ice mass loss in greenland the gulf of alaska and the canadian archipelago seasonal cycles and decadal trends over the past several decades mountain glaciers and ice caps have been significant contributors to sea level rise here we estimate the ice mass changes in the canadian archipelago the gulf of alaska and greenland since 2003 by analyzing time varying gravimetry data from the gravity recovery and climate experiment prior to 2013 interannual ice mass variability in the gulf of alaska and in regions around greenland remains within the average estimated over the whole data span beginning in summer 2013 ice mass in regions around greenland departs positively from its long term trend over greenland this anomaly reached almost 500 gt through the end of 2014 overall long term ice mass loss from greenland and the canadian archipelago continues to accelerate while losses around the gulf of alaska region continue but remain steady with no significant acceleration

resolving mass flux at high spatial and temporal resolution using grace intersatellite measurements 1 the grace mission is designed to monitor mass flux on the earth s surface at one month and high spatial resolution through the estimation of monthly gravity fields although this approach has been largely successful information at submonthly time scales can be lost or even aliased through the estimation of static monthly parameters through an analysis of the grace data residuals we show that the fundamental temporal and spatial resolution of the grace data is 10 days and 400 km we present an approach similar in concept to altimetric methods that recovers submonthly mass flux at a high spatial resolution using 4 4 blocks at 10 day intervals we estimate the mass of surplus or deficit water over a 52 60 grid centered on the amazon basin for july 2003 we demonstrate that the recovered signals are coherent and correlate well with the expected hydrological signal

localized analysis of satellite tracking data for studying time variable earth s gravity fields 1 we present a method to analyze the observations of relative distance change between two low earth orbiting satellites of the gravity recovery and climate experiment grace mission after removing the effects caused by the mean gravity field and better known temporal mass redistribution the gravitational acceleration exerted by the block mean mass within a region on the earth surface is formulated by point mass approximation and by spherical harmonic expansion in addition to the regional mass parameters the arc dependent parameters initial relative state vectors is simultaneously modeled to remove the signals not associated with the mass variation within the focus area while a certain level of approximation that is committed when locally formulating the gravitational acceleration vector for numerical integration causes model error we benefit from regionally estimating time variable mass with improved spatial and temporal resolutions in addition various temporal parameterizations depending on geographical areas and expected signals can be applied for the regional analysis in a straightforward manner and it helps to retrieve even sub daily time variable signals such as tides from many years of grace data we present the results of hydrology and ocean tide recovery in south america africa north america and antarctica from the analysis of 3 5 years of grace tracking data and compare them with the traditional global harmonic approach the algorithm development thoroughly described here will be helpful for the science community to exploit fundamental data range rate of the grace mission in addition to monthly gravity products

in situ dynamic monitoring of stress revolution with time and space under coal seam floor during longwall mining in situ dynamic monitoring was used to obtain spatial and temporal strain and stress data in the floor strata during longwall mining at the no 1604 working face in nantun coal mine china the results reveal the presence of four stress stages distributed at four sections along the mining direction weak response stage significant increase stage dramatic decrease stage and slow restoration stage three vertical structural zones are identified under the excavation floor 1 fracture zone 2 deformation zone and 3 lightly affected zone based on detailed analysis of the collected data the relationship between the maximum vertical stress increment and depth is inversely exponential whereas the relationship between the maximum horizontal stress increment and depth is linear the monitoring results are conducive to determining the maximum depth of fracture zone under the coal seam floor and width of the significant stress increase stage which are important factors in controlling groundwater inrush in operating coal mines

crustal dilatation observed by grace after the 2004 sumatra andaman earthquake we report the detection of an earthquake by a space based measurement the gravity recovery and climate experiment grace satellites observed a 15 microgalileo gravity change induced by the great december 2004 sumatra andaman earthquake coseismic deformation produces sudden changes in the gravity field by vertical displacement of earth s layered density structure and by changing the densities of the crust and mantle grace s sensitivity to the long spatial wavelength of gravity changes resulted in roughly equal contributions of vertical displacement and dilatation effects in the gravity measurements the grace observations provide evidence of crustal dilatation resulting from an undersea earthquake

grace measurements of mass variability in the earth system monthly gravity field estimates made by the twin gravity recovery and climate experiment grace satellites have a geoid height accuracy of 2 to 3 millimeters at a spatial resolution as small as 400 kilometers the annual cycle in the geoid variations up to 10 millimeters in some regions peaked predominantly in the spring and fall seasons geoid variations observed over south america that can be largely attributed to surface water and groundwater changes show a clear separation between the large amazon watershed and the smaller watersheds to the north such observations will help hydrologists to connect processes at traditional length scales tens of kilometers or less to those at regional and global scales

recent glacier mass changes in the gulf of alaska region from grace mascon solutions the mass changes of the gulf of alaska goa glaciers are computed from the gravity recovery and climate experiment grace inter satellite range rate data for the period april 2003 september 2007 through the application of unique processing techniques and a surface mass concentration mascon parameterization the mass variations in the goa glacier regions have been estimated at high temporal 10 day and spatial 2 2 arc degrees resolution the mascon solutions are directly estimated from a reduction of the grace k band inter satellite range rate data and unlike previous grace solutions for the goa glaciers do not exhibit contamination by leakage from mass change occurring outside the region of interest the mascon solutions reveal considerable temporal and spatial variation within the goa glacier region with the largest negative mass balances observed in the st elias mountains including the yakutat and glacier bay regions the most rapid losses occurred during the 2004 melt season due to record temperatures in alaska during that year the total mass balance of the goa glacier region was 84 5 gt a 1 contributing 0 23 0 01 mm a 1 to global sea level rise from april 2003 through march 2007 highlighting the large seasonal and interannual variability of the goa glaciers the rate determined over the period april 2003 march 2006 is 102 5 gt a 1 which includes the anomalously high temperatures of 2004 and does not include the large 2007 winter balance year snowfall the mascon solutions agree well with regional patterns of glacier mass loss determined from aircraft altimetry and in situ measurements

accuracy assessment of global barotropic ocean tide models the accuracy of state of the art global barotropic tide models is assessed using bottom pressure data coastal tide gauges satellite altimetry various geodetic data on antarctic ice shelves and independent tracked satellite orbit perturbations tide models under review include empirical purely hydrodynamic forward and assimilative dynamical i e constrained by observations ten dominant tidal constituents in the diurnal semidiurnal and quarter diurnal bands are considered since the last major model comparison project in 1997 models have improved markedly especially in shallow water regions and also in the deep ocean the root sum square differences between tide observations and the best models for eight major constituents are approximately 0 9 5 0 and 6 5 cm for pelagic shelf and coastal conditions respectively large intermodel discrepancies occur in high latitudes but testing in those regions is impeded by the paucity of high quality in situ tide records long wavelength components of models tested by analyzing satellite laser ranging measurements suggest that several models are comparably accurate for use in precise orbit determination but analyses of grace intersatellite ranging data show that all models are still imperfect on basin and subbasin scales especially near antarctica for the m2 constituent errors in purely hydrodynamic models are now almost comparable to the 1980 era schwiderski empirical solution indicating marked advancement in dynamical modeling assessing model accuracy using tidal currents remains problematic owing to uncertainties in in situ current meter estimates and the inability to isolate the barotropic mode velocity tests against both acoustic tomography and current meters do confirm that assimilative models perform better than purely hydrodynamic models

steric sea level variations inferred from combined topex poseidon altimetry and grace gravimetry in this study we propose to estimate the steric sea level variations over a 2 year period april 2002 through december 2003 by combining global mean sea level gmsl based on topex poseidon t p altimetry with time variable geoid averaged over the oceans as observed by the grace gravity recovery and climate experiment satellite in effect altimetry derived gmsl changes results from two contributions steric thermal plus salinity effects due to sea water density change and ocean mass change due to water exchange with atmosphere and continents on the other hand grace data over the oceans provide the ocean mass change component only the paper first discusses the corrections to apply to the grace data then the steric contribution to the gmsl is estimated using grace and t p data comparison with available thermal expansion based on in situ hydrographic data is performed

analysis of a grace global mascon solution for gulf of alaska glaciers we present a high resolution gravity recovery and climate experiment grace mascon solution for gulf of alaska goa glaciers and compare this with in situ glaciological climate and other remote sensing observations our grace solution yields a goa glacier mass balance of 65 11 gt a 1 for the period december 2003 to december 2010 with summer balances driving the interannual variability between october november 2003 and october 2009 we obtain a mass balance of 61 11 gt a 1 from grace which compares well with 65 12 gt a 1 from icesat based on hypsometric extrapolation of glacier elevation changes we find that mean summer june august air temperatures derived from both ground and lower troposphere temperature records were good predictors of grace derived summer mass balances capturing 59 and 72 of the summer balance variability respectively large mass losses during 2009 were likely due to low early melt season surface albedos measured by the moderate resolution imaging spectroradiometer modis and likely associated with the 31 march 2009 eruption of mount redoubt southwestern alaska grace data compared well with in situ measurements at wolverine glacier maritime alaska but poorly with those at gulkana glacier interior alaska we conclude that although goa mass estimates from grace are robust over the entire domain further constraints on subregional and seasonal estimates are necessary to improve fidelity to ground observations

regional surface mass anomalies from grace kbr measurements application of l curve regularization anda priori hydrological knowledge 1 we present a method of directly estimating surface mass anomalies at regional scales using satellite to satellite k band ranging kbr data from the gravity recovery and climate experiment grace twin satellite mission geopotential differences based primarily on kbr measurement are derived using a modified energy integral method with an improved method to calibrate accelerometer measurements surface mass anomalies are computed based on a downward continuation process with optimal regularization parameters estimated using the l curve criterion method we derive the covariance functions in both space and space time domains and use them as light constraints in the regional gravity estimation process in the amazon basin study region the space time covariance function has a time correlation distance of 1 27 months which is evident that observations between neighboring months are correlated and the correlation should be taken into account however most of the current grace solutions did not consider such temporal correlations in our study the artifact in the regional gravity solution is mitigated by using the covariance functions the averaged commission errors are estimated to be only 6 86 and 5 85 for the solutions based on the space covariance function scf and the space time covariance function stcf respectively our regional gravity solution in the amazon basin study region which requires no further post processing shows enhanced regional gravity signatures reduced gravity artifacts and the gravity solution agrees with nasa gsfc s grace mascon solution to about 1 cm rms in terms of water thickness change over the amazon basin study region the regional gravity solution also retains the maximum signal energy while suppressing the short wavelength errors

glacier changes in alaska can mass balance models explain grace mascon trends temperature and precipitation data from three weather stations in the st elias mountains of alaska and northwestern canada were used to drive one dimensional 1 d elevation dependent and 0 d degree day mass balance models model outputs were optimized against a 10 day resolution time series of mass variability during 2003 07 obtained from gravity recovery and climate experiment grace mass concentration mascon solutions the models explained 52 60 of the variance in the grace time series modelled mass variations matched the phase of the grace observations and all optimized model parameters were within the range of values determined from conventional mass balance and meteorological observations we describe a framework for selecting appropriate weather stations and mass balance models to represent glacier variations of large regions there is potential for extending these calibrated mass balance models forwards or backwards in time to construct mass balance time series outside of the grace measurement window

grace hydrological estimates for small basins evaluating processing approaches on the high plains aquifer usa the gravity recovery and climate experiment grace satellites provide observations of water storage variation at regional scales however when focusing on a region of interest limited spatial resolution and noise contamination can cause estimation bias and spatial leakage problems that are exacerbated as the region of interest approaches the grace resolution limit of a few hundred km reliable estimates of water storage variations in small basins require compromises between competing needs for noise suppression and spatial resolution the objective of this study was to quantitatively investigate processing methods and their impacts on bias leakage grace noise reduction and estimated total error allowing solution of the trade offs among the methods tested is a recently developed concentration algorithm called spatiospectral localization which optimizes the basin shape description taking into account limited spatial resolution this method is particularly suited to retrieval of basin scale water storage variations and is effective for small basins to increase confidence in derived methods water storage variations were calculated for both csr center for space research and grgs groupe de recherche de geodesie spatiale grace products which employ different processing strategies the processing techniques were tested on the intensively monitored high plains aquifer 450 000 km2 area where application of the appropriate optimal processing method allowed retrieval of water storage variations over a portion of the aquifer as small as 200 000 km2

time variable gravity from grace first results eleven monthly grace gravity field solutions are now available for analyses we show those fields can be used to recover monthly changes in water storage both on land and in the ocean to accuracies of 1 5 cm of water thickness when smoothed over 1000 km the amplitude of the annually varying signal can be determined to 1 0 cm results are 30 better for a 1500 km smoothing radius and 40 worse for a 750 km radius we estimate the annually varying component of water storage for three large drainage basins the mississippi the amazon and a region draining into the bay of bengal to accuracies of 1 0 1 5 cm

determination and localized analysis of intersatellite line of sight gravity difference results from the grail primary mission 1 the line of sight los gravity difference between two coorbiting spacecrafts is determined in terms of intersatellite range acceleration measurements available from the gravity recovery and interior laboratory grail the precise orbit data are crucial for retrieving gravity difference from range acceleration and aligning the los data particularly in altitude a relative orbit error of a few centimeters in position and a few tens m s in velocity is commensurate with the grail ranging instrument noise at a few gal in los gravity difference the power spectrum as well as the topography correlation and admittance is quantified by upward continuing the topographic potential forward modeling the los gravity along the spacecraft trajectory i e bouguer correction and comparing with the grail los observations based on the data analysis from the primary grail mission i found that the los gravity difference observation produced near unity correlation with topography potential out to degree 550 higher than the global estimate over the areas covered by the low altitude orbit 20 km the crustal density was estimated to be 2500 2600 kg m3 with regional variations of about 10 by minimizing the bouguer coherence of the grail data at the degree band 150 300 systematic decrease in the density estimates by 3 4 or 100 kg m3 was observed at shorter wavelengths degree band 300 500 it implies the inadequacy of a uniform density model across the entire lithosphere and suggests radial stratification of the bulk density or porosity due to spatially localized characteristic the los gravity difference data are well suited to regional analysis at the highest possible resolution

gravity field of the orientale basin from the gravity recovery and interior laboratory mission the orientale basin is the youngest and best preserved major impact structure on the moon we used the gravity recovery and interior laboratory grail spacecraft to investigate the gravitational field of orientale at 3 to 5 kilometer km horizontal resolution a volume of at least 3 4 0 2 106 km3 of crustal material was removed and redistributed during basin formation there is no preserved evidence of the transient crater that would reveal the basin s maximum volume but its diameter may now be inferred to be between 320 and 460 km the gravity field resolves distinctive structures of orientale s three rings and suggests the presence of faults associated with the outer two that penetrate to the mantle the crustal structure of orientale provides constraints on the formation of multiring basins

reconstruction of paleo wave conditions during the late pleistocene from marine terrace deposits monterey bay california the santa cruz coastal terrace fringes much of the northern monterey bay region california it consists mainly of a regressive sequence of high energy barred nearshore marine sediments deposited during the last sangamonian highstand of sea level this sequence can be sub divided into several depth dependent facies on the basis of paleo current data and vertical sequence of sedimentary structures these include a lower shoreface facies deposited in 10 16 m water depth an upper shoreface facies including both a storm dominated assemblage and a surf zone assemblage deposited in 0 10 m water depth and a foreshore facies deposited in the swash zone up to 3 5 m above high tide the magnitudes of the storm events responsible for depositing these sediments were estimated by calculating paleo wave heights using a variety of criteria e g critical threshold equations breaker depths berm heights in addition the climate and paleogeography during the deposition of these sediments were essentially the same as today allowing the use of present day wave statistics to estimate the frequency of these storm events the largest storms formed offshore flowing currents e g rip wind forced and possibly storm surge ebb currents that resulted in the deposition of approximately 30 of the sediments seaward of the surf zone however the magnitude and frequency of these events are unknown the remaining 70 of the sediment beyond the surf zone was deposited in response to smaller storm waves which were on the average at least 1 6 m high such waves presently occur no more than 15 of the time sediments deposited during fairweather conditions i e the remaining 85 of the time have a low preservation potential and are generally not preserved in this facies in contrast surf zone sediments were deposited by a variety of processes associated with waves whose maximum offshore heights were probably 2 2 m such waves presently occur up to 92 of the time sediments within the swash zone were deposited by waves up to 3 m high the largest of which presently occur approximately 2 of the time most of the sediments were deposited by storms of intermediate magnitude and frequency different facies however appear to preferentially record events of different recurrence intervals in particular surf zone sediments were deposited under relatively small storm and post storm conditions whereas sediments deposited farther offshore record increasingly larger less frequent storm events relatively rare events e g the 100 or 1000 yr events do not appear to have significantly affected sedimentation in these nearshore environments

snow load effect on the earth s rotation and gravitational field 1979 1985 a global monthly snow depth data set has been generated from the nimbus 7 satellite observations using passive microwave remote sensing techniques in this paper we analyze 7 years of data 1979 1985 to compute the snow load effects on the earth s rotation and low degree zonal gravitational field a uniform sea level decrease has been assumed in order to conserve water mass the resultant time series show dominant seasonal cycles the annual peak to peak variation in j2 is found to be 2 3 x 10 o that in j3 to be 1 1 x 10 o and believed to decrease rapidly for higher degrees the corresponding change in the length of day is 41 us the annual wobble excitation is 4 9 marc sec 109 o for the prograde motion component and 4 8 marc sec 28 o for the retrograde motion component the excitation power of the chandler wobble due to the snow load is estimated to be about 25 db less than the power needed to maintain the observed chandler wobble the superior quality of the satellite data over conventional data acquired by ground observations and modeling is demonstrated we also discuss the role of atmospheric water and the problems arising from the lack of snow load observations over the antarctic and greenland ice sheets

an experimental investigation of the effect of bedslope and grain pivot angle on the threshold of marine gravel transport abstract a theoretical model developed by dyer 1986 for the effect of bedslope on bed shear stress for transport threshold crit under unidirectional flows is tested in a series of laboratory experiments data are presented from 230 laboratory threshold experiments for 1 cm glass spheres with two situation of grain pivot angle on bedslopes ranging from 10 to 15 the experimental results support the dyer model and indicate that for rhombohedral bed packing it can be developed to include the effect of grain pivot angle at threshold

an expression for land surface water storage monitoring using a two formation geological weighing lysimeter summary field studies have demonstrated that ground surface rainfall accumulation can be detected at depth by synchronous increases in static confined groundwater pore pressures this opens the way for geological weighing lysimeters providing disturbance free water storage monitoring of the surface environment in effect by weighing a significant land area in real time such systems require specific hydrogeological conditions which are not easily verified by field observations and replicated observations from multiple geological formations are a prerequisite for quality control given replication over two monitored formations we introduce an expression which utilises the respective formation piezometric water levels to give an improved combined estimate of the ground surface water budget the expression utilises raw piezometric levels and has the advantage of direct correction for earth tide noise which may sometimes be influenced by local effects in addition to the pure solar lunar tidal potential the expression is particularly simple if the two formations have similar but possibly unknown undrained poisson ratios and porosities surface water budgets can then be estimated using only the respective formation barometric coefficients and piezometric levels an example application to two vertically separated confined aquifers at a new zealand site indicate an improved accuracy over single formation observations the two formation expression for surface storage could find use as an accurate water budget tool with particular application to monitoring diffuse hydrological systems such as wetlands arid regions and heavily forested localities

regional high resolution spatiotemporal gravity modeling from grace data using spherical wavelets we determine a regional spatiotemporal gravity field over northern south america including the amazon region using grace inter satellite range rate measurements by application of a wavelet based multiresolution technique a major advantage of this method is that we are able to represent the amazon hydrological signals in form of time series of detail signals with level dependent temporal resolution the coarser structures generally require only ten days whereas the medium and finer details are computable from one month of data to this end we employ the basic property of multiresolution representations which is to split a signal into detail signals each related to a specific resolution level and computable from data covering a specific part of the spectrum our results which for the first time fully exploit the spatial and temporal resolutions of grace data in modeling amazon hydrological fluxes are in good agreement with hydrological models and gps derived height variations

ocean tidal solutions in antarctica from grace inter satellite tracking data 1 long wavelength components of the oceanic tides surrounding antarctica are estimated directly from three years of grace satellite to satellite ranging measurements an inversion is performed for the major constituents m2 o1 and s2 with k1 excluded because of inadequate phase sampling the tides are parameterized as localized average mass anomalies over areas approximately 3002 km2 other parameters including satellite state adjustments are estimated simultaneously with the tides qualitative comparison of our solutions with in situ tide measurements shows agreement in spatial pattern clearly indicating regions where our adopted prior model is inadequate to exploit these solutions follow on work must assimilate these long wavelength components into a high resolution numerical tidal model

the gravity recovery and climate experiment mission overview and early results 1 the grace mission is designed to track changes in the earth s gravity field for a period of five years launched in march 2002 the two grace satellites have collected nearly two years of data a span of data available during the commissioning phase was used to obtain initial gravity models the gravity models developed with this data are more than an order of magnitude better at the long and mid wavelengths than previous models the error estimates indicate a 2 cm accuracy uniformly over the land and ocean regions a consequence of the highly accurate global and homogenous nature of the grace data these early results are a strong affirmation of the grace mission concept

wind field differences between three meteorological reanalysis data sets detected by evaluating atmospheric excitation of earth rotation 1 we compared atmospheric excitations of the varying earth rotation calculated from three different meteorological reanalysis data sets ncep ncar ncep doe and era 40 over 23 years from 1979 to 2001 atmospheric excitations are evaluated by atmospheric angular momentum aam functions we found that differences in aam functions are primarily caused by differences in the wind data especially the northward wind data between the three reanalysis data sets differences between the ncep doe and era 40 aam functions are larger than those between the ncep ncar and ncep doe ones the northward wind differences that have a large effect on the equatorial aam functions originate from the upper troposphere at the tropics and midlatitudes in the southern hemisphere especially in three regions east pacific off latin america africa and the indian ocean the eastward wind differences are seen at midlatitudes in the southern hemisphere these differences are not confined to a single frequency the difference spectra show a reddish frequency dependence with some peaks in seasonal bands and tidal diurnal bands since the eastward and northward winds over the tropics can most efficiently change the earth s spin rate and polar motion respectively the wind accuracy over the tropics directly determines the accuracy in evaluations of the atmospheric excitations

accelerated west antarctic ice mass loss continues to outpace east antarctic gains a b s t r a c t article history while multiple data sources have confirmed that antarctica is losing ice at an accelerating rate different measurement techniques estimate the details of its geographically highly variable mass balance with different levels of accuracy spatio temporal resolution and coverage some scope remains for methodological improvements using a single data type in this study we report our progress in increasing the accuracy and spatial resolution of time variable gravimetry from the gravity recovery and climate experiment grace we determine the geographic pattern of ice mass change in antarctica between january 2003 and june 2014 accounting for glacio isostatic adjustment gia using the ij05 r2 model expressing the unknown signal in a sparse slepian basis constructed by optimization to prevent leakage out of the regions of interest we use robust signal processing and statistical estimation methods applying those to the latest time series of monthly grace solutions we map antarctica s mass loss in space and time as well as can be recovered from satellite gravity alone ignoring gia model uncertainty over the period 2003 2014 west antarctica has been losing ice mass at a rate of 121 8g t yr and has experienced large acceleration of ice mass losses along the amundsen sea coast of 18 5g t yr 2 doubling the mass loss rate in the past six years the antarctic peninsula shows slightly accelerating ice mass loss with larger accelerated losses in the southern half of the peninsula ice mass gains due to snowfall in dronning maud land have continued to add about half the amount of west antarctica s loss back onto the continent over the last decade we estimate the overall mass losses from antarctica since january 2003 at 92 10 gt yr

validation of high resolution grace mascon estimates of glacier mass changes in the st elias mountains alaska usa using aircraft laser altimetry we acquired center line surface elevations from glaciers in the st elias mountains of alaska northwestern canada using aircraft laser altimetry during 2000 05 and compared these with repeat measurements acquired in 2007 the resulting elevation changes were used to estimate the mass balance of 32 900 km 2 of glaciers in the st elias mountains during september 2003 to august 2007 yielding a value of 21 2 3 8gta 1 equivalent to an area averaged mass balance of 0 64 0 12 m a 1 water equivalent w e high resolution 2 arc degrees spatial and 10 day temporal gravity recovery and climate experiment grace mass balance estimates during this time period were scaled to glaciers of the st elias mountains yielding a value of 20 6 3 0 gt a 1 or an area averaged mass balance of 0 63 0 09 m a 1 w e the difference in balance estimates altimetry minus grace was 0 6 4 8 gta 1 well within the estimated errors differences likely resulted from uncertainties in subgrid sampling of the grace mass concentration mascon solutions and from errors in assigning an appropriate near surface density in the altimetry estimates the good correspondence between grace and aircraft altimetry data suggests that high resolution grace mascon solutions can be used to accurately assess mass balance trends of mountain glacier regions that are undergoing large changes

assessment of gravity recovery and climate experiment grace temporal signature over the upper zambezi the temporal signature of terrestrial storage changes inferred from the gravity recovery and climate experiment grace has been assessed by comparison with outputs from a calibrated hydrological model lumped elementary watershed lew of the upper zambezi and surroundings and an inspection of the within month ground track coverage of grace together with spatial temporal rainfall patterns the comparison of the hydrological model with grace reveals temporal inconsistencies between both data sets because the lew model has been calibrated and validated with independent data sources we believe that this is a grace artifact the within month ground track coverage shows an irregular orbit behavior which may well cause aliasing in the grace monthly deconvolutions this aliasing is the most probable cause of observed temporal inconsistencies between grace and other data sets

present rate of uplift in fennoscandia from grace and absolute gravimetry abstract fennoscandia is a key region for studying effects of glacial isostatic adjustment the associated mass variations can be detected by the gravity recovery and climate experiment grace satellite mission which observes the earth s gravity field since april 2002 as well as by absolute gravimetry field campaigns since 2003 annual absolute gravity ag measurements have been performed in fennoscandia by the institut fur erdmessung ife institute of geodesy of the leibniz universitat hannover germany within a multi national cooperation this offers a unique opportunity for validation and evaluation of the grace results in this preliminary study the grace results are compared to secular gravity changes based on the surveys from 2004 to 2007 with the fg5 220 gravimeter of the ife the results from grace monthly solutions provided by different analysis centres show temporal gravity variations in fennoscandia the included secular variations are in good agreement with former studies the uplift centre is located west of the bothnian bay the whole uplift area comprises northern europe nevertheless the differences between the grace solutions are larger than expected and the different centre specific processing techniques have a very strong effect on possible interpretations of grace results the comparison of grace to the ag measurements reveals that the determined trends fit well with results from grace at selected stations especially for the solution provided by the gfz variations of land hydrology clearly influence results from grace and the ag measurements

eolian features produced by the december 1977 windstorm southern san joaquin valley california high wind velocities during a windstorm in december of 1977 in the southern san joaquin valley california created eolian features and effects of a magnitude not previously reported in the literature three principal mechanisms of sediment movement by wind were studied by examining the size distribution of deposits in telephone poles saltation and suspension feeder pens and abandoned buildings saltation and suspension and gravel ripples surface creep the maximum grain sizes of rocks lodged in telephone poles at heights of 240 160 and 80 cm are 7 mm x 11 mm x 6 mm 10 mm x 15 mm x 6 mm and 20 mm x 23 mm x 5 mm respectively in some areas with rocky soils lag materials formed gravel ripples

pivoting analyses of the selective entrainment of sediments by shape and size with application to gravel threshold measured variations of pivoting angles with grain size shape reliability and angularity and imbrication are employed in analyses of grain threshold to examine how these factors influence selective grain entrainment and sorting with a bed of uniform grain sizes as employed experimentally to establish the standard threshold curves such as that of shields the threshold condition depends on grain shape and fabric the analysis demonstrates quantitatively that there should be a series of nearly parallel threshold curves depending on grain pivoting angles for a given grain size the order of increasing flow strength required for entrainment is spheres smooth ellipsoids depending on their reliability angular grains and imbricated ellipsoids depending on their imbrication angles the relative threshold values for these different grain shapes and fabric are predicted according to their respective pivoting angles but remain to be directly tested by actual threshold measurements the pivoting angle of a grain also depends on the ratio of its size to those it rests upon this dependence permits an evaluation of selective entrainment by size of grains from a bed of mixed sizes the condition generally found in natural sediments the pivoting model predicts systematic departures from the standard threshold curves for uniform grain sizes such departures have been found in recent studies of gravel threshold in rivers and offshore tidal currents the pivoting model is compared with those threshold data with reasonable agreement however more controlled measurements are required for a satisfactory test of the model it is concluded that variations in pivoting angles for grain entrainment are significant to the processes of selective sorting by grain size and shape

deos mass transport model dmt 1 based on grace satellite data methodology and validation summary the deos mass transport release 1 dmt 1 model has been produced on the basis of intersatellite k band ranging data acquired by the grace satellite mission the functional model exploited in the data processing can be considered as a variant of the acceleration approach each element of the data vector is defined as a linear combination of three successive range measurements and can be interpreted as the line of sight projection of a weighted average of intersatellite accelerations as such the data vector can be directly linked to parameters of the gravitational field in this way a series of unconstrained monthly gravity field solutions is produced each of which is defined as a set of spherical harmonic coefficients complete to degree 120 at the post processing stage the unconstrained solutions are filtered with a statistically optimal wiener type filter based on full covariance matrices of noise and signal as such the dmt 1 model is free from along track artefacts which are typical for many other grace gravity models the accuracy of the dmt 1 model has been analysed in different ways first the signals observed in areas with minimal mass variations sahara east antarctica and the middle of the pacific ocean are analysed and interpreted as an upper bound of the noise in the dmt 1 model it is concluded that the pointwise errors after filtering are of the order of 2 3 cm in terms of equivalent water heights for the mean mass variations in an area of 10 6 km 2 the corresponding error reduces to 1 5 2 cm second a time series of mass variations in the marie byrd land antarctica has been analysed where the true signal mostly caused by postglacial rebound is expected to be close to a linear trend the rms of the post fit residuals is found to be 3 3 cm which is consistent with the error analysis in areas with minimal mass variations thirdly the dmt 1 model has been applied to estimate mass variations in 2003 2006 in lake victoria africa where a large drop of water level is observed in recent years the obtained linear trend 31 3c m yr 1 is in good agreement with that derived from the satellite altimetry data 35 1c m yr 1

recent contributions of glaciers and ice caps to sea level rise satellite measurements of earth s gravity field show that the mass loss of glaciers and ice caps contributed to sea level rise by approximately 0 4 millimetres per year between 2003 and 2010 the extent to which mass loss from ice covered land areas contributes to sea level rise is not known accurately in part because previous global estimates use different techniques for glaciers ice caps and ice sheets the gravity recovery and climate experiment grace satellite has provided monthly measurements of the global gravity field since 2002 using grace data jacob et al assess regional mass loss between 2003 and 2010 and conclude that mass loss from ice covered land areas contributed almost 1 5 mm per year to the sea level rise estimated mass loss from the high mountains of asia was negligible in contrast to some other reports glaciers and ice caps gics are important contributors to present day global mean sea level rise1 2 3 4 most previous global mass balance estimates for gics rely on extrapolation of sparse mass balance measurements1 2 4 representing only a small fraction of the gic area leaving their overall contribution to sea level rise unclear here we show that gics excluding the greenland and antarctic peripheral gics lost mass at a rate of 148 30 gt yr 1 from january 2003 to december 2010 contributing 0 41 0 08 mm yr 1 to sea level rise our results are based on a global simultaneous inversion of monthly grace derived satellite gravity fields from which we calculate the mass change over all ice covered regions greater in area than 100 km2 the gic rate for 2003 2010 is about 30 per cent smaller than the previous mass balance estimate that most closely matches our study period2 the high mountains of asia in particular show a mass loss of only 4 20 gt yr 1 for 2003 2010 compared with 47 55 gt yr 1 in previously published estimates2 5 for completeness we also estimate that the greenland and antarctic ice sheets including their peripheral gics contributed 1 06 0 19 mm yr 1 to sea level rise over the same time period the total contribution to sea level rise from all ice covered regions is thus 1 48 0 26 mm 1 which agrees well with independent estimates of sea level rise originating from land ice loss and other terrestrial sources6

three forms of variability in argentine basin ocean bottom pressure ocean bottom pressure data are examined from a year long deployment of two bottom pressure recorders separated by 417 km in the argentine basin three forms of variability are found at high frequencies periods shorter than 2 hours the signal appears to be due to gravity wave propagation with the waves preferentially coming from the west at intermediate frequencies periods between 2 hours and 12 days the two records are highly coherent and in phase reflecting large scale coherent fluctuations which are well reproduced in a barotropic ocean model however the dominant mode is at a period of 20 days with a phase lag of about 90 100 degrees between the two records consistent with the a mode of variability previously inferred from satellite altimetry and current meters although the slightly shorter period is consistent with the suggestion that more than one mode contributes to the altimeter observations comparison with altimetry demonstrates that aliasing of higher frequency signals is not a significant source of error and confirms that a previously used altimetry mapping technique reduces the apparent amplitude of the mode the pressure records show a transport change of about 280 sv over one 12 day period and altimetry suggests that regions of higher variability exist the mode is only weakly excited in barotropic models but is strongly excited in a baroclinic model with a realistic eddy field suggesting that it is intrinsically linked to interactions between eddies mean flow and topography

understanding ice sheet mass balance progress in satellite altimetry and gravimetry satellite remote sensing has come to dominate the measurement of glacier and ice sheet change three independent methods now exist for assessing ice sheet mass balance and we focus on progress in two satellite altimetry icesat and gravimetry grace with improved spatial and temporal sampling and synergy with ice flow measurements both the mechanisms and causes changing mass balance can be investigated we present examples of mass losses due to widespread intensifying glacier dynamic thinning in northwest greenland but local ablation rates in the northeast that are unchanged for decades advances in grace processing reveal greenland net ice sheet mass loss continuing into 2010 at 19530 gt a 1 a similarly negative trend in the gulf of alaska has significant spatial and temporal variation that highlights the importance of intense summer melting here strong summer melt on the antarctic peninsula also precipitated recent ice shelf collapse and prompted rapid dynamic thinning of tributary glaciers at up to 70ma 1 thinning continued for years to decades after collapse and propagated far inland while understanding of the physical mechanisms of change continues to improve estimates of future behaviour and in particular the near future glacial sea level contribution still rely on projections from such observations we introduce the suite of new sensors that will monitor the ice sheets into the future

grace observations of m2 and s2 ocean tides underneath the filchner ronne and larsen ice shelves antarctica 1 by processing the grace satellite to satellite tracking data and estimating the temporal gravity fields regionally over the southern polar region with a 5 day interval we observed m2 and s2 ocean tides underneath the filchner ronne and larsen ice shelves antarctica based on the predicted aliased periods we extracted the m2 and s2 signals from the time series of 5 daily mean grace regional gravity estimates the grace observations agreed well with the predicted tides from the fes2004 and cats02 01 models after smoothing the models to the commensurate spatial resolution as grace overall the grace and the models agreed within 10 20 difference in the tidal amplitude and 20 in phase for both m2 and s2 our results suggest that grace provides valuable observations of ocean tides with a spatial resolution as short as 300 km over the remote area lacking of quality observations such as the antarctica ice shelves

impact of short period non tidal temporal mass variability on grace gravity estimates 1 using orbital simulations of the gravity recovery and climate experiment grace spacecraft we examined the effects on gravity recovery due to short period non tidal temporal mass variability in the atmosphere ocean and continental hydrology we found that the magnitude of the aliasing error was strongly correlated with the power of the high frequency variability of the models degree error relative to measurement error increased by a factor of 20 due to atmospheric aliasing corresponding to geoid anomalies of approximately 1 mm at 500 km wavelengths by a factor of 10 due to the ocean model and by a factor of 3 due to the continental hydrology model de aliasing done with approximate models gave the greatest reduction in aliasing error for the mid degrees and higher for the atmosphere the residual error was 1 5 times that of the aliasing error a barotropic ocean model reduced the aliasing error due to a baroclinic model to nearly the level of measurement noise

estimating palaeowind strength from beach deposits abstract the geological record of past wind conditions is well expressed in the coarse gravel cobble and boulder beach deposits of quaternary palaeolakes in the great basin of the western usa and elsewhere this paper describes a technique using the particle size distribution of beach deposits to reconstruct palaeowind conditions when the lakes were present the beach particle technique bpt is first developed using coarse beach deposits from the 1986 87 highstand of the great salt lake in utah combined with instrumental wind records from the same time period next the bpt is used to test the hypothesis that wind conditions were more severe than at present during the last highstand of lake lahontan 13 ka which only lasted a decade or two at most the largest 50 beach clasts were measured at nine beach sites located along the north west and south sides of antelope island in the great salt lake all of which formed in 1986 87 at these sites the largest clast sizes range from 10 to 28 cm b axis and fetch lengths range from 25 to 55 km nearshore wave height was calculated by assuming that the critical threshold velocity required to move the largest clasts represents a minimum estimate of the breaking wave velocity which is controlled by wave height shoaling transformations are undertaken to estimate deep water wave heights and ultimately wind velocity wind estimates for the nine sites using the bpt range from 6 5 to 17 4 m s 1 which is in reasonable agreement with the instrumental record from salt lake city airport the same technique was applied to eight late pleistocene beaches surrounding the carson sink sub basin of lake lahontan nevada using the bpt estimated winds for the eight sites range from 9 7 to 27 1 m s 1 the strongest winds were calculated for a cobble boulder beach with a fetch of 25 km instrumental wind records for the 1992 99 period indicate that wind events of 9 12 m s 1 are common and that the strongest significant wind event 9 m s 1 for 3 h reached an average velocity of 15 5 m s 1 based on this preliminary comparison it appears that the late pleistocene western great basin was a windier place than at present at least for a brief time