a fortran visualization program for spherical data on a yin yang grid a fortran 90 program to visualize data on the yin yang grid system is developed the purpose of this study is to provide simulation researchers with a source code as a starting point of their own custom made visualization tools a basic but sufficiently diverse set of visualization methods are implemented using a fortran 90 binding for opengl for scalar and vector fields defined or simulated on the yin yang grid

a novel fluorescent tracer for real time tracing of clay transport over soil surfaces clay is an important vector for the transport of pollutants in the environment including nutrients pesticides and metals therefore the fate of many chemicals in soil systems is closely linked to that of clay understanding the mechanisms responsible for clay transport has been hampered by the lack of a suitable tracer producing a tracer that accurately mimics clay transport is challenging due to the small size of the particles and their unique physical properties here we describe the design and synthesis of a tracer using natural clay particles as a foundation exploiting the natural ability of clay to sorb molecules to coat the clay with a thin layer of fluorophore application of the tracer has been demonstrated through the collection of real time images of the tracer moving over the surface of a soil box during a rainfall event these images allow for the first time clay to be tracked spatially and temporally without need to remove soil for analysis thus resulting in minimal experimental artefacts custom written software has been used to extract high resolution data describing tracer movement and extent throughout the experiment

œdipus a new tool to study the dynamics of planetary interiors summary we present a new numerical method to describe the internal dynamics of planetary mantles through the coupling of a dynamic model with the prediction of geoid and surface topography our tool is based on the simulation of thermal convection with variable viscosity in a spherical shell with a finite volume formulation the grid mesh is based on the cubed sphere technique that divides the shell into six identical blocks an investigation of various numerical advection schemes is proposed we opted for a high resolution flux limiter method benchmarks of thermal convection are then presented on steady state tetrahedral and cubic solutions and time dependent cases with a good agreement with the few recent programs developed to solve this problem a dimensionless framework is proposed for the calculation of geoid and topography introducing two dimensionless numbers such a formulation provides a good basis for the systematic study of the geoid and surface dynamic topography associated to the convection calculations the evaluation of geoid and surface dynamic topography from the gridded data is performed in the spectral domain the flow solver is then tested extensively against a precise spectral program producing response functions for geoid as well as bottom and surface topographies for a grid mesh of a reasonable size 6 64 64 64 a very good agreement to within 1 per cent is found up to spherical harmonic degree 15

using rare earth elements to monitor sediment sources from a miniature model of a small watershed in the three gorges area of china abstract understanding soil erosion processes at different landscape positions is important in order to predict and control watershed soil losses rare earth elements rees can be used to trace eroded soil sources but their efficacy may be soil dependent we constructed a miniature watershed model of a small watershed located in the three gorges area of china and used oxides of eight rees to trace the erosion of a purple soil the miniature watershed was divided into eight regions containing a different landform type as a potential sediment source a different ree was applied in each region redistributions of the rees under three successive simulated rainfall events with intensities of 1 0 1 5 or 2 0 mm min 1 were examined the percentage contribution from each region to the total soil loss from the watershed fluctuated relative to landform type during the three rainstorms contributions from the lower main gully decreased before stabilizing while those from the upper main gully increased before decreasing and those from other sources all increased before stabilizing overall the contribution of the gully system comprising main and branch gullies was greater than that of the slopes contributions from the gully system tended to decrease with increases in rainfall intensity and rainstorm duration while those from the slopes increased a comparison of the calculated and actual soil loss masses indicated that the accuracy of the ree tracing method was less for the coarse textured purple soil than those previously found for fine textured soils the increased errors likely due to the assumption used in the calculation that there is no particle size selectivity during erosion needs to be addressed this pilot study provided a technical reference for the use of rees in monitoring sediment sources from a natural watershed and a theoretical basis for soil conservation in the three gorges area

global anisotropy in the upper mantle inferred from the regionalization of phase velocities a data set of 2600 paths for rayleigh waves and 2170 paths for love waves was selected in order to resolve azimuthal anisotropy of surface waves in the period range 70 250 s the epicenters were chosen so that the paths provide uniform spatial and azimuthal coverage of earth a synthetic seismogram is computed for each path and compared to the observed seismogram in order to infer the phase velocity along each path to process such a large data set a new tomographic technique is designed a good correlation is found with surface tectonics in the whole period range for love waves and at shorter periods for rayleigh waves the directions of maximum velocities are also well correlated with plate tectonics motions for the 2 azimuthal term of rayleigh waves when the power spectrum of heterogeneities is computed it is found that for love waves the even orders are usually larger than the odd orders for rayleigh waves the degrees 2 and 6 dominate only at long periods suggesting a deep origin for these components

the stability and structure of primordial reservoirs in the lower mantle insights from models of thermochemical convection in three dimensional spherical geometry large scale chemical lateral heterogeneities are inferred in the earth s lowermost mantle by seismological studies we explore the model space of thermochemical convection that can maintain reservoirs of dense material for a long period of time by using similar analysis in 3 d spherical geometry in this study we focus on the parameters thought to be important in controlling the stability and structure of primordial dense reservoirs in the lower mantle including the chemical density contrast between the primordial dense material and the regular mantle material buoyancy ratio thermal and chemical viscosity contrasts volume fraction of primordial dense material and the clapeyron slope of the phase transition at 660 km depth we find that most of the findings from the 3 d cartesian study still apply to 3 d spherical cases after slight modifications varying buoyancy ratio leads to different flow patterns from rapid upwelling to stable layering and large thermal viscosity contrasts are required to generate long wavelength chemical structures in the lower mantle chemical viscosity contrasts in a reasonable range have a second order role in modifying the stability of the dense anomalies the volume fraction of the initial primordial dense material does not effect the results with large thermal viscosity contrasts but has significant effects on calculations with intermediate and small thermal viscosity contrasts the volume fraction of dense material at which the flow pattern changes from unstable to stable depends on buoyancy ratio and thermal viscosity contrast an endothermic phase transition at 660 km depth acts as a filter allowing cold slabs to penetrate while blocking most of the dense material from penetrating to the upper mantle

relating magnetic susceptibility ms to the simulated thematic mapper tm bands of the chinese loess application of tm image for soil ms mapping on loess plateau 1 magnetic susceptibility ms is a very important physical attribute of the earth s soils and surficial sediments soil containing deposits in the loess plateau of central china offer a unique opportunity to study the relationship between soil reflectance and ms in this paper data on ms and diffuse reflectance spectra obtained from seven loess plateau sections were used to establish quantitative relationships between ms and spectral parameters related to remote sensing by integrating the diffuse reflectance values corresponding to thematic mapper tm channels five tm bands were simulated and served as independent variables for a multiple linear regression relating the bands to ms the resulting calibration equation provides good estimates of ms values and has excellent correlation coefficients 0 90 for all the test samples the application of the regression equation for mapping soil ms was performed using the enhanced tm image from northwest part of loess plateau the ms values obtained from tm data are convincing and compare well with the limited field test data the spatial ms variations on the tm image clearly show a decrease toward the northwest and are in a good agreement with the monsoon directions results of this study demonstrate that the surface ms signal in soil can be mapped with data from satellite based remote sensors operating in the visible and near infrared bands the future possibilities of this method in other soil types and climates need to be explored

the influences of lower mantle viscosity stratification on 3d spherical shell mantle convection we have studied the dynamical effects of a stratified viscosity profile on time dependent mantle circulations by using a 3d boussinesq spherical shell convection model this particular viscosity profile taken from the inversion of geoid data has the distinct feature of having a large viscosity maximum in the middle lower mantle surface rayleigh numbers ranging from 5 104 to 8 106 have been considered there are several distinct differences in both the morphologies of the plumes and the sinking currents from constant viscosity models in a viscously stratified lower mantle plumes are formed invariably only after the cold downwelling has reached the bottom the mean mantle temperature is reduced and this allows for the sinking of very cold material into the deep mantle the number of upwelling plumes is reduced and the overall circulation is stabilized with well organized triple junctions of cold sheets developed the presence of internal heating increases the number of upwelling plumes and breaks up the network of downwelling sheets these plumes become larger in size and have a hotter interior because of the nearly stationary character

near surface scholte wave velocities at ekofisk from short noise recordings by seismic noise gradiometry we propose a new approach for imaging the subsurface using a stochastic wavefield of interface waves present in the ambient seismic field unlike seismic interferometry our technique does not rely on cross correlations to obtain the green s function between two seismic receivers rather it relies on the local measurements of phase velocity obtained directly from the ratio between second order temporal and spatial derivatives of the wavefield we process 10 min of ambient seismic noise recording made using a large and dense array installed over ekofisk we image a subsidence induced geomechanical imprint on the scholte wave phase velocities in the near surface this resulting phase velocity pattern is verified by comparison to results from a seismic noise cross correlation tomography

role of a low viscosity zone in stabilizing plate tectonics implications for comparative terrestrial planetology 1 earth s near surface layer its lithosphere is broken into quasi rigid plates that form the upper thermal boundary layer for mantle convection since the discovery of plate tectonics it has been widely conjectured but only recently demonstrated that this peculiar style of convection may be facilitated by an upper mantle low viscosity zone lvz over which the plates glide easily the lvz or asthenosphere concept dates from 19th century investigations of isostatic support of mountain belts and is supported by modern evidence for a seismic low velocity zone and by studies of postglacial rebound and dynamic compensation of the earth s gravity field here we show in both two dimensional 2 d cartesian and 3 d spherical earth models that combining a pronounced lvz and a plastic yield stress to allow localized weakening of the cold thermal boundary layer results in a distinctly plate tectonic style of convection with 30 toroidal surface motion for the 3 d case recycling of water into the upper mantle at subduction zones is a plausible cause of earth s lvz whereas venus is dry and lacks both an lvz and plate tectonics

lateral variations in cmb heat flux and deep mantle seismic velocity caused by a thermal chemical phase boundary layer in 3d spherical convection article i nfo numerical simulations of thermo chemical multi phase compressible mantle convection in a three dimensional spherical shell are used to investigate the relationship between lateral variations in seismic shear wave velocity vs above the core mantle boundary cmb and lateral variations in heat flux across the cmb qcmb when compositional variations and the post perovskite phase transition are included for simple thermal convection the vs qcmb relationship is reasonably but not perfectly linear the post perovskite transition introduces a non linearity that amplifies fast vs anomalies in cold regions but there is still a unique mapping between vs and qcmb lateral variations in composition such as piles of dense material introduce another non linearity that affects hot upwelling regions and introduces a non uniqueness in vs qcmb if the dense material e g morb is seismically fast compared to the surrounding material in this case dense piles are ringed by sharp low vs anomalies if the cmb is covered by a global dense layer than variations in vs and qcmb are reduced but so is the mean value of qcmb in all cases the peak to peak lateral variation in qcmb is similar to or larger than twice the mean value which might create problems for generating a dynamo according to existing numerical dynamo simulations analytical scalings are developed to explain the observed trends

preliminary experiments to assess the effectiveness of magnetite powder as an erosion tracer on the loess plateau abstract soil water erosion monitoring is essential for long term soil conservation and ecological restoration on the loess plateau region of china traditional approaches such as runoff plots and water weirs in a watershed provide reliable spatially averaged soil erosion data but cannot validate process based erosion prediction models for dynamic soil erosion evaluation erosion tracer techniques are capable of quantitatively determining spatial distribution of soil erosion ideal tracers are expected to provide highly contrasting values compared with background ones and be analyzed efficiently and acquired cost effectively in this laboratory study magnetite powder was selected as an erosion tracer to test the tracer was implanted into loessial soils from the loess plateau using a wet soil tracer mixing procedure the effectiveness of magnetite powder as an erosion tracer was evaluated in aspects of basic magnetic features between the tracer and soils distribution under different soil aggregate sizes mobility along soil profiles and detachment of tracer labeled loessial soils by shallow surface flow along a slope results showed that magnetite powder was bound tightly to loessial soil aggregates with no noticeable vertical mobility under long term leaching conditions and almost synchronous detachment with the eroded soils furthermore the tracer is an inexpensive tracer approximately 0 08 us kg 1 which has higher magnetic susceptibility over two or three orders of magnitude than ordinary soils and high sensitivity of analysis

using magnetic susceptibility to assess soil degradation in the eastern rif morocco 25 pag 4 tabl 7 fig the definitive version is available at http www3 interscience wiley com journal 2388 home

impact megadomes and the origin of the martian crustal dichotomy abstract we show that a sufficiently energetic impact can generate a melt volume which after isostatic adjustment and differentiation forms a spherical cap of crust with underlying depleted mantle depending on impact energy and initial crustal thickness a basin may be retained or impact induced crust may be topographically elevated retention of a martian lowland scale impact basin at impact energies 3 1028 3 1029 j requires an initial crustal thickness greater than 10 km formation of impact induced crust with size comparable to the martian highlands requires a larger impact energy 1 3 1030 j and initial crustal thickness

velocity of water flow along saturated loess slopes under erosion effects abstract rainfall or snow melted water recharge easily saturates loose top soils with a less permeable underlayer such as cultivated soil slope and partially thawed top soil layer and thus may influence the velocity of water flow this study suggested a methodology and device system to supply water from the bottom soil layer at the different locations of slopes water seeps into and saturates the soil when the water level is controlled at the same height of the soil surface the structures and functions of the device the components and the operational principles are described in detail a series of laboratory experiments were conducted under slope gradients of 5 10 15 and 20 and flow rates of 2 4 and 8 l min 1 to measure the water flow velocities over eroding and non eroded loess soil slopes under saturated conditions by using electrolyte tracing results showed that flow velocities on saturated slopes were 17 to 88 greater than those on non saturated slopes flow velocity increased rapidly under high flow rates and slope gradients saturation conditions were suitable in maintaining smooth rill geomorphology and causing fast water flow the saturated soil slope had a lubricant effect on the soil surface to reduce the frictional force resulting in high flow velocity the flow velocities of eroding rills under different slope gradients and flow rates were approximately 14 to 33 lower than those of non eroded rills on saturated loess slopes compared with that on a saturated loess slope the eroding rill on a non saturated loess slope can produce headcuts to reduce the flow velocity this study helps understand the hydrodynamics of soil erosion and sediment transportation of saturated soil slopes

yin yang grid an overset grid in spherical geometry 1 a new kind of overset grid named yin yang grid for spherical geometry is proposed the yin yang grid is composed of two identical component grids that are combined in a complemental way to cover a spherical surface with partial overlap on their boundaries each component grid is a low latitude part of the latitude longitude grid therefore the grid spacing is quasi uniform and the metric tensors are simple and analytically known one can directly apply mathematical and numerical resources that have been written in the spherical polar coordinates or latitude longitude grid the complemental combination of the two identical component grids enables us to make efficient and concise programs simulation codes for geodynamo and mantle convection simulations using finite difference scheme based on the yin yang grid are developed and tested the yin yang grid is suitable for massively parallel computers

the study of detachment and deposition on a hillslope using a magnetic tracer soil erosion by water involves the processes of detachment transport and deposition of soil materials by the erosive forces of raindrops and surface flow of water the redistribution of sediment within a field sized area is important in estimating the effect of erosion and deposition on productivity in helping the conservation planner to target efforts to reduce erosion and to evaluate erosion models the objective of this study was to use a magnetic tracer with size and density similar to soil aggregates to study detachment and deposition on a hillslope two interconnected plots were established on a hillslope two rainfall intensities 35 and 70 mm h 1 combined with two different inflow rates 4 and 10 l min 1 were applied to the upper of the two plots no rain or water was applied to the lower plot which was used to study the deposition of eroded sediments from the upper plot a 5 concentration of magnetic tracer was placed in the upper plot and mixed to depth of 3 cm from this initial condition areas of tracer detachment and deposition were identified using a magnetic sensor areas of detachment were associated with a decrease in magnetic signal while areas of deposition were associated with an increase in the magnetic signal in the lower plot deposition of tracer correlated well with the magnetic susceptibility readings results indicated that the tracer was effective for identifying areas of net detachment and deposition however the tracer to soil ratio did not remain constant for all treatments for this reason a wider range of sizes and densities of the tracer should be tested if the method is to be useful to quantify erosion rates d 2002 elsevier science b v all rights reserved

seismic velocity changes caused by an overburden stress abstractan increase in seismic velocity with depth is a common rock property one that can be encountered practically everywhere overburden pressure increases vertical stress producing a nonlinear elastic response application of a conventional nonlinear theory to this problem leads to transverse isotropy with explicit relationships between nonlinear constants and elastic anisotropy parameters these relationships can be used in velocity depth trend removal and in computing offset dependent corrections for stacking and migration assumptions about small static stress and the use of linearized solutions for its evaluation are invalid for overburden problems more accurate approximations are required realistic tomography models should account for elastic anisotropy as a basic feature our theory gives an accurate fit to well and stacking velocity data for the los angeles basin overburden stress is a likely cause of shear wave generation by underground explosions

determining magnetic susceptibility in loess paleosol sections by near infrared reflectance spectroscopy 1 loess deposits are widespread covering about 10 percent of the earth s land surface magnetic susceptibility ms an important parameter in loess deposits is a function of the concentration of magnetic minerals which exhibit diagnostic features in their visible and near infrared nir spectra therefore ms should correlate with spectral reflectance to determine if a relationship exists between ms and reflectance spectra we analyzed nir spectra and ms of over 550 samples from seven loess paleosol sequences on loess plateau of central china nir reflectance data were first converted into eight spectral bands and then a step wise multiple linear regression was applied to a calibration dataset to establish a model to predict ms values test datasets indicate our model is very successful all produced an r2 0 9 by applying this new method for estimating ms to hyperspectral remote sensing data we anticipate mapping soil quality and ms on the loess plateau

wave gradiometry and its link with helmholtz equation solutions applied to usarray in the eastern u s wave gradiometry is an array processing technique utilizing the shape of seismic wavefields captured by usarray ta stations to determine fundamental wave propagation characteristics we first explore a compatibility relation that links the displacement spatial gradients to seismogram displacements and velocities through two unknown coefficients a and b these coefficients are solved for through iterative damped least squares inversion to provide estimates of phase velocity back azimuth radiation pattern and geometrical spreading we show that the a coefficient corresponds to the gradient of logarithmic amplitude and the b coefficient corresponds approximately to the local wave slowness a and b vector fields are interpolated to explore a second compatibility relation through solutions to the helmholtz equation for most wavefields passing through the eastern u s we show that the a coefficients are generally orthogonal to the b coefficients where they are not completely orthogonal there is a strong positive correlation between b and changes in geometrical spreading which can be further linked with areas of strong energy focusing and defocusing we finally obtain isotropic rayleigh wave phase velocity maps for 15 periods between 20 and 150 s by stacking results from 37 earthquakes which show a velocity change along the approximate boundary of the early paleozoic continental margin we also observe two low velocity anomalies one centered over the central appalachians where eocene basaltic volcanism has occurred and the other within the northeastern u s possibly associated with the great meteor hotspot track

impact origin for the martian crustal dichotomy half emptied or half filled 1 one possible mechanism for martian hemispherical dichotomy formation is excavation of the northern lowland basin in the existing crust by a single giant impact here we explore a related scenario in which the impact melt volume is sufficient to fill the excavated cavity produce a thickened crust and generate a topographic basin centered on the opposite side of the planet we investigate this mechanism by formulating a model for viscous spreading of a partially molten layer over a spherical surface we derive numerical solutions and calculate the final area of the spreading layer as a function of impactor size and shape of the layer boundary due to an initially asymmetric melt region results are compared with observations including lowland basin size shape of the dichotomy boundary age difference between crustal provinces and crustal thickness

global transport on a spherical multiple cell grid abstractsecond and third order upstream nonoscillatory uno advection schemes are applied on a spherical multiple cell smc grid for global transport similar to the reduced grid the smc grid relaxes the courant friedrichs lewy cfl restriction of the eulerian advection time step on the conventional latitude longitude grid by zonally merging cells toward the poles round polar cells are introduced to remove the polar singularity of the spherical coordinate system the unstructured feature of the smc grid allows unused cells to be removed out of memory and transport calculations solid body rotation and deformation flow tests are used for comparison with other transport schemes application on the global ocean surface is used to demonstrate the flexibility of the smc grid by removing all land points and making possible the extension of global ocean surface wave models to cover the arctic in response to the retreating sea ice in recent summers numerical results suggest that uno schemes on the smc grid

time domain parallelization for computational geodynamics 1 i present a time domain parallelization approach for geodynamic modeling this algorithm named parareal is based on the use of coarse sequential and fine parallel propagators to predict and to iteratively correct the solution of the governing equations over a given time interal although the method has been successfully used to solve differential equations in various scientific areas it has not been applied to model solid state convective motions relevant to the earth and other planetary mantles in that case the time dependence of the velocity is only implicit which requires modifications to the original algorithm the performances of this adapted version of the parareal algorithm were investigated using theoretical model predictions in good agreement with numerical experiments i show that under optimum conditions the parallel speedup increases linearly with the number of processors and speedups close to 10 were measured using only few tens of cpus this parareal approach can be used alone or combined with any spatial parallel algorithm allowing significant additional increase in speedup with increasing number of processors

dye tracer technique for rill flows by velocity profile measurements abstract water flow on hillslope soil surface supplies energy which is required to detach soil particles to transport and deposit sediments therefore flow velocity is a key variable related to hillslope hydrodinamics of soil erosion processes among the different methods available for measuring velocity of shallow interrill and rill flow the trace technique is widely used trace technique is applied by adding a material salt magnetic material water isotope floating object and then measuring the speed of the material to travel a known distance from the injection point when flow velocity is measured using a dye tracing method the mean velocity is calculated by multiplying the measured surface velocity of the leading edge of the tracer plume by a correction factor which was generally empirically deduced the main uncertainty of the dye tracing technique stands in the estimate of this correction factor which is the ratio between the mean flow velocity and the surface velocity the main goal of this paper is establishing a theoretical relationship for calculating the correction factor by using a power velocity profile at first the developed analysis demonstrated that the correction factor only depends on the exponent of the power velocity distribution eq 5 then this theoretical expression of the correction factor was applied using the velocity profiles measured by baiamonte and ferro for the condition of sediment free flow in motion on a rough bed and by coleman for a sediment laden flow moving on a smooth flume using the correction factor values calculated by the velocity measurements carried out for the sediment free flow in motion on a rough bed the relationship between the correction factor and roughness height was established in agreement with a previous study by ali et al for a sediment free flow the correction factor increases with roughness height finally the velocity profile measurements carried out for a sediment laden flow in motion on a smooth bed were used to state the effect of sediment load on the correction factor this last analysis allowed to conclude in agreement with li and abrahams and zhang et al that the correction factor decreases when the sediment load increases

an improved method for shallow water flow velocity measurement with practical electrolyte inputs summary the measurement of shallow water flow velocity is of interest to hill slope hydrology and soil erosion mechanics lei et al lei t xia w zhao j 2005 method for measuring velocity of shallow water flow for soil erosion with an electrolyte tracer journal of hydrology 301 139 145 proposed an electrolyte pulse method for the purpose but found that the velocity measured at short distances from the salt injector was not as well estimated as those further away from the injector though it is desirable to estimate velocity at short distances for the purpose of portable device development in this study the system was improved over the previous development an additional sensor was added at the salt injection location to register the input signal as the actual boundary condition function instead of using the pulse assumption two function forms a normal distribution function normal model and a sine function sine model were suggested to approximate the measured boundary conditions these two determined boundary models were used to fit the experimentally obtained data using the least square method to determine the model parameters of the boundary conditions the determined normal model and the sine model were both used to solve the transport processes as the convolution integrals of the pulse response and the actually determined boundary functions so as to determine the shallow water flow velocity laboratory experiments were conducted to get data to verify the proposed methods and computational procedures the experiment device included a flume 4 m long and 15 cm wide a solute injector a data logger for control and data acquisition and a computer with specially designed software for data measurement and velocity estimation the experiments involved three flow rates 12 24 and 48 l min 1 and three slope gradients 4 8 and 12 six sensors were used to measure the solute transport processes at 5 30 60 90 120 and 150 cm from the location where the salt solute was injected into the water flow the solutions of both the normal model and sine model fitted the measured data very well for all the experimental conditions the velocities at different distances from the salt solution injector and under different flow rates and slope gradients as computed by the two models were almost identical which indicated the feasibility of the method and the computational procedures as well as the two suggested models for velocity estimation the velocity values estimated by the normal and sine models agreed also with those measured by using the floating objects and the volumetric method these demonstrated the rationality of the improved methods for shallow water flow velocity measurement the results will be useful to design a practical system for the measurement of shallow water flow velocity

the impacts of mantle phase transitions and the iron spin crossover in ferropericlase on convective mixing is the evidence for compositional convection definitive new results from a yin yang overset grid based control volume model high resolution seismic tomographic images from several subduction zones provide evidence for the inhibition of the downwelling of subducting slabs at the level of the 660 km depth seismic discontinuity furthermore the inference of old 140 myr sinking slabs below fossil subduction zones in the lower mantle has yet to be explained we employ a control volume methodology to develop a new anelastically compressible model of three dimensional thermal convection in the mantle of a terrestrial planet that fully incorporates the influence of large variations in material properties the model also incorporates the influence of 1 multiple solid solid pressure induced phase transitions 2 transformational superplasticity at 660 km depth and 3 the high spin low spin iron spin transition in ferropericlase at midmantle pressures the message passing interface parallelized code is successfully tested against previously published benchmark results the high resolution control volume models exhibit the same degree of radial layering as previously shown to be characteristic of otherwise identical 2 d axisymmetric spherical models the layering is enhanced by the presence of moderate transformational superplasticity and in the presence of the spin crossover in ferropericlase stagnation of cold downwellings occurs in the range of spin crossover depths 1700 km although this electronic spin transition has been suggested to be invisible seismically recent high pressure ab initio calculations suggest it to have a clear signature in body wave velocities which could provide an isochemical explanation of a seismological signature involving the onset of decorrelation between vp and vs that has come to be interpreted as requiring compositional layering

towards self consistent modeling of the martian dichotomy the influence of one ridge convection on crustal thickness distribution in order to find an explanation for the origin of the martian crustal dichotomy a number of recent papers have examined the effect of layered viscosity on the evolution of a degree 1 mantle convection e g roberts and zhong roberts j h zhong s 2006 j geophys res 111 e06013 and yoshida and kageyama yoshida m kageyama a 2006 j geophys res 111 doi 10 1029 2005jb003905 b03412 it was found that a mid mantle viscosity jump combined with highly temperature and depth dependent rheology are effective in developing a degree 1 convection within a short timescale such a layered viscosity profile could be justified by martian mineralogy however the effect of a degree 1 convective planform on the crustal thickness distribution has not yet been demonstrated it is not obvious whether a thinner crust due to sublithospheric erosion and crustal thinning or a thicker crust due to enhanced crustal production would form above the hemisphere of mantle upwelling also the general shape of the dichotomy which is not strictly hemispherical has not yet been fully investigated here we propose a model of the crustal patterns produced by numerical simulations of martian mantle convection using the finite volume multigrid code stagyy tackley p j 2008 phys earth planet int 107 7 18 doi 10 1016 j pepi 2008 08 005 a self consistent treatment of melting crustal formation and chemical differentiation has been added to models of three dimensional thermal convection this allows us to obtain global maps of the crustal thickness distribution as it evolves with time the obtained results demonstrate that it is indeed possible to form a crustal dichotomy as a consequence of near degree 1 mantle convection early in mars history we find that some of the observed patterns show intriguing first order similarities to the elliptical shape of the martian dichotomy in all models the region of thick crust is located over the region of mantle upwelling which itself is a ridge like structure spread over roughly one half of the planet a planform we describe as one ridge convection

low degree mantle convection with strongly temperature and depth dependent viscosity in a three dimensional spherical shell 1 a series of numerical simulations of thermal convection of boussinesq fluid with infinite prandtl number with rayleigh number 10 7 and with the strongly temperature and depth dependent viscosity in a three dimensional spherical shell is carried out to study the mantle convection of single plate terrestrial planets like venus or mars without an earth like plate tectonics the strongly temperature dependent viscosity the viscosity contrast across the shell is 10 5 makes the convection under stagnant lid short wavelength structures numerous cylindrical upwelling plumes are developed because of the secondary downwelling plumes arising from the bottom of lid this convection pattern is inconsistent with that inferred from the geodesic observation of the venus or mars additional effect of the stratified viscosity at the upper lower mantle the viscosity contrast is varied from 30 to 300 are investigated it is found that the combination of the strongly temperature and depth dependent viscosity causes long wavelength structures of convection in which the spherical harmonic degree l is dominant at 1 4 the geoid anomaly calculated by the simulated convections shows a long wavelength structure which is compared with observations the degree one l 1 convection like the martian mantle is realized in the wide range of viscosity contrast from 30 to 100 when the viscosity is continuously increased with depth at the lower mantle

rare earth element oxides for tracing sediment movement the development of soil conservation plans and evaluation of spatially distributed erosion models require knowledge of rates of soil loss and sedimentation on different landscape elements and slope positions characterization of soil erosion rates and patterns within watersheds is important for the understanding of erosion processes and landscape evolution experimental data that show spatial translocation of soil on slopes are limited a method for obtaining spatially distributed information on sediment movement employing rare earth element ree oxides is proposed five ree oxides in powder form were uniformly mixed with the soil on different parts of a 10 slope in a 4 4 m soil bed particle translocation was measured during eight simulated rainfalls at 60 mm h 1 intensity a laser scanner was utilized to obtain digital elevation models dems of the soil surface that were used as the reference data to compare with the tracer method ree concentration in soil and runoff samples was determined by inductively coupled plasma mass spectrometry icp ms erosion rates for different slope positions estimated from ree concentrations correlated with those calculated from the dems with relative differences for different slope sections of 4 40 the enrichment ratio for this type of tracer was 1 7 the amount of sediment produced on different parts of the slope varied with the greatest erosion occurring on the upper middle part of the slope the experiment showed that the multi element tracer method provided a satisfactory way to study soil erosion distribution on a uniform slope d 2003 elsevier b v all rights reserved

comparison of rill flow velocity over frozen and thawed slopes with electrolyte tracer method summary freeze thaw erosion is the primary soil water erosion form in high altitude and or high latitude regions the water flow velocity along an eroding rill over frozen and thawed slopes is vital to understanding of rill erosion hydrodynamics this study experimentally measured rill flow velocity over frozen and thawed slopes using electrolyte trace method under pulse boundary model the experiments used three flow rates of 1 2 and 4 l min 1 three slope gradients of 5 10 and 15 the temperature of the rill flow water was supplied at 0 c as controlled with ice water mixture seven sensors were used to measure flow velocity by tracing the solute transport process at 10 110 210 310 410 510 and 610 cm distances from the electrolyte injection position the measured velocity became steady at a distance of about 3 m from the electrolyte injection location where the effect of the pulse boundary condition on the analytic solution to the partial differential equation becomes negligible results showed that flow velocity increased with slope gradient and flow rate on frozen slopes a significant effect was observed on the steepest slope or at the highest flow rate over the thawed slope which changed slightly on the gentle slopes and low flow rates flow velocity was about 25 30 and 40 higher on the frozen soil than on the thawed slope at 5 10 and 15 slopes and about 30 higher over the frozen slope at all flow rates this study demonstrates that water over a frozen slope flows much faster than over a thawed slope this study helps in the study and further understanding of the hydrodynamics of soil erosion and sediment transport behaviors of frozen and thawed slopes

assessing the role of slab rheology in coupled plate mantle convection models reconstructing the 3d structure of the earth s mantle has been a challenge for geodynamicists for about 40 yr although numerical models and computational capabilities have substantially progressed parameterizations used for modeling convection forced by plate motions are far from being earth like among the set of parameters rheology is fundamental because it defines in a non linear way the dynamics of slabs and plumes and the organization of lithosphere deformation in this study we evaluate the role of the temperature dependence of viscosity variations up to 6 orders of magnitude and the importance of pseudo plasticity on reconstructing slab evolution in 3d spherical models of convection driven by plate history models pseudo plasticity which produces plate like behavior in convection models allows a consistent coupling between imposed plate motions and global convection which is not possible with temperature dependent viscosity alone using test case models we show that increasing temperature dependence of viscosity enhances vertical and lateral coherence of slabs but leads to unrealistic slab morphologies for large viscosity contrasts introducing pseudo plasticity partially solves this issue producing thin laterally and vertically more continuous slabs and flat subduction where trench retreat is fast we evaluate the differences between convection reconstructions employing different viscosity laws to be very large and similar to the differences between two models with the same rheology but using two different plate histories or initial conditions

tracer techniques in aeolian research approaches applications and challenges abstract aeolian processes the entrainment transport and deposition of sediments by wind impacts climate biogeochemical cycles food security environmental quality and human health considering the multitude of interactions between aeolian processes and all the major components of the earth system there is a growing interest in the scientific community to quantify the wind related sediment movement process and redistribution rates at different spatial and temporal scales however this quantification is rather challenging due to the complexities of physical mechanisms involved in aeolian processes and the inherent fundamental differences from the rather well studied processes controlling fluvial erosion traditional techniques such as erosion plots and surveying methods for monitoring wind erosion are capable of quantifying sediment movement on small scales but they have a number of limitations in terms of the representativeness of the data obtained spatial and temporal resolution and the patterns over extended areas and the costs involved the demand for alternative methods of soil loss and sediment redistribution assessment in order to complement and enhance the existing methods has directed attention to use tracing approaches for monitoring rates and spatial patterns of sediment redistribution at various scales a comprehensive synthesis of available information from different scientific disciplines on aeolian tracer techniques their applications and limitations are important in understanding the role of aeolian processes and their interactions with the earths systems in changing climate and management scenarios the objective of this paper is to provide a scientific review of the current tracer approaches in aeolian studies including fallout radionuclides rare earth elements sediment finger printing and soil magnetism as well as giving an introduction of the potential tracers that are in development

velocity measurement of water flow within gravel layer with electrolyte tracer method under virtual boundary condition summary the measurement velocity of water flow along gravel rich hill slope is of great interest for hydrological simulation and prediction in alpine watersheds the alpine terrain is often covered by rock debris of different origin size and type here summarized as gravel for the sake of simplicity to do this water flow velocity within a gravel layer was measured using the electrolyte tracer method under virtual boundary conditions an improved method over pulse electrolyte tracer method models employing two virtual boundary conditions a sine function and a normal distribution function are suggested as preferable for determining flow velocity by simulating the transport processes of electrolytes along a gravel covered flume at different flow rates 3 6 and 12 l min 1 and slope gradients 4 8 and 12 flow velocities as well as determination coefficients and mean square errors were calculated at five measurement locations 0 3 0 6 0 9 1 2 and 1 5 m using model simulation the feasibility and accuracy of velocity measurements for water flow within gravel layers are justified to the extent that the two models fit well with the experimental data the velocity values predicted by the two models are almost identical and finally the relations between velocity and discharge and between velocity and slope gradient are rationally explained the estimated velocity results also agree well with those previously measured by commonly used methods such as the pulse boundary method and the conventional dye tracer method our results show that the virtual boundary conditions method when used to measure water flow velocity within a gravel layer predicts the flow velocity more rationally than the pulse boundary and dye tracer methods and with greater precision this study suggests that this method is not only readily applicable for obtaining water flow velocity measurements within gravel layers but also for understanding hydrodynamics in typical watershed

azimuthal anisotropy in the earth from observations of sks at geoscope and nars broadband stations abstract we have analyzed observations of low frequency sks waves recorded on horizontal components at several broadband stations of the geoscope and nars arrays splitting of sks is consistently observed and in good agreement with a hypothesis of azimuthal anisotropy due to transverse anisotropy with a horizontal axis in the upper mantle beneath the receivers we have designed an inversion method which takes advantage of observations made simultaneously at different azimuths and which permits us to obtain estimates of the direction of fast axis of anisotropy as well as the time delay between the orthogonal quasi shear waves in general the directions of fast velocity obtained both for stations around the atlantic and around the pacific appear to be related to directions of past and present plate motions

zonal flow formation in the earth s core as zonal flows are common in turbulent convection regimes such as in the atmospheres of giant planets and the earth s oceans they might also be present in the earth s outer core which is thought to be in a turbulent state takehiro miyagoshi and colleagues have investigated numerical simulations of the earth s geodynamo with lower viscosities than most previous simulations have been able to use and have identified a new convection regime of core flow that exhibits a dual structure inner sheet like radial plumes surrounded by westward cylindrical zonal flow thus convection in the earth s outer core may therefore resemble that seen in planetary atmospheres and oceans more closely than was expected zonal jets are common in nature and are spontaneously generated in turbulent systems because the earth s outer core is believed to be in a turbulent state it is possible that there is zonal flow in the liquid iron of the outer core by investigating numerical simulations of the geodynamo with lower viscosities than most previous simulations have been able to use a convection regime of the outer core is now found that has a dual structure comprising inner sheet like radial plumes and an outer westward cylindrical zonal flow zonal jets are very common in nature well known examples are those in the atmospheres of giant planets and the alternating jet streams found in the earth s world ocean1 zonal flow formation in nuclear fusion devices is also well studied2 a common feature of these zonal flows is that they are spontaneously generated in turbulent systems because the earth s outer core is believed to be in a turbulent state it is possible that there is zonal flow in the liquid iron of the outer core here we report an investigation at the current low viscosity limit of numerical simulations of the geodynamo we find a previously unknown convection regime of the outer core that has a dual structure comprising inner sheet like radial plumes and an outer westward cylindrical zonal flow we numerically confirm that the dual convection structure with such a zonal flow is stable under a strong self generated dipole magnetic field

measuring sheet erosion using synthetic color contrast aggregates the bulk of eroded soils measured at the outlets of plots slopes and watersheds are suspended sediments splash induced sheet erosion it is depending on rainfall intensity and antecedent soil moisture contents and contributes to a significant proportion of soil loss that usually is ignored in soil erosion and sediment studies a digital image processing method for tracing and measuring non suspended soil particles detached transported by splash runoff was therefore used in the present study accordingly fine mineral pumice grains aggregated with white cement and coloured with yellow pigment powder with the same size shape and specific gravity as those of natural soil aggregates called synthetic color contrast aggregates were used as tracers for detecting soil particle movement subsequently the amount of non suspended soil particles detached and moved downward the slope was inferred with the help of digital image processing techniques using matlab r2010b software mathworks natick massachusetts usa the present study was conducted under laboratory conditions with four simulated rainfall intensities between 30 90 mm h 1 five antecedent soil moisture contents between 12 44 v v 1 and a slope of 30 using sandy loam soils taken from a summer rangeland in the alborz mountains northern iran a range of total transported soil between 90 34 and 1360 93 g m 2 and net splash erosion between 36 82 and 295 78 g m 2were observed the results also showed the sediment redeposition ratio ranging from 87 27 sediment delivery ratio sdr 12 73 to 96 39 sdr 3 61 in various antecedent soil moisture contents of rainfall intensity of 30 mm h 1 and from 80 55 sdr 19 45 to 89 42 sdr 10 58 in rainfall intensity of 90 mm h 1 copyright 2013 john wiley sons ltd

effects of low viscosity post perovskite on the stability and structure of primordial reservoirs in the lower mantle we performed numerical experiments of thermochemical convection in 3 d spherical geometry to investigate the effects of a low viscosity of post perovskite ppv on the stability and structure of primordial reservoirs of dense material in the lower mantle of the earth our results show that weak ppv 1000 viscosity reduction in regions containing ppv strongly increases the core mantle boundary cmb heat flux the volume averaged mantle temperature with weak ppv is slightly higher than that with regular ppv except in the lowermost mantle this is because weak ppv weakens the base of the cold downwellings allowing cold slabs to spread more easily and broadly along the cmb the stability and size of the dense reservoirs is not substantially altered by weak ppv in the weak ppv case slabs spreading along the cmb slightly decreases the stability of dense reservoirs i e the amount of dense material entrained upward is slightly larger than in the regular ppv case i e viscosity of ppv identical to that of perovskite furthermore the topography and steepness of these reservoirs slightly increase however as in the regular ppv case the dense reservoirs are maintained over periods of time comparable to the age of the earth

developing a magnetic tracer to study soil erosion abstract soil erosion is commonly measured as the quantity of sediment leaving a plot or watershed the techniques for measuring soil erosion patterns and sediment redistribution within plots or watersheds by direct monitoring are very limited the objective of this study was to develop a direct and non intrusive tracer method to study the sources patterns and rates of erosion and deposition of sediments in erosion plots the magnetic tracer developed in this study consisted of polystyrene plastic beads embedded with a magnetic powder magnetite the magnetized beads with a mean weight diameter of 3 2 mm and particle density of about 1 2 g cm 3 were uniformly mixed with soil and tested in the laboratory using simulated rainfall and inflow studies to simulate the interrill and rill components of soil erosion respectively in the interrill and rill experiments the tracer was transported in the same proportion it was initially mixed with the soil given this fact a magnetometer which measures the soil s magnetic susceptibility could be used to identify areas of deposition or detachment the magnetic susceptibility would be increased or reduced depending on whether deposition or detachment occurs to simulate detachment and deposition a magnetometer was tested for different tracer concentrations and different thickness of soil containing the tracer the magnetometer promises to be a sensitive accurate and useful tool to study the spatial variation of soil erosion when magnetic tracers are used

interactions of scales of convection in the earth s mantle abstract the existence of undulations of the geoid gravity and bathymetry in ocean basins as well as anomalies in heat flow point to the existence of small scale convection beneath tectonic plates the instabilities that could develop at the base of the lithosphere are sufficiently small scale 60 ma they form networks that are shaped by the plate evolution slabs plumes and the geometry of continental boundaries plumes impacting the boundary layer from below have a particular influence through rejuvenating the thermal lithosphere they create a wake in which new instabilities form downstream these wakes form channels that are about 1000 km wide and thus are possibly detectable by seismic tomography beneath fast plates cold sinking instabilities are tilted in the direction opposite to plate motion while they sink vertically for slow plates these instabilities are too small to be detected by usual seismic methods since they are about 200 km in lateral scale however this preferred orientation of instabilities below fast plates could produce a pattern of large scale azimuthal anisotropy consistent with both plate motions and the large scale organisation of azimuthal anisotropy obtained from recent surface wave models