residual mean solutions for the antarctic circumpolar current and its associated overturning circulation abstract residual mean theory is applied to the streamwise averaged antarctic circumpolar current to arrive at a concise description of the processes that set up its stratification and meridional overturning circulation on an f plane simple solutions are found in which transfer by geostrophic eddies colludes with applied winds and buoyancy fluxes to determine the depth and stratification of the thermocline and the pattern of associated residual meridional overturning circulation

an analytical model of wave overtopping flow velocities on dike crests and landward slopes abstract an accurate description of the maximum flow velocity across flood protective structures is necessary in order to determine the stability of the landward slope and the amount of cover erosion in this paper two new formulas are derived to describe the change in the maximum overtopping flow velocity along the dike crest and the adjacent landward slope these formulas are coupled in an effort to accurately predict the velocities in wave overtopping events this analytical model is validated using 244 data points from flume tests and 300 data points from field tests on river dikes in the netherlands the modelled flow velocity shows good agreement with the measured flow velocity with a nash sutcliffe efficiency factor varying from 0 49 to 0 87 also the derived formulas are compared with existing formulas for wave overtopping flow velocities and overall showed a better performance for a wide range of geometries and covers

on the transport and angular momentum balance of channel models of the antarctic circumpolar current abstract angular momentum balances are discussed both in general as well as in the context of simple channel models of the antarctic circumpolar current acc particular emphasis is placed on the close relationship between the angular momentum balance and the meridional circulation it is found that topographic form drag is established very early in the integration whereas interfacial form drag can take much longer to develop restrictions on the geostrophic portion of the meridional circulation imposed by zonally reconnecting potential vorticity contours in the upper ocean allow derivation of an estimate for the steady state transport the estimate assumes there to be little or no circumpolar flow at great depth an assumption that stems from the belief that the band of zonally reconnecting geostrophic contours in the southern ocean does not extend to the ocean floor the predicted transport is proportional to the strength of the stratification and compares favorably with numerical results in the lite

global ocean meridional overturning abstract a decade mean global ocean circulation is estimated using inverse techniques incorporating air sea fluxes of heat and freshwater recent hydrographic sections and direct current measurements this information is used to determine mass heat freshwater and other chemical transports and to constrain boundary currents and dense overflows the 18 boxes defined by these sections are divided into 45 isopycnal neutral density layers diapycnal transfers within the boxes are allowed representing advective fluxes and mixing processes air sea fluxes at the surface produce transfers between outcropping layers the model obtains a global overturning circulation consistent with the various observations revealing two global scale meridional circulation cells an upper cell with sinking in the arctic and subarctic regions and upwelling in the southern ocean and a lower cell with sinking around the antarctic continent and abyssal upwelling mainly below the crests of the major bathymetric ridges

wave run up and overtopping reduction by block revetments with enhanced roughness abstract block revetments that are placed in special patterns in a way that lower standard sets are surrounded by sets of higher protruding units have been studied by means of physical model tests this paper focuses on prediction formulae for the wave run up and wave overtopping reduction by means of special pattern block revetments this reduction is significant and leads to lower crest levels of dikes reducing or limiting crest levels without reducing safety is often a preferred solution in areas where dikes form an integral part of the existing area and where raising dikes will lead to social drawbacks or a negative impact on the landscape

influence of oblique wave attack on wave overtopping at smooth and rough dikes with a berm abstract oblique wave attack can significantly reduce the amount of wave overtopping at coastal structures compared to perpendicular wave attack guidelines exist to estimate the influence of oblique waves on wave overtopping guidelines to estimate the influence of a berm in the seaward slope are also available these guidelines for the reducing effects of oblique waves and the reducing effects of a berm are frequently applied in combination although limited data is available for this combination of reducing effects to develop a method that can account for the reducing effects of oblique waves and a berm in the seaward slope of a dike physical model tests have been performed in a wave basin on structures with smooth and rough slopes based on these data wave overtopping guidelines for breaking waves on dikes have been validated and one of the guidelines has been extended to take the influence of oblique waves berms and roughness into account

the role of closed gyres in setting the zonal transport of the antarctic circumpolar current abstracteddy permitting simulations are used to show that basinlike gyres can be observed in the large scale barotropic flow of a wind driven channel with a meridional topographic ridge this is confirmed using both two layer quasigeostrophic and 25 level primitive equation models at high horizontal resolution comparing results from simulations with and without the topographic ridge it is shown that the zonal baroclinic transport in the channel increases with increasing wind stress when the bottom topography is flat but not when there is a meridional ridge the saturation of transport for increasing wind occurs in conjunction with the development of recirculating gyres in the large scale barotropic streamfunction this suggests that the total circulation can be thought of as a superposition of a gyre mode which has zero circumpolar transport and a free circumpolar mode which contains all of the transport basinlike gyres arise in the channel because the topography steers the barotropic streamlines a

an investigation of periglacial slope stability in relation to soil properties based on physical modelling in the geotechnical centrifuge results are presented from eight scaled centrifuge modelling experiments designed to investigate mass movement processes on thawing ice rich slopes four pairs of simple planar slope models were constructed one in each pair being of sufficient gradient to promote slope failure during soil thaw and the second having a gradient below the threshold for instability four frost susceptible soils were used three were normally consolidated and had different clay contents 2 12 and 20 and the fourth comprised the 20 clay soil but was over consolidated prior to model testing modelling protocols included freezing from the surface downwards under an open hydraulic system and thawing from the surface downwards under an enhanced gravitational field within the geotechnical centrifuge thereby utilising scaling laws to simulate correct prototype self weight stresses during thaw slopes below the stability threshold gradient were subjected to between 2 and 4 cycles of freezing and thawing simulating annual cycles those above the stability threshold were subjected to only one cycle since they failed during the first thaw phase thermal conditions pore water pressures surface movements and profiles of displacement are reported measured pore pressures are used in slope stability analyses based on a simple planar infinite slope model profiles of solifluction shear strain and mechanisms of slope failure are both shown to be sensitive to small changes in soil properties particularly clay content and stress history in all cases pore pressures rose rapidly immediately following thaw remained below the threshold for failure in low gradient models but exceeding the threshold to trigger landslides on steeper slopes upward seepage of melt water away from the thaw front contributed to loss of shear strength mechanisms of slope failure differed between test soils ranging from mudflow in non cohesive silt to active layer detachment sliding in over consolidated silt clay during solifluction shear strain was greatest at the surface in non cohesive silt and decreased rapidly with depth but in test soils containing clay the zone of maximum shear strain was located lower in the displacement profiles

three dimensional investigations of wave overtopping on rubble mound structures to study the influence of wave obliquity and directional spreading on wave overtopping of rubble mound breakwaters a total of 736 three dimensional model tests were carried out at aalborg university the results of these tests are presented and analysed in this paper yielding a new empirical reduction factor to describe the influence of wave obliquity and directional spreading on the average wave overtopping discharges the study shows that perpendicularly incident long crested waves result in conservative values of the overtopping discharge for the tested cross section

interpretation of recent southern hemisphere climate change climate variability in the high latitude southern hemisphere sh is dominated by the sh annular mode a large scale pattern of variability characterized by fluctuations in the strength of the circumpolar vortex we present evidence that recent trends in the sh tropospheric circulation can be interpreted as a bias toward the high index polarity of this pattern with stronger westerly flow encircling the polar cap it is argued that the largest and most significant tropospheric trends can be traced to recent trends in the lower stratospheric polar vortex which are due largely to photochemical ozone losses during the summer fall season the trend toward stronger circumpolar flow has contributed substantially to the observed warming over the antarctic peninsula and patagonia and to the cooling over eastern antarctica and the antarctic plateau

oblique wave attack on rubble mound breakwaters abstract stability formulae for armour layers of rubble mound breakwaters are usually being applied assuming perpendicular wave attack often the effects of oblique waves are neglected this is however a conservative assumption since the stability of armour slopes generally increases for oblique waves new wave basin tests have been performed to assess the effects of oblique waves on the stability of rock slopes and the stability of cube armoured rubble mound breakwaters the physical model tests were focussed on wave directions between perpendicular 0 and parallel 90 the test programme included tests with long crested waves and tests with short crested waves the results show that for rock slopes the influence of oblique waves is larger for long crested waves based on the test results a design guideline is provided to account for effects of oblique waves on the stability of rock slopes armour layers with a double layer of cubes and armour layers with a single layer of cubes

application of grey theory based model to prediction of land subsidence due to engineering environment in shanghai land subsidence is a common geological hazard the long term accumulation of land subsidence in shanghai has caused economic loss to the city since the 1990s the engineering structures have become a new cause of land subsidence many factors affect the process of land subsidence although such a process cannot be explicitly expressed by a mathematical formula it is not a black box whose internal structure parameters and characteristics are unknown therefore the grey theory can be applied to the prediction of land subsidence and provides useful information for the control of land subsidence in this paper a grey model gm gm 1 1 with unequal time intervals was used to predict the subsidence of a high rise building in the lujiazui area of shanghai and the results were compared with the monitored data the prediction of subsidence was also corroborated by laboratory tests and the results were compared with measured data and the predicted data by the adaptive neuro fuzzy inference system anfis it is found that the gm 1 1 with unequal time intervals is accurate and feasible for the prediction of land subsidence

the role of ocean gateways in the dynamics and sensitivity to wind stress of the early antarctic circumpolar current the date of inception of the antarctic circumpolar current is debated due to uncertainty in the relative opening times of drake passage and the tasman seaway using an idealized eddy resolving numerical ocean model we investigate whether both ocean gateways have to be open to allow for a substantial circumpolar current we find that overlapping continental barriers do not impede a circumpolar transport in excess of 50sv as long as a circumpolar path can be traced around the barriers however the presence of overlapping barriers does lead to an increased sensitivity of the current s volume transport to changes in wind stress this change in sensitivity is interpreted in terms of the role of pressure drops across continental barriers and submerged bathymetry in balancing the momentum input by the surface wind stress specifically when the pressure drop across continents is the main balancing sink of momentum the zonal volume transport is sensitive to changes in wind stress changes in zonal volume transport take place via altering the depth independent part of the circumpolar transport rather than that arising from thermal wind shear in such a scenario isopycnals continue to slope steeply across the model southern ocean implying a strong connection between the deep and surface oceans this may have consequences for the meridional overturning circulation and its sensitivity to wind stress

the influence of a berm and roughness on the wave overtopping at dikes abstract a reliable estimation of average wave overtopping discharge is important for dike design and safety assessment berms and roughness elements are widely applied to reduce the overtopping discharge over dikes in this study the effects of a berm and roughness on the wave overtopping discharge are investigated by means of physical model tests new empirical formulae are derived from the analysis of the experimental data in order to provide more accurate estimations of reductive influence of berms and roughness on the wave overtopping discharge additionally a new formula is developed to estimate the reductive influence of varying roughness along the waterside slopes with a berm the new equations show a significantly better performance within the tested range when compared with existing formulae for the average overtopping discharge

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

land subsidence and pore structure of soils caused by the high rise building group through centrifuge model test abstract in the urban area of shanghai the dewatering of groundwater was controlled strictly and the engineering environment effect of the high rise building group became to be the main cause of land subsidence in shanghai based on the high rise building group in the soft soil area in shanghai the mechanism of land subsidence was studied in this paper by the centrifuge model test the central area of the building group has larger subsidence and the subsidence superimposition effect is obvious it can exceed the allowance and cause land subsidence hazard the land subsidence affected by the different building distances was also studied for smaller building distances the subsidence superimposition effect is more obvious the engineering characteristics of soils are controlled by the state of pore structure of soils to a great extent the parameter of specific subsidence was put forward as a tie to analyze the relationship between land subsidence and pore structure of soils the pore structure of each soil layer was studied by the mercury intrusion porosimetry test mip and the pore distribution of each soil layer was studied by the fractal theory there are mainly macropores in silty clay of layer no 4 clayey soil of layer no 8 silty sand of layer no 7 and layer no 9 in shanghai the ink bottle effect exists in the intrusion stage in the mip test there are four different fractal dimensions in silty clay of layer no 4 and clayey soil of layer no 8 and three different fractal dimensions in silty sand of layer no 7 and layer no 9

influence of oblique wave attack on wave overtopping and forces on rubble mound breakwater crest walls abstract at the crest of rubble mound structures a crest wall is often present to reduce the consumption of material compared to breakwaters without a crest wall to design the crest wall several methods based on estimates of the hydraulic wave loads are available these methods are focussed on waves that approach breakwaters perpendicular in practice the dominant wave conditions are often not perpendicular but approach the breakwater under an angle oblique waves can significantly reduce the amount of wave overtopping and reduce the wave loads on coastal structures compared to perpendicular waves therefore physical model tests have been performed in a wave basin where the wave loads on crest walls and the wave overtopping discharges have been measured under oblique wave attack design guidelines have been developed to take the reduction due to oblique waves into account together with available methods to predict the wave forces and wave overtopping for perpendicular wave attack the obtained results enable a more advanced design of crest walls

sensitivity of the southern ocean overturning circulation to surface buoyancy forcing 1 the sensitivity of the southern ocean overturning to altered surface buoyancy forcing is investigated in a series of eddy permitting idealised simulations the modelled response indicates that heat and freshwater fluxes in the southern hemisphere mid latitudes may play a significant role in setting the strength of the overturning circulation enhanced buoyancy fluxes act to increase the meridional overturning up to a limit approaching the wind driven ekman transport the sensitivity of the overturning to surface buoyancy forcing is strongly dependent on the relative locations of the wind stress profile buoyancy forcing and upwelling region the numerical simulations provide support for the hypothesis that changes in upwelling during deglaciations may have been driven by changes in heat and freshwater fluxes instead of or in addition to changes in wind stress

equilibration of the antarctic circumpolar current by standing meanders the insensitivity of the antarctic circumpolar current acc s prominent isopycnal slope to changes in wind stress is thought to stem from the action of mesoscale eddies that counterbalance the wind driven ekman overturning a framework verified in zonally symmetric circumpolar flows substantial zonal variations in eddy characteristics suggest that local dynamics may modify this balance along the path of the acc analysis of an eddy resolving ocean gcm shows that the acc can be broken into broad regions of weak eddy activity where surface winds steepen isopycnals and a small number of standing meanders across which the isopycnals relax meanders are coincident with sites of i strong eddy induced modification of the mean flow and its vertical structure as measured by the divergence of the eliassen palm flux and ii enhancement of deep eddy kinetic energy by up to two orders of magnitude over surrounding regions within meanders the vorticity budget shows a balance between the advection of relative vorticity and horizontal divergence providing a mechanism for the generation of strong vertical velocities and rapid changes in stratification temporal fluctuations in these diagnostics are correlated with variability in both the eliassen palm flux and bottom speed implying a link to dissipative processes at the ocean floor at larger scales bottom pressure torque is spatially correlated with the barotropic advection of planetary vorticity which links to variations in meander structure from these results it is proposed that the flexing of standing meanders provides an alternative mechanism for reducing the sensitivity of the acc s baroclinicity to changes in forcing separate from an acc wide change in transient eddy characteristics

role of residual overturning for the sensitivity of southern ocean isopycnal slopes to changes in wind forcing abstractthe antarctic circumpolar current plays a central role in the ventilation of heat and carbon in the global ocean in particular the isopycnal slopes determine where each water mass outcrop

circumpolar response of southern ocean eddy activity to a change in the southern annular mode 1 analysis of satellite altimeter data reveals anomalously high eddy kinetic energy eke in the antarctic circumpolar current acc during the period 2000 2002 around 2 3 years earlier 1998 the circumpolar eastward wind stress as quantified by the southern annular mode sam showed a significant positive peak and we have shown previously that the acc peaked around 1998 in response an eddy resolving ocean model is used to investigate the delay between wind forcing and the eddy response and demonstrates that the lag is due to the time taken to influence the deep circulation of the acc winds over the southern ocean have shown a strong climatic increase over the past few decades if this increase in winds is also reflected as an increase in eddy activity as our analysis suggests it might then the increased poleward heat flux may have played a significant role in the observed warming of the southern ocean citation meredith m p and a m hogg 2006 circumpolar response of southern ocean eddy activity to a change in the southern annular mode geophys res lett 33 l16608 doi 10 1029 2006gl026499

study on land subsidence under different plot ratios through centrifuge model test in soft soil territory since the mid 1990s multi storied buildings high rise buildings and skyscrapers have been emerging due to the new round of great scale development on the soft soil littoral land subsidence in soft soil areas caused by engineering environmental effect especially by construction of high dense building groups attracts more and more attention the plot ratio may be one of the most important factors on engineering induced land subsidence thus three geotechnical centrifugal model tests were conducted under three conditions of different plot ratios to study the ground settlement mechanism of high dense building groups in soft soil territory it is concluded that the subsidence superimposition effect is obvious in the central area of high dense building groups the settlement increases with the growth of plot ratio the urban planning department should take this subsidence situation into account when determining the construction plot ratio to utilize the earth more aptly and safely