convection within the inner core and thermal implications estimation of the rayleigh numbers of the inner core leads to the conclusion that even with low internal heating rates this region of the earth is convecting this work presents an axisymmetrical model able to investigate convection in a sphere and its applications to the earth s inner core rayleigh numbers ranging from the critical onset of the convection to ten thousand times the critical have been explored the thermal implications of a convecting inner core have been pointed out in all the cases the temperature profiles are very close to the adiabat leading to the possibility of a partially molten regions in the inner core indeed the most important effects appear in the first tens of kilometers just below the inner core surface and could be at the origin of the low quality factors q and q revealed by seismological studies

distinct layering in the hemispherical seismic velocity structure of earth s upper inner core the existence of hemispherical variation in the earth s inner core is well documented but consensus has not yet been reached on its detailed structure the uppermost layers are a region of particular importance as they are directly linked to the growth processes and post solidification mechanisms of the inner core here we use a large pkikp pkikp differential travel time residual data set to derive a model for the upper inner core providing new constraints on its isotropic and anisotropic velocity and the amount of scattering we find that the eastern and western hemisphere are separated by sharp boundaries this is incompatible with the recently proposed inner core translation model but might be explained by differences in outer core convection and inner core solidification rates the eastern hemisphere displays weak anisotropy of 0 5 1 0 the western hemisphere on the other hand is characterized by the presence of an isotropic upper layer with a thickness of 57 5 km with anisotropy of 2 8 appearing at deeper depths the boundary between the isotropic layer and the deeper anisotropy appears sharp we also detect for the first time a high velocity layer at the top of the eastern hemisphere with a thickness of 30 km which we interpret as being due to an increased amount of light elements there appears to be no relationship between the layered structure in the two hemispheres with abrupt changes in velocity with depth in one hemisphere without any significant change at the same depth in the other hemisphere our results indicate that there is a difference in composition and mineral structure between the hemispheres resulting in differing responses to external processes

imaging the inner core under africa and europe abstract the inner core under africa is thought to be a region where the nature of inner core texture changes from the strongly anisotropic western part of the inner core to the weakly anisotropic or isotropic eastern part of the inner core additionally observations of a difference in isotropic velocity between the two hemispheres have been made a very large new dataset of simultaneous pkpdf and pkpbc observations on which differential travel times have been measured is used to examine the upper 360 km of the inner core under europe africa and the surrounding oceans inversion of the differential travel time data for laterally varying inner core anisotropy reveals that inner core anisotropy is stronger under central africa and the atlantic ocean than under the western indian ocean no hemispherical pattern is present in voigt isotropic velocities indicating that the variation in anisotropy is due to differing degrees of crystal alignment in the inner core not material differences when anisotropy is permitted to change with depth the upper east most part of the study region shows weaker anisotropy than the central and western regions when depth dependence in the inner core is neglected the hemisphere boundary is better represented as a line at 40 e than one at 10 e however it is apparent that the variation of anisotropy as a function of depth means that one line of longitude cannot truly separate the more and less anisotropic regions of the inner core the anisotropy observed in the part of the inner core under africa which lies in the western hemisphere is much weaker than that under central america showing that the western hemisphere is not uniformly anisotropic as the region of low anisotropy spans a significant depth extent it is likely that heterogeneous heat fluxes in the core which may cause variations in inner core anisotropy have persisted for several hundred million years

inner core structure behind the pkp core phase triplication the structure of the earth s inner core is not well known between depths of 100 200 km beneath the inner core boundary this is a result of the pkp core phase triplication and the existence of strong precursors to pkp phases which hinder the measurement of inner core compressional pkikp waves at epicentral distances between roughly 143 and 148 consequently interpretation of the detailed structure of deeper regions also remains difficult to overcome these issues we stack seismograms in slowness and time separating the pkp and pkikp phases which arrive simultaneously but with different slowness we apply this method to study the inner core s western hemisphere beneath south and central america using paths travelling in the quasi polar direction between 140 and 150 epicentral distance which enables us to measure pkikp pkikp differential traveltimes up to greater epicentral distance than has previously been done the resulting pkikp pkikp differential traveltime residuals increase with epicentral distance which indicates a marked increase in seismic velocity for polar paths at depths greater than 100 km compared to reference model ak135 assuming a homogeneous outer core these findings can be explained by either i inner core heterogeneity due to an increase in isotropic velocity or ii increase in anisotropy over the studied depth range although this study only samples a small region of the inner core and the current data cannot distinguish between the two alternatives we prefer the latter interpretation in the light of previous work

large variations in travel times of mantle sensitive seismic waves from the south sandwich islands is the earth s inner core a conglomerate of anisotropic domains 1 cylindrical anisotropy in earth s inner core has been invoked to account for travel times of pkp core sensitive seismic waves such as from the south sandwich islands ssi earthquakes observed in alaska which depart from predictions newly collected travel time residuals from seismic waves from the ssi region that sample only earth s mantle pcp and p waves have a comparable range to the pkp differential travel time residuals yet they are insensitive to core structure this observation suggests that mantle structure affects pkp travel time residuals more than previously acknowledged and challenges the existing conceptual framework of a uniform inner core anisotropy the inner core could be a conglomerate of anisotropic domains and the pkp travel times are most likely influenced by the geometry of inner core sampling and inhomogeneous mantle structure this concept reconciles observed complexities in travel times while preserving a net inner core anisotropy that is required by observations of earth s free oscillations

historical evolution and controls on mega blowouts in northeastern qinghai tibetan plateau china abstract mega blowouts are very large scale deflationary landforms formed by wind erosion they are abundant in the gonghe basin northeast margin of the qinghai tibet plateau qtp and little is known about the evolution dynamics or controls on the mega blowout development here we report on mega blowouts morphodynamic expansion rates based on 4 years of monitoring also presented is a remotely sensed longer term 48 years morphologic change record which is used to understand the initiation growth and evolution of mega blowouts in alpine grasslands links between the morphodynamics and blowout controlling factors are analysed the expansion rates of the monitored blowouts vary according to blowout area with different parts of the blowouts expanding at different rates generally longitudinal downwind mega blowout expansion is greatest with upwind headwall expansion via collapse being particularly significant the growth of depositional lobes downwind of mega blowouts tends to be faster than growth of the deflation basins merging of adjacent blowouts is one of the key mechanisms for mega blowout development and extension sediment characteristics wind erosion water erosion and freeze thaw processes also all play a part in mega blowout initiation and expansion however the relative roles that these factors play may differ according to a blowout s evolutionary stage due to an almost unlimited depth of sand very low water table and short grass vegetation cover evolution into parabolic dunes is limited a large proportion of sand patches and small blowouts around the mega blowouts are still developing in the gonghe basin proving that land degradation is still ongoing future work will focus on the feedback mechanisms between the blowout morphodynamics climate change and anthropogenic impacts

secondary flow deflection in the lee of transverse dunes with implications for dune morphodynamics and migration measurements of lee side airflow response from an extensive array of meteorological instruments combined with smoke and flow streamer visualization is used to examine the development and morphodynamic significance of the lee side separation vortex over closely spaced transverse dune ridges a differential deflection mechanism is presented that explains the three dimensional pattern of lee side airflow structure for a variety of incident flow angles these flow patterns produce reversed along dune and deflected surface flow vectors in the lee that are inferred to result in net lateral diversion of sand transport over one dune wavelength for incident angles as small as 10 from crest transverse i e 80 from the crest line this lateral displacement increases markedly with incident flow angle when expressed as the absolute value of the total deflection in degrees reversed and multi directional flow occurs for incident angles between 90 and 50 these results document the three dimensional nature of flow and sand transport over transverse dunes and provide empirical evidence for an oblique migration model copyright 2013 john wiley sons ltd

implication of the lopsided growth for the viscosity of earth s inner core abstract a particular mode of convection called translation has recently been put forward as an important mode of inner core dynamics because this mechanism is able to explain the observed east west asymmetry of p wave velocity and attenuation monnereau et al 2010 translation is a particular solution to navier stokes equation with permeable boundary conditions but depending on the viscosity of the solid core modes with higher spherical harmonics degree can develop at low viscosity these modes can be dominant and dissipate the degree l 1 of thermal heterogeneities hence a viscosity threshold may be expected below which translation cannot take place thereby constraining the viscosity of iron at inner core conditions using a hybrid finite difference spherical harmonics navier stokes solver we investigate here the interplay between translation and convection in a 3d spherical model with permeable boundary conditions our numerical simulations show the dominance of pure translation for viscosities of the inner core higher than 4 10 18 pa s translation is almost completely hampered by convective motions for viscosities lower than 10 17 pa s and the phase change becomes an almost impermeable boundary between these values a well developed circulation at the harmonic degree l 1 persists but composed of localized cold downwellings a passive upward flow taking place on the opposite side the melting side such a convective structure remains compatible with the seismic asymmetry

internal loading of an inhomogeneous compressible earth with phase boundaries summary we use an approach described by dehant wahr 1991 to estimate the geoid and boundary topography caused by mass loads inside the earth we show how the estimates are affected by compressibility and a radially varying density distribution and by the presence of phase boundaries with density discontinuities we compare results for earth models that have a chemical boundary at 670 km depth with those that have a phase boundary at that depth we find that the 670 km topographies predicted for models with a chemical boundary are several times larger than for models with a phase boundary depending principally on the value of the clapeyron slope in the phase case the geoid predicted in the chemical boundary case is about 30 40 per cent smaller than that predicted in the phase case the effects of compressibility and radially varying density are likely to be small we estimate the laterally varying structure inside the fluid core by computing the topography on constant potential surfaces within the core we conclude that this structure is not likely to be a complicating factor when using nutation and earth tide observations to estimate the flattening of the core mantle boundary finally we compute the inner core outer core icb topography for loading inside the mantle and for loading inside the inner core we show that in the first case the icb topography is small and dominated by long wavelengths in the second case we conclude that if the density heterogeneities inside the inner core are two orders of magnitude smaller than in the mantle the icb topography can be about 100 m peak to peak

influence of topography on wind speed over a coastal dune and blowout system at jockey s ridge nc usa this study examines the spatial distribution of wind speed across a coastal dune system located at jockey s ridge state park north carolina the study area consists of a trough blowout through a foredune ridge and the landforms that have developed behind the foredune wind speed and direction were measured simultaneously with single sensors placed at a fixed height in 13 locations across the blowout dune complex fractional wind speed up is computed for sampling stations using data from a mast located on the beach as the reference results show that wind speeds were generally accelerated across the study site the highest speeds were recorded on the foredune ridges adjacent to the blowout wind was accelerated through the center of the blowout throat and along the downwind lateral wall further into the blowout at the base of the ramp to the depositional lobe higher wind speeds shifted to the upwind lateral wall and continued to accelerate up the ramp as air exited to the rear significant variations in the wind speed up pattern were associated with different wind approach angles with greater speed up occurring when the winds were aligned normal to the dune system the speed up decreased as the angle of approach became increasingly oblique to the ridge the patterns of wind speed up across the site point to the influence of topography on airflow to quantify the relationship measures of several topographic variables were obtained along sample transects running upwind from each sample station along flow lines representing different wind approach angles examination of correlation coefficients between wind speed up and topographic variables suggests that for groups of stations with similar topographic characteristics 30 50 of the variations in speed up may be explained by the upwind topographic variability copyright 2014 john wiley sons ltd

spatial temporal evolution of aeolian blowout dunes at cape cod abstract this paper explores historical evolution of blowouts at cape cod national seashore ccns usa a site that hosts one of the world s highest densities of active and stabilized blowouts the spatial temporal analysis of moving polygons stamp method is applied to a multi decadal dataset of aerial photography and lidar to extract patterns of two dimensional movement and morphometric changes in erosional deflation basins and depositional lobes blowout development in ccns is characterized by several geometric overlap and movement proximity responses including i generation and disappearance ii extension and contraction iii union or division iv clustering and v divergence by stabilization other possible movement events include migration amalgamation and proximal stabilization but they were not observed in this study generation events were more frequent than disappearance events the former were highest between 1985 and 1994 while the latter were highest between 2000 and 2005 high rates of areal change in erosional basins occurred between 1998 and 2000 3932 m2 a 1 the lowest rate 333 m2 a 1 between 2005 and 2009 and the maximum rate 4589 m2 a 1 between 2009 and 2011 union events occurred mostly in recent years 2000 2012 while only one division was observed earlier 1985 1994 net areal changes of lobes showed gradual growth from a period of contraction 1119 m2 a 1 between 1998 and 2000 to rapid extension 2030 m2 a 1 by 2010 which is roughly concurrent with rapid growth of erosional basins between 2005 and 2009 blowouts extended radially in this multi modal wind regime and despite odd shapes initially they became simpler in form more circular and larger over time net extension of erosional basins was toward ese 109 while depositional lobes extended sse 147 lobes were aligned with the strongest winter sand drift vector although their magnitude of areal extension was only 33 that of the basins these differences in extension responses likely result from more complex and evolving flow form interactions inside erosional basins historical photographs and ccns documents suggest that blowout evolution may be influenced by land use changes such as revegetation campaigns in 1985 that were followed by high blowout generation high magnitude regional storm events e g hurricanes also play a role the analytical framework presented provides a systematic means for two dimensional geomorphic change detection and pattern analysis that can be applied to other landscapes

mega blowouts in qinghai tibet plateau morphology distribution and initiation blowouts are wind eroded landforms that are widely distributed in the north eastern part in qinghai tibet plateau qtp china these blowouts are thought to form in response to climate change and or human activity but little is known about their morphodynamics using field surveys remote sensing and geographic information system gis spatial analysis the distribution and morphology of blowouts are analysed and their initiation considered results show the qtp mega blowouts are some of the largest in the world the orientations of the trough shaped blowouts are parallel with the prevailing wind but the saucer and bowl shaped blowouts are influenced by bi directional transport whilst regional patterns of blowout shape and size were observed to reflect the extent of aeolian sediments and wind regimes the relationship between the different morphological parameters showed consistency during initial stages of development the length to width ratios of blowouts increase rapidly with area but after they reach a mega size this relationship stabilizes as blowouts widen initial luminescence dating shows that blowouts appear to have initiated 100 to 500 years ago coinciding with the little ice age lia climate event when northwest winds are known to have intensified further work is required to confirm this initiation period and establish the significance of mega blowouts for landscape degradation and human activities

seismic velocity and attenuation structures in the top of the earth s inner core 1 we collect a global data set of pkikp and pkikp phases recorded by the global seismic network and many regional seismic arrays to study seismic structure in the top of the earth s inner core the pkikp and pkikp observations show different characteristics between those sampling the eastern hemisphere 40 e 180 e of the inner core and those sampling the western hemisphere 180 w 40 e pkikp phases 1 arrive about 0 4 s earlier than the theoretical arrivals based on preliminary reference earth model prem for those sampling the eastern hemisphere of the inner core and about 0 3 s later for those sampling the western hemisphere 131 141 2 bifurcate at smaller epicentral distances for those sampling the eastern hemisphere compared to those sampling the western hemisphere and 3 have smaller amplitudes for those sampling the eastern hemisphere waveform modeling of these observations suggests two different types of models for the two hemispheres of the top of the inner core with a model in the eastern hemisphere having a p velocity increase of 0 765 km s across the inner core boundary a small radial velocity gradient of 0 000055 km s km and an average q value of 250 and a model in the western hemisphere with a p velocity increase of 0 633 km s across the inner core boundary a radial velocity gradient of 0 000533 km s km and an average q value of 600 the hemispherical difference of seismic structures may be explained by different geometric inclusions of melt and or different alignments of iron crystals with anisotropic properties in both velocity and attenuation we speculate that this large scale pattern of seismic heterogeneities may be caused by a large scale heat flow anomaly at the bottom of the outer core and or different vigorousness of convection in the top of the inner core between the two hemispheres

pkp travel times at near antipodal distances implications for inner core anisotropy and lowermost mantle structure abstract previous studies from pkp ab df differential travel times at large distances suggest that the central part of the inner core is very anisotropic these differential times however can be affected greatly by strong heterogeneity in the lowermost mantle here we examine a unique data set of pkp travel times from global digital and analog stations at near antipodal distances where the effects of both inner core anisotropy and mantle heterogeneity are the greatest our results show that the ab df residuals for the polar paths are consistently larger than those of the equatorial paths by over 3 4 standard deviations we also measured df and ab absolute times and found that the df residuals are negatively correlated with the ab df residuals while the ab residuals have a much weaker correlation with the ab df residuals we compare several mantle models with the data our results suggest that the mantle structure can explain part of the residuals of the equatorials paths but cannot explain the polar path anomalies these results strongly suggest that most of the ab df anomalies for the polar paths are likely from the inner core anisotropy and not from mantle heterogeneity assuming a uniform cylindrical anisotropy model the average inner core anisotropy amplitude is about 2 5 on the other hand equatorial paths from events in the west pacific and recorded at south america show a steep azimuthal change in ab df times about 4 s over a 60 azimuthal range the sharp change is well predicted by existing p and s tomographic models the azimuthal change occurs as the ab paths sweep across the great slow anomaly in the central pacific the high correlation between the p and s velocities suggests that the central pacific slow anomaly may be of thermal origin

melting induced stratification above the earth s inner core due to convective translation several observed properties of earth s solid inner core and liquid outer core remain enigmatic including an east west seismic asymmetry and the presence of a roughly 250 kilometre thick layer of reduced seismic velocity at the base of the outer core alboussiere et al now suggest a model that can produce both of these features based on experiment and numerical modelling they propose that simultaneous crystallization and melting at opposite sides of earth s inner core surface can result in a translational mode of thermal convection within the inner core which also introduces an asymmetry between hemispheres these authors show that simultaneous crystallization and melting at the surface of the earth s inner core can result in a translational mode of thermal convection within the inner core producing the observed stratified layer of reduced seismic velocity at the base of the outer core the dynamical model they propose also introduces an asymmetry between hemispheres that may explain the enigmatic east west asymmetry in seismic properties of the inner core in addition to its global north south anisotropy1 there are two other enigmatic seismological observations related to the earth s inner core asymmetry between its eastern and western hemispheres2 3 4 5 6 and the presence of a layer of reduced seismic velocity at the base of the outer core6 7 8 9 10 11 12 this 250 km thick layer has been interpreted as a stably stratified region of reduced composition in light elements13 here we show that this layer can be generated by simultaneous crystallization and melting at the surface of the inner core and that a translational mode of thermal convection in the inner core can produce enough melting and crystallization on each hemisphere respectively for the dense layer to develop the dynamical model we propose introduces a clear asymmetry between a melting and a crystallizing hemisphere which forms a basis for also explaining the east west asymmetry the present translation rate is found to be typically 100 million years for the inner core to be entirely renewed which is one to two orders of magnitude faster than the growth rate of the inner core s radius the resulting strong asymmetry of buoyancy flux caused by light elements is anticipated to have an impact on the dynamics of the outer core and on the geodynamo

thermal and electrical conductivity of solid iron and iron silicon mixtures at earth s core conditions we report on the thermal and electrical conductivities of solid iron and iron silicon mixtures fe0 92si0 08 and fe0 93si0 07 representative of the composition of the earth s solid inner core at the relevant pressure temperature conditions obtained from density functional theory calculations with the kubo greenwood formulation we find thermal conductivities view the mathml source and electrical conductivities view the mathml source at the top of the inner core centre of the earth these values are respectively about 45 56 and 18 25 higher than the corresponding conductivities in the liquid outer core the higher conductivities are due to the solid structure and to the lower concentration of light impurities these values are much higher than those in use for previous inner core studies k by a factor of four and by a factor of three the high thermal conductivity means that heat leaks out by conduction almost as quickly as the inner core forms making thermal convection unlikely the high electrical conductivity increases the magnetic decay time of the inner core by a factor of more than three lengthening the magnetic diffusion time to 10 kyr and making it more likely that the inner core stabilises the geodynamo and reduces the frequency of reversals

formation of parabolic dunes from barchan and transverse dunes along israel s mediterranean coast the mediterranean coastal dunes of israel underwent a land use change during the second half of the 20th century due to intense agricultural and pastoral activity the coastal dunes were stripped of natural vegetation until the end of the first half of the 20th century the barchan and transverse dunes were shaped by strong southwesterly winter winds a decrease in human activity during the second half of the 20th century brought about a renewal of natural vegetation on the dune crest the only area with neither erosion nor deposition the establishment of vegetation on the crest changes the dynamics of these barchan and transverse dunes so that not all of the sand eroded from the windward side is carried to the lee slip face some is trapped by plants consequently there is a change in the shape of the windward slope from convex to concave and the dune gradually becomes parabolic in this study we trace the morphodynamics of the dunes by analysing 12 sets of aerial photographs which were taken from 1944 to 1995 the average rate of advance of 15 dunes has decreased from 3 4 m a 1 to 1 9 m a 1 while the vegetation cover has increased from 4 3 to 17 per cent during this period copyright 2002 john wiley sons ltd

seismic anisotropy of the earth s inner core resulting from flow induced by maxwell stresses seismological observations indicate that the inner core of the earth is elastically anisotropic1 anisotropic structures are likely to be formed by dynamic processes and therefore such observations have the potential to provide constraints on flow in the inner core and on the geodynamo itself but in addition to the difficulties in estimating the relevant physical properties of iron under inner core conditions2 3 4 even the macroscopic processes responsible for generating seismic anisotropy in this region have yet to be determined5 6 7 8 9 as a result the geodynamic significance of seismic anisotropy in the inner core has remained unknown here i propose based on geodynamic and mineral physics considerations that flow induced by the stress due to the magnetic field the maxwell stress near the inner core boundary produces an axisymmetric fabric responsible for the observed seismic anisotropy the resultant seismic anisotropy reflects the geometry of the magnetic field near the inner core boundary and therefore seismological observations might provide constraints on the geodynamo this flow also causes non uniform release of energy at the inner core boundary associated with solidification and melting which may affect the pattern of convection in the outer core

anisotropy in the deep earth abstract seismic anisotropy has been found in many regions of the earth s interior its presence in the earth s crust has been known since the 19th century and is due in part to the alignment of anisotropic crystals in rocks and in part to patterns in the distribution of fractures and pores in the upper mantle seismic anisotropy was discovered 50 years ago and can be attributed for the most part to the alignment of intrinsically anisotropic olivine crystals during large scale deformation associated with convection there is some indication for anisotropy in the transition zone particularly in the vicinity of subducted slabs here we focus on the deep earth the lower mantle and core where anisotropy is not yet mapped in detail nor is there consensus on its origin most of the lower mantle appears largely isotropic except in the last 200 300 km in the d region where evidence for seismic anisotropy has been accumulating since the late 1980s mostly from shear wave splitting measurements recently a picture has been emerging where strong anisotropy is associated with high shear velocities at the edges of the large low shear velocity provinces llsvps in the central pacific and under africa these observations are consistent with being due to the presence of highly anisotropic mgsio 3 post perovskite crystals aligned during the deformation of slabs impinging on the core mantle boundary and upwelling flow within the llsvps we also discuss mineral physics aspects such as ultrahigh pressure deformation experiments first principles calculations to obtain information about elastic properties and derivation of dislocation activity based on bonding characteristics polycrystal plasticity simulations can predict anisotropy but models are still highly idealized and neglect the complex microstructure of polyphase aggregates with strong and weak components a promising direction for future progress in understanding the origin of seismic anisotropy in the deep mantle and its relation to global mantle circulation is to link macroscopic information from seismology and microscopic information mineral physics through geodynamics modeling anisotropy in the inner core was proposed 30 years ago to explain faster p wave propagation along the direction of the earth s axis of rotation as well as anomalous splitting of core sensitive free oscillations there is still uncertainty about the origin of this anisotropy in particular it is difficult to explain its strength based on known elastic properties of iron as it would require almost perfect alignment of iron crystals indeed the strongly anomalous p travel times observed on paths from the south sandwich islands to alaska may or may not be due to inner core anisotropy and will need to be explained before consensus can be reached on the strength of anisotropy in the inner core and its origin

geodynamic estimates of the viscosity of the earth s inner core recent seismological studies1 2 have suggested that the inner core is rotating relative to the bulk of the earth a situation which according to numerical simulations3 may be sustained by convective flow in the liquid outer core on the other hand large gravitational forces due to the heterogeneous distribution of mass in the earth s mantle should be sufficient to keep the inner core aligned with the mantle4 here i show that the differential rotation of the inner core can be reconciled with these strong gravitational forces by allowing the shape of the inner core to adjust as it rotates so permitting an estimate of the effective viscosity of this innermost region of the earth the inferred rotation rate constrains the viscosity of the inner core to be less than 1016 pa s or greater than 1020 pa s as two different dynamical regimes are possible the viscosity estimates for these two regimes have very different implications for the origin of seismic anisotropy in the inner core

geomorphologic characteristics and evolution of managed dunes on the south west coast of france abstract the calibrated foredunes of the aquitaine coast sw france constitute an example of secular extensive application of nature based solution being one of the longest and largest dune systems in europe this iconic landscape offers considerable services to coastal societies since the mid half of the 18th century human work on sediment flows has resulted in the emergence of large sets of foredunes currently constituting an almost 230 km long managed barrier against inland sand invasion coastline erosion coastal flooding and also a major reserve of biodiversity last massive mechanic shaping of the foredunes following a so called ideal profile date back to the 1970s 80s and aimed to limit erosion dynamics and sediment mobility since they have been facing multiples disruptions over the years which have considerably modified their morphology especially during the last decades calibrated foredunes are currently exhibiting impressive dimensions with a mean dune height of about 16 6 m peaking at 30 m in some locations and a dune width mean along the coast of 187 m today 55 5 of them meet the ideal profile shape standards or surpass the in terms of dimensions whereas 21 5 of the calibrated foredunes are considered narrowed and need specific attention this regional analysis based on extensive airborne lidar datasets from 2011 to 2018 includes i a dune morphology classification based on several basic geomorphological indicators dune width height crest position back dune elevation compared to a calibrated idealised shaped profile ii a quantification of marine beach dune and aeolian sediments flows in m year and m m2 year and forms on dunes scarps blowouts depositional lobes as an indicator of the recent dynamics affecting dune morphology and iii a study of management control of calibrated foredunes 4613 interventions including actions taken after the outstanding winter of 2013 2014 as expected intensive dune management are mainly focused where assets are directly threatened the study highlights the importance and the efficiency of human management on dune evolutions long term dune form stability control of gullies and incipient frontal blowout after marine erosion protection of human issues however today management actions wind fence branch cover planting and reshaping are not conditioned by foredune morphology or last decade s beach dune dynamic sediment availability chronic coastline erosion considering long term erosion projections and expected impact of climate change the analysis shows the need of more global and extensive strategies in order to preserve the protection role of foredunes in the coming decades

the influence of topography and approach angles on local deflections of airflow within a coastal blowout the spatial variability of air flow through complex topography is an important but not fully understood component of dune development and dynamics this study examines the spatial variability of the wind field in a linear blowout in coastal dunes at jockey s ridge state park on the outer banks of north carolina a spatial array of single height anemometers and wind vanes were placed within the blowout topography exerted a significant steering effect when onshore winds approached from directions within 50 of the blowout axis under those conditions wind flow in the blowout aligned to the axis regardless of approach angle maximizing the potential for erosion and transport in the trough in other locations aspect variations caused deflection both proportional and disproportional to changes in the approaching wind when prevailing winds approached from directions more oblique than 50 to the blowout axis topographic steering through the blowout trough was reduced and secondary flow generated by flow separation over the trough became more prominent during those approach angles wind directions and speeds within the upper blowout trough became erratic as vortices and turbulence dominated the flow minimizing transport potential the changing characteristics of airflow in the blowout relative to differing approach angles has implications on dune development and variations in transport potential under changing conditions copyright 2013 john wiley sons ltd

seismology of the core the purpose of this report is to review seismological research related to the earth s core published during the period 1991 1994 the review period 1987 1990 is covered in masters 1991 i have attempted to provide a complete overview of research conducted in the united states research carried out in other parts of the world is only partially reviewed this report is divided into two main sections concerned with the inner and outer core respectively the section on the inner core discusses exciting recent developments related to its apparent anisotropy presents the latest views on its attenuation and considers implications for its growth and composition the discussion of the outer core focuses on its velocity profile and core oscillations

seismological evidence for differential rotation of the earth s inner core the travel times of seismic waves that traverse the earth s inner core show a small but systematic variation over the past three decades this variation is best explained by a rotation of the inner core that moves the symmetry axis of its known seismic anisotropy the inferred rotation rate is on the order of 1 per year faster than the daily rotation of the mantle and crust

foredunes and blowouts initiation geomorphology and dynamics this paper reviews the initiation dynamics geomorphology and evolution of incipient foredunes established foredunes and blowouts incipient foredunes may be initiated in a variety of ways leading to the formation of ramps terraces or ridges depending on progradation rates vegetation type and cover sediment transport rates and scale of erosional processes vegetation cover morphology growth rates and types combine with aerodynamic processes to determine dune and swale morphology established foredunes are classified into five morpho ecological types and the flow behaviour over two types is detailed a new model of foredune evolutionary paths at various possible time scales is presented blowout initiation dynamics and sediment transport and evolution is examined throughout the review the gaps in present understanding of dune processes and a range of ideas for new research possibilities are provided

elastic anisotropy in textured hcp iron to 112 gpa from sound wave propagation measurements we report the first experimental determination of elastic anisotropy in highly textured polycrystalline hexagonal closed packed hcp iron obtained at room temperature and 112 gpa by inelastic x ray scattering ixs in a diamond anvil cell dac the compressional sound velocity vp at 50 and 90 from the c axis was determined to be vp 50 9900 200 m s and vp 90 9450 150 m s respectively the difference of 4 5 between the two velocities is of the same order of the seismic observations of the anisotropy in earth s inner core combining our new results with the equation of state of hcp iron we derive the pressure dependence of the shear velocity vs the vs values extrapolated to inner core densities are 30 higher than the prem results the extrapolated vp values are instead in fair agreement with the prem seismic model though differences in the slope remain furthermore assuming a strong texture characterized by cylindrical symmetry we provide an estimate for the single crystal elastic modulus c11 as a function of pressure while our results are in general agreement with the predominant existence of hcp iron in earth s inner core the remaining differences might be assigned to the presence of another solid iron phase light elements or liquid inclusions as well as anharmonic high temperature effects

three years of morphologic changes at a bowl blowout cape cod usa this study presents measurements of blowout topography obtained with annual terrestrial laser surveys carried out over a three year period at a single large bowl blowout located in the provincelands dunes section of cape cod national seashore in massachusetts the study blowout was selected because its axis is aligned with northwest winds that dominate the region and because it was seemingly interacting with a smaller saucer blowout that had recently formed on the southern rim of the primary feature assuming that blowouts enlarge both horizontally and vertically in response to the wind regime the objectives of the study were to determine both the amount of horizontal growth that the blowout experiences annually and the spatial patterns of vertical change that occur within the blowout changes to the blowout lobe surrounding the feature were also determined for areas with sparse enough vegetation cover to allow laser returns from the sand surface the results show that the blowout consistently expanded outward during the three years with the greatest expansion occurring at its southeast corner opposite the prevailing winds the most significant occurrence was the removal in the first year of the ridge that separated the two blowouts resulting in a major horizontal shift of the southern rim of the new combined blowout this displacement then continued at a lesser rate in subsequent years the rim also shifted horizontally along the northwest to northeast sections of the blowout significant vertical loss occurred along the main axis of the blowout with the greatest loss concentrated along the southeast rim on the lobe there were large areas of deposition immediately downwind of the high erosion zones inside the blowout however there were also small erosion areas on the lobe extending downwind from eroding sections of the rim this study shows that 1 blowouts can experience significant areal and volumetric changes in short periods of time 2 significant changes may occur relatively suddenly when adjacent blowouts combine into a single feature and 3 the sediment transport paths are highly controlled by the topography the joining of two blowouts not only creates a new larger feature but it also releases large amounts of sediment that are then distributed across the landscape downwind creating a potential for major changes to a landscape over the longer term

depth dependence of anisotropy of earth s inner core both body wave pkp travel times creager 1992 song and helmberger 1993a mcsweeney and creager 1993 shearer 1994 and fits to the splitting of core modes tromp 1993 show general agreement that the top 300 km of inner core is very anisotropic the anisotropy displays axial symmetry around the earth s spin axis with the polar direction 3 faster than the equatorial direction one key problem now is the depth dependence of the inner core anisotropy here we extend our polar path studies to include both long period and short period modeling for the pkp phases at ranges 120 to 173 arrivals from the top of the inner core pkikp and reflections from the inner core boundary pkikp can be observed distinctly in short period records at ranges 130 to 140 and as waveform distortions in the long period records at ranges 130 to 146 these waveforms provide a new set of data for examining the topmost 150 km of the inner core which is not well sampled by the previous body wave travel times record sections of waves traversing the inner core nearly parallel to the earth s spin axis polar paths from three events two beneath the south sandwich islands and one along the macquarie ridge recorded at world wide standardized seismograph network canadian network and long range seismic measurements stations are analyzed our results suggest that the top 150 km of the inner core is only weakly anisotropic less than 1 with strong evidence indicating that the top 60 km is not anisotropic at all

flow and sediment transport dynamics in a slot and cauldron blowout and over a foredune mason bay stewart island rakiura nz abstract this study is the first to simultaneously compare flow and sediment transport through a blowout and over an adjacent foredune and the first study of flow within a highly sinuous slot and cauldron blowout flow across the foredune transect is similar to that observed in other studies and is primarily modulated by across dune vegetation density differences flow within the blowout is highly complex and exhibits pronounced accelerations and jet flow it is characterised by marked helicoidal coherent vortices in the mid regions and topographically vertically forced flow out of the cauldron portion of the blowout instantaneous sediment transport within the blowout is significant compared to transport onto and or over the adjacent foredune stoss slope and ridge with the blowout providing a conduit for suspended sediment to reach the downwind foredune upper stoss slope and crest medium term 4 months aeolian sedimentation data indicates sand is accumulating in the blowout entrance while erosion is taking place throughout the majority of the slot and deposition is occurring downwind of the cauldron on the foredune ridge the adjacent lower stoss slope of the foredune is accreting while the upper stoss slope is slightly erosional longer term 16 months pot trap data shows that the majority of foredune upper stoss slope and crest accretion occurs via suspended sediment delivery from the blowout whereas the majority of the suspended sediment arriving to the well vegetated foredune stoss slope is deposited on the mid stoss slope the results of this study indicate one mechanism of how marked alongshore foredune morphological variability evolves due to the role of blowouts in topographically accelerating flow and delivering significant aeolian sediment downwind to relatively discrete sections of the foredune

origin and evolution of playas and blowouts in the semiarid zone of tierra de pinares duero basin spain abstract a large number of blowouts and playas occur in the marginal sectors of the aeolian deposits located in the southern sector of the duero depression tierra de pinares in spain the blowouts are relict landforms that were developed on sand sheets by deflation during dry periods with lower vegetation cover and a deeper water table the studied blowouts form complexes of nw se and nnw sse elongated hollows with accompanying dunes up to 4 km long in the leeward margins some hollows host lakes or swampy areas related to a shallow water table the dunes formed by ne ene winds show steep windward slopes and gentle leeward slopes the studied playas with prevalent nnw sse orientations result from the aeolian excavation of terrace deposits and the underlying marly bedrock it is probable that the formation of these depressions in an initial stage was related to deflation processes affected preferentially nnw sse sandy channels perpendicular to the dominant wind direction the precipitation of salts in the playas generates aggregates of clay particles peloids that are easily removed by the wind once the bottom reached the substratum the deepening of the depressions progressed by the deflation of particles produced by weathering of the argillaceous bedrock

using pkikp coda to determine inner core structure 2 determination of qc 1 despite the similar and rather uniform composition of two components of the core the solid inner part presents a much larger attenuation compared to the liquid outer part more over several authors have reported evidence of scattered seismic energy coming from the inner core ic this implies that the ic has lateral variations in structure or composition with a scale length from one to tens of kilometers these seismic scatterers could be caused by changes in crystal grain size variations in the orientation of anisotropy or the presence of partial melt and or impurities this work pursues the characterization of inner core scattering ics using a global data set of high frequency pkikp waveforms recorded at short period small aperture seismic arrays we apply a methodology used in the study of heterogeneities in the crust and upper mantle that consists of curve fitting of the observed scattered energy with a standard model along with a stripping technique to isolate the pkikp coda from the rest e g p pcp and pp codas from the observed pkikp codas we found an average qc 500 for the inner core reflecting a scattering attenuation at least comparable to the intrinsic attenuation we found a geographical dependence in the observations of pkikp coda with most of them coming from the pacific ocean and asia and relatively few observations coming from the atlantic ocean the simplest explanation is that the ics has a quasi hemispherical variation similar to other properties such as p wave velocity jump at the inner core boundary attenuation in the upper ic strength of anisotropy and or thickness of an overlaying isotropic layer this phenomenon is probably related to the solidification texturing of iron crystals showing hemispherical differences in the growth of the inner core

seismic anisotropy in the earth s innermost inner core testing structural models against mineral physics predictions using an updated data set of ballistic pkikp travel time data at antipodal distances we test different models of anisotropy in the earth s innermost inner core imic and obtain significantly better fits for a fast axis aligned with earth s rotation axis rather than a quasi equatorial direction as proposed recently reviewing recent results on the single crystal structure and elasticity of iron at core conditions we find that an hcp structure with the fast c axis parallel to earth s rotation is more likely but a body centered cubic structure with the 111 axis aligned in that direction results in very similar predictions for seismic anisotropy these models are therefore not distinguishable based on current seismological data in addition to match the seismological observations the inferred strength of anisotropy in the imic 6 7 implies almost perfect alignment of iron crystals an intriguing albeit unlikely situation especially in the presence of heterogeneity which calls for further studies

constructing notches in foredunes effect on sediment dynamics in the dune hinterland measurements were carried out on the island of ameland the netherlands to determine whether notches cut into foredunes stimulated the supply of fresh calcareous beach and dune sand into the white and grey dune habitats behind the dunes increasing these habitats biological quality sediment characteristics and dynamics deposition flux and grain size properties as well as aspects of the vegetation occurrence composition and cover density were studied along six transects three behind an intact foredune and three behind a foredune with a notch cut into it compared to an intact foredune the notched foredune exhibited higher deposition and accumulation behind the dune the extra supply of sand was small however and for the notches studied limited to the zone within approximately 50 60 m of the foredune s crest farther away from the dune the effect of the notches became negligible the presence of a notch did affect the grain size composition of sediment deposited behind the foredune for intact foredunes the grain size composition behind the dune was similar to that on the dune itself when a notch had been cut the sediment was finer behind the foredune gradually coarsening away from the dune sand spray deposition of sand eroded from the dune and transported in modified saltation during heavy winds explains these granulometric results the effect of the notches on the vegetation in the grey dune habitat behind the foredune was small and for the notches studied limited to the first approximately 35 m of the grey dune area between 30 and 65 m from the foredune s crest the notches had a greater effect on the white dune habitat but in the opinion of the authors this remained disproportionately small relative to the effort required for notch excavation and maintenance

interdiffusion of earth s core materials to 65 gpa and 2200 k abstract diffusion of iron and nickel in an fe 64 ni 36 alloy was measured via the use of focused ion beam fib milling and energy dispersive x ray spectroscopy edx to 65 gpa and 2200 k the experiments were performed using a combination of micro fabricated samples in the laser heated diamond anvil cell dac increasing the pressure range for experimentally determined interdiffusion coefficients in feni alloys by 40 gpa diffusivity in the iron nickel system follows a homologous temperature relationship d d 0 exp 19 3 2 7 t m t where d 0 is 4 6 7 10 4 m 2 s 1 with zero pressure activation energy 301 40 kj mol 1 consistent with measurements at lower pressures at inner core conditions this predicts an inner core solid state diffusivity of 1 10 14 m 2 s 1 t m t 0 95 with an inner core viscosity of 10 20 10 22 pa s assuming power law creep n 3 with a deviatoric stress of 10 3 10 4 pa

complex seismic anisotropy in the top of the earth s inner core beneath africa 1 we report complex seismic anisotropy in the top 80 km of the earth s inner core beneath africa the anisotropy in the top 80 km of the inner core is constrained using differential travel times amplitude ratios and waveforms of the pkikp pkikp phases sampling africa along various directions the differential pkikp pkikp time residuals relative to the preliminary reference earth model prem along the polar paths are larger than those along the equatorial paths by 0 1 4 s indicating the presence of seismic anisotropy in the top 80 km of the inner core furthermore the observations along the polar paths show complex regional variations beneath africa the differential pkikp pkikp travel time residuals vary from 1 2 s beneath eastern africa to 0 1 s beneath central africa and to 0 2 to 0 8 s beneath western africa a correlation between small pkikp pkikp amplitude ratios and large differential pkikp pkikp travel time residuals is observed the waveform data are spatially binned into six groups to constrain the regional dependence of velocity and attenuation anisotropy in the top 80 km of the inner core overall the seismic data can be explained by an isotropic upper inner core uic overlying an anisotropic lower inner core lic in the top 80 km of the inner core across africa the thickness of the isotropic uic varies from 0 to 50 km and the p velocity transition from the isotropic uic to the anisotropic lic is sharp with velocity increases laterally varying from 1 6 to 2 2 the attenuation structure along the polar paths has a q value of 600 for the isotropic uic and q values varying from 150 to 400 for the anisotropic lic the complex seismic anisotropy in the top of the inner core is found in a region where a rapid change of the inner core boundary icb between 1993 and 2003 was discovered wen 2006 and may be explained by complex alignments of iron crystals resulting from a localized anomalous solidification of the inner core

a wind tunnel study of flow structure adjustment on deformable sand beds containing a surface mounted obstacle roughness elements of varied scale and geometry commonly appear on the surfaces of sedimentary deposits in a wide range of planetary environments they perturb the local fluid flow so that the entrainment transport and deposition of particles surrounding each element is fundamentally altered fluid dynamists have expended much effort in examining the flow structures surrounding idealized elements mounted on fixed planar walls however self regulation occurs in sedimentary systems as a result of the bed surface undergoing rapid topographic modification with sediment transport until it reaches a stable form that enhances the net physical roughness the present wind tunnel study examines how the flow pattern surrounding an isolated cylinder a problem extensively studied in classical fluid mechanics is altered through morphodynamic development of a deep well that envelopes the windward face and side walls of the roughness element spatial patterns in the fluid velocity turbulence intensity and reynolds stress obtained from laser doppler anemometer lda measurements suggest that the flow structures surrounding such a cylinder are fundamentally altered through self regulation of the bed topography as it reaches steady state for example flow stagnation and the turbulent dissipation of momentum are substantially increased at selected points surrounding the upwind face and side walls of the cylinder respectively along the center line of the wake flow to the rear of the cylinder several structures arising from flow separation are annihilated by strong upwelling of the airflow exhausted from the terminus of the well feedback plays a complex time dependent role in this system

flow dynamics and geomorphology of a trough blowout the dynamics and geomorphological development of a trough blowout located at fiona beach in the myall lakes national park in nsw australia are examined wind speeds velocities and flow structure were measured utilizing an array of miniature rimco cup anemometers gill bivane and uvw instruments and wind vanes flow measurements indicate that when the wind approaches the trough blowout parallel to the throat orientation jets occur both in the deflation basin and along the erosional walls relative flow deceleration and expansion occurs up the depositional lobe jets are formed over the depositional lobe crest accompanied by downwind flow separation on the leeward side of the lobe and flow separation and the formation of corkscrew vortices occur over the crests of the erosional walls maximum erosion and transport occurs up the deflation basin and onto the depositional lobe trough blowout morphologies are explained as a function of these flow patterns when the wind approaches the blowout obliquely the flow is steered considerably within the blowout and the degree and complexity of topographic steering is dependent on the blowout topography the flow is usually extremely turbulent and large corkscrew vortices are common the local topography of a blowout can be very important in determining overall sand transport and blowout evolutionary conditions and paths estimates of potential sand transport within the blowout may be up to two orders of magnitude lower than actual rates if remotely sensed wind data are used

the innermost inner core of the earth evidence for a change in anisotropic behavior at the radius of about 300 km since the discovery of the inner core in 1936 no additional spherical subshell of the earth has been observed based on an extensive seismic data set we propose the existence of an innermost inner core with a radius of 300 km that exhibits a distinct transverse isotropy relative to the bulk inner core specifically within the innermost inner core the slowest direction of wave propagation is 45 from the east west direction in contrast the direction of the slowest wave propagation in the overlying inner core is east west the distinct anisotropy at the center of the earth may represent fossil evidence of a unique early history of inner core evolution

regionally heterogeneous uppermost inner core observed with hi net array studies of velocity structure in the earth s inner core and its volumetric variations illuminate our understanding of inner core dynamics and composition here we use an extensive number of seismograms recorded by the hi net array to construct complete empirical curves of pkpbc pkpdf differential traveltimes the nature of these curves implies that significant variations in traveltimes are accumulated during the passage of pkpdf waves through the uppermost inner core and rules out outer core structure effects uniform cylindrical anisotropy of a plausible strength in the uppermost inner core can also be ruled out as a cause of the observed traveltime variations because the range of sampled ray angles is too narrow the configuration and strength of inhomogeneities from a recent tomographic model of the lowermost mantle cannot account for the observed traveltime variations therefore we infer that either variations of p wave isotropic velocity on the scale of about hundred km and less are present in the uppermost inner core or the material may be organized in distinctive anisotropic domains and both of these features may be superimposed on long wavelength hemispherical structure if the former holds true the absolute magnitude of required p wave velocity perturbations from referent values is 0 60 0 10 in the quasi eastern and 1 55 0 15 in the quasi western hemisphere 0 85 0 05 and 1 10 0 10 respectively with the lowermost mantle correction the existence of these variations is a plausible physical outcome given that vigorous compositional convection in the outer core and variations in heat exchange across the inner core boundary may control the process of solidification

anisotropy in inner core attenuation a new type of data to constrain the nature of the solid core during the last decade the presence of velocity anisotropy inside the inner core with a fast axis parallel to the earth s rotation axis has been well established the quantitative analysis of the amplitudes of waves which sample a particular region of the inner core under africa but exhibit various orientations allows us to document and characterize the presence of anisotropy in attenuation the analysis is based on a comparison of both amplitudes and travel times of the pkp df wave which samples the inner core and the pkp bc wave which has nearly the same path but bottoms inside the liquid core the data reveal that the direction of strong attenuation correlates with that of fast velocity when referred to the same epicentral distance and focal depth the pkp df pkp bc amplitude ratio are about five times lower for paths tilted by 25 with respect to the earth rotation axis than for nearly equatorial paths a clear negative correlation is observed between travel time and amplitude residuals when the angle to earth rotation axis varies this first quantitative analysis combined with experimental results on oriented crystals and mushy media may bring important constraints on the mechanism responsible for anisotropy in the inner core

mineral physics of iron and of the core mineral physics is a field of materials physics and materials chemistry confined to the study of materials pertinent to the earth and planetary interiors in the last two decades emphasis has been given to research on the values of physical properties in materials appropriate to the earth s mantle and core braginsky and roberts 1995 listed the physical properties that play a key role in their analysis of convection of the earth s core and the dynamo these connect mineral physics to geomagnetism of the core this review will be concerned primarily with progress made in the last four years in refining values of these properties

planet within a planet rotation of the inner core of earth the time dependence of the orientation of earth9s inner core relative to the mantle was determined using a recently discovered 10 degree tilt in the axis of symmetry of the inner core9s seismic velocity anisotropy two methods of analyzing travel time variations for rays traversing the inner core on the basis of 29 years of data from the international seismological centre 1964 1992 reveal that the inner core appears to rotate about 3 degrees per year faster than the mantle an anomalous variation in inner core orientation from 1969 to 1973 coincides in time with a sudden change jerk in the geomagnetic field

structure and dynamics of earth s inner core abstract the seismological exploration of the earth s inner core has revealed unexpected and puzzling structural complexities its elastic anisotropy is now well established and has been shown to vary spatially there is a well defined hemispherical dichotomy in anisotropy and attenuation and significant variations in the radial direction with weaker anisotropy in the uppermost regions and possibly different properties in an innermost inner core of radius 300 600 km perhaps even more puzzling is the observation of a stably stratified layer at the base of the outer core which has recently been proposed to result from melting of inner core material if confirmed the presence of this layer has major implications for our understanding of convection in the outer core inner core differential rotation with respect to the mantle remains controversial we will review here recent progress in understanding the dynamics of the inner core a number of different models have been proposed for the development of the inner core s structure and formation of the stable layer at the base of the outer core and particular care will be taken to clarify under which conditions the proposed mechanisms can be active

wind direction and complex sediment transport response across a beach dune system evidence from a field study on wind flow and sediment transport across a beach dune system under onshore and offshore conditions including oblique approach angles indicates that sediment transport response on the back beach and stoss slope of the foredune can be exceedingly complex the upper air flow measured by a sonic anemometer at the top of a 3 5 m tower located on the dune crest is similar to regional wind records obtained from a nearby meteorological station but quite different from the near surface flow field measured locally across the beach dune profile by sonic anemometers positioned 20 cm above the sand surface flow form interaction at macro and micro scales leads to strong modulation of the near surface wind vectors including wind speed reductions due to surface roughness drag and adverse pressure effects induced by the dune and wind speed increases due to flow compression toward the top of the dune as well as pronounced topographic steering during oblique wind approach angles a conceptual model is proposed building on the ideas of sweet and kocurek sedimentology 37 1023 1038 1990 walker and nickling earth surface processes and landforms 28 111 1124 2002 and lynch et al earth surface processes and landforms 33 991 1005 2008 geomorphology 105 139 146 2010 which shows how near surface wind vectors are altered for four regional wind conditions a onshore detached b onshore oblique attached and deflected c offshore detached and d offshore oblique attached and deflected high frequency measurements of sediment transport intensity during these different events demonstrate that predictions of sediment flux using standard equations driven by regional wind statistics would by unreliable and misleading it is recommended that field studies routinely implement experimental designs that treat the near surface wind field as comprising true vector quantities with speed and direction in order that a more robust linkage between the regional upper air wind field and the sediment transport response across the beach dune profile be established copyright 2012 john wiley sons ltd

jet flow over foredunes jet flows which are localized flows exhibiting a high speed maxima are relatively common in nature and in many devices they have only been occasionally observed on dunes and their dynamics are poorly known this paper examines computational fluid dynamic cfd two dimensional 2d modelling of jet flow over a foredune topography flow was simulated in 10 increments from onshore 0 to highly oblique alongshore 70 incident wind approach angles cfd modelling reveals that the formation of a jet is not dependent on a critical wind speed and an increase in incident wind velocity does not affect the magnitude of jet flow a jet is first formed at 1 0m seawards of the foredune crest on the prince edward island foredune morphology example examined here a jet is not developed when the incident wind is from an oblique approach angle greater than 50 because there is significantly less flow acceleration across a much lower slope at this incident angle the presence of a scarp does influence the structure of the crest jet in that the jet is more pronounced where a scarp is present surface roughness affects the magnitude of jet expansion and jets are better developed on bare surfaces compared to vegetated ones

constraints on inner core anisotropy from pkp df travel times pkp df travel times reported by the international seismological centre isc are analyzed to study the depth dependence of inner core anisotropy plots of pkp df travel time residuals versus range for different subsets of the data clearly show large anomalies at ranges beyond about 149 for those paths with inner core ray angles within 30 of the rotation axis on average the times are about 3 to 5 s earlier for these paths than for rays at other angles consistent with recent waveform measurements of anomalous pkp df times by creager 1992 and song and helmberger 1993 and indicative of inner core anisotropy in which the p velocity is about 3 faster for n s paths than e w paths the size of these apparent anomalies in the isc data are much larger than those inferred from several previous analyses of isc pkp df data which indicated 0 5 to 2 s anomalies at these ranges the earlier studies applied binning and averaging schemes to the data using windows that were overly tight thus excluding some of the most anomalous data points and biasing the results toward smaller anomalies to avoid this problem i apply a method for computing summary ray residuals that finds the maxima in smoothed histograms of the residuals and does not rely on a fixed interval to window the data points standard errors on each summary ray residual are estimated using a bootstrap technique that randomly resamples the data plots of the summary ray residuals for several range intervals reveal a small number of independent paths nearly parallel to the rotation axis for which the arrivals are 3 to 5 s early although the data are sparse for paths within 30 of the rotation axis anisotropy does not appear to diminish with depth within the inner core and may cause a much larger anomaly near 180 than the 2 s value obtained in several prior studies of isc data the uniform anisotropy models of creager 1992 and song and helmberger 1993 fit the bulk of the data reasonably well however the observed residuals at ranges between 132 and 140 are smaller than those predicted by most anisotropy models suggesting that the anisotropy may diminish within the outermost 50 km of the inner core

transgressive dunefield landforms and vegetation associations dona juana veracruz mexico transgressive dune fields often comprise a multiplicity of landforms where vegetation processes largely affect landform dynamics which in turn also affect vegetation processes these associations have seldom been studied in detail this paper examines four separate landform types in a complex coastal transgressive dunefield located in the central gulf of mexico in order to assess the relationships between dunefield habitat local environmental factors vegetation associations and landform evolution topographic surveys using tape and clinometer were conducted in conjunction with vegetation survey transects at four locations across the dona juana dunefield vegetation surveys allowed the estimation of relative plant cover of each plant species found along the transects a large variety of landforms were found at the dona juana dunefield deflation plains gegenwalle counter ridges transverse dune trailing ridges blowouts and parabolic dunes akle fish scale shaped dunefields and precipitation ridges with plant species associations developing on these different landforms equally variable flood tolerant species were located in the lower parts deflation plain and gegenwalle ridges whereas the older and dryer parts were covered by coastal matorral shrubs burial tolerant species were dominant in the most mobile areas blowouts and akle dunefield and margin the dune trailing ridge with relatively milder conditions showed the highest richness with no dominant species a dual interaction was found such that colonizing species both create and affect topography and in turn topography determines vegetation association and succession patterns in coastal dunes the vegetation and abiotic environment namely the different landforms and the inherent micronevironmental variability interact tightly and generate a complex and highly dynamic biogeomorphic system where substrate mobility and colonization processes reinforce one another in positive feedback copyright 2010 john wiley sons ltd

internal loading of a compressible earth effect of a solid lithosphere abstract this paper shows the importance of including a lithosphere in the earth model when inferring a mantle viscosity profile or density velocity conversion factor from mantle circulation the free slip and no slip conditions are investigated at the mantle lithosphere boundary results obtained for earth models that include a lithosphere are compared with those obtained for models where no lithosphere is considered in particular it is shown that models without a lithosphere are inconsistent with the no slip condition at the mantle lithosphere interface because they introduce a tangential stress discontinuity at that level with regard to the estimations of the mantle viscosity profile from the comparison between observed and computed geoids and plate velocities the principal results obtained previously using the no slip condition without a lithosphere i e the best fit is obtained for a one cell convection with a large viscosity jump at a depth of 670 km are still valid nevertheless to infer a precise viscosity profile or density velocity conversion factor when using the no slip condition a lithosphere must be accounted for because the results are different for models with and without a lithosphere

airflow and aeolian sediment transport patterns within a coastal trough blowout during lateral wind conditions blowouts are depressions that occur on coastal dunes deserts and grasslands the absence of vegetation in blowouts permits high speed winds to entrain and remove sediment whereas much research has examined patterns of wind flow and sediment transport on the stoss slopes and lee of sand dunes no study has yet investigated the connections between secondary air flow structures and sediment transport in a blowout where zones of streamline compression expansion and steering are less clearly delineated in this study we investigated the variability of sediment flux and its relation to near surface wind speed and turbulence within a trough blowout during wind flow that was oblique to the axis of the blowout wind flow was measured using six three dimensional 3d ultrasonic anemometers while sediment flux by eight sand traps all operating at 25 hz results demonstrated that sediment flux rates were highly variable throughout the blowout deflation basin even over short distances 0 5 m where flow was steadiest flux was greatest consequently the highest rates of sediment transport were recorded on the erosional wall crest where flow was compressed and accelerated the strength of correlation between sediment flux and wind parameter improved with an increase in averaging interval from 10 seconds to 1 minute at an interval of 10 seconds however wind speed correlated best with flux at seven of eight traps whereas at an interval of one minute turbulent kinetic energy tke provided the best correlation with flux at six of the eight traps correlation between sediment flux and wind parameters was best in the centre of the blowout and poorest on the erosional wall crest the evidence from this paper suggests for the first time that tke may be a better predictor of sediment transport at minute scale averaging intervals particularly over landforms where wind flow is highly turbulent

drowned shelf edge deltas barrier islands and related features along the outer continental shelf north of the head of de soto canyon ne gulf of mexico abstract four drowned shelf edge delta complexes two drowned shelf deltas three drowned barrier islands large areas of hardground and fields of bedforms on the mid and outer continental shelf and uppermost slope north of the head of de soto canyon ne gulf of mexico were mapped with high resolution multibeam echosounder deltas formed not during the last eustatic low stand but during one or more interstadials when eustatic sea levels were only 60 to 80 m below present sea level the barrier islands and deltas must have been cemented prior to rapid falls of eustatic sea level that occurred during global glaciations cementation is necessary to have preserved the barrier islands from erosion and subsequent destruction by the rapid sea level rise during the last deglaciation the preservation of the relict bathymetry is so good that features that superficially resemble trough blowouts are found in association with one of the relict barrier islands asymmetric bedforms on the midshelf in water depths of 50 to 60 m indicate transport directions to the sw but asymmetric bedforms in water depths of the upper slope between 100 and 120 m on the s and se flanks of the drowned shelf edge deltas indicate a different current direction a separate flow that is a continuation of a sw flowing current that was previously found on the upper slope off nw florida

impact of atmospheric circulation patterns on coastal dune dynamics nw spain article i nfo dunes in temperate latitudes have experienced a significant stabilization in recent times essentially as a conse quence of the expansion of dense vegetation cover yet the causes for this gradual stabilization as well as the causes promoting antecedent aeolian mobilization remainpoorlyunderstood the traba coastal dune field located in nw spain was examined to explore the causes inducing aeolian activity and subsequent stabilization since 1940 morphological changes were identified through the combination of aerial photographs and geophysical techniques local wind field regimes were simulated using a regional climate model to obtain the variability of the most relevant modes of atmospheric circulation in the north atlantic and european regions north atlantic oscillation nao eastern atlantic ea and scandinavian scand this allows us to identify the impact of these circulation modes over dune dynamics results document an episode of aeolian activity during the 1950s followed by a gradual stabilization and fixation of the dune coincident with a decrease on storm and wind inten sity yet aeolian sand movement remained active insmall areas blowouts occurring mainly during the summer ne winds associated with a negative phase of the ea explain the movement of sand within the dune field under favorable conditions of sand supply on the other hand sand supply to the dune field from the beach was promoted by nw winds coincident with the summer negative phase of nao during winter the negative nao favored frequent sw winds associated with the passage of intense storms which in turn explain sand remobilization from the beach making sediment available for the nw winds to blow inland with this work it is proven that to understand past and future aeolian activity requires critical consideration of the variability and impact of the two principal modes of atmospheric circulation in the north atlantic nao and ea the scand mode explaining alowerpercentageofthelocalwind fieldvariabilitywasalsoincludedtoachievehigher significance levels of explained variance

tidal despinning of the mantle inner core superrotation and outer core effective viscosity dissipation of tidal energy in the oceans causes a net transfer of angular momentum from the spin of the earth to the relative orbital motions of the moon and sun these torques couple directly to the mantle and cause it to despin viscous coupling across the outer core is an effective means of communicating this change to the inner core the ekman time scale for dissipation of transient fluid motions associated with unsteady torques is much shorter than the time scale for adjustment of inner core and mantle rotational velocities in the steady couette flow regime the relative amplitude and phase of rotational variations in this system with respect to the applied torques are given in terms of core viscosity and torque variation frequency any short period variations in mantle torques will leave the inner core largely unchanged and the influence of long period and secular torques applied to the mantle is efficiently transmitted to the inner core the system response to a steady tidal torque applied to the mantle leaves the inner core with a small excess rotational velocity relative to the mantle proportional to the product of outer core viscosity and the applied mantle torque recent estimates of an inner core super rotation of 1 degree year imply an effective outer core viscosity of 10 3 pa s glacial cycle variations in tidal torques somewhat complicate this picture but do not yield significantly different viscosity estimates however they do imply that the differential rotation velocity varies by roughly a factor of 2 over a 100 kyr glacial cycle the tidal shear strain may also contribute to development of anisotropy in the inner core

internal structure of a trough blowout determined from migrated ground penetrating radar profiles ground penetrating radar gpr was used to investigate the relationship between the geomorphological development of a large aeolian trough blowout and the stratigraphy and internal sedimentary structure of its associated deposits although analogous many of the data processing techniques routinely applied in seismic reflection are very rarely applied in gpr studies in this study a simple migration program was used that significantly enhanced the quality of gpr images from a large trough blowout at raven meols on the sefton coast northwest england these improvements aided subsequent data interpretation which was achieved through application of the principles of radar stratigraphy gpr shows the pre blowout dunes to have a complex internal structure that suggests they were formed in the presence of at least a partial vegetation cover subsequent to stabilization of these dunes a thin soil developed this dune soil forms an important radar sequence boundary and delineates a complex topography beneath the depositional lobe of the blowout the internal structure of the depositional lobe of the blowout does not conform to a model of simple radial foreset deposition as derived from contemporary process studies reported in the literature instead the pattern of deposition has been extensively modified by the antecedent dune topography and by varying spatial and temporal exposure to important sand transporting winds that is partly controlled by interactions between the regional wind pattern and local dune morphology trough blowout deposits in coastal aeolian sedimentary sequences are likely to be recognized by the presence of laterally continuous packets of relatively high angle cross strata which often display a spatially variable radial dip pattern that is only very poorly or partially developed in addition a soil or other surface representing a significant hiatus in dune deposition is likely to underlie the blowout deposits the topography of which will show a clear relationship to the dip and orientation of the overlying cross strata

high resolution measured and modelled three dimensional airflow over a coastal bowl blowout abstract blowouts are common landforms found within coastal dunes their dynamics are primarily driven by aeolian transport caused by surface wind stress though patterns of deflation and deposition within blowouts are poorly understood as near surface wind flow is complex three dimensional wind flows around blowouts have yet to be properly quantified especially within zones of separation re attachment and acceleration this has been largely due to inadequate measurement of airflow and a lack of suitable airflow models with this in mind we present results from a study that has quantified alongshore and oblique onshore wind flow dynamics over a bowl blowout on the belmullet peninsula ireland using ultrasonic three dimensional anemometry measuring at 50 hz and three dimensional computational fluid dynamic cfd modelling we measure and model for the first time in 3d a detailed picture of the heterogeneity of wind flow over this type of terrain during alongshore wind conditions wind speeds within the deflation basin were retarded by 50 compared to the foredune zone and flow separation restricted to a small zone in lee of the windward rim wind was directed into the deflation basin through a gap in a western erosional wall termed the blowout throat in oblique onshore wind airflow orientated with the blowout throat remained unchanged in direction and slowed by only 30 compared to wind speed on the foredune in lee of the erosional wall adjacent to the blowout throat small zones of flow separation occurred close to the erosional wall in both cases the highest variation in wind speed and direction occurred in zones of separation and attachment whilst flow increased in steadiness with height over the erosional walls the results illustrate that wind is manipulated according to localised topography within the bowl blowout itself resulting zones of potential sediment transport erosion and deposition are spatially complex and alter with wind direction the presence of a blowout throat has a significant influence on airflow patterns within a deflation basin modelled cfd and measured anemometer data demonstrated excellent comparisons for wind direction and speed allowing much greater spatial measurement resolution than physical instrumentation simulated turbulence did not correlate well with measured data highlighting the requirement for high frequency three dimensional anemometry in areas of complex flow

late holocene cliff top blowout activation and evolution in the cooloola sand mass south east queensland australia cliff top dunes are a locally important geomorphic features of sedimentary coasts they are traditionally interpreted as being sourced by or with sand derived from the beach below the cliff this paper presents the results of a stratigraphic and geochronological study of carlo sand blow a coastal blowout that has developed on top of a high sandy cliff in the cooloola sand mass south east queensland we use a combination of sedimentological pedological and geophysical techniques along with optically stimulated luminescence dating to determine the depositional history and evolution of the blowout we demonstrate that the blowout is dominantly nourished by sand eroded from its floor rather than the adjacent beach the original dune surface dates to the first half of the last glacial period c 40 70 ka and this dune was deflated in the late holocene dune activity is directly associated with cliff undercutting because of coastal retreat in the late holocene but coastal erosion on its own is not capable of maintaining aeolian activity blowout activity occurred between 2 6 and 2 3 ka and again at 0 3 ka with aeolian sand burying palaeosols both soil surfaces contained charcoal and tree stumps in growth position and our study suggests that fire is the immediate trigger for blowout reactivation it is likely that these fires were anthropogenic in origin because the site is somewhat protected from natural fire and the ages coincide with intensification of human use of coastal sites in the area

core structure re examined using new teleseismic data recorded in antarctica evidence for at most weak cylindrical seismic anisotropy in the inner core we present a significant addition to the data set of traveltimes of seismic pkp waves that sample the earth s lowermost mantle and core along the earth s rotation axis recorded at permanent global seismic network gsn and temporary sscua deployment broad band seismographic stations in antarctica the new data improve the previously poor and biased coverage that underlies the seismic constraints on recent models of inner core structure and anisotropy on the one hand new differential pkp traveltime measurements improve the sampling of predominantly the eastern inner core hemisphere pkpab df and pkpbc df differential traveltime residuals with respect to the spherically symmetric model ak135 are consistently smaller than two seconds along the north south paths sampled axially symmetric models of inner core seismic anisotropy with fast axis parallel to the earth s rotation axis require a weak anisotropy of 0 7 0 1 per cent to be consistent with our pkpbc df observations pkpbc df residuals from the quasi eastern hemisphere indicate 0 4 0 1 per cent anisotropy if only pkpbc df observations from the top 200 km of this hemisphere are considered this is reduced to 0 1 0 2 per cent consistent with an isotropic layer on the other hand new absolute pkp traveltime measurements add to the sampling of both hemispheres of the inner core but it is difficult to use them with more confidence to assess structure of the core since they are affected by crustal and mantle structure and source uncertainties the newly collected data set also increases constraints on d structure beneath the south pole in contrast to previous inferences based on data from northern stations we find no evidence of a velocity heterogeneity in the outer core near the inner core boundary associated with the cylinder tangent to the inner core in the southern hemisphere

tectonic history of the earth s inner core preserved in its seismic structure seismic data show that the earth s inner core is structurally complex numerical simulations suggest that whereas the deeper structure may be inherited from past episodes of inner core growth the origin of the shallow structure is due to ongoing deformation

earth s core and the geodynamo earth s magnetic field is generated by fluid motion in the liquid iron core details of how this occurs are now emerging from numerical simulations that achieve a self sustaining magnetic field early results predict a dominant dipole field outside the core and some models even reproduce magnetic reversals the simulations also show how different patterns of flow can produce similar external fields efforts to distinguish between the various possibilities appeal to observations of the time dependent behavior of the field important constraints will come from geological records of the magnetic field in the past

on the transition between 2d and 3d dunes sediment transport in sand bedded alluvial channels is strongly conditioned by bedforms the planimetric morphology of which can be either two or threedimensional experiments were undertaken to examine the processes that transform the bed configuration from two dimensional 2d dunes to threedimensional 3d dunes a narrowly graded 500 lm size sand was subjected to a 0ae15 m deep non varying mean flow ranging from 0ae30 to 0ae55 m sec 1 in a 1 m wide flume changes in the planimetric configuration of the bed were monitored using a high resolution video camera that produced a series of 10 sec time lapsed digital images image analysis was used to define a critical value of the non dimensional span sinuosity of the bedform crestlines that divides 2d forms from 3d forms significant variation in the non dimensional span is observed that cannot be linked to properties of the flow or bedforms and thus appears random images also reveal that once 2d bedforms are established minor transient excesses or deficiencies of sand are passed from one bedform to another the bedform field appears capable of absorbing a small number of such defects but as the number grows with time the resulting morphological perturbations produce a transition in bed state to 3d forms that continue to evolve but are pattern stable the 3d pattern is maintained by the constant rearrangement of crestlines through lobe extension and starving downstream bedforms of sediment which leads to bifurcation the experiments demonstrate that 2d bedforms are not stable in this calibre sand and call into question the reliability of bedform phase diagrams that use crestline shape as a discriminator

microstructure and micromotion in recrystallization flow of octachloropropane a first look advance of the genetic theory of metamorphic fabric depends in part on improved understanding of dynamic recrystallization processes and the effects of these processes upon various fabric elements this paper describes aspects of the microstructural evolution and associated small scale motion in a dynamically recrystallizing sheet of octachloropropane the material was deformed in progressive pure shear at 2 10 3 sec 1 with interruptions for photography and u stage measurement at 70 of its absolute melting temperature the dominant recrystallization process is migration of grain boundaries with consequent major adjustment of the shapes and sizes of grains but no marked change in the average grain size and no creation of new grains typical grains in the fully deformed material 30 bulk shortening have a composite structure with primitive high strain regions inherited directly from the undeformed state rimmed by successively younger regions of lower strain accreted behind outwardmoving boundaries an array of second phase marker particles permits distinction between grain boundary motion with and through the material and reveals an unexpected ability of grains as a whole to migrate short distances up a bulk strain gradient the markers also show that the only important deformation process is intragranular deformation and that it is proceeding at somewhat different rates in different grains the central problem posed by the observations is to explain the direction and speed of each migrating boundary two hypotheses were tested neither with outstanding success one of these hypotheses is that grain boundary migration is part of a strain accomodation process that operates between grains stretching or shortening at different rates parallel to their mutual boundary

geomorphological analysis and classification of foredune ridges based on terrestrial laser scanning tls technology abstract along the north adriatic sea coast italy vulnerability to climate change is further aggravated by anthropogenic influences such as strong subsidence rate due to deep groundwater and gas abstraction tourism and industry impacts in this context conservation and restoration of coastal sand dunes become extremely important especially because of their importance in terms of natural coastal defense this paper proposes an innovative geomorphological approach based on terrestrial laser scanning tls which allows us to measure and monitor morphometric dune evolution with high precision and details several tls surveys were performed along the ravenna coast adriatic sea italy and the resulting digital elevation models dems were analyzed in order to classify the foredune ridges in three geomorphological sub zones the topographic areal and volumetric variations over time of geomorphological units were calculated by gis tools in order to identify seasonal trends or particular pattern meteo marine climate conditions were also analyzed and principal component analysis pca was performed to correlate changes in morphology with meteo marine forcing factors highlighting the ones that most influence dune evolution and dynamics

airflow and sand transport variations within a backshore parabolic dune plain complex ne graham island british columbia canada onshore aeolian sand transport beyond the beach and foredune is often overlooked in the morphodynamics and sediment budgets of sandy coastal systems this study provides detailed measurements of airflow sand transport via saltation and modified suspension vegetation density and surface elevation changes over an extensive 325 30 m swath of a backshore foredune parabolic dune plain complex near surface 30 cm wind speeds on the backshore ranged from 4 3 to 7 3 m s 1 gusting to 14 0 m s 1 oblique onshore flow is steered alongshore near the incipient foredune then landward into a trough blowout where streamline compression flow acceleration to 1 8 times the incident speed and increasing steadiness occur highest saltation rates occur in steady topographically accelerated flow within the blowout as such the blowout acts as a conduit to channel flow and sand through the foredune into the foredune plain beyond the blowout flow expands vegetation roughness increases and flow decelerates over the foredune plain localized flow steering and acceleration to 1 6 times the incident speed occurs followed by a drop to 40 of incident flow speed in a densely vegetated zone upwind of an active parabolic dune at 250 m from the foredune sediment properties reflect variations in near surface flow and transport processes well sorted fine skewed backshore sands become more poorly sorted and coarse skewed in the blowout due to winnowing of fines sorting improves and sands become fine skewed over the foredune plain toward the parabolic dune due to grainfall of finer sands winnowed from the beach and foredune during the fall winter season significant amounts of sand up to 110 kg m 2 are transported via modified suspension and deposited as grainfall up to 300 m landward of the foredune no distinct trend in grainfall was found although most fell on the depositional lobe of the blowout and at 200 m near an isolated active parabolic dune grainfall amounts may reflect several transporting events over the measurement period and the transport process is likely via localized modified suspension from the crest of the foredune and other compound dune features in the foredune plain this evidence suggests that the process of grainfall delivery though often overlooked in coastal research may be a key process in maintaining active dunes hundreds of metres from the shoreline in a densely vegetated foredune plain the effectiveness of this process is controlled by seasonal changes in vegetation cover and wind strength as well as shorter term e g tidally controlled variations in sand availability from the beach

parabolic dune reactivation and migration at napeague ny usa insights from aerial and gpr imagery abstract observations from mapping since the 19th century and aerial imagery since 1930 have been used to study changes in the aeolian geomorphology of coastal parabolic dunes over the last 170 years in the walking dune field napeague ny the five large parabolic dunes of the walking dune field have all migrated across or are presently interacting with a variably forested area that has affected their migration stabilization and morphology this study has concentrated on a dune with a particularly complex history of stabilization reactivation and migration we have correlated that dune s surface evolution as revealed by aerial imagery with its internal structures imaged using 200 mhz and 500 mhz ground penetrating radar gpr surveys both 2d transect and high resolution 3d gpr imagery image downwind dipping bedding planes which can be grouped by apparent dip angle into several discrete packages of beds that reflect distinct decadal scale episodes of dune reactivation and growth from aerial and high resolution gpr imagery we document a unique mode of reactivation and migration linked to upwind dune formation and parabolic dune interactions with forest trees this study documents how dune dune and dune vegetation interactions have influenced a unique mode of blowout deposition that has alternated on a decadal scale between opposite sides of a parabolic dune during reactivation and migration the pattern of recent parabolic dune reactivation and migration in the walking dune field appears to be somewhat more complex and perhaps more sensitive to subtle environmental pressures than an idealized growth model with uniform deposition and purely on axis migration this pattern believed to be prevalent among other parabolic dunes in the walking dune field may occur also in many other places where similar observational constraints are unavailable

patterns of wind flow and aeolian deposition on a parabolic dune on the southeastern shore of lake michigan abstract sand deposition and patterns of wind flow were studied on green mountain beach gmb dune a large lake michigan coastal dune that is transitional between a trough blowout and a fully developed parabolic dune deposition pins were used to study the amount and pattern of aeolian sand deposition on the lee slopes of gmb dune over 20 months in the late fall and winter sand supported by ice between the grains accumulated on the upper to mid slopes and became over steepened 38 during measurement periods containing two major storms with wind gusts up to 25 m s a total of 44 of the deposition on the lee slope occurred compared to an average of 9 for comparable time periods between storms sand was delivered by mass movement to the lower slopes during the spring thaw very little sand was deposited on lee slopes during the summer maximum sand deposition occurred near the dune axis oriented southwest northeast and then decreased rapidly along the limbs maximum sand transport and dune migration were oriented towards the northeast despite the dominant regional winds during the fall and winter being from the west and northwest arrays of anemometers and wind vanes were used to study airflow patterns within gmb dune on five different days these studies indicate that steering of winds in the deflation area of the dune may be responsible for the northeasterly sediment transport they also suggest however that the ability of the dune to steer winds and thus control the direction of sand transport and deposition decreases when the angle between the oncoming winds and the dune axis is too great

physical and logistical considerations of using ultrasonic anemometers in aeolian sediment transport research abstract recently ultrasonic anemometers uas have become available for precise high frequency measurement of three dimensional velocity and turbulence properties except for a few wind tunnel and computational fluid dynamics cfd simulations advances in aeolian sediment transport and bedform research have been limited to field studies using instrumentation that is either incapable of measuring turbulence e g cup anemometers or unable to withstand sediment laden airflow e g hotfilms in contrast extensive progress has occurred in fluvial research where turbulence instrumentation has been available for some time this paper provides a pragmatic discussion on using uas in aeolian research recent advances using this technology are reviewed and key physical and logistical considerations for measuring airflow properties and near surface shear stress using uas over complex terrain are discussed physical considerations include limitations of applying boundary layer theory to flow over natural surfaces such as non logarithmic velocity profiles resulting from roughness and topographically induced effects and the inability of instrumentation to measure within the thin constant stress region these constraints hinder accurate shear velocity u shear stress and sand transport estimation uas allow measurement of turbulent reynolds stress rs that in theory should equal profile derived shear stress discrepancies often exist between these quantities however due to three dimensional spanwise flow components and rapid distortion effects i e unbalanced production and dissipation of turbulence common in flow over complex terrain while the rs approach yields information on turbulent contributions to near surface stress generation little evidence exists showing that rs is a better measure of forces responsible for sediment transport consequently predictive equations for sediment transport using rs do not exist there is also a need to identify the role of micro turbulent events e g burst sweep cycles and macro turbulent structures e g separation cells shear layers in aeolian dynamics in field settings to validate recent wind tunnel and cfd simulations a conundrum exists regarding whether velocity data should be rotated to correct for potential sensor misalignment effects in unsteady non uniform flow over complex terrain streamline angles vary spatially and temporally with height and location thus determination of and correction to true streamline coordinates is difficult caution should be exercised with correction methods that remove implicit vertical velocity trends as this may preclude detection of geomorphically important flow behaviour e g lift at a dune crest and may complicate interpretations of rs instruments should be aligned with the underlying surface and flow visualization should be used to adjust sensor measurement planes as close as possible to local streamlines logistical considerations include sensor design advantages and operational limitations data communication formats and field deployment strategies each can affect measurement accuracy and are easily overlooked sampling range frequency and period are also important as they limit the range of velocities and scales of turbulence that can be characterized ultrasonic anemometers offer a new sampling resolution to measure turbulent airflow properties in field settings with proper considerations of their limitations uas may allow researchers to close the gap between fluvial research and develop more robust models of aeolian processes and morphodynamics

short period pkp phases and the anelastic mechanism of the inner core abstract short period seismograms are synthesized for pkp phases in anelastic earth models the synthetics were constructed using a synthetic technique valid at grazing incidence a source time function appropriate for deep focus earthquakes and an instrument response for either a short period wwssn or sro seismograph the agreement between predicted and observed amplitudes and spectral ratios requires neither a low q zone at 0 2 2 hz nor a low or negative p velocity gradient at the bottom of the outer core thin low q zones beneath the inner core boundary fit spectral ratio data that sample the upper 200 km of the inner core but fail to fit data that sample the lower inner core only a model having q 1 0 003 0 004 at 0 2 2 hz nearly constant with depth in the inner core satisfies all of the spectral ratio and amplitude data the assumption of a bulk viscosity of 10 10 3 pa s for the liquid phase of a partially molten inner core combined with the observation of low shear attenuation in the inner core at frequencies less than 0 005 hz limit the physical parameters associated with two possible attenuation mechanisms 1 fluid flow and viscous relaxation due to ellipsoidally shaped inclusions of melt and 2 the solid liquid phase transformation induced by the stress change during the passage of a seismic wave both mechanisms require an order of 0 1 partial melt to reproduce the observed q 1 in the outer core the time constant of the mechanism of phase transformation is predicted to be 10 4 10 6 s confirmation of small shear attenuation in the inner core in the frequency band of seismic body waves would favor the mechanism of phase transformation

interdiffusion of solid iron and nickel at high pressure interdiffusion rates in solid fcc iron nickel alloys have been measured at pressures between 1 and 23 gpa and temperatures between 1423 and 1973 k the experiments were performed using piston cylinder and multianvil devices with diffusion couples comprising pure iron and nickel rods placed end to end concentration profiles in quenched samples were measured by electron microprobe and interdiffusion coefficients were determined using the boltzmann matano method over the entire range of pressure and temperature studied interdiffusion coefficients in the iron rich alloys are described well by a simple exponential function of the homologous temperature d doexp 20 4tm t where tm is the melting temperature of the alloy at the pressure of interest and d0 is a constant equal to 2 7 10 4 m 2 s these data are consistent within an order of magnitude with data for other close packed fcc and hcp metals at the same homologous temperatures at the conditions of earth s inner core diffusion coefficients are predicted to be too small for bulk diffusive exchange between the inner and outer core to be significant it is thus reasonable to model the chemical evolution of the outer core under the assumption that crystallization of the inner core is a perfect fractional process

convection and anisotropy of the inner core estimation of the rayleigh number of the inner core suggests that this region is convecting the flow pattern is likely to produce crystallographic preferred orientation of the elastically anisotropic hexagonal closest packed phase of iron such that compressional wave velocities would be greater in the axial relative to the equatorial direction by roughly 1 percent this result is in agreement with seismological evidence that the inner core is elastically anisotropic

comparison of organic and inorganic carbon isotope patterns across the frasnian famennian boundary abstract the carbon isotopic composition of organic matter is reported for two frasnian famennian boundary sections from the rheinische schiefergebirge germany during the late frasnian 13 c org values commonly range from 27 5 to 26 highest 13 c org values around 24 are encountered immediately above and below the kellwasser horizons all samples from the kellwasser horizons are depleted in 13 c org by 2 5 to 4 7 this depletion is explained by a higher proportion of biomass derived from isotopically depleted chemoautotrophic bacteria a comparison of the positive 13 c excursions shows that the 13 c org shifts precede the 13 c carb shifts by some 10 5 years consequently 13 c values document a shift towards lower values below the upper kellwasser horizon a contribution of terrestrial organic matter as well as a thermal alteration of the 13 c org signals do not provide compelling explanations for the earlier 13 c org shift increases in primary productivity or carbon burial rate will change the co 2 aq content of surface waters affect the carbon isotope fractionation during photosynthetic carbon uptake and thus enrich organic carbon in 13 c however both processes cannot account for the earlier onset of the 13 c org shift because the 13 c carb record should document the resulting 13 c enrichment in surface waters as well a reduction in the calcium carbonate precipitation rate due to the global extinction of the reef ecosystem may have played an important role in reducing the co 2 aq content of surface waters without changing the isotopic composition of surface waters whether this process or other factors such as a rise in sea surface temperature or a change in the phytoplankton association account for the earlier onset of the positive shift in the 13 c org curve must be determined by further studies that may be able to confirm the global significance of the reported 13 c org pattern in frasnian famennian boundary sections from other parts of the globe

pkp bc versus pkp df differential travel times and aspherical structure in the earth s inner core pkp bc versus pkp df differential travel times show coherent patterns of residuals indicating aspherical structure within the earth s inner core using a waveform correlation method we measure 318 differential pkp bc versus pkp df travel times from 5 years of global digital seismograph network gdsn short period data at ranges between 145 and 155 in addition we obtain 19 470 probable bc versus df travel times at these ranges by searching through 23 years of the international seismological centre isc catalog plots of residuals versus turning point location and residuals versus ray direction show clear patterns which indicate that the differential travel times are highly correlated along similar ray paths this pattern is robust with respect to range and source depth these anomalies are almost certainly due to aspherical inner core structure since pkp bc and pkp df have nearly coincident ray paths in the mantle and outer core the gdsn and isc residual patterns are in general agreement but the isc residuals underpredict the gdsn residuals by about a factor of 2 the isc data have better spatial coverage particularly for n s ray paths within the inner core these n s ray paths show positive residuals of about 0 5 s indicating faster inner core p velocities in this direction a result consistent with previous studies of absolute pkp df travel times but derived from an independent data set due to the sparse ray coverage of our data either heterogeneity or anisotropy within the inner core with about 1 velocity variations could explain these residual patterns however inversions of the isc data for heterogeneity require many more free parameters to achieve the same variance reduction as a simple two parameter anisotropy model

responses of three dimensional flow to variations in the angle of incident wind and profile form of dunes greenwich dunes prince edward island canada abstract this study reports the responses of three dimensional near surface airflow over a vegetated foredune to variations in the conditions of incident flow during an 8 h experiment two parallel measurement transects were established on morphologically different dune profiles i a taller concave convex west foredune transect with 0 5 m high densely vegetated 45 seaward incipient foredune and ii a shorter concave straight east foredune transect with lower sparsely vegetated 14 seaward incipient foredune five stations on each transect from the incipient dune to the crest were equipped with ultrasonic anemometers at 0 6 and 1 65 m height and logged at 1 hz incident conditions were recorded from a 4 m tower over a flat beach winds increased from 6 m s 1 to 20 m s 1 and were generally obliquely onshore ene 73 three sub events and the population of 10 minute averages of key properties of flow u w s cvu from all sample locations on the east transect n 235 are examined to identify location and profile specific responses over 52 of the incident direction of flow from 11 to 63 onshore topographic steering and forcing cause major deviations in the properties and vectors of near surface flow from the regional wind topographic forcing on the concave straight dune profile increases wind speed and steadiness toward the crest with speed up values to 65 in the backshore wind speed and steadiness of flow are least responsive to changes in incident angle in the backshore because of stagnation of flow and are most responsive at the lower stoss under pronounced streamline compression on the steeper concave convex profile speed and steadiness decrease toward the crest because of stagnation of flow at the toe and flow expansion at the slope inflection point on the lower stoss net downward vertical velocity occurs over both profiles increases toward the crest and reflects enhanced turbulent momentum conveyance toward the surface all of these flow responses are enhanced with faster speeds of incident flow and or more onshore winds significant onshore steering of near surface vectors of flow to 37 occurs and is greatest closer to the surface and during highly oblique winds 15 onshore therefore even subtle effects of streamline compression and amplification of flow under alongshore conditions effectively steer flow and sand transport toward the dune as topographic forcing and steering cause significant three dimensional deviations in near surface properties of flow most regional scale and or two dimensional models of dune process response dynamics are insufficient for characterizing coastal and desert dune sediment budgets and morphodynamics in particular deflection of sand transport vectors with greater fetch distances than those derived from regional winds may occur coincident flow transport and morphological response data are required to better quantitatively model these processes

a local crossing path study of attenuation and anisotropy of the inner core 1 we report results from studying a region under the north pacific using 46 ray paths along east west and north south directions to study the nature of inner core anisotropy and find an anisotropy signal in differential pkpbc pkpdf at about the resolution of the data with north south paths faster than east west but no dependence of attenuation on wavespeed or depth in this part of the inner core inner core q is 130 52 255 between 140 340 km depth the observations also provide constraints on the degree of homogeneous meridional anisotropy possibly present in the core to between 0 1 and 0 6 velocity differences in the fast and slow directions significantly smaller than the 2 4 axi symmetric anisotropy in the inner core the small meridional component to anisotropy argues against significant contributions to anisotropy from low order inner core convection or stresses imposed on the inner core by the outer core field

geomorphic response to late holocene climate variation and anthropogenic pressure northeastern prince edward island canada abstract geomorphic response provides an index to climate change and variability differing time scales of both weather climate events and landform response complicate interpretation anthropogenic modification particularly in coastal and aeolian dune environments represents a further geomorphic influence northeastern prince edward island pei canada is a marine dominated environment subjected to rising sea level throughout the late holocene the combination of rising sea levels increased anthropogenic utilization of the coast for residential and tourism purposes and limited offshore winter ice conditions have resulted in accelerated erosion and degradation of the dunes and coastline the aeolian succession indicates that temporal and spatial transitions from isolated shield dunes to parabolic dunes to linked coastal transverse dune complexes are characteristic of the coastal dune fields sand supply is the most significant control on dune morphology development and extent superimposed dome dunes and shield dunes are prevalent in areas of anthropogenic disturbance dune migration along the coastal zone has varied considerably with rates locally in excess of 10 m a over short times winters marked by relatively limited sea ice and scarce snow cover resulting from more temperate winter conditions allow increased erosion by strong storms deflation of dune crests and development of blowouts is notably accentuated along human trails the climate variations recorded in atlantic canada over the past decade fall within the range of those recorded previously within the twentieth century and thus do not indicate conclusive evidence of a pronounced trend of climate change in this region however analysis of northeastern pei demonstrates that dune coastlines can evolve rapidly in response to short term and intermediate term climate variation particularly when coupled with anthropogenic pressure similar geomorphic effects in combination with climate variation and storm activity should be anticipated along other dune coastlines that have been subjected to intense anthropogenic utilization during earlier periods of the quaternary

event scale dynamics of a parabolic dune and its relevance for mesoscale evolution parabolic dunes are widespread aeolian landforms found in a variety of environments despite modeling advances and good understanding of how they evolve there is limited empirical data on their dynamics at short time scales of hours and on how these dynamics relate to their medium term evolution this study presents the most comprehensive data set to date on aeolian processes airflow and sediment transport inside a parabolic dune at an event scale this is coupled with information on elevation changes inside the landform to understand its morphological response to a single wind event results are contextualized against the medium term years allowing us to investigate one of the most persistent conundrums in geomorphology that of the significance of short term findings for landform evolution our field data suggested three key findings 1 sediment transport rates inside parabolic dunes correlate well with wind speeds rather than turbulence 2 up to several tonnes of sand can move through these landforms in a few hours and 3 short term elevation changes inside parabolic dunes can be complex and different from long term net spatial patterns including simultaneous erosion and accumulation along the same wall modeled airflow patterns along the basin were similar to those measured in situ for a range of common wind directions demonstrating the potential for strong transport during multiple events mesoscale analyses suggested that the measured event was representative of the type of events potentially driving significant geomorphic changes over years with supply limiting conditions playing an important role in resultant flux amounts

texture and anisotropy the study of preferred orientation of minerals in rocks dates back to omalius d halloy 1833 who attributes a special significance to the alignment of crystals as an indicator of the formation process much later the influence of crystal alignment on physical properties was quantified e g weissenberg 1922 voigt 1928 reuss 1929 only recently has this field emerged as a coherent part of earth science research linking such branches as mineralogy petrology structural geology geodynamics and seismology the reason for this was the emergence of quantitative methods to analyze preferred orientation or texture as it was first called by naumann 1850 these methods were largely developed in collaboration with materials science and mechanics quantitative measurements detailed field studies rigorous data analysis theories to predict textures and improvements in characterizing seismic anisotropy in the earth are leading to a coherent picture that is now being refined though seismologists have long accepted that there is a causal relationship between anisotropic propagation of seismic waves the deformation field and crystal orientation the prevailing view is still largely the mythological concept that seismic fast directions align with the flow direction while this may be approximately the case for olivine deformed under certain conditions it is certainly no universal law as we will try to illustrate in this review the fast direction of a crystal depends on the mineral species and its crystal structure the alignment of crystals depends on microscopic intra crystalline deformation systems and the deformation history both relationships are complex and not intuitive but there are well established theories to compute single crystal physical properties as well as orientation patterns simulations can be compared with experimental data and then applied with some caution to the macroscopic earth this review is intended to provide a brief introduction highlighting some of the issues with

support for equatorial anisotropy of earth s inner inner core from seismic interferometry at low latitudes abstract anisotropy of earth s inner core provides a key role to understand its evolution and the earth s magnetic field recently using autocorrelations from earthquake s coda we found an equatorial anisotropy of the inner inner core iic in apparent contrast to the polar anisotropy of the outer inner core oic to reduce the influence of the polar anisotropy and reduce possible contaminations from the large fresnel zone of the pkikp 2 and pkiikp 2 phases at low frequencies we processed coda noise of large earthquakes 10 000 40 000 s after magnitude 7 0 from stations at low latitudes within 35 during 1990 2013 using a number of improved procedures of both autocorrelation and cross correlation we extracted 52 array stacked high quality empirical green s functions egfs an increase of over 60 from our previous study the high quality data allow us to measure the relative arrival times by automatic waveform cross correlation the results show large variation 10 9 s in the differential times between the pkikp 2 and pkiikp 2 phases the estimated influence of the fresnel zone is insignificant