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

stability of the atlantic meridional overturning circulation and stratification in a zonally averaged ocean model effects of freshwater flux southern ocean winds and diapycnal diffusion the atlantic meridional overturning circulation amoc is a crucial component of the global climate system in this study using a zonally averaged ocean model we reexamine the sensitivity of this circulation and ocean density structure in general to several types of external forcing the basin of the model extends from northern high latitudes to antarctica and includes an implicit representation of a circumpolar channel in the south and ocean circulation is driven by surface buoyancy fluxes and wind forcing in contrast to earlier two dimensional studies of the amoc our approach involves a careful treatment of the residual mean circulation comprising the eulerian mean and eddy induced flows which is especially important for the southern ocean dynamics using boundary conditions consistent with present day observations the model reproduces realistic ocean stratification and meridional overturning the structure intensity and stability of the overturning are then extensively studied using three control parameters the strength of westerly wind stress over the southern ocean the magnitude of freshwater fluxes imposed on the northern atlantic and ocean diapycnal diffusivity in a realistic parameter range we estimate the amoc sensitivity to changes in the southern ocean winds on the order of 1 sv per 20 increase in the wind stress the overturning also increases with diapycnal diffusivity but the dependence is weaker than in the absence of the winds the model can undergo a shutdown of the overturning subject to a hysteresis when either the freshwater forcing gradually increases or the wind stress decreases the hysteresis loop disappears for large values of isopycnal diffusivity changes in the amoc intensity are accompanied by changes in the volume transport of the antarctic circumpolar current specifically the amoc collapse leads to a strengthening of this transport ultimately our calculations produce stability maps for the steady states of the meridional overturning circulation and provide a general framework that potentially can be used to compare different models or to understand past abrupt climate changes related to reorganization of the amoc

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

a model of the zonally averaged stratification and overturning in the southern ocean the ocean area south of the antarctic circumpolar current acc frontal system is a region of major watermass modification influx of north atlantic deep water nadw small scale mixing eddy transport and diffusion as well as the fluxes of momentum and buoyancy at the sea surface combine in a complex array of processes to generate the unique stratification of the southern ocean with its southward uprising isopycnals and northward flux of antarctic intermediate water aaiw and antarctic bottom water comprehensive analytical models of this scenario are rare the authors develop and apply a model based on zonally and temporally averaged theory to explain the conversion of nadw into aaiw with all of the aforementioned processes contained in an extremely simplified way eddies appear via a transformed eulerian mean tem approach with a conventional downgradient parameterization of the meridional density flux the structure of the eddy coefficient is estimated from hydrographic and wind stress data by a simple inverse approach mixing is limited to a near surface layer and is treated in a most simple entrainment form the model determines the zonal mean density stratification in the southern ocean and the baroclinic transport of the acc from the applied wind stress and the surface density flux and unravels the role and importance of the different processes responsible for shaping the stratification ekman and eddy induced advection and pumping mixing surface buoyancy flux and eddy induced diffusion all of these processes must be present to yield an agreement between the simulated stratification and the observed one but details of their parameterization might not be too critical the acc transport is shown to have a contribution forced by the local wind stress as well as another contribution relating to the nonlocal forcing by wind stress and density flux over the entire antarctic zone

a constitutive model for the deformation of a rock mass containing sets of ubiquitous joints abstract as part of the rock mass the discontinuities inherently affect the strength and the deformational behavior of rock mass existing models can either handle the pre or post peak deformation of intact rock or joints alone however a model which can determine the failure mode and simulate the complete pre and post deformation of rock mass with multi sets of joints is not yet available this study focusses on rock mass with multi sets of ubiquitous joints and establishes a mathematic model and an associated numerical implementation accounting for the anisotropy in strength and deformation induced by the existence of joints accordingly an approach incorporating the existing models or methods to enable simulation of the complete deformation of rock mass is proposed in addition to the pre and post peak deformation characteristics for intact rock the pre peak deformation of joint such as the closure shear and dilatancy effect as well as its post peak deformation such as the reduction on roughness have also been taken into account a series of comparisons validates that the proposed model is capable of presenting the joint induced anisotropy in strength and deformation of rock mass determining the possible failure modes and reasonably simulating the complete stress strain relationship as well

the dependence of southern ocean meridional overturning on wind stress an eddy resolving numerical model of a zonal flow meant to resemble the antarctic circumpolar current is described andanalyzedusing the framework of j marshallandt radko in additionto windand buoyancy forcing at the surface the model contains a sponge layer at the northern boundary that permits a residual meridional overturning circulation moc to exist at depth the strength of the residual moc is diagnosed for different strengths of surface wind stress it is found that the eddy circulation largely compensates for the changes in ekman circulation the extent of the compensation and thus the sensitivity of the moc to the winds depend on the surface boundary condition a fixed heat flux surface boundary severely limits the ability of the moc to change an interactive heat flux leads to greater sensitivity to explain the moc sensitivity to the wind strength under the interactive heat flux transformed eulerian mean theory is applied in which the eddy diffusivity plays a central role in determining the eddy response a scaling theory for the eddy diffusivity based on the mechanical energy balance is developed and tested the average magnitude of the diffusivity is found to be proportional to the square root of the wind stress the moc sensitivity to the winds based on this scaling is compared with the true sensitivity diagnosed from the experiments

eddy transport and mixing in a wind and buoyancy driven jet on the sphere abstract the baroclinically unstable wind and buoyancy driven flow in a zonally reentrant pie shaped sector on a sphere is numerically modeled and then analyzed using the transformed eulerian mean tem formalism mean fields are obtained by zonal and time averaging performed at fixed height the very large latitudinal extent of the basin 50 7 s latitude to the equator allows the latitude variation of the coriolis parameter to strongly influence the flow persistent zonal jets are observed in the statistically steady state reynolds stress terms play an important role in redistributing zonal angular momentum convergence of the lateral momentum flux gives rise to a strong eastward jet with an adjacent westward jet equatorward and weaker multiple jets poleward an equally prominent feature of the flow is a strong and persistent eddy that has the structure of a kelvin cat s eye and generally occupies the zonal width of the basin at latitudes 15 10 s a strongly mixed surface diabatic zone overlies the

what sets the strength of the middepth stratification and overturning circulation in eddying ocean models abstract the processes maintaining stratification in the oceanic middepth between approximately 1000 and 3000 m are explored using an eddy resolving general circulation model composed of a two hemisphere semienclosed basin with a zonal reentrant channel in the southernmost eighth of the domain the middepth region lies below the wind driven main thermocline but above the diffusively driven abyssal ocean here it is argued that middepth stratification is determined primarily in the model s antarctic circumpolar current competition between mean and eddy overturning in the channel leads to steeper isotherms and thus deeper stratification throughout the basin than would exist without the channel isotherms that outcrop only in the channel are nearly horizontal in the semienclosed portion of the domain whereas isotherms that also outcrop in the northern hemisphere deviate from horizontal and are accompanied by geostrophically balanced meridional transport a northern source of deep water water with temp

strength of jointed rock masses jointed rock masses comprise interlocking angular par ticles or blocks of hard brittle material separated by discontinuity surfaces which may or may not be coated with weaker materials the strength of such rock masses depends on the strength of the intact pieces and on their freedom of movement which in turn depends on the number orientation spacing and shear strength of the discontinuities a complete understanding of this problem presents formidable theoretical and experi mental problems and hence simplifying assumptions are required in order to provide a reasonable basis for estimating the strength of jointed rock masses for engineering design purposes this paper summarizes some of the basic information upon which such simplifying assumptions can be made a simple empirical failure criterion is presented and its application in engineering design is illustrated by means of a number of practical examples des masses jointives de rochers comprennent des particules angulaires enchevetrees ou des

homogenization of potential vorticity in planetary gyres the mean circulation of planetary fluids tends to develop uniform potential vorticity q in regions where closed time mean streamlines or closed isolines of mean potential vorticity exist this state is established in statistically steady flows by geostrophic turbulence or by wave induced potential vorticity flux at the outer edge of the closed contours the expelled gradients of q are concentrated beyond this transition lies motionless fluid or a different flow regime in which the planetary gradient of q may be dominant the homogenized regions occur where direct forcing by external stress or heating within the closed isoline is negligible upon the potential density surface under consideration in the stably stratified ocean such regions are found at depths greater than those of direct wind induced stress or penetrative cooling in channel models of the atmosphere we again find constant q when mesoscale eddies cause the dominant potential vorticity flux in the real atmosphere the results here can apply only where internal heating is negligible the derivations given here build upon the prandtl batchelor theorem which applies to non rotating steady two dimensional flow supporting evidence is found in numerical circulation models and oceanic observations

a laboratory model of thermocline depth and exchange fluxes across circumpolar fronts a laboratory experiment has been constructed to investigate the possibility that the equilibrium depth of a circumpolar front is set by a balance between the rate at which potential energy is created by mechanical and buoyancy forcing and the rate at which it is released by eddies in a rotating cylindrical tank the combined action of mechanical and buoyancy forcing builds a stratification creating a large scale front at equilibrium the depth of penetration and strength of the current are then determined by the balance between eddy transport and sources and sinks associated with imposed patterns of ekman pumping and buoyancy fluxes it is found that the depth of penetration and transport of the front scale like l and wel2 respectively where fw g9 e we is the ekman pumping g9 is the reduced gravity across the front f is the coriolis parameter and l is the width scale of the front last the implications of this study for understanding those processes that set the stratification and transport of the antarctic circumpolar current acc are discussed if the laboratory results scale up to the acc they suggest a maximum thermocline depth of approximately h 5 2 km a zonal current velocity of 4 6 cm s 21 and a transport t 5 150 sv 1 sv 106 m3 s 21 not dissimilar to what is observed

potential vorticity constraints on the dynamics and hydrography of the southern ocean abstract constraints on the hydrography and geostrophic velocity shear of the southern ocean implicit in its potential vorticity field are discussed and illustrated by diagnostic study of observed and modeled potential vorticity fields a stress driven thermodynamically inactive eddy resolving quasigeostrophic model of the southern ocean suggests that through the systematic erosion of potential vorticity gradients by geostrophic eddies the large scale flow equilibrates toward a state in which interior potential vorticity gradients are small observations of the large scale isopycnal distribution of potential vorticity ipv deduced from climatological hydrographic data reveal a much richer structure the most striking feature of the ipv field is the presence of large near surface gradients of ipv a vortocline coinciding with the axis of the antarctic circumpolar current acc to the south of this front potential vorticity pv is large to its north pv has low values and relative to those foun

influence of enhanced abyssal diapycnal mixing on stratification and the ocean overturning circulation abstractthe meridional overturning circulation moc is composed of interconnected overturning cells that transport cold dense abyssal waters formed at high latitudes back to the surface turbulent diapycnal mixing plays a primary role in setting the rate and patterns of the various overturning cells that constitute the moc the focus of the analyses in this paper will be on the influence of sharp vertical variations in mixing on the moc and ocean stratification mixing is enhanced close to the ocean bottom topography where internal waves generated by the interaction of tides and geostrophic motions with topography break it is shown that the sharp vertical variations in mixing lead to the formation of three layers with different dynamical balances governing meridional flow specifically an abyssal bottom boundary layer forms above the ocean floor where mixing is largest and hosts the northward transport of the heaviest waters from the southern channel to the closed basins a deep layer forms above the b

late cenozoic paleomagnetism and chronology of andean basins of bolivia evidence for possible oroclinal bending new paleomagnetic and radioisotopic data are reported from two late tertiary high elevation non marine basins in the eastern cordillera of bolivia 1 quebrada honda located at 22 s lat consists of a 300 m thick section containing abundant santacrucian or friasian middle miocene fossil mammals this locality is constrained by mean 40 k 40 ar ages of 12 83 0 11 ma and 11 96 0 11 ma and the local magnetostratigraphy is correlated to chrons c5aa through c5a on the magnetic polarity time scale mpts the fossil mammals from quebrada honda have an extrapolated age of about 13 0 to 12 7 ma 2 micana located at 17 s lat consists of a 205 m thick section containing late miocene fossil mammals including a megatheriid sloth and the tiny mesothere microtypotherium cf m choquecotense this locality is constrained by a fission track age determination of 6 9 1 1 ma and the local magnetostratigraphy is correlated to chron 7 on the mpts the fossil mammals from this section have an extrapo

configuration of a southern ocean storm track abstractdiagnostics of ocean variability that reflect and influence local transport properties of heat and chemical species vary by an order of magnitude along the southern ocean s antarctic circumpolar current acc topographic hotspots are important regions of localized transport anomalies this study uses a primitive equation channel model to investigate the structure of eddy kinetic energy eke one measure of variability in an oceanic regime a storm track approach emphasizes the importance of stationary eddies which result from flow interactions with topography on setting eke distributions the influence of these interactions extends far downstream of the topography and impacts eke patterns through localized convergence and divergence of heat unlike for zonal averages local contributions to the stationary fluxes from terms that integrate to zero in a zonal average are important the simulations show a strong sensitivity of the zonal structure as well as the distribution and amplitude of sta

control of lower limb overturning circulation in the southern ocean by diapycnal mixing and mesoscale eddy transfer a simple model is developed of the lower limb of the meridional overturning circulation in the southern ocean based on residual mean theory it is hypothesized that the strength of the lower limb overturning is strongly controlled by the magnitude of abyssal diapycnal mixing and that of mesoscale eddy transfer k in particular it is argued that k the scaling and associated theory find support in a suite of sensitivity experiments with an idealized ocean general circulation model this study shows that intense diapycnal mixing is required to close the buoyancy budget of the lower limb overturning circulation in contrast to the upper limb where air sea buoyancy fluxes can provide the required diabatic forcing

the diabatic deacon cell abstract southern ocean air sea fluxes from the coads dataset are examined for compatibility between buoyancy gain and northward ekman transport an analysis in density classes points to an upwelling of upper circumpolar deep water and subsequent buoyancy gain from air sea exchange as water flows northward in the ekman layer the upper circumpolar deep water layer is too shallow to admit southward geostrophic flow along topography and an eddy mass flux mechanism for southward transport in this layer to replenish the upwelling is advanced based on observed large scale potential vorticity gradients estimates of the strength and vertical structure of the meridional flow are given using repeated hydrographic sections and a new climatology

links between the southern annular mode and the atlantic meridional overturning circulation in a climate model abstract the links between the atmospheric southern annular mode sam the southern ocean and the atlantic meridional overturning circulation amoc at interannual to multidecadal time scales are investigated in a 500 yr control integration of the l institut pierre simon laplace coupled model version 4 ipsl cm4 climate model the antarctic circumpolar current as described by its transport through the drake passage is well correlated with the sam at the yearly time scale reflecting that an intensification of the westerlies south of 45 s leads to its acceleration also in phase with a positive sam the global meridional overturning circulation is modified in the southern hemisphere primarily reflecting a forced barotropic response in the model the amoc and the sam are linked at several time scales an intensification of the amoc lags a positive sam by about 8 yr this is due to a correlation between the sam and the atmospheric circulation in the northern north atlantic that reflects a symmetric e

multi peak deformation behavior of jointed rock mass under uniaxial compression insight from particle flow modeling abstract evaluation of mechanical properties of jointed rock mass is very important for geological engineering problems related to underground opening slope stability dam foundation and hydraulic fracturing etc it is generally known that both strength and deformability of rock mass may change with joint geometry and arrangement by pfc particle flow code modeling this paper aims at understanding the damage mechanism of the multi peak deformation behavior of jointed rock mass with different joint orientations and continuity factors under uniaxial compression observed in the physical model tests with the smooth joint contact model not only has the inherent roughness in conventional joint model been avoided but also we can monitor the joint aperture number of closed joints and forces acting on the joints during the damage process it is shown that mobilization of joint strength plays an important role in the multi peak deformation behavior of rock mass if the joint strength is slightly mobilized or immobilized i e most joints keep open during the test strain softening occurs however if the joint strength is significantly or fully mobilized yielding platform or strain hardening may happen

estimates and implications of surface eddy diffusivity in the southern ocean derived from tracer transport abstract near surface effective diffusivities associated with geostrophic eddies in the southern ocean are estimated by numerically monitoring the lengthening of idealized tracer contours as they are strained by surface geostrophic flow observed by satellite altimetry the resulting surface diffusivities show considerable spatial variability and are large 2000 m2 s 1 on the equatorward flank of the antarctic circumpolar current and are small 500 m2 s 1 at the jet axis regions of high and low effective diffusivity are shown to be collocated with regions of respectively weak and strong isentropic potential vorticity gradients the maps of diffusivity are used along with climatological estimates of surface wind stress and air sea buoyancy flux to estimate surface meridional residual flows and the relative importance of eulerian and eddy induced circulation in the streamwise averaged dynamics of the antarctic circumpolar current

water mass transformations in the southern ocean diagnosed from observations contrasting effects of air sea fluxes and diapycnal mixing abstracttransformation and formation rates of water masses in the southern ocean are estimated in a neutral surface framework using air sea fluxes of heat and freshwater together with in situ estimates of diapycnal mixing the air sea fluxes are taken from two different climatologies and a reanalysis dataset while the diapycnal mixing is estimated from a mixing parameterization applied to five years of argo float data air sea fluxes lead to a large transformation directed toward lighter waters typically from 45 to 63 sv 1 sv 106 m3 s 1 centered at 27 2 while interior diapycnal mixing leads to two weaker peaks in transformation directed toward denser waters 8 sv centered at 27 8 and directed toward lighter waters 16 sv centered at 28 3 hence air sea fluxes and interior diapycnal mixing are important in transforming different water masses within the southern ocean the transformation of dense to lighter waters by diapycnal mixing within the southern ocean is slightly larger tho

a model of the upper branch of the meridional overturning of the southern ocean a zonal average model of the upper branch of the meridional overturning circulation of the southern ocean is constructed and used to discuss the processes wind buoyancy eddy forcing and boundary conditions that control its strength and sense of circulation the geometry of the thermocline wedge set by the mapping between the vertical spacing of buoyancy surfaces the stratification on the equatorial flank of the antarctic circumpolar current and their outcrop at the sea surface is seen to play a central role by setting the interior large scale potential vorticity distribution it is shown that the action of eddies mixing this potential vorticity field induces a residual flow in the meridional plane much as is observed with upwelling of fluid around antarctica northward surface flow and subduction to form intermediate water

the three dimensional overturning circulation of the southern ocean during the woce era a box inverse model of the southern ocean during the world ocean circulation experiment is constructed to investigate the three dimensional structure of the regional overturning circulation in that era the model has many features in common with various preceding inverse studies but also contains several novel elements that make it well suited for addressing many of the significant uncertainties that surround the circulation at present the net overturning circulation of the southern ocean is found to consist of two well defined cells of similar strength the upper cell consists of a northward transport of 18 8 5 5 sv of surface mode and intermediate waters lighter than the 27 5 kg m 3 isoneutral and an equivalent southward flow in the approximate 27 5 27 9 kg m 3 neutral density range encompassing the bulk of the upper circumpolar deep water the lower cell involves the northward export of 18 6 0 9 sv of antarctic bottom water and lower circumpolar deep water denser than 28 08 kg m 3 and an opposing transport in the lighter classes of that water mass substantial structural differences between the overturning circulations of the atlantic indian and pacific basins are indicated by the model s solution overall the diagnosed southern ocean circulation shares many qualitative and some quantitative features with previous inverse estimates particularly as regards the large scale depth integrated lateral circulation and associated energy fluxes in the subtropics and in the antarctic circumpolar current and the strength of the upper overturning cell however it also suggests several significant adjustments to current views of the regional circulation most notable amongst these are the subpolar circulation of the southern ocean is more vigorous and zonally interconnected than generally thought the associated lower overturning cell is more intense than indicated by most preceding estimates contrary to common perception sub surface mixing processes play a role of comparable importance to air sea ice exchanges of buoyancy in underpinning the dianeutral closure of the southern ocean overturning even at shallow mode and intermediate water levels and the connection between north atlantic deep water formation and southern ocean upwelling is fundamentally three dimensional such that deep waters from the north atlantic must upwell dianeutrally before being returned to the permanent pycnocline of the northern oceans

can eddies set ocean stratification abstract a simple theory is presented for the buoyancy anomaly and depth of penetration of a warm lens created by a surface buoyancy flux and ekman pumping in an initially homogeneous rotating fluid it is assumed that the overturning of isopycnals induced by pumping and differential heating balances the counteroverturning tendency of baroclinic instability baroclinic eddies not only develop on the stratified lens but also play a fundamental role in setting its stratification the theory is successfully tested against numerical and laboratory experiments in which the mechanically induced deepening of a buoyant lens is arrested by its baroclinic instability finally the possibility is discussed that the eddy transfer process studied here might play a role in setting the stratification and depth of the main thermocline in the ocean

multiple equilibria of the global thermohaline circulation abstract a general circulation model with a highly idealized geometry is used to investigate which fundamentally different equilibria of the global thermohaline circulation may exist the model comprises two identical basins representing the atlantic and pacific oceans which are connected by a circumpolar channel in the south the model circulation is driven in addition to wind forcing by restoring the sea surface temperature to prescribed values and specified freshwater fluxes in the surface salinity budget mixed boundary conditions the boundary conditions are symmetric with respect to the equator and identical for both oceans four fundamentally different stable steady states are found under the same set of boundary conditions two of the equilibria show both oceans in the same state with high altitude deep water formation occuring either in both northern or in both southern oceans respectively two additional equilibria exist in which the thermohaline circulations of the basins differ fundament

connecting antarctic cross slope exchange with southern ocean overturning previous idealized investigations of southern ocean overturning have omitted its connection with the antarctic continental shelves leaving the influence of shelf processes on antarctic bottom water aabw export unconsidered in particular the contribution of mesoscale eddies to setting the stratification and overturning circulation in the antarctic circumpolar current acc is well established yet their role in cross shelf exchange of water masses remains unclear this study proposes a residual mean theory that elucidates the connection between antarctic cross shelf exchange and overturning in the acc and the contribution of mesoscale eddies to the export of aabw the authors motivate and verify this theory using an eddy resolving process model of a sector of the southern ocean the strength and pattern of the simulated overturning circulation strongly resemble those of the real ocean and are closely captured by the residualmean theory over the continental slope baroclinic instability is suppressed and so transport by mesoscale eddies is reduced this suppression of the eddy fluxes also gives rise to the steep v shaped isopycnals that characterize the antarctic slope front in aabw forming regions of the continental shelf furthermore to produce water on the continental shelf that is dense enough to sink to the deep ocean the deep overturning cell must be at least comparable in strength to wind driven mean overturning on the continental slope this results in a strong sensitivity of the deep overturning strength to changes in the polar easterly winds

paleomagnetic study of upper miocene rocks from northern chile implications for the origin of late miocene recent tectonic rotations in the southern central andes paleomagnetic studies in the southern central andes have shown the widespread presence of clockwise vertical axis rotations rock units sampled in these studies however are heterogeneously distributed in stratigraphic age with most paleomagnetic data from northern chile being from mesozoic and lower tertiary rocks whereas most data in the southern altiplano puna and cordillera oriental are from upper tertiary rocks in this paper we present the results of a paleomagnetic study on upper miocene sedimentary rocks and ignimbrites from the precordillera of northern chile at 22 s these rocks are coeval with the initiation of crustal shortening in the eastern foreland fold thrust belt which some tectonic models relate to oroclinal rotation of northern chile primary magnetizations in rocks from widely distributed sites in two ignimbrites indicate that no relative rotations have occurred between sites suggesting the study area has acted as a single coherent block with respect to vertical axis rotational deformation although minor inadequate sampling of paleosecular variation can affect our data set its time averaged paleomagnetic direction is indistinguishable from the expected late miocene reference direction indicating no paleomagnetically significant rotation of the study area since circa 11 ma this suggests that late miocene recent oroclinal rotation of the northern chilean forearc if present must be either very low or nonuniform a direct implication of this result is that much of the unquestionable tectonic rotations detected from upper miocene rocks in the southern central andes is of local origin available structural data permit us to relate several of these rotations with shear in dextral transfer zones in the foreland thrust belt on the east side of the andes

inferring the pattern of the oceanic meridional transport from the air sea density flux abstract an extension of walin s water mass transformation analysis is proposed that would make it possible to assess the strength of the adiabatic along isopycnal component of the meridional overturning circulation moc it is hypothesized that the substantial fraction of the adiabatic moc component can be attributed to the difference in subduction rates at the northern and southern outcrops of each density layer the push pull mechanism the gcm generated data are examined and it is shown that the push pull mode accounts for approximately two thirds of the isopycnal water mass transport in the global budget and dominates the atlantic transport much of the difference between the actual interhemispheric flux and the push pull mode can be ascribed to the influence of the antarctic circumpolar current characterized by the elevated at least in the gcm values of the diapycnal transport when the diagnostic model is applied to observations it is discovered that the reconstructed moc is consistent in te

a theory of the interhemispheric meridional overturning circulation and associated stratification abstracta quantitative theoretical model of the meridional overturning circulation and associated deep stratification in an interhemispheric single basin ocean with a circumpolar channel is presented the theory includes the effects of wind eddies and diapycnal mixing and predicts the deep stratification and overturning streamfunction in terms of the surface forcing and other parameters of the problem it relies on a matching among three regions the circumpolar channel at high southern latitudes a region of isopycnal outcrop at high northern latitudes and the ocean basin between the theory describes both the middepth and abyssal cells of a circulation representing north atlantic deep water and antarctic bottom water it suggests that although the strength of the middepth overturning cell is primarily set by the wind stress in the circumpolar channel middepth stratification results from a balance between the wind driven upwelling in the channel and deep water formation at high northern latitudes d

isopycnal mixing suppression by the antarctic circumpolar current and the southern ocean meridional overturning circulation abstractthe meridional overturning circulation moc in the southern ocean is investigated using hydrographic observations combined with satellite measurements of sea surface height a three dimensional spatial and vertical estimate of the isopycnal eddy diffusivity in the southern ocean is obtained using the theory of ferrari and nikurashin that includes the influence of suppression of the diffusivity by the strong time mean flows it is found that the eddy diffusivity is enhanced at depth reaching a maximum at the critical layer near 1000 m the estimate of diffusivity is used with a simple diffusive parameterization to estimate the meridional eddy volume flux this estimate of eddy volume flux is combined with an estimate of the ekman transport to reconstruct the time mean overturning circulation by comparing the reconstruction with and without suppression of the eddy diffusivity by the mean flow the influence of the suppression on the overturning is illuminated it is shown that the suppressio

strength of a blocky rock mass based on an extended plane of weakness theory abstract the strength of a rock mass is the major factor affecting the design and construction of civil and mining structures built in or on rock rock masses are usually fractured as a result of various geological processes over time the effect of joints on the strength of a rock has been studied mainly using analytical or experimental methods whereas the strength of fractured rock is usually expressed in terms of empirical failure criteria in this study the original plane of weakness theory is presented and applied to rock models with various numbers of joint sets persistent or not biaxial compressive tests are then performed on the same specimens using a discrete element code to account for the roughness of the discontinuities the original theory is extended by imposing the non linear barton bandis shear strength criterion for the discontinuities this extended theory of one plane of weakness is validated against the responses of discrete numerical rock models with various combinations of fracturing both the original and extended theories are then applied to simulate the response of physical experiments undertaken by several researchers in order to investigate their validity and the bounds of their usage the numerical results are in accordance with the theoretical ones while the theoretical results have an either quantitative or qualitative similarity with the experimental ones quantitative differences appear especially when the specimens fail in different modes than assumed by the models

semi adiabatic model of the deep stratification and meridional overturning abstractan analytical model of the atlantic deep stratification and meridional overturning circulation is presented that illustrates the dynamic coupling between the southern ocean and the midlatitude gyres the model expressed here in terms of the two and a half layer framework predicts the stratification and meridional transport as a function of the mechanical and thermodynamic forcing at the sea surface the approach is based on the classical elements of large scale circulation theory ideal thermocline inertial western boundary currents and eddy controlled antarctic circumpolar current acc models which are combined to produce a consistent three dimensional view of the global overturning the analytical tractability is achieved by assuming and subsequently verifying that the pattern of circulation in the model is largely controlled by adiabatic processes the time mean and eddy induced isopycnal advection of buoyancy the mean stratification of the lower thermocline is determined by the surface fo

the surface branch of the zonally averaged mass transport circulation in the troposphere the near surface branch of the overturning mass transport circulation in the troposphere containing the equatorward flow is examined in isentropic and geometric coordinates a discussion of the zonal momentum balance within isentropic layers shows that the equatorward flow at a given latitude is confined to isentropic layers that typically intersect the surface at that latitude as a consequence of mass transport within the surface mixed layer much of the equatorward flow occurs in layers with potential temperatures below the mean surface potential temperature in the conventional transformed eulerian mean formulation for geometric coordinates the surface branch of the overturning circulation is represented in an unrealistic manner streamlines of the residual circulation do not close above the surface a modified residual circulation is introduced that is free from this defect and has the additional advantage that its computation unlike that of the conventional residual circulation does not require division by the static stability which may approach zero in the planetary boundary layer it is then argued that cold air advection by the residual circulation is responsible for the formation of surface inversions at all latitudes in idealized gcms with weak thermal damping also included is a discussion of how a general circulation theory for the troposphere must be built upon a theory for the near surface meridional mass fluxes

evidence for enhanced eddy mixing at middepth in the southern ocean abstract satellite altimetric observations of the ocean reveal surface pressure patterns in the core of the antarctic circumpolar current acc that propagate downstream eastward but slower than the mean surface current by about 25 the authors argue that these observations are suggestive of baroclinically unstable waves that have a steering level at a depth of about 1 km detailed linear stability calculations using a hydrographic atlas indeed reveal a steering level in the acc near the depth implied by the altimetric observations calculations using a nonlinear model forced by the mean shear and stratification observed close to the core of the acc coinciding with a position where mooring data and direct eddy flux measurements are available reveal a similar picture albeit with added details when eddy fluxes are allowed to adjust the mean state computed eddy kinetic energy and eddy stress are close to observed magnitudes with steering levels between 1 and 1 5 km broadly consistent with observatio

neogene paleomagnetism and oroclinal bending of the central andes of bolivia geophysical and tectonic evidence suggests that the principal vertical axis bending of the bolivian orocline is a late cenozoic event related to subduction and andean uplift to further test this hypothesis paleomagnetic data are presented from miocene basins within the altiplano and cordillera oriental of bolivia located in the presumed southern limb of the orocline to factor out potential vgp data samples were collected from sedimentary sections spanning at least 0 5 m y new paleomagnetic data are presented for two sites i e gerdas 21 s latitude 16 15 ma and quehua 20 s latitude 13 7 ma in conjunction with previously published paleomagnetic results from middle to late tertiary rocks from bolivia and peru spanning some 16 of latitude 6 22 s a consistent pattern of oroclinal development is as follows significant counterclockwise rotation about 15 20 in the northern limb negligible rotation in the axis at the latitude of the arica deflection and significant clockwise rotation about 15 20 in the southern limb although these paleomagnetic data could represent independent mesoscale 102 to 104 km2 block rotations the preferred interpretation is that they confirm the hypothesis that a significant portion about 30 40 of the oroclinal bending occurred during the late cenozoic using the unit mean paleomagnetic declinations in the well dated sections minimum rates of oroclinal bending during the late cenozoic are calculated to range from 0 6 m y to 1 7 m y the remaining 15 20 of observed curvature of the orocline probably resulted from an earlier phase of andean deformation or may represent the shape of the ancestral andes

a multibasin residual mean model for the global overturning circulation the ocean s overturning circulation is inherently three dimensional yet modern quantitative estimates of the overturning typically represent the subsurface circulation as a two dimensional two cell streamfunction that varies with latitude and depth only this approach suppresses information about zonal mass and tracer transport in this article the authors extend earlier zonally averaged overturning theory to explore the dynamics of a figure eight circulation that cycles through multiple basins a three dimensional residual mean model of the overturning circulation is derived and then simplified to a multibasin isopycnal box model to explore how stratification and diabatic water mass transformations in each basin depend on the basin widths and on deep and bottom water formation in both hemispheres the idealization to multiple two dimensional basins permits zonal mass transport along isopycnals in a southern ocean like channel while retaining the dynamical framework of residual mean theory the model qualitatively reproduces the deeper isopycnal surfaces in the pacific basin relative to the atlantic this supports a transfer of antarctic bottom water from the atlantic sector to the pacific sector via the southern ocean which subsequently upwells in the northern pacific basin a solution for the full isopycnal structure in the southern ocean reproduces observed stratification differences between atlantic and pacific basins and provides a scaling for the diffusive boundary layer in which the zonal mass transport occurs these results are consistent with observational indications that north atlantic deep water is preferentially transformed into antarctic bottom water which undermines the importance of an adiabatic upper overturning cell in the modern ocean

the eddy driven thermocline the role of baroclinic eddies in transferring thermal gradients laterally and thus determining the stratification of the ocean is examined the hypothesis is that the density differences imposed at the surface by differential heating are a source of available potential energy that can be partially released by mesocale eddies with horizontal scales on the order of 100 km eddy fluxes balance the diapycnal mixing of heat and thus determine the vertical scale of penetration of horizontal thermal gradients i e the depth of the thermocline this conjecture is in contrast with the current thinking that the deep stratification is determined by a balance between diapycnal mixing and the large scale thermohaline circulation eddy processes are analyzed in the context of a rapidly rotating primitive equation flow driven by specified surface temperature with isotropic diffusion and viscosity the barotropic component of the eddies is found to be responsible for most of the heat flux and so the eddy transport is horizontal rather than isopycnal this eddy transport takes place in the shallow surface layer where eddies as well as the mean temperature undergo diabatic irreversible mixing scaling laws for the depth of the thermocline as a function of the external parameters are proposed in the classical thermocline theory the depth of the thermocline depends on the diffusivity the rotation rate and the imposed temperature gradient in this study the authors find an additional dependence on the viscosity and on the domain width

the role of eddy transfer in setting the stratification and transport of a circumpolar current abstract high resolution numerical experiments of a circumpolar current are diagnosed to study how lateral and vertical transfer of buoyancy by geostrophic eddies balances advection by a meridional circulation driven by surface wind stresses and buoyancy fluxes a theory is developed in the framework of the residual circulation to relate the vertical and horizontal stratification set up to the transfer properties of eddies and the patterns of imposed wind and buoyancy forcing simple expressions are found for the depth of penetration stratification baroclinic transport and residual circulation of the current finally the ideas are applied to the antarctic circumpolar current acc and yield predictions for how its properties depend on wind and buoyancy forcing

a theory of deep stratification and overturning circulation in the ocean abstract a simple theoretical model of the deep stratification and meridional overturning circulation in an idealized single basin ocean with a circumpolar channel is presented the theory includes the effects of wind eddies and diapycnal mixing predicts the deep stratification in terms of the surface forcing and other problem parameters makes no assumption of zero residual circulation and consistently accounts for the interaction between the circumpolar channel and the rest of the ocean the theory shows that dynamics of the overturning circulation can be characterized by two limiting regimes corresponding to weak and strong diapycnal mixing the transition between the two regimes is described by a nondimensional number characterizing the strength of the diffusion driven compared to the wind driven overturning circulation in the limit of weak diapycnal mixing deep stratification throughout the ocean is produced by the effects of wind and eddies in a circumpolar channel and maintained even in the