sea ice models for climate study retrospective and new directions scientific observations of sea ice began more than a century ago but detailed sea ice models appeared only in the latter half of the last century the high albedo of sea ice is critical for the earth s heat balance and ice motion across the ocean s surface transports fresh water and salt the basic components in a complete sea ice model must include vertical thermodynamics and horizontal dynamics including a constitutive relation for the ice advection and deformational processes this overview surveys topics in sea ice modeling from the global climate modeling perspective emphasizing work that significantly advanced the state of the art and highlighting promising new developments

glaciological applications with landsat 7 imagery early assessments enhanced thematic mapper plus etm data from landsat 7 are providing glaciologists with an ever expanding data set that makes a comprehensive monitoring of the global cryosphere feasible for the first time in history examples of etm data illustrate its ability to satisfy major scientific needs in the glaciological subdisciplines of sea ice glacier ice cap and ice sheet research with high resolution optical satellite imagery examples shown include use as proxy ground truth positioning glacier termini and snowlines and determining snow facies boundaries the additional etm panchromatic band at a higher spatial resolution of 15 m improves the spatial accuracy of these applications the glaciological aspects of the landsat 7 long term acquisition plan are discussed to show how the timing and location of the image acquisitions will generate a cryospheric data set of unprecedented utility for future research

systematic analysis of crustal anisotropy along the karadere duzce branch of the north anatolian fault s u m m a r y we perform a systematic analysis of crustal anisotropy along and around the karadere duzce branch of the north anatolian fault naf which ruptured during the 1999 mw 7 4 izmit and mw 7 1 duzce earthquakes a method consisting of an iterative grid search for the best shear wave splitting parameters in sliding time windows is applied to 22 000 measurements recorded in the 6 month period after the izmit main shock based on objective criteria 6600 measurements are assigned high quality and used for further detailed analysis most stations near the rupture zone have fast polarization directions that are parallel to and change with the nearby fault strike the average delay times for ray paths that propagate along the rupture zone are larger than for the other paths these results suggest the existence of an approximately 1 km broad zone around the karadere duzce branch with fault parallel cracks or shear fabric however some fault zone fz stations record bimodal or scattered polarization directions while stations near large structural complexities e g branching and offsets show average fast polarization directions that are almost perpendicular to the local fault strike the average fast polarization directions from ray paths that propagate inside the almacik block south of the karadere duzce branch are neither parallel to the local fault strike nor to the expected regional maximum compressive stress direction the large overall spatial variations of the results imply that multiple structures and mechanisms contribute to the observed crustal anisotropy in our study area most stations do not exhibit a clear dependency of shear wave splitting delay time with increasing depth and hypocentral distance indicating that the anisotropy is confined primarily to the top 3 4 km of the crust using the observed average delay time at fz stations and assumed propagation distance of 3 5 km we estimate the apparent crack density in the damaged shallow fz rock to be approximately 7 per cent

tutorial on seismic interferometry part 1 basic principles and applications seismic interferometry involves the crosscorrelation of responses at different receivers to obtain the green s function between these receivers for the simple situation of an impulsive plane wave propagating along the x axis the crosscorrelation of the responses at two receivers along the x axis gives the green s function of the direct wave between these receivers when the source function of the plane wave is a transientas in exploration seismology or a noise signalas in passive seismology then the crosscorrelation gives the green s function convolved with the autocorrelation of the source function direct wave interferometry also holds for 2d and 3d situations assuming the receivers are surrounded by a uniform distribution of sources in this case the main contributions to the retrieved direct wave between the receivers come from sources in fresnel zones around stationary points the main application of direct wave interferometry is the retrieval of seismic surface wave responses from ambient noise and the subsequent tomographic determination of the surfacewave velocity distribution of the subsurface seismic interferometry is not restricted to retrieving direct waves between receivers in a classic paper claerbout shows that the autocorrelation of the transmission response of a layered medium gives the plane wave reflection response of that medium this is essentially 1d reflected wave interferometry similarly the crosscorrelation of the transmission responses observed at two receivers of an arbitrary inhomogeneous medium gives the 3d reflection response of that medium one of the main applications of reflected wave interferometry is retrieving the seismic reflection response from ambient noise and imaging of the reflectors in the subsurface a common aspect of direct and reflected wave interferometry is that virtual sources are created at positions where there are only receivers without requiring knowledge of the subsurface medium parameters or of the positions of the actual sources

compression behavior of canadian oil sands the compression behavior of canadian oil sands was investigated by running high stress oedometer compression tests up to 65 mpa an x ray microtomography investigation confirmed the significant disturbance affecting the core samples showing large pores located between dense intact clusters made up of angular sand grains compression tests confirmed the significant effects of disturbance on the com pression characteristics providing a much softer response without any memory of the significant load applied by the 3 to 4 km thick ice sheet during the quaternary period high stress compression allowed us to bring back the samples close to the in situ estimated porosity providing compression characteristics estimated fromaloading cycle close totheintact ones despiteobviousdifferencesinfabric includingtheeffects attributable to grain crushing at high stress creep behavior was also observed and an estimate of the order of magnitude of the creep strain corresponding to the quaternary period is provided doi 10 1061 asce gt 1943 5606 0000808 2013 american society of civil engineers ce database subject headings oils compression sand soil type x rays canada author keywords heavy oil oil sand high stress compression x ray microtomography core disturbance

modeling global sea ice with a thickness and enthalpy distribution model in generalized curvilinear coordinates abstract a parallel ocean and ice model poim in generalized orthogonal curvilinear coordinates has been developed for global climate studies the poim couples the parallel ocean program pop with a 12 category thickness and enthalpy distribution ted sea ice model although the poim aims at modeling the global ocean and sea ice system the focus of this study is on the presentation implementation and evaluation of the ted sea ice model in a generalized coordinate system the ted sea ice model is a dynamic thermodynamic model that also explicitly simulates sea ice ridging using a viscous plastic rheology the ted model is formulated such that all the metric terms in generalized curvilinear coordinates are retained following the pop s structure for parallel computation the ted model is designed to be run on a variety of computer architectures parallel serial or vector when run on a computer cluster with 10 parallel processors the parallel performance of the poim is close to that of a correspon

role of rafting in the mechanical redistribution of sea ice thickness 1 ice draft data derived from upward looking sonar observations collected during a scientific ice expeditions scicex submarine cruise in the arctic ocean have been used to test the ice thickness distribution theory of thorndike et al 1975 two separate ice draft surveys 40 days apart were made during the fall of 1996 in a circular lagrangian region 180 km across air temperature and deformation data from buoys in the region were used to force an ice thickness distribution model in an effort to reproduce the changes observed over the 40 day interval initial tests with an elementary ridging treatment were unsuccessful in predicting the observed change in the ice thickness distribution the shape of the distribution suggested that both ridging and rafting of ice were involved in the redistribution process modifying the theory to include rafting along with ridging resulted in much improved agreement between the modeled and observed ice thickness distributions this result taken together with many other field observations leads us to believe that rafting is an important component of the mechanical redistribution of ice thickness during the fall

geological and industrial implications of extensive dilatancy anisotropy extensive dilatancy anisotropy is the hypothesized distribution of stress aligned fluid filled microcracks pervading most rocks in the earth s crust the geometry of the cracks and the aligning stress field can be monitored by analysing the waveforms of shear waves propagating through the rockmass the ability to estimate some of the parameters of the crack and stress geometry by analysing shear wave particle displacements has widespread implications

landslide reconstruction using seismic signal characteristics and numerical simulations case study of the 2017 6 24 xinmo landslide abstract landslide modeling based on seismic signal characteristics is an effective method to study landslide evolution the scientific challenge lies in how to systematically characterize and reconstruct the entire landslide evolution process using the recorded seismic data we selected the 2017 6 24 xinmo landslide as a case study empirical mode decomposition emd is used to analyze the seismic signals from 14 seismic stations near the landslide area numerical simulations using two dimensional discrete element methods dem are performed to simulate landslide dynamics using the calculated kinetic energy profile after analyzing the short time fourier transform stft and fast fourier transform fft characteristics of the signal the landslide process is reconstructed and compared with the dem simulation the landslide process is observed to consist of a stationary stage slipping stage transition stage entrainment transportation stage and a deposition stage this is the first study that uses seismic signals to identify a transition stage which is a feature that is difficult to constrain from field survey and analysis alone landslide development and movement in the transition stage are discussed considering the sedimentology of the study area this study provides improved theoretical guidance for the reconstruction and characterization of landslide processes by seismic signals

remapping the thickness distribution in sea ice models in sea ice models with multiple thickness categories the ice thickness distribution evolves in time the evolution of the thickness distribution as ice grows and melts is analogous to one dimensional fluid transport and can be treated by similar numerical methods one such method remapping is applied here thickness categories are represented as lagrangian grid cells whose boundaries are projected forward in time the thickness distribution is approximated as a linear or quadratic polynomial in each displaced category and ice area and volume are transferred between categories so as to restore the original boundaries in simple test problems and in a single column model with forcing typical of the central arctic remapping performs significantly better than methods previously used in sea ice models it is less diffusive than a scheme that fixes the ice thickness in each category and behaves better numerically than a scheme that represents the thickness distribution as a set of delta functions also remapping converges faster i e with fewer thickness categories than the alternative schemes with five to seven categories the errors due to finite resolution of the thickness distribution are much smaller than the errors due to other sources linear remapping performs as well as the more complex quadratic version and is recommended for climate modeling its computational cost is minimal compared to other sea ice model components

did glacials start with global warming abstract correlation of paleoclimatic evidence with orbital changes shows that the build up of polar ice accelerated when low obliquity coincided with perihelion in northern hemisphere winter under low obliquity the insolation was channeled to the tropics at the expense of both polar caps as perihelion moved from winter solstice toward spring equinox the solar beam in astronomic winter and spring became stronger than in summer and autumn this orbital configuration under climate conditions like today would lead to warming of tropical oceans but cooling of the polar regions the areally weighted global mean surface temperature which is dominated by the low latitudes would increase consequently during the first millennia the early glacial ice build up was most likely accompanied by global warming it was the associated increase of meridional insolation and temperature gradients which were instrumental in the transition to a glacial a significant part of the current global warming is due to the gradual temperature increase of the tropical oceans as the changing orbital configuration today resembles that of the last interglacial glacial transition the warming is likely to have a natural component

changes in the modeled ice thickness distribution near the surface heat budget of the arctic ocean sheba drifting ice camp 1 in the polar oceans the ice thickness distribution controls the exchange of heat between the ocean and the atmosphere and determines the strength of the ice the surface heat budget of the arctic ocean sheba experiment included a year long field program centered on a drifting ice station in the beaufort and chukchi seas in the arctic ocean from october 1997 through october 1998 here we use camp observations and develop methods to assimilate ice thickness and open water observations into a model in order to estimate the evolution of the thickness distribution in the vicinity of the camp a thermodynamic model is used to simulate the ice growth and melt and an ice redistribution model is used to simulate the opening and ridging processes data assimilation procedures are developed and then used to assimilate observations of the thickness distribution assimilated observations include those of the thin end of the distribution determined by aircraft surveys of the surface temperature and helicopter photographic surveys and aircraft microwave estimates of the open water fraction the deformation of the ice was determined primarily from buoy and radarsat geophysical processor system rgps measurements of the ice velocity because of the substantial convergence and ridging observed in the spring and summer the estimated mean ice thickness increases by 59 from 1 53 to 2 44 m over the year in spite of a net thermodynamic ice loss for most multiyear ice

upper crust seismic anisotropy study and temporal variations of shear wave splitting parameters in the western gulf of corinth greece during 2013 abstract during 2013 the western gulf of corinth wgoc central greece experienced a period of increased seismicity with a total of over 4700 earthquakes this fact in combination with the existence of dense seismological networks provided an excellent opportunity for the study of crustal seismic anisotropy of special note is the seismic crisis period of may october during which the main feature was the occurrence of the helike seismic swarm polarigrams and hodograms were employed to analyze local waveforms this method resulted in 659 measurements of shear wave splitting parameters namely the direction of the fast shear wave s fast the time delay t d between the two split shear waves and the source polarization direction a pattern of a general wnw ese anisotropy direction parallel to the goc s fault systems strike is established with the exception of two stations located in adjacent areas at the north this is in agreement with the existence of fluid filled microcracks oriented according to the regional stress field the obtained splitting parameters are compared to the results of other anisotropy studies performed in the wgoc a detailed analysis of the temporal evolution of the normalized time delay t n was performed to associate temporal stress changes to seismicity fluctuations increase in normalized time delays and drop before the occurrence of the first significant event belonging to the july cluster which occurred between the 13th and the 16th of the same month was observed for most of the analyzed stations

observation of perennial arctic sea ice melt and freeze up using passive microwave data the onset of spring melt and autumn freeze up of arctic sea ice are shown through comparison with coincident ers 1 synthetic aperture radar sar and surface air temperature data to produce significant and detectable changes in the passive microwave signature melt onset is marked by a sharp rise in brightness temperatures resulting from the increased emissivity of moisture in the snow cover freeze up is accompanied by a sharp drop in brightness temperatures because of volume scattering by bubbles in the upper ice layer an algorithm is developed to detect melt and freeze up from passive microwave data and is applied to the scanning multichannel microwave radiometer smmr and special sensor microwave imager ssm i data from 1979 to 1996 the mean accuracy of melt and freeze up dates determined from the ssm i is estimated to be 2 and 3 days respectively the reduced temporal sampling of the smmr degrades the accuracy by 1 day on average melt onset varies from late may in the southern beaufort sea to mid june in the central arctic north of the canadian archipelago while freeze up varies between mid september and mid august the shortest melt season appears to occur north of the canadian archipelago rather than at the north pole which is consistent with the fact that minimum summer air temperatures are centered over greenland the mean standard deviations of the interannual variability of melt and freeze up are 6 8 and 11 4 days respectively

influence of the sea ice thickness distribution on polar climate in ccsm3 abstract the sea ice simulation of the community climate system model version 3 ccsm3 t42 gx1 and t85 gx1 control simulations is presented and the influence of the parameterized sea ice thickness distribution itd on polar climate conditions is examined this includes an analysis of the change in mean climate conditions and simulated sea ice feedbacks when an itd is included it is found that including a representation of the subgrid scale itd results in larger ice growth rates and thicker sea ice these larger growth rates represent a higher heat loss from the ocean ice column to the atmosphere resulting in warmer surface conditions ocean circulation most notably in the southern hemisphere is also modified by the itd because of the influence of enhanced high latitude ice formation on the ocean buoyancy flux and resulting deep water formation changes in atmospheric circulation also result again most notably in the southern hemisphere there are indications that the itd also modifies simulated sea

simulating the ice thickness distribution in a coupled climate model climate simulations in a global coupled model are investigated using a dynamic thermodynamic sea ice and snow model with sophisticated thermodynamics and a subgrid scale parameterization for multiple ice thicknesses in addition to the sea ice component the model includes a full primitive equation ocean and a simple energy moisture balance atmosphere we introduce a formulation of the ice thickness distribution that is lagrangian in thickness space the method is designed to use fewer thickness categories because it adjusts to place resolution where it is needed most and it is free of diffusive effects that tend to smooth eulerian distributions experiments demonstrate that the model does reasonably well in simulating the mean arctic climate we find the climate of the arctic and northern north atlantic is sensitive to resolving the ice thickness distribution when comparing the model results to a simulation with a two level sea ice model the ice thickness distribution causes ice export through fram strait to be more variable and more strongly linked to meridional overturning in the north atlantic ocean the lagrangian formulation of the ice thickness distribution allows for the inclusion of a vertical temperature profile with relative ease compared to an eulerian method we find ice growth rates and ocean surface salinity differ in our model with a well resolved vertical temperature profile in the ice and snow and an explicit brine pocket parameterization compared to a simulation with semtner zero layer thermodynamics although these differences are important for the climate of the arctic the effects of an ice thickness distribution are more dramatic and extend into the northern north atlantic sensitivity experiments indicate that five ice thickness categories with 50 cm vertical temperature resolution capture the effects of the ice thickness distribution on the heat and freshwater exchange across the surface in the presence of sea ice in these simulations

an investigation of boundary forcing sensitivities in a regional climate model the sensitivity of a regional climate model to lateral upper and lower dynamical forcing is evaluated for a pan arctic domain the experiments focus on a month long case study of may 1990 but the results are shown to be extendable to january and july 1990 although the control simulation is found to adequately represent major tropospheric circulation features a large negative geopotential height bias of up to 700m is found at the upper levels of the model experiments find these biases are remedied through the replacement of a reflective rigid lid upper boundary condition with a local wave absorbing layer geopotential height biases are reduced to a maximum underestimation of only 50m at the upper boundary substantial improvement is also found in the simulated temperature and zonal wind profiles transient heat and momentum fluxes and stationary eddies as seen through the eliassen palm flux divergence with this wave absorbing upper boundary condition in place additional improvement is found using a gravity wave drag parameterization appropriate for this domain s 100km horizontal resolution additional sensitivity to lateral forcing is examined and the relative role of the upper boundary condition to skillful simulations within the arctic basin domain is discussed

east antarctic sea ice albedo thickness distribution and snow cover characteristics of springtime sea ice off east antarctica were investigated during a cruise of the australian national antarctic research expedition in october through december 1988 the fractional coverage of the ocean surface the ice thickness and the snow cover thickness for each of several ice types were estimated hourly for the region near the ship these observations were carried out continuously during the 4 weeks the ship was in the ice thin and young ice types were prevalent throughout the region and the observations show a systematic increase in the total area weighted pack ice thickness including open water area from only 0 2 m within 50 km of the ice edge to 0 45 m close to the coast ice thickness averaged over the ice covered region only is also relatively thin ranging from 0 35 m near the ice edge to 0 65 m in the interior these values are probably typical of average winter thickness for the area the average snow cover thickness on the ice increased from 0 05 m near the ice edge to 0 15 m in the interior average ice concentration increased from less than 6 10 near the ice edge to 8 10 in the interior the ship observed concentrations were in good agreement with concentrations derived from passive microwave satellite imagery except in some regions of high concentration in these regions the satellite derived concentrations were consistently lower than those estimated from the ship possibly because of the inability of the satellite sensors to discriminate the appreciable percentage of very thin ice observed within the total area spectral albedo was measured for nilas young grey ice grey white ice snow covered ice and open water at wavelengths from 420 to 1000 nm allwave albedo was computed by using the spectral measurements together with estimates of near infrared albedo and modeled spectral solar flux area averaged albedos for the east antarctic sea ice zone in spring were derived from representative allwave albedos together with the hourly observations of ice types these area averaged surface albedos increased from about 0 35 at the ice edge to about 0 5 at 350 km from the edge remaining at 0 5 to the coast of antarctica the low average albedo is in part due to the large fraction of open water within the pack but extensive fractions of almost snow free thin ice also play an important role

comparison of different retrieval techniques for melt ponds on arctic sea ice from landsat and modis satellite data melt ponds are regularly observed on the surface of arctic sea ice in late spring and summer they strongly reduce the surface albedo and accelerate the decay of actic sea ice until now only a few studies have looked at the spatial extent of melt ponds on arctic sea ice knowledge of the melt pond distribution on the entire arctic sea ice would provide a solid basis for the parameterization of melt ponds in existing sea ice models due to the different spectral properties of snow ice and water a multispectral sensor such as landsat 7 etm is generally applicable for the analysis of distribution an additional advantage of the etm sensor is the very high spatial resolution 30 m an algorithm based on a principal component analysis pca of two spectral channels has been developed in order to determine the melt pond fraction pca allows differentiation of melt ponds and other surface types such as snow ice or water spectral bands 1 and 4 with central wavelengths at 480 and 770 nm respectively are used as they represent the differences in the spectral albedo of melt ponds a landsat 7 etm scene from 19 july 2001 was analysed using pca the melt pond fraction determined by the pca method yields a different spatial distribution of the ponded areas from that developed by others a modis subset from the same date and area is also analysed the classification of modis data results in a higher melt pond fraction than both landsat classifications

sea ice albedo climate feedback mechanism abstract the sea ice albedo feedback mechanism over the arctic ocean multiyear sea ice is investigated by conducting a series of experiments using several one dimensional models of the coupled sea ice atmosphere system in its simplest form ice albedo feedback is thought to be associated with a decrease in the areal cover of snow and ice and a corresponding increase in the surface temperature further decreasing the areal cover of snow and ice it is shown that the sea ice albedo feedback can operate even in multiyear pack ice without the disappearance of this ice associated with internal processes occurring within the multiyear ice pack e g duration of the snow cover ice thickness ice distribution lead fraction and melt pond characteristics the strength of the ice albedo feedback mechanism is compared for several different thermodynamic sea ice models a new model that includes ice thickness distribution the ebert and curry model the maykut and untersteiner model and the semtner level 3 an

interaction of the okhotsk sea diurnal tides with the kashevarov bank polynya satellite images show the existence of a recurrent polynya directly over and in the vicinity of kashevarov bank our modeling results using a coupled ice ocean model show that tides are important in the establishment and maintenance of this polynya ice appears and grows in areas surrounding the bank while over the bank tidal mixing transports heat to the sea surface resulting in ice melt and polynya formation the strong cooling of the upper sea layer forms a 100 200 m thick surface layer with negative temperatures the large current amplitudes of the basic tidal waves k1 and o1 generate through nonlinear interactions a clockwise residual current and ice drift as well as secondary oscillations in the semidiurnal fortnightly and other tidal bands in general ice causes an amplification of the tidal currents and density driven components of the residual circulation over kashevarov bank while the barotropic component of the residual flow is weakened because of the underice boundary layer

ridging and strength in modeling the thickness distribution of arctic sea ice a theory describing evolution of the ice thickness distribution the probability density of ice thickness was proposed by thomdike et al 1975 and has been used in several sea ice models the advantage of this theory over the widely used two level formulation is that it treats ridging explicitly as a redistribution of ice thickness and ice strength as a function of energy losses incurred by ridge formation however the parameterization of these processes remains rather speculative and largely untested and so our purpose here is to explore these parameterizations using a numerical model based on this theory the model uses a 160 km resolution grid of the arctic and 7 years of observed atmospheric forcing data 1979 1985 monthly oceanic heat flux and current fields are obtained from a 40 km resolution coupled ice ocean model run separately with the same forcing by requiring the computed monthly mean ice drift to have the same magnitude as observed buoy drift we estimate the primary strength parameter the ratio of total to potential energy change during ridging this ratio depends on the value of other parameters however the standard case has a ratio of 17 which is within the range estimated by hopkins 1994 in simulations of individual ridging events the effects of ridge redistribution and shear ridging parameters are illustrated by a series of sensitivity studies and comparisons between observed and modeled ice thickness distributions and ridge statistics in addition these comparisons highlight the following shortcomings of the thickness distribution theory as it is presently implemented first the process of first year to multiyear ridge consolidation is ignored and second the observed preferential melt of thick ridged ice is not reproduced

comparison of aerial video and landsat 7 data over ponded sea ice the development of melt ponds on arctic sea ice during spring and summer is of great importance to the arctic climate system as it accelerates the decay of the sea ice and greatly reduces the albedo both melt pond development and its spatial distribution are needed to understand the surface energy balance in summer previously a technique was developed for classifying summer sea ice characteristics including the amount of open water white snow covered ice wet ice and melt ponds using landsat 7 enhanced thematic mapper plus etm spectral information in this paper we refine this technique through the use of airborne video data coincident with landsat etm imagery obtained over baffin bay on june 27 2000 the video images having a resolution of about 1 5 m at an aircraft altitude of 1 4 km are classified into open water ponded or wet ice and unponded sea ice comparison of the video and landsat imagery shows that many of the melt ponds are too small to cover an entire landsat pixel resolution of 30 m so that the landsat classification scheme would underestimate melt pond fraction thirteen high resolution video images are classified to develop a method to calculate fractions of open water ponded or wet ice and unponded ice from landsat 7 data a comparison between these classified video images and landsat retrievals yields a correlation coefficient of 0 95 with rms errors of less than 9 for the two ice types and 2 for open water comparisons of landsat and video analyses not used in the development of the algorithm yield correlation coefficients of 0 87 for open water 0 68 for ponded ice and 0 78 for unponded ice the rms differences are 10 8 and 11 respectively

pore structure characteristics of debris flow source material in the wenchuan earthquake area abstract wide grading loose soils wgls are a special slope deposit that often serve as a source for debris flows in the western mountainous area of china previous research indicated that rainfall infiltration induced the migration of fine particles within soil slopes and lead to the initiation of shallow failure and subsequent debris flows clearly soil pore structure exerts a profound influence on seepage during rainfall infiltration which is closely related to soil permeability and corresponding internal erosion the current understanding of the mechanisms of fine particle migration is limited because of the complexity of wgls micropore structure the challenge lies in how to systematically characterize wgls pore structure so that it provides a foundation for future numerical simulations of fine particle migration induced debris flows in this study the characteristics of wgls pore structure were analyzed quantitatively using scanning electron microscopy the results revealed that wgls predominantly contained micropores and mesopores the pore size distribution exhibited a bimodal nature with one peak occurring at a pore diameter of 12 m and another at 72 m the pore complexity of all samples exceeded 0 75 which indicates a low aspect ratio for each pore the average diameter of the fine particles that migrated was then determined with a laboratory seepage test a preliminary jamming probability analysis based on three dimensional micropore reconstruction and average fine particle diameter indicate that jamming is most prevalent along the slope

a numerical characterization workflow for assessing the strength and failure modes of heterogeneous oil sands understanding the strength and failure modes of overburden and reservoir are critical components in safety assessments for oil sands surface mining and in situ thermal recovery operations currentl

complex and variable crustal and uppermost mantle seismic anisotropy in the western united states deformation in the crust and mantle measured using seismic anisotropy is poorly constrained in the western united states because of inconsistencies in the existing data a three dimensional model that reconciles these discrepancies reveals that seismic anisotropy in the crust correlates with different geological provinces but is unrelated to anisotropy in the underlying mantle

albedo of summer snow on sea ice ross sea antarctica 1 surface all wave albedo and physical parameters grain radius mass density surface temperature and stratification of an austral summer snow cover on sea ice were measured in the ross sea during january february 1999 it was observed that 1 from north to south the snow surface temperature decreases albedo increases snow mass density decreases snow composite grain radius decreases and number density of composite grains increases 2 the size of the clusters of snow grains i e melt clusters and well bonded chains of grains rather than the size of the individual snow grains is the dominant parameter controlling albedo the smaller the snow composite grain radius and the larger the number density are the higher the albedo is and 3 in determining the snow albedo grain size dominates over the number density and the upper layers dominate over the lower layers a comparison of the statistical relation between albedo and the averaged grain size shows that statistical significance is independent of the selection of the grain size averaging method suggestions for snow albedo parameterization are made

surface wave dispersion across tibet direct evidence for radial anisotropy in the crust recordings in western tibet of rayleigh and love waves at periods less than 70 s from aftershocks of the 2008 sichuan earthquake cannot be matched by an isotropic velocity model beneath tibet these intermediate period rayleigh and love waves require marked radial anisotropy in the middle crust of tibet with the vertically polarized s waves propagating more slowly than s waves with horizontal polarization the magnitude of anisotropy inferred using paths entirely within tibet is slightly greater than that obtained previously from a tomographic inversion of a dataset covering a larger region anisotropy in the middle crust likely reflects deformation of the middle crust and is consistent with the notion of mid crustal flow and thinning of the crust

the aerodynamic roughness of different types of sea ice the aerodynamic roughness for all major types of sea ice is specified on the basis of surface layer measurements from ship and ice floe platforms median neutral surface drag coefficients cdn 1000 for grease and nilas ice are 0 7 and 1 6 small medium large and fused pancake ice have cdn equal to 0 9 1 6 2 4 and 1 9 young ice cdn ranges from 2 3 to 3 1 very smooth first year or multiyear ice with no pressure ridges has cdn equal to 1 5 pack ice has median values of 2 0 and 2 2 for first year and multiyear ice marginal ice zone ice averages 3 1 and 3 4 first year multiyear if unaffected by wave action wave affected ice has cdn values of 4 2 and 4 6 first year multiyear extremely rough multiyear ice in intense shear or compaction regions has cdn equal to 8 0 open ocean areas within 100 km of an ice edge averaged 1 8 while ice free water downwind of ice with small or no waves is 1 4 these values can be adjusted if heat fluxes are present the accuracy of the cdn averages is estimated to be 20 or better

on the response of the equilibrium thickness distribution of sea ice to ice export mechanical deformation and thermal forcing with application to the arctic ocean the areal ice distribution in a pack ice field is described using a number of classes characterized by different ice thicknesses each class may have a snow layer on top and evolves according to the thermodynamic forcing same for all classes and is followed through time mechanical forcing leads to ice export and deformation the ice export is quantified by the parameter e describing the areal export of ice per unit of time the deformation is quantified by the parameter r describing the area of open water generated by deformation per unit of time the fraction of summer heat absorbed in leads and utilized for ice melting is quantified by the parameter gop the model is applied to the arctic ocean it is run to a steady state for different combinations of e r and gop and the response of the thickness distribution to these parameters may thereby be quantified it is shown that the ice generally gets thinner for increasing export the response to deformation is dependent on gop such that the mean thickness increases with r for small gop i e no effect or just a small melting effect of the heat absorbed in leads but decreases with r for large gop the overall effect of gop is that the mean thickness decreases with increasing gop for gop close to 1 and moderate values of e and r the ice sheet melts completely in the summer

numerical simulation of northern hemisphere sea ice variability 1951 1980 the dynamic thermodynamic sea ice model of hibler 1979 is used to simulate northern hemisphere sea ice growth drift and decay over a 30 year period 1951 1980 the model is run with a daily time step and is forced by interannually varying fields of geostrophic wind and temperature derived thermodynamic fluxes the results include documentation of the sensitivities to the source of the thermodynamic forcing data and to the number of thickness levels in the thermodynamic formulation the fields of ice velocity and thickness show strong seasonal as well as interannual variability the pacific gyre is found to be well developed in spring and autumn but less so in winter and summer the mean drift pattern results in thicknesses of 4 5 m offshore of northern canada and greenland while winter thicknesses of 2 m are typical of the alaskan and eurasian coastal waters annual net growth ranges from 0 1 to 0 6 m over much of the arctic basin and baffin bay to over 1 0 m in the eastern bering sea annual net melt of 0 5 1 5 m occurs in the western bering sea and the north atlantic marginal ice zone no significant temporal trends are detectable in the total mass of simulated ice the simulated interannual fluctuations in 20 longitudinal sectors correlate at 0 4 0 9 with corresponding observed fluctuations during 1961 1976 the correlations are smaller when dynamics are omitted from the model the simulated velocities show no bias but considerable scatter relative to the drift of the arctic buoys in 1979 and 1980 an analysis of the regional mass budgets shows that the normal seasonal cycle is controlled primarily by the thermodynamic processes but that the thickness anomalies in much of the arctic are attributable primarily to dynamic processes during winter spring and autumn thermodynamic processes contribute more strongly to summer anomalies and to anomalies near the ice edge the tendency for ice anomalies to be advected by the pattern of mean drift is apparent in multiseason lag correlations involving subregions of the arctic basin and the peripheral seas the simulated outflows of ice mass through the fram and bering straits vary by factors of 2 3 in successive years the simulated outflow in the fram strait is 20 30 smaller when ocean currents are omitted from the model

on the numerical resolution in a thermodynamic sea ice model the numerical integration of the heat conduction equation is one of the main components in a thermodynamic sea ice model the spatial resolution in the ice normally varies from a minimum of three layers up to a few tens of layers the temporal resolution varies from a few minutes up to hours in this paper the impact of numerical resolution on the prediction of a one dimensional thermodynamic ice model is studied analytical solutions for idealized cases were derived and compared with the numerical results for the full ice model groups of simulations were made applying average climatic weather forcing data corresponding to the ice freezing ice thermal equilibrium and ice warm up seasons special attention was paid to the effect of model spatial resolution early in the freezing season the influence of resolution on model predictions is not significant when the shortwave radiation becomes large its absorption within the ice or snow cover was found to modulate the effect of numerical resolution on predictions of ice temperature and surface heat fluxes e g the model run with a coarse spatial resolution yielded large daily variations in surface temperature resolution also affects the in ice temperature profile for process studies a two layer scheme for the solar radiation penetrating into the ice is suitable for a fine spatial resolution ice model

mechanisms in the development of anomalous sea ice extent in the western arctic a case study interannual cycles and trends in arctic ice cover are dominated by strong regional variability arctic sea ice extent exhibited a record minimum within the arctic basin during september 1990 dominated by a rapid retreat in the chukchi east siberian and laptev seas simulations using a coupled regional model reproduced the enhanced cyclonic activity and enhanced ice melt which led to this large retreat in sea ice cover sensitivity experiments showed that accurate initial ice conditions are crucial for a realistic simulation of the ice anomaly pointing to the need for adequate spin up in coupled model experiments it was also found that thermodynamic melt can account for the bulk of the total loss in ice mass over the summer season in 1990 but without dynamics the spatial patterns characteristic of the ice reductions are not reproduced well also transport of ice was crucial to initiate the formation of the anomaly even if the formation was delayed until later in the season the ice albedo feedback is important in allowing the continued formation of the ice anomaly throughout the summer interannual variations in atmospheric circulation that yield regional differences in ice thickness provide a preconditioning that significantly affected development of the ice anomaly this suggests that circulation modes play an important role in determining ice severity along the siberian coast

the relation between ice deformation oceanic heat flux and the ice thickness distribution in the arctic ocean a one dimensional ocean model coupled with an ice model where the ice cover is partitioned into a number of thickness categories is used to investigate how the ice thickness distribution in the arctic ocean depends on the two deformation processes export net divergence and ridging the model standard case generates vertical profiles of temperature salinity and an ice thickness distribution similar to the observations the standard case oceanic heat flux agrees well with recently deduced heat fluxes from arctic ice dynamics joint experiment aidjex data the oceanic heat flux is about 18 w m 2 during summer and about 1 w m 2 during winter it is found that the mean ice thickness decreases with increasing ice export in close agreement with other investigations however the dependence of the mean ice thickness on ridging activity is found to be very weak the change of the mean ice thickness is only 12 cm when increasing the ridging activity in the model from 0 to 0 4 yr 1 where the larger value represents an estimate of the actual ridging activity in the arctic ocean in a sensitivity study different types of ridging and albedo parameterizations are tested and this weak dependence is found to be very robust other properties of the model ice cover are sensitive to ridging though the equilibrium thickness of undeformed ice decreases with both export and ridging activity the annual maximum open water fraction and the amplitude of the seasonal thickness variation increases with export and ridging

a thickness and enthalpy distribution sea ice model abstract the theory of sea ice thickness distribution developed by thorndike et al has been extended to include sea ice enthalpy distribution the extended theory conserves both ice mass and thermal energy in the form of the heat stored in the ice by jointly solving a thickness distribution equation and an enthalpy distribution equation both equations have been implemented in a one dimensional dynamic thermodynamic sea ice model with 12 ice thickness categories following the numerical procedure of hibler the implementation of the enthalpy distribution equation allows the sea ice model to account for any changes in the ice thermal energy induced by sea ice processes as a result the model is able to conserve not only the ice mass but also its thermal energy in the presence of ice advection growth melting and ridging conserving ice thermal energy in a thickness distribution sea ice model improves the prediction of ice growth summer ice melt in particular and therefore ice thickness inability to

anatomy of the high frequency ambient seismic wave field at the tcdp borehole 1 the taiwan chelungpu fault drilling project tcdp installed a vertical seismic array between 950 and 1270 m depth in an active thrust fault environment in this paper we analyze continuous noise records of the tcdp array between 1 and 16 hz we apply multiple array processing and noise correlation techniques to study the noise source process properties of the propagation medium and the ambient seismic wave field diurnal amplitude and slowness patterns suggest that noise is generated by cultural activity the vicinity of the recording site to the excitation region indicated by a narrow azimuthal distribution of propagation directions leads to a predominant ballistic propagation regime this is evident from the compatibility of the data with an incident plane wave model polarized direct arrivals of noise correlation functions and the asymmetric arrival shape evidence for contributions from scattering comes from equilibrated earthquake coda energy ratios the frequency dependent randomization of propagation directions and the existence of correlation coda waves we conclude that the ballistic and scattered propagation regime coexist where the first regime dominates the records but the second is weaker yet not negligible consequently the wave field is not equipartitioned correlation signal to noise ratios indicate a frequency dependent noise intensity iterations of the correlation procedure enhance the signature of the scattered regime discrepancies between phase velocities estimated from correlation functions and in situ measurements are associated with the array geometry and its relative orientation to the predominant energy flux the stability of correlation functions suggests their applicability in future monitoring efforts

large scale patterns and variability of snowmelt and parameterized surface albedo in the arctic basin abstract visible band satellite imagery is used to manually map surface brightness changes over sea ice throughout the arctic basin from may to mid august over a 10 yr period these brightness changes are primarily due to snowmelt atop the ice cover using image processor techniques parameterized albedos are estimated for each brightness class snowmelt begins in may in the marginal seas progressing northward with time finally commencing near the pole in late june large year to year differences are found in the timing of melt exceeding one month in some regions parameterized albedo for most regions of the pack ice exceed 0 70 during may declines rapidly during june and reaches a seasonal low of between 0 40 and 0 50 by late july for august regional albedos which also include areas of open water beyond the southern pack ice limit are up to 0 16 lower than the corresponding values for pack ice areas only

trends in large deformation analysis of landslide mass movements with particular emphasis on the material point method traditional geotechnical analyses for landslides involve failure prediction i e onset of failure and the design of structures that can safely withstand the applied loads the analyses provide limited information on the post failure behaviour modern numerical methods are able to simulate large mass movements and there is an opportunity to utilise such methods to evaluate the risks of catastrophic damage if a landslide occurs in this paper various large deformation analysis methods are introduced and their applicability for solving landslide problems is discussed since catastrophic landslides often involve seepage forces consideration of the coupled behaviour of soil and pore fluid is essential two approaches to model soil pore fluid coupling in large deformation analysis using the material point method mpm are introduced an example simulation is presented for each approach one on a model levee failure and the other on a natural cut slope failure the selborne experiment conducted by cooper and co workers in 1998 in the levee failure case mpm simulation was able to capture a complex failure mechanism including the development of successive shear bands the simulation was also able to predict excess pore pressure generation during the failure propagation and the subsequent consolidation stage the simulations demonstrated the importance of the dilation characteristics of soil as well as changes in geometry for the post failure behaviour in the selborne case mpm was able to simulate the progressive failure of brittle overconsolidated clay the evolution of shear stresses along the failure surface was also captured by the mpm the changes in the pore pressure and the actual shape of the failure surface were simulated by the mpm the importance of accurately modelling the shear band within the mpm framework is highlighted

determination of the age distribution of sea ice from lagrangian observations of ice motion a procedure for monitoring the local age distribution of the arctic sea ice cover is presented the age distribution specifies the area covered by ice in different age classes in our approach a regular array of grid points is defined initially on the first image of a long time series and an ice tracker finds the positions of those points in all subsequent images of the series these lagrangian points mark the corners of a set of cells that move and deform with the ice cover the area of each cell changes with each new image or time step a positive change indicates that ice in a new age class was formed in the cell a negative change is assumed to have ridged the youngest ice in the cell reducing its area the ice in each cell ages as it progresses through the time series the area of multiyear ice in each cell is computed using an ice classification algorithm any area that is not accounted for by the young ice or multiyear ice is assigned to a category of older first year ice we thus have a fine age resolution in the young end of the age distribution and coarse resolution for older ice the age distribution of the young ice can be converted to a thickness distribution using a simple empirical relation between accumulated freezing degree days and ice thickness or using a more complicated thermodynamic model we describe a general scheme for implementing this procedure for the arctic ocean from fall freeze up until the onset of melt in the spring the concept is illustrated with a time series of five ers 1 sar images spanning a period of 12 days such a scheme could be implemented with radarsat sar imagery to provide basin wide ice age and thickness information

disposition of solar radiation in sea ice and the upper ocean a one dimensional sea ice model with an ice thickness distribution is presented to examine the disposition of the incoming surface shortwave radiation within the sea ice and the upper ocean the sea ice model consists of 15 different ice thickness categories and an open water leads category ice growth melting on horizontal and vertical surfaces meltwater pond growth and drainage and snow accumulation evolve independently for each of the ice categories leads melt ponds and thinner ice categories are of particular interest as these features account for nearly all of the solar energy that is transmitted into the upper ocean beneath the ice pack also examined is the surface reflection and absorption internal ice absorption and lateral melting for ponded and pond free ice area averaged results show that 69 of the total annual solar energy is reflected 15 is absorbed by the snow cover 12 is absorbed by the ice and 4 is transmitted to the ocean mixed layer through thin ice and leads

strong near surface seismic anisotropy of taiwan revealed by coda interferometry abstract we report the near surface v p shear wave velocity v s v p v s ratio poisson s ratio and v s anisotropy of taiwan by applying seismic coda interferometry to 34 borehole surface station pairs we find clear characteristic cos 2 dependence of v s in all the determinations and about half of the amplitudes of anisotropy are larger than 10 with the largest amplitudes up to 34 the patterns of anisotropy fall into two categories opa orogeny parallel anisotropy and saa stress aligned anisotropy both types of anisotropy fit well the local geological fabrics and or the ambient stress and show strong correlation with the poisson s ratios at the borehole sites with these new findings and reported tomographic results we infer that the saa are likely confined to the uppermost portion of the crust in particular to the fluid saturated late quaternary deposits the strong near surface anisotropy also implies that delay times contributed by the shallow crust might have been underestimated in studies of shear wave splitting measurements using the direct arrivals of earthquake waves

impact of melt ponds on arctic sea ice simulations from 1990 to 2007 1 the extent and thickness of the arctic sea ice cover has decreased dramatically in the past few decades with minima in sea ice extent in september 2007 and 2011 and climate models did not predict this decline one of the processes poorly represented in sea ice models is the formation and evolution of melt ponds melt ponds form on arctic sea ice during the melting season and their presence affects the heat and mass balances of the ice cover mainly by decreasing the value of the surface albedo by up to 20 we have developed a melt pond model suitable for forecasting the presence of melt ponds based on sea ice conditions this model has been incorporated into the los alamos cice sea ice model the sea ice component of several ipcc climate models simulations for the period 1990 to 2007 are in good agreement with observed ice concentration in comparison to simulations without ponds the september ice volume is nearly 40 lower sensitivity studies within the range of uncertainty reveal that of the parameters pertinent to the present melt pond parameterization and for our prescribed atmospheric and oceanic forcing variations of optical properties and the amount of snowfall have the strongest impact on sea ice extent and volume we conclude that melt ponds will play an increasingly important role in the melting of the arctic ice cover and their incorporation in the sea ice component of global circulation models is essential for accurate future sea ice forecasts

determination of mechanical properties of flysch using laboratory methods abstract the paper deals with the determination of the mechanical properties of heterogeneous rocks in the laboratory and proposes a methodology for predicting the rock mass strength of flysch formations consisting of siltstone sandstone alternations in different proportions in order to simulate such formations composite specimens comprising superimposed disks of intact sandstone and siltstone material with different thickness ratios were prepared wave velocity p and s uniaxial and triaxial compressive strength and young s modulus of the composite samples were determined in the laboratory according to the laboratory results the uniaxial compressive strength and young s modulus decrease with the increase of the siltstone percentage in the specimens and yield the strength of siltstone when the siltstone percentage in the rock is equal to 37 additionally the triaxial compression tests on composite samples revealed a significant decrease of the m i parameter for a siltstone percentage of only 17 a comparison is made between the results of the present study with similar laboratory and empirical references from literature finally it was possible to suggest how the relation between uniaxial compressive strength ci and siltstone percentage sl may differ according to the ratio of the compressive strength of the two main rocks weak and strong which comprise the heterogeneous rock

sensitivity of sea ice to physical parameterizations in the giss global climate model 1 the giss coupled model is used to investigate the sensitivity of sea ice to each of the following parameterizations 1 two sea ice dynamics cf cavitating fluid vp viscous plastic 2 the specification of oceanic isopycnal mixing coefficients in the gent and mcwillams isopyncal mixing gm and 3 the wajsowicz viscosity diffusion wv the large scale sea ice properties are highly sensitive to sea ice dynamics with the inclusion of resistance to shear stress vp captures the major observed sea ice drift features and improves the simulations of sea ice concentrations thickness and export through fram strait relative to cf gm significantly improves the simulation of vertical temperature distributions in the southern ocean although it leads to a dramatic reduction of antarctic sea ice cover the reduced oceanic isopycnal mixing coefficients lead to arctic sea ice that tends to be less and thinner in almost the entire arctic except in the north pacific and labrador sea while antarctic sea ice that extends more equatorward throughout the circumpolar regions the responses of sea ice to wv show an enlargement and thickening of sea ice in the arctic within the ice packs around the antarctic and a reduction and thinning of sea ice in the northern weddell and ross seas on the basis of these experiments two composite experiments with the best parameterizations are investigated the atmospheric responses associated with sea ice changes are discussed while improvements are seen there are still many unrealistic aspects that will require further improvements to sea ice and ocean components

sea ice thickness distribution in the greenland sea and eurasian basin may 1987 upward sonar data from a 3400 km track in the greenland sea and the eurasian basin of the arctic ocean obtained by a british submarine in may 1987 have been statistically analyzed mean ice thicknesses in the greenland sea show significant melting with downstream distance at an average rate of 0 38 m per degree of latitude equivalent to about 2140 km3 yr 1 of freshwater input between 80 n and 75 n in the region north of fram strait between 82 n and 80 n there is remarkable consistency between mean ice drafts in 1987 and in three previous cruises 1976 1979 1985 while between greenland and the north pole there was a significant thinning in 1987 relative to 1976 in fram strait the mean ice draft shows evidence of thinning within the region of influence of a semipermanent eddy ice draft distributions show that the probability density function of deformed ice follows a negative exponential distribution and that the change of shape of the distribution with downstream distance in the greenland sea is due to preferential melting of thicker ice pressure ridge draft distributions also fit a negative exponential while their spacings fit a lognormal distribution lead width distribution follows a power law with an exponent of 1 45 for narrow leads and 2 50 for wider leads if leads are defined as having a 1 m maximum draft 1 67 and 2 76 for a 0 5 m maximum draft lead spacings follow a negative exponential distribution for moderate spacings 400 1500 m but with an excess of lead pairs at small and very large spacings

modeling the thermodynamics of a sea ice thickness distribution 1 sensitivity to ice thickness resolution a one dimensional ice thickness distribution model is presented to determine the minimum number of ice thicknesses necessary to resolve the area averaged annual cycles of ice thickness and turbulent fluxes the baseline case includes 40 ice thickness categories ice thickness and area meltwater ponds ice salinity and age snow cover and surface albedo evolve independently for each ice category a ridging and ice export parameterization and a coupled one dimensional ocean mixed layer model are also included sensitivity studies indicate that 16 ice thickness categories can accurately resolve the baseline annual cycles of area averaged ice thickness and the summertime turbulent fluxes in this model provided that one third of the thickness categories represent ice thinner than 0 8 m resolving the distribution of ice in this thickness range is important in simulating the area averaged ice characteristics wintertime values of the turbulent fluxes differ from the baseline by up to 1 w m 2 for fewer than 40 ice thickness categories the large difference in turbulent fluxes between open water and ice thicker than 1 6 m makes the area averaged value sensitive to the number of ice thickness categories since this number can affect the categories that are merged the categories that melt completely ice that is ridged and the resolution of the ice thickness distribution this makes an accurate simulation of the baseline wintertime turbulent fluxes difficult model simulations with fewer than 40 categories provide a reasonable estimate of the baseline response to a surface longwave heat flux perturbation of greater than 5 w m 2 the annually area averaged ice thickness is within 10 cm the model response to a heat flux perturbation of less than 5 w m 2 is similar for a wide range of ice thickness categories since the thickness distribution of ice thinner than 1 m is not affected

the alaskan arctic frontal zone forcing by orography coastal contrast and the boreal forest abstract experiments have been conducted with a regional climate model to indicate the conditions required to generate preferred regions of frontal activity in the alaskan region several objective methods of frontal identification were first investigated it was found that the vertical component of relative vorticity a thermal front parameter t850 n where t850 is the 850 hpa temperature and n is a unit vector in the direction of the 850 hpa temperature gradient and a parameter derived from the q vector as a measure of vertical motionwere useful in combination to determine the occurrence of fronts the preferred locations for frontal activity were located to the southern side of the eastern brooks range and over the alaska range these diagnostics were then used to characterize frontal frequency in a series of experiments removing topographic and vegetation contrasts it was found that the removal of the treeline contrast and its associated heating gradient had a small effect on frontal frequ

observation of autumn freeze up in the beaufort and chukchi seas using the ers 1 synthetic aperture radar we present observations of the transition in sea ice backscattering signatures from late summer into early winter in the beaufort and chukchi seas during 1991 and 1992 using data from the ers 1 synthetic aperture radar sar we employ both analyzed surface temperature fields and direct observations of near surface temperature from drifting buoys consistent with previous surface based observations backscattering from sea ice surviving at the end of summer increases strongly and rapidly when temperatures fall below freezing for the final time in the autumn apparently because of increased volume scattering from bubbles in the upper part of the ice areally averaged backscattering sometimes overshoots typical winter multiyear ice values by 1 2 db before settling back over a period of approximately a week the backscattering temperature link forms a sufficient basis for an algorithm to estimate retrospectively from time series of sar images the date of freeze up defined here to be the date on which all liquid water in the bubbly upper layer of surviving sea ice freezes and remains frozen for the duration of the ensuing autumn and winter we present a prototype algorithm and use it to estimate freeze up dates in nine lagrangian cells in the beaufort sea during the autumn of 1992 we observe a 12 day spread in freeze up dates between latitudes of approximately 73 n and 82 n with dates in the northernmost cells of august 29 30 and those in the southernmost cells of september 7 two cells at latitudes of 75 n 77 n appear to freeze up earlier than cells further north but present uncertainties limit the significance of this observation

reflections from a randomly grooved interface ultrasonic modelling and finite diff erence calculation1 this study utilizes ultrasonic water tank modelling to examine the complexities which can result when seismic energy is diffracted by even a simple 3d interface structure ultrasonic laboratory modelling is carried out in our in house water tank using an aluminum block to simulate very simple ocean bottom topography the topography consists of parallel depressions which simulate valleys running parallel to a mid ocean spreading ridge this study shows that the phase and amplitude of primary ocean bottom reflections can vary strongly with the azimuth of propagation the trailing energy coda also varies dramatically as a function of propagation direction showing the importance of developing a seismic model which includes the full 3d azimuthal distribution of interface structure

application of seismic interferometry to extract p and s wave propagation and observation of shear wave splitting from noise data at cold lake alberta canada we extract downward propagating p and s waves from industrial noise generated by human and or machine activity at the surface propagating down a borehole at cold lake alberta canada and measure shear wave splitting from these data the continuous seismic data are recorded at eight sensors along a downhole well during steam injection into a 420 470 m deep oil reservoir we crosscorrelate the waveforms observed at the top sensor and other sensors to extract estimates of the direct p and s wave components of the green s function that account for wave propagation between sensors fast high frequency and slow low frequency signals propagating vertically from the surface to the bottom are found for the vertical and horizontal components of the wave motion which are identified with p and s waves respectively the fastest s wave polarized in the east northeast west southwest direction is about 1 9 faster than the slowest s wave polarized in the northwest southeast direction the direction of polarization

seismic evidence for widespread western us deep crustal deformation caused by extension morgan moschetti and colleagues use ambient noise tomography data from the western united states to show that strong radial seismic anisotropy exists in the deep crust confined mainly to the geological provinces that have undergone significant extension during the cenozoic era since about 65 million years ago the coincidence of crustal radial anisotropy with these extensional provinces supports the hypothesis that the deep crust within these regions has undergone widespread and relatively uniform strain in response to crustal thinning and extension here a method of seismic wave imaging known as ambient noise tomography is used to generate high resolution images of seismic wave speeds in the crust and uppermost mantle the observations reveal strong and uniform anisotropy where waves travel through rock at different speeds depending on direction in the deep crust in areas of the western united states that have undergone significant extension during the past 65 million years laboratory experiments have established that many of the materials comprising the earth are strongly anisotropic in terms of seismic wave speeds1 observations of azimuthal2 3 and radial4 5 anisotropy in the upper mantle are attributed to the lattice preferred orientation of olivine caused by the shear strains associated with deformation and provide some of the most direct evidence for deformation and flow within the earth s interior although observations of crustal radial anisotropy would improve our understanding of crustal deformation and flow patterns resulting from tectonic processes large scale observations have been limited to regions of particularly thick crust6 here we show that observations from ambient noise tomography in the western united states reveal strong deep middle to lower crustal radial anisotropy that is confined mainly to the geological provinces that have undergone significant extension during the cenozoic era since 65 myr ago 7 8 the coincidence of crustal radial anisotropy with the extensional provinces of the western united states suggests that the radial anisotropy results from the lattice preferred orientation of anisotropic crustal minerals caused by extensional deformation these observations also provide support for the hypothesis that the deep crust within these regions has undergone widespread and relatively uniform strain in response to crustal thinning and extension9 10 11

scale of experiment and rock physics trends because rock is heterogeneous at all scales it is often invalid to assign a single porosity permeability resistivity or velocity to a volume in the subsurface well data demonstrate that these properties can vary appreciably between two points just a foot apart the same happens at the pore scale consider for example a ct scan of a 1 3 mm berea sandstone cube figure 1 the porosity of this sample as calculated by counting the blue pore space pixels is 0 164

heterogeneity and anisotropy of the lithosphere of se tibet from surface wave array tomography 1 understanding the geotectonic evolution of the southeastern tibetan plateau requires knowledge about the structure of the lithosphere using data from 77 broadband stations in sw china we invert rayleigh wave phase velocity dispersion curves from ambient noise interferometry t 1 0 40 s and teleseismic surface waves t 2 0 150 s for 3 d heterogeneity and azimuthal anisotropy in the lithosphere to 150 km depth our surface wave array tomography reveals 1 deep crustal zones of anomalously low shear wave speed and 2 substantial variations with depth of the pattern of azimuthal anisotropy upper crustal azimuthal anisotropy reveals a curvilinear pattern around the eastern himalayan syntaxis with fast directions generally parallel to the main strike slip faults the mantle pattern of azimuthal anisotropy is different from that in the crust and varies from north to south the tomographically inferred 3 d variation in azimuthal anisotropy helps constrain the source region of shear wave splitting south of 26 n off the high plateau most of the observed splitting can be accounted for by upper mantle anisotropy but for stations on the plateau proper with thick crust crustal anisotropy cannot be ignored on long wavelengths the pattern of azimuthal anisotropy in the crust differs from that in the mantle this is easiest explained if deformation varies with depth the deep crustal zones of low shear wave speed and presumably mechanical strength may represent loci of ductile deformation but their lateral variation suggests that in se tibet localized crustal channel flow and motion along the major strike slip faults are both important

a diatom based sea ice reconstruction for the vaigat strait disko bugt west greenland over the last 5000 yr abstract a diatom based sea ice concentration sic transfer function was developed by using 72 surface samples from west of greenland and around iceland and validated against associated modern sic canonical correspondence analysis on surface sediment diatoms and monthly average of sic indicated that april sic is the most important environmental factor controlling the distribution of diatoms in the area justifying the development of a diatom based sic transfer function the agreement between reconstructed sic based on diatoms from west greenland and the satellite and modelled sea ice data during the last 75 yr suggests that the diatom based sic reconstruction is reliable for studying the palaeoceanography off west greenland relatively warm conditions with a strong influence of the irminger current ic were indicated for the early part of the record 5000 3860 cal yr bp corresponding in time to the latest part of the holocene thermal maximum between 3860 and 1510 cal yr bp april sic oscillated around the mean value 55 and during the time interval 1510 1120 cal yr bp and after 650 cal yr bp was above the mean indicating more extensive sea ice cover in disko bugt agreement between reconstructed april sic and changes in the diatom species suggests that the sea ice condition in disko bugt was strongly influenced by variations in the relative strength of two components of the west greenland current i e the cold east greenland current and the relatively warm ic further analysis of the reconstructed sic record suggests that solar radiation may be an important forcing mechanism behind the historic sea ice changes

unprecedented low twentieth century winter sea ice extent in the western nordic seas since a d 1200 we reconstructed decadal to centennial vari ability of maximum sea ice extent in the western nordic seas for a d 1200 1997 using a combination of a regional tree ring chronology from the timberline area in fennoscandia and d 18 o from the lomonosovfonna ice core in svalbard the reconstruction successfully explained 59 of the variance in sea ice extent based on the calibration period 1864 1997 the significance of the reconstruction statistics reduction of error coefficient of efficiency is computed for the first time against a realistic noise background the twentieth century sustained the lowest sea ice extent values since a d 1200 low sea ice extent also occurred before mid seventeenth and mid eighteenth centuries early fifteenth and late thirteenth centuries but these periods were in no case as persistent as in the twentieth century largest sea ice extent values occurred from the seventeenth to the nineteenth centuries during the little ice age lia with relatively smaller sea ice covered area during the sixteenth century mod erate sea ice extent occurred during thirteenth fifteenth centuries reconstructed sea ice extent variability is dominated by decadal oscillations frequently associated with decadal components of the north atlantic oscilla tion arctic oscillation nao ao and multi decadal lower frequency oscillations operating at 50 120 year sea ice extent and nao showed a non stationary rela tionship during the observational period the present low sea ice extent is unique over the last 800 years and results from a decline started in late nineteenth century after the lia

physical dielectric and c band microwave scattering properties of first year sea ice during advanced melt 1 this paper investigates the influence of solar heating and intermittent cloud cover on the physical and dielectric properties of naturally snow free warm 2 first year sea ice fyi in the southeastern margin of the beaufort sea during advanced melt a simple three layer physical model describing the surface is introduced and copolarized c band microwave signatures are simulated using a multilayer scattering model forced with four sets of measured surface parameters modeled backscatter signatures are compared to coincident surface based c band scatterometer signatures in order to elucidate the signature controlling properties of the ice results show that 50 mhz impedance probe dielectric measurements of desalinated upper ice layers exhibit statistically significant diurnal variations due to the link between solar forcing and the availability of free water in brine free upper ice layers enhanced downwelling longwave radiation to the surface from low level stratus clouds is positively linearly associated r 0 709 with volumetric moisture mv detected in upper ice layers model results show that desalinated upper ice layers contribute volume scattering from smooth snow free fyi under the observed surface mv range sustained cloud free periods result in the formation of a 0 5 2 5 cm granular surface layer composed of 5 2 mm ice grains which enhances backscatter under relatively dry conditions sensitivity analyses show that layer thickness plays a significant role in scattering due to the increased number density of inclusions which act as discrete scatterers and sufficient energy may penetrate to and scatter from the saline columnar ice layer under relatively dry conditions only mv 2

surface wave tomography from microseisms in southern california received 5 april 2005 revised 23 may 2005 accepted 9 june 2005 published 26 july 2005 1 since it has already been demonstrated that point topoint seismic propagation green functions can be extracted from seismic noise it should be possible to image earth structure using the ambient noise field seismic noise data from 148 broadband seismic stations in southern california were used to extract the surface wave arrival times between all station pairs in the network the seismic data were then used in a simple but densely sampled tomographic procedure to estimate the surface wave velocity structure within the frequency range of 0 1 0 2 hz for a region in southern california the result compares favorably with previous estimates obtained using more conventional and elaborate inversion procedures this demonstrates that coherent noise field between station pairs can be used for seismic imaging purposes citation sabra k g p gerstoft p roux w a kuperman and m c fehler 2005 surface wave tomography from microseisms in southern california geophys res lett 32 l14311 doi 10 1029 2005gl023155

arctic sea ice regional albedo variability and trends 1982 1998 1 whole summer and monthly sea ice regional albedo averages for june july and august from 1982 to 1998 have been processed from advanced very high resolution radiometer data time series for albedo sea ice concentration sea ice extent and surface air temperature have been calculated for the sea ice cover for the northern hemisphere as a whole and for six subregions the arctic ocean the kara and barents seas the greenland sea the labrador sea hudson bay and the canadian archipelago the slope of the summer albedo trend for the northern hemisphere is 0 0007 0 0008 year the largest monthly slope 0 0016 0 0011 year is found for june and the lowest slope 0 0004 0 0014 year is found for august among the subregions the greenland sea has the steepest negative summer trend of 0 0038 0 0012 year during the period while for the arctic ocean the albedo trend is near zero the calculated trends for the summer sea ice concentration and extent for the northern hemisphere are also negative with a slopes of 0 093 0 069 year and 42 300 15 200 km2 yr respectively in general the albedo in the central arctic is between 0 5 and 0 7 the highest albedo values are mainly found in the arctic ocean north of greenland the lowest albedo 0 2 0 3 occurs in the fringe area of the arctic ocean e g on the coasts of alaska and siberia low albedo values also exist on the east coast of greenland and in hudson bay

toward the modeling of enhanced basal melting in ridge keels observations from sonar data have suggested enhanced melting of thick ridged ice relative to level ice there are several mechanisms that may account for this intensified melting in this paper we examine the effects of two dimensional 2 d heat conduction and enlarged basal surface area due to the sloping sides of the keel on heat conduction and melt rates the cross section of the 2 d ridge is taken to be an isosceles triangle with a rounded crest this is roughly the shape observed and allows a convenient numerical representation in polar coordinates for comparison ridges of similar shape are also represented as a collection of 1 d columns of varying thickness similar to what is implicit in typical ice thickness distribution models the results show that 2 d ridges inhibit the heat conduction compared to 1 d ridges owing to the dominating effect of weaker temperature gradients the slope of the keel is the dominant factor in determining the temperature gradient a size distribution of 2 d ridges reduces heat transfer to the atmosphere by 3 w m 2 compared to a similar distribution of 1 d ridges over an annual cycle basal ablation along the keel is insignificant for 2 d ridges with small slopes whereas ridges with large slopes show ablation rates determined by the ice ocean heat flux these melt rates imply a transition from a triangular to a more rounded shape the 1 d ridge geometry is not adequate to simulate the net melting at the keel base over an annual cycle melt rates are calculated along the ridge keel and for level ice over a 40 day period for comparison with observations for 1 d ridges all ice thicker than 5 m melts more slowly than the corresponding level ice the inclusion of 2 d heat conduction increases the amount of ablation in the thicker ice relative to the 5 m ice especially for ridges with larger slopes however this increase explains only a small fraction of the enhanced basal melting seen in the observations these results suggest that other mechanisms are important in determining the mass loss from thicker ice

shear wave anisotropy in the crust around the san andreas fault near parkfield spatial and temporal analysis summary we systematically analysed shear wave splitting sws for seismic data observed at a temporary array and two permanent networks around the san andreas fault saf observatory at depth the purpose was to investigate the spatial distribution of crustal shear wave anisotropy around the saf in this segment and its temporal behaviour in relation to the occurrence of the 2004 parkfield m 6 0 earthquake the dense coverage of the networks the accurate locations of earthquakes and the high resolution velocity model provide a unique opportunity to investigate anisotropy in detail around the saf zone the results show that the primary fast polarization directions pds in the region including the saf zone and the northeast side of the fault are nw se nearly parallel or subparallel to the saf strike some measurements on the southwest side of the fault are oriented to the nne ssw direction approximately parallel to the direction of local maximum horizontal compressive stress there are also a few areas in which the observed fast pds do not fit into this general pattern the strong spatial variations in both the measured fast pds and time delays reveal the extreme complexity of shear wave anisotropy in the area the top 2 3 km of the crust appears to contribute the most to the observed time delays however substantial anisotropy could extend to as deep as 7 8 km in the region the average time delay in the region is about 0 06 s we also analysed temporal patterns of sws parameters in a nearly 4 yr period around the 2004 parkfield main shock based on similar events the results show that there are no appreciable precursory coseismic or post seismic temporal changes of sws in a region near the rupture of an m 6 0 earthquake about 15 km away from its epicentre

idealized study of a 2 d coupled sea ice atmosphere model during warm air advection we present a two dimensional coupled mesoscale atmosphere sea ice model and apply it to simulate the air ice interaction during warm air advection the model was run into a steady state under various conditions with respect to the season cloud cover and wind speed the spatial and temporal evolution of the thermodynamics of the ice show and the atmospheric boundary layer abl were investigated the development of the stably stratified abl downwind of the ice edge depended above all on the wind speed and cloud cover if the turbulent heat flux from air to show was large enough to compensate the radiative cooling of the surface a downward conductive heat flux was generated in the upper ice and snow layers the stronger was the surface heating strong wind overcast skies and the shorter its duration on a scale down to a few hours the wider was the region where this downward flux occurred from the point of view of abl modelling the interactive coupling between air and ice was most important when the wind was strong while from the point of view of ice thermodynamic modelling the coupling was most important when the wind was weak

three dimensional compressional wavespeed model earthquake relocations and focal mechanisms for the parkfield california region we present a new three dimensional 3d compressional wavespeed v p model for the parkfield region taking advantage of the recent seismicity associated with the 2003 san simeon and 2004 parkfield earthquake sequences to provide increased model resolution compared to the work of eberhart phillips and michael 1993 epm93 taking the epm93 3d model as our starting model we invert the arrival time data from about 2100 earthquakes and 250 shots recorded on both permanent network and temporary stations in a region 130 km northeast southwest by 120 km northwest southeast we include catalog picks and cross correlation and catalog differential times in the inversion using the double difference tomography method of zhang and thurber 2003 the principal v p features reported by epm93 and michelini and mcevilly 1991 are recovered but with locally improved resolution along the san andreas fault saf and near the active source profiles we image the previously identified strong wavespeed contrast faster on the southwest side across most of the length of the saf and we also improve the image of a high v p body on the northeast side of the fault reported by epm93 this narrow body is at about 5 to 12 km depth and extends approximately from the locked section of the saf to the town of parkfield the footwall of the thrust fault responsible for the 1983 coalinga earthquake is imaged as a northeast dipping high wavespeed body in between relatively low wavespeeds 5 km sec extend to as much as 10 km depth we use this model to derive absolute locations for about 16 000 earthquakes from 1966 to 2005 and high precision double difference locations for 9 000 earthquakes from 1984 to 2005 and also to determine focal mechanisms for 446 earthquakes these earthquake locations and mechanisms show that the seismogenic fault is a simple planar structure the aftershock sequence of the 2004 mainshock concentrates into the same structures defined by the pre 2004 seismicity confirming earlier observations waldhauser et al 2004 that the seismicity pattern at parkfield is long lived and persists through multiple cycles of mainshocks online material 3d v p model and earthquake relocations

tracer studies of pathways and rates of meltwater transport through arctic summer sea ice 1 at the surface heat budget of the arctic ocean sheba program s field site in the northern chukchi sea snow and ice meltwater flow was found to have a strong impact on the heat and mass balance of sea ice during the summer of 1998 pathways and rates of meltwater transport were derived from tracer studies h218o 7be and release of fluorescent dyes complemented by in situ sea ice permeability measurements it was shown that the balance between meltwater supply at the surface averaging between 3 5 and 10 5 mm d 1 and ice permeability between 10 9 m2 determines the retention and pooling of meltwater which in turn controls ice albedo we found that the seasonal evolution of first year and multiyear ice permeability and surface morphology determine four distinct stages of melt at the start of the ablation season stage 1 ponding is widespread and lateral melt flow dominates several tens of cubic meters of meltwater per day were found to drain hundreds to thousands of square meters of ice through flaws and permeable zones significant formation of underwater ice composed between 50 of meteoric water formed at these drainage sites complete removal of snow cover increase in ice permeability and reductions in hydraulic gradients driving fluid flow mark stage 2 concurrent with a reduction in pond coverage and albedo during stage 3 maximum permeabilities were measured with surface meltwater penetrating to 1 m depth in the ice and convective overturning and desalination found to dominate the lower layers of first year and thin multiyear ice enhanced fluid flow into flaws and permeable zones was observed to promote ice floe breakup and disintegration concurrent with increases in pond salinities and 7be advective heat flows of several tens of watts per square meter were derived promoting widening of ponds and increases in pond coverage stage 4 corresponds to freeze up roughly 40 of the total surface melt was retained by the ice cover within the ice matrix as well as in surface and under ice ponds with a total net retention of 15 based on this work areas of improvement for fully prognostic simulations of ice albedo are identified calling for parameterizations of sea ice permeability and the integration of ice topography and refined ablation schemes into atmosphere ice ocean models

spatial orientation and distribution of reservoir fractures from scattered seismic energy wepresentthedetailsofanewmethodfordeterminingthereflection and scattering characteristics of seismic energy from subsurface fractured formations the method is based upon observations we have made from 3d finite difference modeling of the reflected and scattered seismic energy over discrete systems of vertical fractures regularly spaced discrete vertical fracture corridors impart a coda signature which is a ringing tail of scatteredenergy toanyseismicwaveswhicharetransmittedthrough or reflected off of them this signature varies in amplitude and coherence as a function of several parameters including 1 the difference in angle between the orientation of the fractures and the acquisition direction 2 the fracture spacing 3 the wavelength of the illuminating seismic energy and 4 the compliance or stiffness of the fractures this coda energy is most coherent when the acquisition direction is parallel to the strike of thefractures ithasthelargestamplitudewhentheseismicwavelengths are tuned to the fracture spacing and when the fractures have low stiffness our method uses surface seismic reflection tracestoderiveatransferfunctionthatquantifiesthechangeinan apparent source wavelet before and after propagating through a fracturedinterval thetransferfunctionforanintervalwithnoor low amounts of scattering will be more spikelike and temporally compact the transfer function for an interval with high scattering will ring and be less temporally compact when a 3d survey is acquired with a full range of azimuths the variation in the derived transfer functions allows us to identify subsurface areas with high fracturing and to determine the strike of those fractures wecalibratedthemethodwithmodeldataandthenapplied ittotheemiliofieldwithafracturedreservoir themethodyielded results which agree with known field measurements and previously published fracture orientations derived from ps anisotropy

spatiotemporal variations of crustal anisotropy from similar events in aftershocks of the 1999 m7 4 izmit and m7 1 duzce turkey earthquake sequences summary we analyse spatiotemporal variations of crustal anisotropy along the karadere duzce branch of the north anatolian fault from similar earthquakes in the aftershock regions of the 1999 mw7 4izmit and mw7 1 duzce earthquakes the similar earthquake clusters are identified by performing cross correlation on waveforms generated by 18 000 earthquakes depending on the applied similarity criterion about 4 60 per cent of the events belong to similar event clusters splitting parameters averaged within each cluster show significant variations for slightly different ray paths indicating strong spatial variations of crustal anisotropy in this area we also find clear changes in the spatiotemporal seismicity patterns following the duzce main shock large apparent co seismic changes up to 30 per cent of shear wave splitting delay times are observed across the time of the duzce main shock at stations near the epicentral region however the changes can be mostly explained by the spatial variations of ray paths due to the changing seismicity rather than changes in the properties of the anisotropic medium splitting parameters measured within similar earthquake clusters indicate at most 2 per cent changes in delay times associated with the occurrence of the duzce main shock the results do not show systematic precursory changes before the duzce main shock

spectral albedos of sea ice and incident solar irradiance in the southern beaufort sea spectral albedos and incident spectral irradiances have been measured over the wavelength range 400 to 2400 nm on the sea ice near the naval arctic research laboratory narl at pt barrow alaska the observation interval extended from mid may when the ice was still relatively cold until mid june when summer melting was fully established the temporal dependence of albedo for the available surface types was obtained over this time interval showing a general decrease from snow and snow covered ice to blue ice and melt ponds data were also obtained for glacier ice on the athabasca glacier for melting lake ice and for certain other nonice surfaces in the vicinity of narl snow and ice albedos are characteristically highest at visible wavelengths decreasing strongly in the infrared because of the increase in absorption by ice and water local maxima in the spectra correspond to minima in the ice and water absorption variations in albedo are due primarily to differences in the vapor bubble density crystal structure and free water content of the upper layers of the ice incident spectral shortwave radiation was measured as a function of cloudiness and the optical thickness of arctic clouds is significantly less than the thickest clouds at lower latitudes the decrease of the infrared component relatiave to the visible portion of the irradiance with increasing cloud cover is determined this can give rise to an increase in wavelength integrated albedos of as much as 15 using the present data a graphical method is outlined by which visible near infrared satellite imagery can be used to distinguish among melt ponds open leads and other spring and summer sea ice surface types

shear wave anisotropy from cross correlation of seismic noise in the parkfield pilot hole summary we use cross correlation of seismic noise recorded at stations in the san andreas fault observatory at depth safod pilot hole to extract p and s waves and measure s wave anisotropy on the horizontal components the data are recorded at seven three component stations at depths from 1857 to 2097 m in the pilot hole in late september and early 2004 october drilling noise underneath the stations generated propagating waves which were absent in the rest of october estimates of the p and s wave velocities from the cross correlations on the vertical and horizontal components respectively are consistent with velocity measurements taken directly in the borehole we observe polarization of the s wave with a fast polarization direction of 120 130 that is 4 per cent faster than the slow direction cross correlation of the seismic noise can accurately determine s wave anisotropy

spatial variation of shear wave splitting across an active fault and its implication for stress accumulation mechanism of inland earthquakes the atotsugawa fault case 1 we analyzed shear wave splitting of small earthquakes around the atotsugawa fault central japan to infer a spatial variation in the direction of maximum horizontal compression shmax while the angle between the shmax direction and fault strike ranges approximately from 55 to 80 at the stations 2 to 8 km from the fault it approaches 45 at the stations within 1 km from the fault the present result indicates the local stress accumulation due to the localized flow or slip along the deep extension of the fault the finite element modeling of the stress field around the fault suggests that the present existing stress field can be explained by the superposition of the stress field associated with regional deformation and the stable slip along the deep extension of the fault

arctic sea ice albedo derived from rgps based ice thickness estimates the radarsat geophysical processor system rgps uses sequential synthetic aperture radar images of arctic sea ice taken every 3 days to track a large set of lagrangian points over the win ter and spring seasons the points are the vertices of cells which are initially square and 10 km on a side and the changes in the area of these cells due to opening and closing of the ice are used to esti mate the fractional area of a set of first year ice categories the thickness of each category is esti mated by the rgps from an empirical relationship between ice thickness and the freezing degree days since the formation of the ice with a parameterization of the albedo based on the ice thickness the albedo may be estimated from the first year ice distribution we compute the albedo for the first spring processed by the rgps the early spring of 1997 the data include most of the beaufort and chukchi seas we find that the mean albedo is 0 79 with a standard deviation of 0 04 with lower albedo values near the edge of the perennial ice zone the biggest source of error is likely the assumed rate of snow accumulation on new ice

melting of small arctic ice caps observed from ers scatterometer time series 1 time series of active microwave backscatter data from the ers wind scatterometers are used to demonstrate 1 the timing of melt onset can be observed over small ice caps as well as the major ice sheets and multi year sea ice and 2 temporally integrated backscatter reduction r is strongly correlated with total annual positive degree days pdd as measured at four automated weather stations on the surface of the greenland ice sheet the latter is particularly interesting because unlike melt onset r is a measure of melt processes integrated over an entire ablation season both methods work owing to the well known sharp decrease in radar backscatter triggered by the appearance of liquid water in a glacier snowpack melt onset and r are determined for 14 small arctic ice caps from 1992 2000 interannual and regional variability in the timing of melt onset are comparable averaging 33 9 and 38 13 days respectively regional variability in r exceeds interannual variability averaging 906 164 and 309 130 db d respectively the brevity of the derived nine year records limits their statistical testing for trend however their qualitative interpretation suggests that the timing of melt onset is more variable for arctic ice caps than for sea ice and the intensity of summer surface melting increased by about 20 in the 1990s

modeling the thermodynamics of a sea ice thickness distribution 2 sea ice ocean interactions in this paper we examine the coupling of an ice thickness distribution model with an ocean mixed layer model the annual cycle of the modeled mixed layer temperature salinity and depth are compared to observations from the drifting ice stations of the arctic ice dynamics joint experiment aidjex the role of the ice thickness distribution in determining the ice ocean coupling is examined we find that the ice thickness distribution is important for the exchange of heat salt and fresh water between the ice and the ocean especially with regard to the effects of thin first year ice several different parameterizations of the ice ocean turbulent heat exchange are compared the results indicate that the storage of heat in the ocean mixed layer is an important physical process for determining the annual average ice thickness double diffusion and the stabilizing effects of meltwater also impact the exchange of heat between the ocean and ice cover questions remain as to the relative importance of these processes and their accurate parameterization in ice ocean coupled models

experimental investigation of mechanical properties of bedded salt rock abstract because of salt cavern utilization for liquid gas and solid waste storage salt rock mechanical properties are needed for assessments of facility stability and safety bedded salt deposits are widespread and used as much or more than diapiric salt bodies as storage facility hosts but experimental data on the mechanical properties of bedded salt rock with impurities are far less common than data available on relatively pure diapiric salt rocks through laboratory uniaxial and triaxial compression experiments on rock salt halite interlayers anhydrite and bedded composite specimens anhydrite halite and mudstone halite differences in mechanical properties of the various lithologies are explored in the composite specimens the weakest or the most deformable component governs the behavior also the properties of bedded composite lithology specimens tend to be in between the property ranges of the pure lithologies the elastic modulus of the bedded salt rock increases from 5 3 to 24 1 gpa with an increase in the confining stress from 0 to 15 mpa with some evidence of sample damage the ductile transition for halite at the strain rates used is at about 3 10 mpa with increasing 3 the anhydrite halite composite lithology deformation showed strain hardening and a strong trend to ductile behavior as the halite bands tended to dominate the behavior strain incompatibility effects exist along interfaces between creeping and non creeping phases in anhydrite halite composite lithologies mudstone halite rocks tended to be extremely weak compared with all other specimens

the potential of using landsat 7 data for the classification of sea ice surface conditions during summer during spring and summer the surface of the arctic sea ice cover undergoes rapid changes that greatly affect the surface albedo and significantly impact the further decay of the sea ice these changes are primarily the development of a wet snow cover and the development of melt ponds as melt pond diameters generally do not exceed a couple of meters the spatial resolutions of sensors like avhrr and modis are too coarse for their identification landsat 7 on the other hand has a spatial resolution of 30 m 15 m for the pan chromatic band the different wavelengths bands from blue to near infrared offer the potential to distinguish among different surface conditions landsat 7 data for the baffin bay region for june 2000 have been analyzed the analysis shows that different surface conditions such as wet snow and meltponded areas have different signatures in the individual landsat bands consistent with in situ albedo measurements melt ponds show up as blueish whereas dry and wet ice have a white to gray appearance in the landsat true color image these spectral differences enable the distinction of melt ponds the melt pond fraction for the scene studied in this paper was 37