowing inhibition of intertidal animals by incompatible fine fill sediments contributes to ecological impacts and limits recovery in beach ecosystems we experimentally investigated the influence of intertidal zone and burrowing mode on responses of beach invertebrates to altered sediment texture 28 38 fines and ultimately the potential for colonization and recovery of beaches disturbed by beach filling using experimental trials in fill material and natural beach sand we found that the mismatched fine fill sediments significantly inhibited burrowing of characteristic species from all intertidal zones including sand crabs clams polychaetes isopods and talitrid amphipods burrowing performance of all five species we tested was consistently reduced in the fill material and burrowing was completely inhibited for several species the threshold for burrowing inhibition by fine sediment content in middle and lower beach macroinvertebrates varied by species with highest sensitivity for the polychaete 4 fines below the usa regulatory limit of 10 fines followed by sand crabs and clams 20 fines these results suggest broader investigation of thresholds for burrowing inhibition in fine fill material is needed for beach animals burrowing inhibition caused by mismatched fill sediments exposes beach macroinvertebrates to stresses which could depress recruitment and survival at all intertidal zones our results suggest use of incompatible fine fill sediments from dredging projects creates unsuitable intertidal habitat that excludes burrowing macroinvertebrates and could delay beach ecosystem recovery through effects on beach invertebrates that are prey for shorebirds and fish the ecological impacts of filling with mismatched fine sediments could influence higher trophic levels and extend beyond the beach itself

unraveling the geometry of the farallon plate synthesis of three dimensional imaging results from usarray abstract we compare 12 recent three dimensional 3d seismic imaging results that made extensive use of data from the earthscope transportable array ta our goal is to sort out what can be said about the geometry of the farallon plate our main approach is 3d visualization using a kinematic plate motion model as a framework comparison of results from all 12 image volumes indicates that the results are most consistent with a single coherent farallon slab overridden by north american the farallon can be tracked from the trench in the pacific northwest to its remnants in the lower mantle under eastern north america from the trench the lithosphere has a low dip to the volcanic arc immediately east of the arc the slab steepens sharply before undergoing a decrease in dip above the 410 km discontinuity the gently dipping section varies along strike under washington the deflection is minor but to the south the slab flattens to become nearly horizontal beneath southern idaho there is a strong agreement that the high velocity anomaly associated with the slab vanishes under eastern oregon scattered wave imaging results however suggest the top of the anomaly is continuous these can be reconciled if one assumes the wavespeed anomaly has been neutralized by processes linked to the yellowstone system we find that all results are consistent with a 4d kinematic model of the mendocino slab window under nevada and utah in the eastern us the larger scale models all show a lower mantle anomaly related to the older history of farallon subduction the link between the lower mantle and new results in the u s cordillera lies under the high plains where the required usarray coverage is not yet complete image volumes in a unified format are supplied in an electronic supplement

seismic migration processing of p sv converted phases for mantle discontinuity structure beneath the snake river plain western united states we experiment with backprojection migration processing of teleseismic receiver functions from the snake river plain srp broadband seismic experiment previous analyses of data from this experiment have used a common midpoint cmp stacking approach a method widely applied for analysis of p sv converted phases receiver functions to obtain high resolution imaging of upper mantle discontinuities the cmp technique assumes that all p sv conversions are produced by flat lying structures and may not properly image dipping curved or laterally discontinuous interfaces in this paper we adopt a backprojection migration scheme to solve for an array of point scatterers that best produces the large suite of observed receiver functions we first perform synthetic experiments that illustrate the potential improvement of migration processing over cmp stacks application of the migration processing to the srp data set shows most of the major features as in the original cmp work but with a weaker 410 km discontinuity and a more intermittent discontinuity at 250 km apparent depth random resampling tests are also performed to assess the robustness of subtle features in our discontinuity images these tests show that a 20 km elevation of the 660 km discontinuity directly beneath the snake river plain is robust but that the variations in 410 km discontinuity topography that we observe are not stable upon resampling bright spots near 250 km apparent depth are robust upon resampling but interpretation of these features is complicated by possible sidelobe artifacts from topside moho reverberations

structural and surface features of arc shaped radar echoes along an outer tropical cyclone rainband this study uses ground based dual doppler radar and surface observations to document the structural and surface features of the arc shaped radar echoes asres evident along an outer rainband of typhoon longwang as it approached northern taiwan on 1 october 2005 the particular aim of this study is to explore the possible distinction between the present case previously documented tropical cyclone rainbands tcrs and squall lines the dual doppler derived fields show that the leading precipitation of the studied asres exhibited a convective nature with a sharp horizontal gradient of reflectivity and a significant vertical extent theregionsbehindtheleadingconvectionwerecharacterizedbyband relativerear to frontflowatlowlevels and were associated with a broader area of stratiform precipitation the deep layer of front to rear flow extending from the surface to the upper troposphere was generally present ahead of the asres this flow appearstobeliftedupwardatandimmediatelyaheadoftheleadingedgeofthelow levelrear to frontflowto form rearward tilting updrafts these airflow patterns are similar to those of the convective region of squall lines but differ fundamentally from those of previously documented tcrs that were located closer to the inner core of cyclones the detailed analyses of surface fluctuations during the passage of one of the studied asresfurthershowanabruptpressurerise 2mb atemperaturedrop 48c andapronounceddeceleration of inflow air coincident with the leading heavy precipitation the evaluation presented suggests that the convectively generated cold pool may be important in influencing the structures and propagation of the studied asres

finescale vertical structure of a cold front as revealed by an airborne doppler radar abstract in the afternoon of 24 may 2002 a well defined and frontogenetic cold front moved through the texas panhandle detailed observations from a series of platforms were collected near the triple point between this cold front and a dryline boundary this paper primarily uses reflectivity and doppler velocity data from an airborne 95 ghz radar as well as flight level thermodynamic data to describe the vertical structure of the cold front as it intersected with the dryline the prefrontal convective boundary layer was weakly capped weakly sheared and about 2 5 times deeper than the cold frontal density current the radar data depict the cold front as a fine example of an atmospheric density current at unprecedented detail 40 m the echo structure and dual doppler inferred airflow in the vertical plane reveal typical features such as a nose a head a rear inflow current and a broad current of rising prefrontal air that feeds the accelerating front to rear current over the head the 2d cross fro

origin evolution and distribution of shoreface sand ridges atlantic inner shelf u s a abstract a computer mapping system was employed to document the location of 259 shoreface attached and detached sand ridges in water although shoreface attached sand ridges appear to have several different modes of formation a two step process for the development of most shoreface attached and detached sand ridges along u s atlantic barrier island and cape coastlines is proposed 1 sand is deposited as ebb tidal deltas or river deltas along the lower shoreface and or inner continental shelf prior to or during transgression followed by 2 further transgression which reworks the deltaic sand bodies into linear sand ridges at the base of the shoreface by shelf processes the best developed shoreface sand ridge fields along the u s atlantic shelf lie adjacent to shorelines characterized by all of the following 1 transgression 2 mixed energy wave dominated barrier islands and 3 laterally migrating tidal inlet systems tidal inlet systems are natural sediment sinks that capture sand carried by longshore sediment transport ebb tidal delta deposits associated with these migrating tidal inlets provide the initial sand body for the development of shoreface attached sand ridges the oblique orientation and linear form of shoreface attached sand ridges appear to be a function of shoreline transgression lateral inlet migration and wave reworking of ebb tidal delta deposits concentrated along an ebb tidal delta retreat path shelf processes act as modifying agents in the evolution of sand ridges during and after ebb tidal delta deposition in general shoreface attached sand ridges are poorly developed or absent along eroding headlands spits and barrier island shorelines characterized by naturally stabilized tidal inlets these latter inlets and shoreline types are dominated or influenced by one or all of the following 1 antecedent topography 2 higher tidal ranges 3 larger tidal prisms 4 lower wave energies or 5 finer grain sizes the coupling of shoreline and shallow marine sedimentary processes during a transgression is critical to the origin evolution and distribution of shoreface sand ridges in the study area modern shoreface attached sand ridges are also known to occur in different coastal and shelf settings where large amounts of sediment were supplied to the shoreface and inner shelf during or immediately before transgression commonly observed vertical and lateral interrelationships of holocene shoreface attached sand ridges and tidal inlets or distributary channels have important ramifications for the development of shelf sandstone facies models in addition the geometric relationship documented in this study provides predictive petroleum and hard mineral exploration models of the spatial and temporal distribution of shoreface and shelf sand ridges

from gullies to mountain belts a review of sediment budgets at various scales this paper reviews the state of the art in the concept as well as in the application of sediment budgets in sedimentary research sediments are a product of mass dispersal at the earth surface and take part in global cycles sediment budgets aim at quantifying this mass transfer based on the principle of mass conservation and are the key to determine ancient fluxes of solid matter at the earth surface this involves fundamental questions about the interplay of uplift climate and denudation in mountain belts and transfer of sediments from the continents to the oceans as well as applied issues such as soil and gully erosion reservoir siltation and coastal protection first after introducing basic concepts relevant scales and methodologies the different components of quaternary routing systems from erosion in headwaters river systems glacial and paraglacial systems lakes deltas estuaries coasts shelves epicontinental seas and deep sea fans are discussed in terms of their sediment budget most suitable are sedimentologically closed or semi closed depositional environments e g alluvial fans lakes deltas and deep sea fans in a second step the dynamics of passive active and collisional tectonic settings and sediment budgets in related sedimentary basins are explored and new concepts of sediment portioning at large geodynamic scales are introduced ancient routing systems are more or less incomplete and may be intensively fragmented or destroyed in active tectonic settings in terms of sedimentary basin types rifts intracontinental and epicontinental settings are preferred objects of sediment budgets because of their persistence and relatively simple overall sedimentary architecture however closing basins such as foreland forearc retroarc piggy back and wedge top basins may provide excellent snapshots of orogenic sediment fluxes in a third step the large long lived routing systems of the amazon the ganges brahmaputra and the rhine are reviewed for each system estimates of either sediment volumes mass or sediment fluxes of continental and marine subsystems have been compiled in order to receive a complete routing in terms of mass conservation for specific time periods since the late glacial maximum as well as the cenozoic following lessons can be taken from these case studies i depositional centers and fluxes show strong shifts in space and time and call for caution when simply looking at subsystems ii the response times of these large systems are within the milankovich time interval thus lower than predicted from diffusion models iii cyclic routing of sediments in continental basins is much more dominated by climate human control than by eustacy and iv at long time scales ultimate sinks win over intermittent storage it is concluded from this review that the quantitative understanding of global sediment cycling over historic and geologic time and its response to allogenic forcing is still in its infancy and further research is needed towards a holistic view of sediment routing systems at various temporal and spatial scales and their coupling with global biogeochemical cycles this includes i to better determine response times of large routing systems by linking quaternary with cenozoic sediment budgets and continental with marine sub systems ii to combine advanced provenance techniques with sediment budgets in order to reconstruct ancient systems iii to study sediment partitioning at the basin scale iv to reconcile continental supply dominated sequence stratigraphy with the eustatic dominated marine concept and iv to account for non actualism of ancient systems with respect to their erosion and transport mode in particular during glaciations and pronounced arid intervals glacial and eolian sediment routing may cross over hydrologic boundaries of drainage basins thus challenging the principle of mass conservation

detailed structure and sharpness of upper mantle discontinuities in the tonga subduction zone from regional broadband arrays 1 recordings of deep tonga earthquakes from two arrays of 12 broadband seismographs each in the fiji and tonga islands are stacked and searched for reflections and conversions from upper mantle discontinuities in the tonga subduction zone the arrays operated as part of the seismic arrays in fiji and tonga saft experiment from july 2001 to august 2002 in comparison with the commonly used teleseismic approaches the short path lengths for the local data provide smaller fresnel zones and high frequency content for precise mapping of discontinuity topography and sharpness to enhance the low amplitude discontinuity phases s410p p660p and s660p deconvolved seismograms from each event array pair are aligned on the maximum amplitude of the direct p wave and subsequently slant stacked for the 410 km discontinuity the results show no systematic variations in depth with distance to the cold slab the 660 km discontinuity varies between 656 and 714 km in depth for the southern and central parts of the subduction zone the largest depths occur in the core of the tonga slab for the northern part two separate depressions of the 660 km discontinuity are observed these anomalies are interpreted as being induced by the active steeply subducting tonga deep zone and a subhorizontally lying remnant of subducted lithosphere from the fossil vityaz trench respectively interpreting the deflections of the 660 km discontinuity in terms of local temperatures implies a thermal anomaly of 800 k to 1200 k at 660 km depth except for the southern region where it may thicken the width of the depressed 660 km discontinuity region implies that the tonga slab seems to penetrate the 660 km discontinuity with little deformation waveform modeling suggests that both the 410 and 660 km discontinuities are sharp the 660 km discontinuity is at most 2 km thick in many parts of the region and a first order discontinuity cannot be precluded the 410 km discontinuity thickness shows somewhat more variability and ranges from 2 to 10 km outside the slab and is at most 10 km thick within the slab this suggests that the subduction process does not produce dramatic effects on the sharpness of the discontinuities

modification of the quaternary stratigraphic framework of the inner continental shelf by holocene marine transgression an example offshore of fire island new york abstract the inner continental shelf off fire island new york was mapped in 2011 using interferometric sonar and high resolution chirp seismic reflection systems the area mapped is approximately 50 km long by 8 km wide extending from moriches inlet to fire island inlet in water depths ranging from 8 to 32 m the morphology of this inner continental shelf region and modern sediment distribution patterns are determined by erosion of pleistocene glaciofluvial sediments during the ongoing holocene marine transgression much of the shelf is thus an actively forming ravinement surface remnants of a pleistocene outwash lobe define a submerged headland offshore of central fire island east of the submerged headland relatively older pleistocene outwash is exposed over much of the inner continental shelf and covered by asymmetric sorted bedforms interpreted to indicate erosion and westward transport of reworked sediment erosion of the eastern flank of the submerged pleistocene headland over the last 8000 years yielded an abundance of modern sand that was transported westward and reworked into a field of shoreface attached ridges offshore of western fire island west of the submerged headland erosion of pleistocene outwash continues in troughs between the sand ridges resulting in modification of the lower shoreface comparison of the modern sand ridge morphology with the morphology of the underlying ravinement surface suggests that the sand ridges have moved a minimum of 1000 m westward since formation comparison of modern sediment thickness mapped in 1996 1997 and 2011 allows speculation that the nearshore shoreface sedimentary deposit has gained sediment at the expense of deflation of the sand ridges

geologic framework influences on the geomorphology of an anthropogenically modified barrier island assessment of dune beach changes at fire island new york antecedent geology plays a crucial role in determining the inner shelf nearshore and onshore geomorphology observed in coastal systems however the influence of the geologic framework on a system is difficult to extract when evaluating responses to changes due to storms and anthropogenic modifications and few studies have quantified the potential for these influences in dune beach environments this study evaluates topographic change to the dune beach system at fire island new york over a ten year period 1998 2008 at two sites representing eastern and western reaches of the island where morphology has been shown to vary the sites are situated along swaths of coast eroding differentially and where the inner shelf geologic framework differs substantially fewer large storms occurred in the first half of the study period compared with the later part of the study period which includes several severe and prolonged extratropical storms additionally a major beach replenishment project was conducted at one of the study sites topographic data from lidar and rtk gps surveys are used to construct high resolution 3d surfaces which are used to determine volumetric change and to extract 2d alongshore features and profiles for analysis the study sites help to further characterize morphologic differences between eastern and western reaches of the island the western site displays higher sand volumes lower dunes and a lower gradient profile slope when compared with the eastern site in addition to these fundamental morphologic differences the two sites also differ significantly in their response to coastal storms and in the fact that their replenishment histories are different the replenished areas show reduced vulnerability to storms through minimal volume loss and shoreline accretion that should be considered when evaluating the response of replenished areas to episodic events we propose that site specific differences evident throughout the study period can be linked to alongshore variations in the framework geology of the system anthropogenic modifications may have intensified differences already inherent in the system

three dimensional prestack plane wave migration of teleseismic p to s converted phases 2 stacking multiple events 1 in part 1 we developed the theoretical foundations of a prestack migration procedure to image forward scattered p to s pds converted waves in the coda of teleseismic p waves this paper addresses the issue of how to optimally stack data from multiple events migrated by this procedure we apply matrix perturbation theory to develop an objective way to quantify noise in deconvolved pds data application of the theory demonstrates that an optimal stack requires weighting the migrated data from each event by a signal to noise ratio criterion we also find that the migrated pds images have to be binned by back azimuth and balanced prior to the final stack this is necessary to mitigate coherent noise that results from aliased microseism noise that is enhanced by our processing method we processed 23 events recorded by the lodore array in northwestern colorado with our procedure the results indicate the presence of a major lithospheric scale discontinuity defined by a south dipping boundary within the crust that we interpret as the subsurface expression of the cheyenne belt the suture is also marked by a transition in crustal thickness from 35 km on the archean side to over 40 km on the colorado plateau side we also observe a strong difference in the lithospheric mantle pds conversion signature on opposite sides of the suture that suggests delamination and northward convergence of the colorado lithosphere beneath the wyoming province

a mesoscale sediment budget for long island new york abstract a sediment budget encompassing the 140 km shoreline from montauk point to fire island inlet new york derived longshore transport rates for 25 coastal cells using comparative surveys the study area along the south shore of long island a generally straight coast of mainland and barrier island beaches includes the eroding headland at montauk point three jettied inlets two groin fields and three barrier beaches bridging between small scale quantitative surveys and large scale regional geology the sediment budget provides a mesoscale view and quantitative estimates of key coastal processes in the area results integrate changes between the foredunes and lower foreshore to the estimated depth of closure 9 to 12 m below mean sea level for a 24 5 year period 1955 1979 beach fills and losses to washovers and breach channels are incorporated in the analysis the results confirm net westerly transport and provide the first evidence that shoaling in fire island inlet long estimated to be 400 000 m 3 yr is due primarily to cannibalization of the immediate updrift compartments particularly erosion of the foreshore below mean low water this lowers estimates of longshore transport rates along most of the study area compared with previous estimates the offshore source attributed by others to account for fire island s stability appears to be trailing ebb shoals lagging behind inlet migration jettied inlets in the central study area intercept some longshore transport but since stabilization circa 1955 have been ebb dominant preserving the littoral budget seaward of the strandline littoral losses to the lagoons by inlets or washovers were insignificant over the period however breach channels if not closed soon after storms were found to offset years of ebb dominance in jettied inlets by depositing major flood deltas beach fills had measurable and positive effect on the sediment budget along the western half of the study area through the early 1970s the volume of beach fills since 1975 has diminished to about 10 of the earlier rate a field of 15 groins in the central study area is shown to trap 100 of the longshore transport and produce a local drift reversal rates of accretion within the groin cells and erosion along the downdrift compartment dwarf the average rates of change for the majority of littoral compartments in the study area

potential vorticity generation by west african squall lines abstractthe west african summer monsoon features multiple complex interactions between african easterly waves aews moist convection variable land surface properties dust aerosols and the diu

tracking a long lasting outer tropical cyclone rainband origin and convective transformation abstractthis study used radar and surface observations to track a long lasting outer tropical cyclone rainband tcr of typhoon jangmi 2008 over a considerable period of time 10 h from its for

dynamical influence of microphysics in tropical squall lines a numerical study abstract based on environmental conditions of the 22 and 23 june squall lines during the convection profonde tropicale in 1981 copt81 experiment in west africa a series of numerical simulations are performed with a two dimensional nonhydrostatic cloud model to examine the dynamical effect of microphysics in tropical squall lines the role of ice phase microphysics strongly depends on ambient conditions for the environment of strong convective instability the ice phase is important regarding the system scale structure but is not important to the convective scale dynamics on the other hand the ice influence is crucial to the squall line convective system if the environment has a weak convective instability and is almost saturated at low levels

isotope characteristics of meteoric water and groundwater in the sahelo sudanese zone the stable isotopic concentration 18o and 2h of water in phreatic aquifers in the sahelo sudanese zone of africa is representative of the original mean rainfall contributing to ground water recharge the isotopic decrease of 18o in the rainwater and groundwater 0 084 100 km 1 showed an east west gradient this suggests a supply of water vapor transported by the zonal flows east african jet tropical easterly jet and easterly waves thus increasing the contribution from the evaporating surfaces of the indian ocean in relation to that of the guinean monsoon the gradient also indicates the importance of atmospheric recycling of continental water through evapotranspiration a model of conservation of the isotopic masses is presented which takes into account the return of continental vapor toward the rain giving clouds the remaining fraction of water vapor during the east west transit between djibouti and dakar is thus determined by evapotranspiration

roughness of the mantle transition zone discontinuities revealed by high resolution wavefield imaging we processed two independent data sets 2 458 973 three component seismograms from all earthscope transportable array usarray stations and 141 080 pairs of high quality receiver functions from the earthscope automated receiver survey using the generalized iterative deconvolution method and shaped the output with a 0 1 hz ricker wavelet we used these data as input to our 3 d plane wave migration method to produce an image volume of p to s scattering surfaces under all of the lower 48 states model simulations show that compared to the widely used common conversion point stacking method our method is capable of resolving not only dipping discontinuities but also subtler details of amplitude and topography variations at scales near the diffraction limit maps of attributes derived from these discontinuities reveal several previously unobserved features of the 410 and 660 discontinuities d410 and d660 topography with many tens of kilometers is resolved at a range of scales additionally we observed large variations of amplitude on the radial component and in the radial to transverse amplitude ratio that correlate with inferred variations in discontinuity topography we argue that this combination of observations can be explained by roughness at a range of scales the structural fabric we imaged is preferentially aligned orthogonal to the farallon north american relative motion two regions we infer to have exceptional roughness show spatial correlation with locations where tomography models indicate that the subducted slab is passing through the transition zone we suggest that these rough regions are indicators of vertical mantle flows through the transition zone

the 410 km depth discontinuity a sharpness estimate from near critical reflections the abrupt increase in seismic velocity and density about 410 km below the surface of the earth occurs at the depth where a phase change in olivine is expected akaogi et al 1989 katsura and ito 1989 ringwood 1969 we have assembled recordings from 22 short period seismometers in washington and british columbia of 35 nuclear explosions in nevada these data reveal relatively noise free reflections from the 410 discontinuity most of the transition is completed within a depth interval of less than 10 km under the western united states this result adds to the accumulating seismic evidence of a fairly sharp 410 transition

calculating shoreline erosion potential using nearshore stratigraphy and sediment volume outer banks north carolina 1 despite the acknowledged influence of coastal geological framework on the behavior of beaches and barrier islands and a wealth of geological and bathymetric observations from the inner shelf quantitatively connecting those observations to shoreline behavior has been difficult nearshore geologic and morphologic variability described by recent research is not well represented by conventional geologic parameters such as mean grain size and shoreface slope used in most shoreline change models we propose that total nearshore sediment volume as calculated to a continuous seismic reflection surface provides a flexible and robust metric for use in the prediction of shoreline change this method of determining the volume of sediment in the nearshore accounts for three dimensional sandbar morphologies and heterogeneous seafloor sediments the decadal scale shoreline change rate for northeastern north carolina is significantly correlated to the volume of sediment in the nearshore when a geologically defined base is used in volume determinations suggesting that the shallow stratigraphic framework of transgressive coasts is an important influence on decadal shoreline behavior nearshore sediment volume was overestimated when an arbitrary depth constant baseline was used and was not correlated to decadal shoreline change this implies that a volume metric which accounts for both framework geology and variable seafloor morphology better represents the geologic character of the shoreface and may help to improve existing models of shoreline change an empirical model of regional shoreline erosion potential demonstrates the importance of incorporating nearshore sediment volume shallow framework geology and surface morphology when predicting seasonal to decadal shoreline evolution

topography of the transition zone seismic discontinuities phase transformations in mantle mineralogies probably cause the transition zone seismic discontinuities nominally at 410 520 and 660 km depth thermodynamic principles govern phase transformations making them sensitive to changes in the mantle s ambient conditions through the thermodynamic response changes in temperature or composition shift the transformation to a different pressure creating topography on a level discontinuity with this use as an exploratory tool for the mantle in mind we review the basic seismological and phase equilibrium concepts underlying the detection and interpretation of the seismic wave arrivals associated with the transition zone discontinuities reviewing the evidence for and against the phase transition model we conclude that it is viable and describe how discontinuities have been and can be used to probe the physical and chemical state of the transition zone

high resolution transition zone structures of the gorda slab beneath the western united states implication for deep water subduction 1 the current data set from usarray provides an unprecedented opportunity to investigate mantle transition zone structures beneath the western united states we have made transition zone images with the common converted point ccp stacking method more than 9600 high quality receiver functions were stacked with reference to two different three dimensional tomography models and a one dimensional velocity model where the gorda plate passes through the transition zone the 410 discontinuity has been elevated 25 km and the 660 discontinuity has been depressed 35 km we interpret the transition zone topography in terms of mineral physics results in several different ways noting in particular that recent measurements on the clapeyron slope for the ringwoodite to perovskite phase transition under dry conditions give a phase boundary slope of 1 3 to 0 4 mpa k the 35 km deflection of the 660 discontinuity observed in the receiver functions seems to be the evidence that the subducted slab can carry abundant water from the surface to the transition zone and in the transition zone the water in the slab may be fully saturated e g the water content is 2 0 wt analyses of the velocity perturbations in the tomography models and the transition zone thickness indicate that the deep water is likely well confined within the subducted slab we infer that the presence of water in the subducted gorda slab might have contributed 15 km and the thermal anomaly in the slab might have contributed 20 km to the depression of the 660 discontinuity

response of wave dominated and mixed energy barriers to storms wave dominated and mixed energy barriers are extremely dynamic landforms responding to processes operating over a spectrum of time scales ranging from daily to monthly fluctuations related to storm and post storm conditions to century to millennium scale evolution driven by relative sea level change two types of storms are of particular relevance warm core tropical and cold core extratropical cyclones both are responsible for generating very large waves highly energetic surf zone dynamics and sediment transport elevated inshore water levels and extensive morphological responses all cyclones are affected by climate change which governs their frequency intensity and tracks barrier storm response is primarily governed by maximum storm runup and barrier morphology as conceptualised in abby sallenger s storm impact scale model sallenger 2000 this model defines four storm impact regimes and includes erosive as well as accretionary responses on the erosion side the swash regime drives bar and berm flattening the collision regime is marked by dune scarping and beach lowe the overwash regime leads to dune scouring and channel incision and the inundation regime may result in barrier destruction on the deposition side storm berms and beach ridges may form and accrete in the swash and collision regimes localised vertical beach and barrier accretion are associated with the collision and overwash regimes and washover deposition takes place in the overwash and inundation regimes site specific factors play a key role in moderating the morphological response and include storm characteristics type duration and track longshore sediment supply upwelling downwelling currents coastal setting and inner shelf topography the response of a barrier to a tropical or extratropical cyclone can however not be considered in isolation and has to be appreciated in a longer temporal context involving morphological preconditioning due to antecedent wave and water level conditions additionally a simple process response approach of the cause and effect type is inappropriate and a more complex conceptual framework involving thresholds feedbacks resilience and vulnerability will need to be adopted a useful way to visualise and conceptualise more complex storm behaviours and the longer term vulnerability of barriers is the resilience trajectory which maps out the changes in barrier geometry elevation and width over various time scales from weeks to years or even longer and under varying forcing conditions including changes in storminess and sea level rise an increased understanding of barrier response to storms and sequences of storms is required to better quantify long term barrier response to climate change high resolution and comprehensive decadal records of barrier response to storms are a prerequisite to achieve this ambition linking site specific coastal settings hydrodynamic drivers and morphological responses and allowing the recognition of recovery and impact dominated phases the enhanced insights in barrier response to extreme events must then be incorporated into improved coastal response models to help predict the impacts of future climate change on wave dominated and mixed energy barriers around the world 2013 elsevier b v

imaging the earth with passive seismic arrays earthquake and exploration seismology share a common foundation in elastic wave propagation most of what we know about earthquakes is known from the elastic waves they emit while seismic methods in exploration are all about using scattered elastic waves to image earth structure seismologists have been using elastic waves to probe the earth since the very earliest instruments after all it was early seismic measurements that led to the spherical shell model of earth structure crust mantle and core taught to grade school students

heterogeneity of the uppermost mantle beneath russian eurasia from the ultra long range profile quartz the 3850 km long deep seismic sounding profile quartz crosses six major geologic provinces in eurasia and is sourced by 3 nuclear and 48 chemical explosions we present the first interpretation of the entire data set using two dimensional 2 d ray tracing and inversion resolution analysis and 1 d amplitude modeling our interpretation shows a 42 km thick high velocity crust under the baltic shield a 29 km thick crust and high velocity upper mantle under the mezenskaya depression 52 km thick crust with high velocity lower crust and uppermost mantle under the urals and 40 km thick crust under the west siberian basin deepening to 45 km under the altay sayan fold belt high velocity 8 4 km s uppermost mantle is found under the mezenskaya depression and under the east flank of the urals one almost continuous upper mantle boundary occurs at 65 to 80 km depth and another with an approximately 40 km thick lvz occurs at 120 to 140 km depth the shallow upper mantle blocks and the two extensive interfaces indicate strong upper mantle heterogeneity resolution analysis based on direct multivariate model perturbations artificial neural network and principal component analysis indicate the depth uncertainty of the 410 km discontinuity within 6 km and also its trade off with dip and velocities above and below the discontinuity decreased near critical amplitudes of reflections from the 410 km and 660 km discontinuities indicate that these boundaries are most likely represented by gradient zones about 15 20 km thick lithosphere thins asthenospheric velocity decreases and the 410 km discontinuity dips to the se approaching the himalayan orogenic belt

retrieved thermodynamic structure of a subtropical orographically influenced quasi stationary convective line airborne doppler radar and flight level measurements were used to document the three dimensional thermodynamic structure of a convective line that developed off the southeastern coast of taiwan on 16 june 1987 during the taiwan area mesoscale experiment during the period of aircraft observation the convective line appeared to be quasi stationary in a region 90 km away from the coast calculations of perturbation pressure and buoyancy retrieved from the doppler radar derived wind fields show that a high pressure perturbation associated with negative buoyancy existed in the region of heavy precipitation in the lowest level in low levels an elongated zone of low pressure was documented along the line which was closely related to the distributions of buoyancy these retrieved features are basically consistent with those calculated from in situ observations in mid to upper levels the high low pressure perturbation lay around the updraft cores on the upshear downshear of environmental shear the quantitative diagnosis for the perturbation pressure indicates that the positive buoyancy associated with the in cloud latent heat release as well as evaporative cooling occurring near cloud base and subcloud regions is crucial to determine the low level perturbation pressure distributions however dynamic forcing contributing to the pressure perturbation cannot be ignored in middle levels because of updraft shear interaction due to the presence of pronounced cross line wind shear and corresponding updrafts reaching maximum values near midtroposphere in distinct contrast to squall lines which are rapidly moving the near surface temperature gradient across this quasi stationary line was very weak and at low levels no gust front rear inflow or dynamically induced high pressure was evident near the leading edge of the line analyses presented here suggest that the persistent stationary convergence in association with the deceleration of low level southeasterly flow as it approached the nearshore blocked flow played an important role in maintaining and organizing the deep convection in this case

west african squall line thermodynamic structure retrieved from dual doppler radar observations abstract pressure and temperature fields within a west african squall line retrieved from dual doppler radar data collected during the copt 81 convection profonde tropicale experiment are presented the method for derivation of thew results is approximately similar to that proposed by gal chen based on the anelastic equation of motion comparisons between pressure and temperature fields deduced from radar data at the lowest levels and surface network measurements show good agreement the inferred thermodynamic structure displays the influence of a low level frontward flow which is mainly due to a density current of cold air generated in the stratiform region of the squall line and resulting from a mesoscale downdraft this frontward flow contributes to initiate and maintain a frontal updraft through both nonhydrostatic pressure perturbation and temperature difference between entering air and colder frontward flow at higher altitudes mixing with the environment reduces buoyancy in the frontal updr

scaling properties of estuarine beaches abstract estuarine beaches near large rivers are dynamic systems constantly shaped by tides waves and fluvial sediment inputs however little research has been done on the intrinsic characteristics of these geomorphic systems using eleven high resolution bathymetries our results show that human disturbance mingled with natural forcings have induced bathymetric changes in nanhui beach in the changjiang estuary china isobaths display a fractal geometry with a lower fractal dimension when tides smooth the bathymetry and a higher dimension when waves dominate rates of sediment accretion and erosion present a gaussian distribution driven by tidal and wave action episodic extreme wave forcing or frequent land reclamation is responsible for the intermittent adjustment of the estuarine beach bathymetry after these events the distribution of erosion and accretion becomes power law possibly indicating disequilibrium the fractal dimension of isobaths and the distribution of erosion and deposition rates can therefore be used as metrics to determine the dominant processes in estuarine beaches and whether the system is close to equilibrium or not

can sharp seismic discontinuities be caused by non equilibrium phase transformations a long posed problem of the seismic discontinuities at the depths of 410 and 660 km in earth s mantle is whether these discontinuities are caused by phase transitions alone or together with chemical layering among several tests the sharpness of the boundary is one of the most crucial recent data suggest that the transition region thickness is less than 4 km for both the 410 and the 660 km discontinuities this may be smaller than predicted by phase equilibria we suggest that if there is a sufficiently large nucleation barrier for phase transformation and if the transformation front cannot move faster than the convective flow the transformation in rising or descending material does not take place until the metastable overshoot becomes equal to the nucleation barrier an avalanche like transformation following this overshoot occurs in a very narrow region and can be the cause of a sharp seismic discontinuity in this case the topography of the phase boundary is also substantially modified

diagnosis of hydrometeor profiles from area mean vertical velocity data a simple one dimensional microphysical retrieval model is developed for estimating vertical profiles of liquid and frozen hydrometeor mixing ratios from observed vertical profiles of area mean vertical velocity in regions of convective and or stratiform precipitation the mean vertical velocity profiles can be obtained from doppler radar single and dual or other means the one dimensional results are shown to be in good agreement with two dimensional microphysical fields from a previous study sensitivity tests are performed

correlation migration using gaussian beams of scattered teleseismic body waves correlation migration for structural imaging using gaussian beams is described for the inversion of passively recorded teleseismic waves gaussian beam migration is based on an overcomplete frame based representation of the seismic wave field and uses localized slant stack windows of the data paraxial gaussian beams are then utilized for the backpropagation of the seismic waves into the me dium the method can provide stable imaging of seismic data in smoothly varying background media where caustics and triplicated arrivals exist we develop gaussian beam migration for structural imaging which allows for incident teleseismic waves from beneath the structure using directly scattered or surface reflected phases the method is applied to synthetic data computed for a collisional zone model and the inversions show that the gaussian beam migration can image structure using passive teleseismic data the method is next applied to synthetic data that have been con volved with an observed pulse from the 1993 cascadia experiment the autocorre lation is computed and the autocorrelated data are migrated by using gausian beams for direct p to s scattered waves and surface reflected waves although the migra tions of the autocorrelation data with the source pulse included have more noise than the migrations of the impulsive source data the subduction zone structure can still be clearly identified in the migrated results without removal of the source pulses

longshore sediment transport and foreshore change in the swash zone of an estuarine beach abstract estuarine beaches often lack well developed surf zones incident waves break and convert directly to swash on the steep foreshore resulting in greater influence of the swash zone in generating longshore flows and sediment transport this study was conducted to evaluate longshore sediment transport in the swash zone of an eroding estuarine beach and relate transport rates to changes in beach position and volume downdrift of a shore perpendicular structure field data were gathered on a sandy beach on the bay side of fire island new york usa in a short fetch 12 15 km microtidal mean range 0 21 m environment wave and swash processes beach changes and sediment tracer and trapping experiments were conducted during strong onshore winds in march and april 2012 daily topographic surveys of the beach revealed pulses of sediment movement alongshore at small temporal daily and spatial 5 m scales the mid foreshore retreated 2 75 m from the beginning to the end of the 24 days of monitoring this retreat was associated with a loss of 2 1 m3 of sediment per meter of shoreline length the greatest amount of foreshore retreat during a single storm event was 1 27 m associated with a volume loss of 0 9 m3 of sediment per meter mean wind speed on that day was 11 3 m s 1 with a maximum of 18 2 m s 1 significant offshore wave height at the time of maximum wind speed was 0 30 m mean significant wave heights ranged from 0 12 to 0 26 m during the five times when trapping occurred resulting in mean longshore swash velocities of 0 08 to 0 23 m s 1 and transport rates ranging from 0 413 to 1 516 m3 h 1 the longshore sediment transport rates are similar to rates gathered under similar longshore current velocities on microtidal low energy beaches transport rates on beaches in sheltered environments can differ from rates calculated using existing formulas that may be more appropriate for high energy beaches where a greater proportion of sediment is transported in the surf zone than in the energetic swash zone under plunging breakers transport rates calculated from three existing formulae bagnold 1963 cerc 1984 kamphuis 2002 revealed that estimates from bagnold compared most favorably with measured rates because of direct measurements of longshore current velocities rates of erosion on beaches in short fetch environments can be high despite low wave energies because the low narrow beaches have little volume magnifying the importance of seemingly low rates of transport in the swash

receiver function imaging of upper mantle complexity beneath the pacific northwest united states abstract small scale topographic variations on the upper mantle seismic discontinuities provide important constraints on the thermal influences of upwellings and downwellings in geodynamically complex regions subduction of the juan de fuca plate and other tectonic processes dominating the pacific northwest united states in the cenozoic involve massive thermal flux that likely result in an upper mantle that has strong 3 d temperature variations we address the interaction of such processes in the region using receiver functions to image the upper mantle seismic discontinuities at 410 and 660 km we utilized over 15 000 high quality receiver functions gathered from 294 teleseismic earthquakes recorded at 277 regional broadband seismic stations primarily those of the earthscope usarray transportable array we find the average depths of the discontinuities to be 412 km and 658 km respectively with no obvious 520 km discontinuity detected the peak to peak range is greater on the 410 than the 660 suggesting the possibility of more significant regional dynamic processes at upper mantle depths our results are not consistent with a mantle plume below central oregon in the high lava plains region our observation of a thinner transition zone beneath the western snake river plain region however is consistent with a regional increase in mantle temperatures perhaps due to either asthenospheric flow from beneath and around the southern edge of the juan de fuca plate or to vertical flow in the form of regional mantle upwelling related to the snake river plain yellowstone hotspot track further our results are not consistent with a simple subducting juan de fuca slab morphology but rather suggest similar levels of significant complexity in slab structure found by recent regional tomographic studies we find evidence for a thickened and therefore cooler mantle transition zone beneath the wallowa idaho batholith region consistent with tomographic models which suggest broad scale increased seismic velocities to transition zone depths we speculate that this region may be the location of mantle downwelling at larger scales than previously proposed

challenging assumptions of future coastal habitat development around the uk one habitat management requirement forced by 21st century relative sea level rise rslr will be the need to re comprehend the dimensions of long term transgressive behaviour of coastal systems being forced by such rslr fresh approaches to the conceptual modelling and subsequent implementation of new coastal and peri marine habitats will be required there is concern that existing approaches to forecasting coastal systems development and by implication their associated scarce coastal habitats over the next century depend on a certain premise of orderly spatial succession of habitats this assumption is shown to be questionable given the possible future rates of rslr magnitude of shoreline retreat and the lack of coastal sediment to maintain the protective morphologies to low energy coastal habitats of these issues sediment deficiency is regarded as one of the major problem for future habitat development examples of contemporary behaviour of uk coasts show evidence of coastal sediment starvation resulting from relatively stable rslr anthropogenic sealing of coastal sources and intercepted coastal sediment pathways which together force segmentation of coastal systems from these examples key principles are deduced which may prejudice the existence of future habitats accelerated future sediment demand due to rslr may not be met by supply and if short to medium term hold the line policies predominate long term strategies for managed realignment and habitat enhancement may prove impossible goals methods of contemporary sediment husbandry may help sustain some habitats in place but otherwise instead of integrated coastal organization managers may need to consider coastal breakdown segmentation and habitat reduction as the basis of 21st century coastal evolution and planning copyright 2006 john wiley sons ltd