use of grace data to detect the present land uplift rate in fennoscandia after more than 13 years of grace monthly data the determined secular trend of gravity field variation can be used to study the regions of glacial isostatic adjustment gia here we focus on fenn

timing and origin of recent regional ice mass loss in greenland within the last decade the greenland ice sheet gris and its surroundings have experienced record high surface temperatures mote 2007 box et al 2010 ice sheet melt extent fettweis et al 2011 and record low summer sea ice extent nghiem et al 2007 using three independent data sets we derive for the first time consistent ice mass trends and temporal variations within seven major drainage basins from gravity fields from the gravity recovery and climate experiment grace tapley et al 2004 surface ice velocities from inteferometric synthetic aperture radar insar rignot and kanagaratnam 2006 together with output of the regional atmospheric climate modelling racmo2 gr ettema et al 2009 and surface elevation changes from the ice cloud and land elevation satellite icesat sorensen et al 2011 we show that changing ice discharge d surface melting and subsequent run off m r and precipitation p all contribute in a complex and regionally variable interplay to the increasingly negative mass balance of the gris observed within the last decade interannual variability in p along the northwest and west coasts of the gris largely explains the apparent regional mass loss increase during 2002 2010 and obscures increasing m r and d since the 1990s in winter 2002 2003 and 2008 2009 accumulation anomalies in the east and southeast temporarily outweighed the losses by m r and d that prevailed during 2003 2008 and after summer 2010 overall for all basins of the gris the decadal variability of anomalies in p m r and d between 1958 and 2010 w r t 1961 1990 was significantly exceeded by the regional trends observed during the grace period 2002 2011 2012 elsevier b v

antarctic mass rates from grace 1 we estimate mass trends over antarctica using gravity variations observed by the gravity recovery and climate experiment grace satellite mission during its first 3 5 years april 2002 november 2005 an image of surface mass trends is constructed from 1 1 pixels over the entire continent and shows two prominent features a region of mass loss along the coast of west antarctica and one of accumulation in east antarctica after adjusting for bias due to smoothing and to grace s limited spatial resolution and removing post glacial rebound pgr effects the rate in west antarctica is 77 14 km3 year similar to a recent estimate of ice mass loss from satellite altimetry and remote sensing data the prominent east antarctic feature in the enderby land region has a rate of 80 16 km3 year published snow ice mass rates from remote sensing measurements indicate approximate ice mass balance in this region suggesting that this feature is either from unquantified snow accumulation in this region or more likely due to unmodeled pgr

revisiting grace antarctic ice mass trends and accelerations considering autocorrelation previous grace derived ice mass trends and accelerations have almost entirely been based on an assumption that the residuals to a regression model including also semi annual annual and tidal aliasing terms are not serially correlated we consider ice mass change time series for antarctica and show that significant autocorrelation is in fact present we examine power law and autoregressive models and compare them to those that assume white uncorrelated noise the data do not let us separate autoregressive and power law models but both indicate that white noise uncertainties need to be scaled up by a factor of up to 4 for accelerations and 6 for linear rates depending on length of observations and location for the whole of antarctica east antarctica and west antarctica the scale factors are 1 5 1 5 and 2 2 respectively for the trends and for the accelerations 1 5 1 5 and 2 1 substantially lower scale factors are required for offshore time series suggesting much of the time correlation is related to continental mass changes despite the higher uncertainties we find significant 2 sigma accelerations over much of west antarctica overall increasing mass loss and dronning maud land increasing mass gain as well as a marginally significant acceleration for the ice sheet as a whole increasing mass loss

external validation of the grace ggm01c gravity field using gps and doris positioning results 1 we have used the new gravity field model ggm01c derived from grace data to reanalyze doris data from 1993 0 to 2003 2 using the gipsy oasis software and a free network approach we have estimated the position and velocity of each doris station in itrf2000 in order to test the accuracy of these results we have compared them to the positions and velocities of 43 collocated gps stations using local ties and covariance information doris results computed using the ggm01c gravity field instead of the egm96 gravity field show a significantly improved external agreement with gps position agreement of 12 26 mm was reduced to 10 13 mm and velocity agreement of 3 3 3 7 mm yr was reduced to 2 4 3 3 mm yr this can be interpreted as an external test of the accuracy of the new ggm01c gravity field

antarctic circumpolar current transport variability during 2003 05 from grace abstract gravity recovery and climate experiment grace gravity data spanning january 2003 november 2005 are used as proxies for ocean bottom pressure bp averaged over 1 month spherical gaussian caps 500 km in radius and along paths bracketing the antarctic circumpolar current s various fronts the grace bp signals are compared with those derived from the estimating the circulation and climate of the ocean ecco ocean modeling assimilation system and to a non boussinesq version of the regional ocean model system roms the discrepancy found between grace and the models is 1 7 cmh2o 1 cmh2o 1 hpa slightly lower than the 1 9 cmh2o estimated by the authors independently from propagation of grace errors the northern signals are weak and uncorrelated among basins the southern signals are strong with a common seasonality the seasonal cycle grace data observed in the pacific and indian ocean sectors of the acc are consistent with annual and semiannual amplitudes of 3 6 and 0 6 cmh2o 1 1 and 0

new insights on intraplate volcanism in french polynesia from wavelet analysis of grace champ and sea surface data in this paper we discuss the origin of superswell volcanism on the basis of representation and analysis of recent gravity and magnetic satellite data with wavelets in spherical geometry we computed a refined gravity field in the south central pacific based on the grace satellite ggm02s global gravity field and the kms02 altimetric grid and a magnetic anomaly field based on champ data the magnetic anomalies are marked by the magnetic lineation of the seafloor spreading and by a strong anomaly in the tuamotu region which we interpret as evidence for crustal thickening we interpret our gravity field through a continuous wavelet analysis that allows to get a first idea of the internal density distribution we also compute the continuous wavelet analysis of the bathymetric contribution to discriminate between deep and superficial sources according to the gravity signature of the different chains as revealed by our analysis various processes are at the origin of the volcanism in french polynesia as evidence we show a large scale anomaly over the society islands that we interpret as the gravity signature of a deeply anchored mantle plume the gravity signature of the cook austral chain indicates a complex origin which may involve deep processes finally we discuss the particular location of the marquesas chain as suggesting that the origin of the volcanism may interfere with secondary convection rolls or may be controlled by lithospheric weakness due to the regional stress field or else related to the presence of the nearby tuamotu plateau

variations of the earth s figure axis from satellite laser ranging and grace 1 satellite laser ranging slr data were used to determine the variations in the earth s principal figure axis represented by the degree 2 and order 1 geopotential coefficients c21 and s21 significant variations at the annual and chandler wobble frequencies appear in the slr time series when the rotational deformation or pole tides i e the solid earth and ocean pole tides were not modeled the contribution of the ocean pole tide is estimated to be only 8 of the total annual variations in the normalized coefficients based on the analysis of slr data the amplitude of the nontidal annual variation of is only 30 of from the slr time series the estimates of the annual variation in from slr the gravity recovery and climate experiment grace and polar motion excitation function are in a good agreement the nature of the linear trend for the earth s figure axis determined by these techniques during the last several years is in general agreement but does not agree as well with results predicted from current glacial isostatic adjustment gia models the fluid love number for the earth is estimated to be 0 9 based on the position of the mean figure axis from the grace gravity model ggm03s and the mean pole defined by the iers 2003 conventions the estimate of from grace and slr provides an improved constraint on the relative rotation of the core the results presented here indicate a possible tilt of the inner core figure axis of 2 and 3 arc sec displacement for the figure axis of the entire core

the dominant role of the east siberian sea in driving the oceanic flow through the bering strait conclusions from grace ocean mass satellite data and in situ mooring observations between 2002 and 2016 it is typically stated that the pacific to arctic oceanic flow through the bering strait important for arctic heat freshwater and nutrient budgets is driven by local wind and a poorly defined far field pressure head forcing related to sea surface height differences between the pacific and the arctic using monthly arctic wide ocean bottom pressure satellite data and in situ mooring data from the bering strait from 2002 to 2016 we discover the spatial structure of this pressure head forcing finding that the bering strait throughflow variability is dominantly driven from the arctic specifically by sea level change in the east siberian sea ess in turn related to westward winds along the arctic coasts in the comparatively calm summer this explains approximately two thirds of the bering strait variability in winter local wind variability dominates the total flow but the pressure head term while still correlated with the ess dominated sea level pattern is now more strongly related to bering sea shelf sea level variability

grace detects coseismic and postseismic deformation from the sumatra andaman earthquake 1 we show that spherical harmonic sh solutions of the gravity recovery and climate experiment grace are now of sufficient quality to observe effects of co seismic and post seismic deformation due to the rupture from the mw 9 3 sumatra andaman earthquake on december 26 2004 and its companion nias earthquake mw 8 7 on march 28 2005 the improved ggm 03 sh level 2 solutions and improved filtering methods provide estimates with spatial resolution comparable to earlier estimates from range rate level 1 grace data the gravityfield disturbance extends over 1800 km along andaman and sunda subduction zones and changes with time following events gravity changes may be due to afterslip viscoelastic relaxation or other processes associated with dilatation satellite gravity measurements from grace provide a unique new measure of deformation and post seismic processes associated with major earthquakes especially in areas which are primarily oceanic citation chen j l c r wilson b d tapley and s grand 2007 grace detects coseismic and postseismic deformation from the sumatraandaman earthquake geophys res lett 34 l13302

temporal variations of the marine geoid the effects of temporal changes in the marine geoid on estimates of the ocean dynamic topography is being investigated influences from changes of land hydrology ice sheets post glacial rebound

hydrological and oceanic effects on polar motion from grace and models 1 terrestrial water storage tws and ocean bottom pressure obp are major contributors to the observed polar motion excitations second only to atmospheric mass movement however quantitative assessment of the hydrological and oceanic effects on polar motion remains unclear because of the lack of global observations in this paper hydrological and oceanic mass excitations to polar motion are investigated using monthly tws and obp derived from the gravity recovery and climate experiment grace for january 2003 until december 2008 the results from this analysis are compared with hydrological model excitations from the european center for medium range weather forecasts ecmwf and oceanic model excitations obtained from the jet propulsion laboratory jpl using estimating the circulation and climate of the ocean ecco results show that the grace derived obp and tws better explain the geodetic residual polar motion excitations for the px component at the annual period while the grace obp and ecmwf hydrological angular momentum agree better with the geodetic residuals for the annual py excitation grace ocean and hydrology excitations better explain the geodetic residuals for the semiannual py excitation however the jpl ecco and ecmwf models better explain the intraseasonal geodetic residual of polar motion excitation in the px and py components the grace data demonstrate much higher intraseasonal variability than either the models or the geodetic observations

time variations of land water storage from an inversion of 2 years of grace geoids by delivering monthly maps of the gravity field the grace project allows the determination of tiny time variations of the earth s gravity and particularly the effects of fluid mass redistributions at the surface of the earth however grace data represent vertically integrated gravity measurements thus are the sum of all mass redistributions inside the earth s system atmosphere oceans and continental water storage plus solid earth in this paper we apply a generalized least squares inverse approach previously developed by 1 g ramillien a cazenave o brunau global time variations of hydrological signals from grace satellite gravimetry geophys j int 158 2004 813 826 to estimate from the monthly grace geoids continental water storage variations and their associated uncertainties over a 2 year time span april 2002 to may 2004 tests demonstrating the robustness of the method are presented including the separation between liquid water reservoirs surface waters soil moisture groundwaters and snow pack contributions individual monthly solutions of total land water storage from grace with a spatial resolution of 660 km are presented for the 2 year time span we also derive the seasonal cycle map we further estimate water volume changes over eight large river basins in the tropics and compare with model predictions finally we attempt to estimate an average value of the evapotranspiration over each river basin using the water balance equation which links temporal change in water volume to precipitation evapotranspiration and runoff amplitudes of the grace derived evapotranspiration are regionally consistent to the predictions of global hydrological models

combination of various observation techniques for regional modeling of the gravity field modeling a very broad spectrum of the earth s gravity field needs observations from various measurement techniques with different spectral sensitivities typically high resolution regional gravity data are combined with low resolution global observations to exploit the gravitational information as optimally as possible we set up a regional modeling approach using radial spherical basis functions emphasizing the strengths of various data sets by the flexible combination of high and middle resolution terrestrial airborne shipborne and altimetry measurements the basis functions are defined and located in the region of interest in such a manner which the highest measure of information of the input data is captured any functional of the earth s gravity field can be derived as e g quasi geoid heights or gravity anomalies here we present results of a study area in northern germany a comprehensive cross validation to external observation data delivers standard deviations less than 5 cm differences to an existing regional quasi geoid model count on average 6 cm and proof the plausibility of our solution the comparison with existing global models reaches higher standard deviations for the more sensitive gravity anomalies as for quasi geoid heights showing the additional value of our solution in the high frequency domain covering a broad frequency spectrum our regional models can be used as basis for various applications such as refinement of global models national geoid determination and detection of mass anomalies in the earth s interior

revisiting greenland ice sheet mass loss observed by grace in this paper we discuss a new method for determining mass time series for 16 hydrological basins representing the greenland system gs whereby we rely on gravity recovery and climate experiment grace mission data in the same analysis we also considered observed mass changes over ellesmere island baffin island iceland and svalbard ebis the summed contribution of the complete system yields a mass loss rate and acceleration of 252 28 gt yr and 22 4 gt yr2 between march 2003 and february 2010 where the error margins follow from two glacial isostatic adjustment gia models and three processing centers providing grace monthly potential coefficient sets we describe the relation between mass losses in the gs and the ebis region and found that the uncertainties in all areas are correlated the summed contribution of ellesmere island baffin island iceland and svalbard yields a mass loss rate of 51 17 gt yr and an acceleration of 13 3 gt yr2 between march 2003 and february 2010 the new regional basin reconstruction method shows that the mass loss within the southeastern basins in the gs has slowed down since 2007 while mass loss in western basins increased showing a progression to the north of greenland

improving mass redistribution estimates by modeling ocean bottom pressure uncertainties weekly ocean bottom pressure anomalies obp are modeled using the finite element sea ice ocean model fesom the model s obp error mostly unknown so far is assessed by comparing two model simulations each forced by different atmospheric forcing data sets the mean estimated error of modeled obp is found to be 0 04 m per 1 5 1 5 grid cell the error varies strongly from 0 003 m in the equatorial region to 0 31 m in the weddell and ross seas we believe that the spatial variations of the errors are an important improvement over previous error models the new error estimates are implemented in a joint inversion of gravity recovery and climate experiment grace gravity measurements gps site displacements and modeled obp resulting in a larger overall obp weight in the inversion most notably in the polar regions additionally the inversion provides a global mass correction term to adjust the ocean mass budget of the model the estimated term is used to correct the model s fresh water balance making it consistent with grace and gps on seasonal and longer timescales all model results weekly grace estimates and the inverse solutions are compared with measurements from in situ bottom pressure recorders the newly estimated error model of the combination solution results in higher correlations than the previously used constant error model of the combination solution

independent patterns of water mass anomalies over australia from satellite data and models the gravity recovery and climate experiment grace products allow the quantification of total water storage tws changes at global to regional scales however the quantity measured by grace represents mass signals integrated over vertical columns requiring their separation into their original sources such a separation is vital for australia for which grace estimates are affected by leakage from the surrounding oceans the independent component analysis ica method that uses higher order statistics is implemented here to separate grace derived water storage signals over the australian continent from its surrounding oceans covering from october 2002 to may 2011 the performance of ica applied to grace is then compared to the ica of watergap global hydrology model wghm and the ica of the australian water resources assessment awra system to study the influence of rainfall variability on the derived independent patterns use is made of tropical rainfall measuring mission trmm data set from january 2000 to may 2011 implementing ica on grace tws showed a remarkable improvement in separating the continental hydrological signals from the surrounding oceanic anomalies which was not achievable using a conventional principle component analysis reconstructing the continental tws changes using only those independent components of grace that were located over the continent showed a high correlation with wghm tws and awra tws mass concentrations over the oceans and particularly s2 semi diurnal aliased pattern were separated as independent modes correlation analysis between the independent components of grace and climate teleconnections showed that the mass anomalies over the northern ocean gulf of carpentaria and north eastern parts of australia were significantly correlated with the el nino southern oscillation while those over south and south eastern parts of australia were mainly linked to the indian ocean dipole

low degree spherical harmonic influences on gravity recovery and climate experiment grace water storage estimates we estimate terrestrial water storage variations using time variable gravity changes observed by the gravity recovery and climate experiment grace satellites during the first 2 years of the mission we examine how treatment of low degree gravitational changes and geocenter variations affect grace based estimates of basin scale water storage changes using independently derived low degree harmonics from earth rotation eop and satellite laser ranging slr observations grace based water storage changes are compared with estimates from nasa s global land data assimilation system gldas results from the 22 grace monthly gravity solutions covering the period april 2002 to july 2004 show remarkably good agreement with gldas in the mississippi amazon ganges ob zambezi and victoria basins combining grace observations with eop and slr degree 2 spherical harmonic coefficient changes and slr observed geocenter variations significantly affects and apparently improves the estimates especially in the mississippi ob and victoria basins

high resolution interannual mass anomalies of the antarctic ice sheet by combining grace gravimetry and envisat altimetry knowledge of interannual mass variations of the antarctic ice sheet ais associated with its surface mass change is important for correctly interpreting the long term mass trend and evaluating the fidelity of surface mass balance from regional climate models here we revisit the interannual anomalies of mass change from gravity recovery and climate experiment and elevation change from envisat over the ais during 2003 2009 with the objective of obtaining higher resolution interannual mass anomalies based on envisat data high positive correlations 0 6 between the two interannual anomalies are primarily found over the west ais and coastal regions in the east ais occupying more than 40 of the ais by combining the two interannual anomalies we are able to estimate the density of snow ice changing interannually over regions in the ais especially over the amundsen sea sector with significant interannual signals the temporal variability of the density of snow ice associated with interannual anomalies is shown for the first time which agrees with the events of excess snow accumulation and the accelerated ice discharge occurring there furthermore we demonstrate the feasibility of obtaining higher resolution interannual mass anomalies over the west ais based on the density corrected envisat data negative correlations which were also found in a previous study are likely related to errors in the relatively weak interannual signals

a comparative study of changes in the lambert glacier amery ice shelf system east antarctica during 2004 2008 using gravity and surface elevation observations we present results of a regional comparative study of surface mass changes from 2004 to 2008 based on gravity recovery and climate experiment grace the ice cloud and land elevation satellite icesat and chinare observations over the lambert glacier amery ice shelf system las estimation of the icesat mass change rates benefitted from the density measurements along the chinare traverse and a spatial density adjustment method for reducing the effect of spatial density variations in the high elevation inland region a positive trend was estimated from both icesat and grace data which is in line with the chinare accumulation measurements in the coastal region there were areas with high level accumulations in both icesat and grace trend maps in many high flow speed glacier areas negative mass change rates may be caused by dynamic ice flow discharges that have surpassed the snow accumulation overall the mass change rate estimate in the las of 2004 2008 from the grace icesat and chinare data is 5 41 4 59 gt a 1 indicating a balanced to slightly positive mass trend along with other published results this suggests that a longer term positive mass trend in the las may have slowed in recent years

the pole tide and its effect on grace time variable gravity measurements implications for estimates of surface mass variations gravity recovery and climate experiment grace provides monthly solutions for the earth s gravity field in the form of spherical harmonic coefficients these can be used to infer changes in mass at the earth s surface the pole tide the response of the earth and oceans to polar motion causes gravity signals dominated by harmonics of degree 2 order 1 if the pole tide is not removed from grace data it affects the coefficients of those harmonics c21 s21 and introduces errors when using those coefficients to determine surface mass variations the pole tide is partially removed by grace processing centers before solving for the gravity field but long period pole tide signals are not usually included in the grace pole tide correction and so those signals are still present in the grace coefficients we discuss this issue from the standpoint of somebody who uses the grace gravity fields to infer changes in surface mass we arrive at a recommendation for an optimal grace pole tide correction we describe how to modify the c21 s21 coefficients provided by the processing centers so that they conform with our recommendation we discuss the size of the pole tide contributions to c21 s21 compared to those of the direct load induced contributions as an example we show how an incompletely removed pole tide can impact grace results for the trend in ocean mass we consider the impact of mantle anelasticity on long period pole tide corrections and conclude that it is unlikely to affect those corrections by more than 20

the sustainability of water resources in high mountain asia in the context of recent and future glacier change high mountain asia contains the largest volume of glacier ice outside the polar regions and contain the headwaters of some of the largest rivers in central asia these glaciers are losing mass at a mean rate of between 0 18 and 0 5 m water equivalent per year while glaciers in the himalaya are generally shrinking those in the karakoram have experienced a slight mass gain both changes have occurred in response to rising air temperatures due to northern hemisphere climate change in the westerly influenced indus catchment glacier meltwater makes up a large proportion of the hydrological budget and loss of glacier mass will ultimately lead to a decrease in water supplies in the monsoon influenced ganges and brahmaputra catchments the contribution of glacial meltwater is relatively small compared to the indus and the decrease in annual water supplies will be less dramatic therefore enhanced glacier melt will increase river flows until the middle of the twenty first century but in the longer term into the latter part of this century river flows will decline as glaciers shrink declining meltwater supplies may be compensated by increases in precipitation but this could exacerbate the risk of flooding

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

large scale ocean circulation from the grace ggm01 geoid 1 the grace gravity model 01 ggm01 computed from 111 days of grace k band ranging kbr data is differenced from a global mean sea surface mss computed from a decade of satellite altimetry to determine a mean dynamic ocean topography dot as a test of the ggm01 gravity model large scale zonal and meridional surface geostrophic currents are computed from the topography and are compared with those derived from a mean hydrographic surface reduction in residual rms between the two by 30 60 and increased correlation indicates that the ggm01 geoid represents a dramatic improvement over older geoid models which were developed from multiple satellite tracking data altimetry and surface gravity measurements for the first time all major current systems are clearly observed in the dot from space based measurements

a joint analysis of gps displacement and grace geopotential data for simultaneous estimation of geocenter motion and gravitational field this work is funded by the university of newcastle to support nasa s grace and grace follow on projects as an international science team member to the missions and by australian research council dp170100224 as well as nasa support to j sauber as a science team member

time variations in ocean bottom pressure from a few hours to many years in situ data numerical models and grace satellite gravimetry in situ ocean bottom pressure obp obtained from 154 different locations irregularly scattered over the globe is carefully processed to isolate signals related to the ocean general circulation and large scale sea level changes comparison against a global numerical ocean model experiment indicates poor correspondence for periods below 24 hr possibly related to residual tidal signals and small timing errors in the atmospheric forcing applied to the ocean model correspondence increases rapidly for periods between 3 and 10 days where wind driven dynamics are already well understood and consequently well implemented into numerical models coherence decreases again for periods around 30 days and longer where processes not implemented into ocean general circulation models as barystatic sea level changes become more important correspondence between in situ data and satellite based obp as obtained from the gravity recovery and climate experiment grace german research centre for geosciences rl05a gravity fields critically depends on the postprocessing of level 2 stokes coefficients that also includes the selection of appropriate averaging regions for the grace based mass anomalies the assessment of other available grace level 2 products indicates even better fit of more recent solutions as itsg grace2016 and the center for space research and jet propulsion laboratory rl05 mascons in view of the strong high frequency component of obp however a higher temporal resolution of the oceanic grace products would be rather advantageous

space borne gravimetric satellite constellations and ocean tides aliasing effects summary ocean tides redistribute mass at high temporal frequencies satellite missions that aim to observe medium to low frequency mass variations need to take into account this rapidly varying mass signal correcting for the effects of ocean tides by means of imperfect models might hamper the observation of other temporal gravity field signals of interest this paper explores different methods for mitigating aliasing errors for the specific example of observing mass variations due to land hydrology including temporal filtering of time series of gravity solutions spatial smoothing and the use of satellite constellations for this purpose an earth system model esm was constructed which included state of the art time varying components for ocean atmosphere solid earth hydrology ice sheets and ocean tides using the esm we simulated the retrieval of the hydrologically driven gravity field changes using a number of different satellite constellations we find that 1 the ocean tide aliasing strongly depends on the satellite constellation the choice of orbital parameters and the length of the data span 2 the aliasing effect manifests itself differently for different geographical regions 3 the aliasing causes a peculiar striping pattern along the ground track of the satellite orbits 4 optimizing the choice of orbital parameters of a single grace type tandem can be more effective at reducing the aliasing of ocean tide model errors than flying more tandems finally we corroborate the experiences with grace data analysis that appropriate post processing techniques can significantly improve the quality of the retrieved gravity changes

antarctic regional ice loss rates from grace abstract using recent improved time variable gravity solutions from the gravity recovery and climate experiment grace we estimate rates of antarctic ice mass change for the period january 2003 through september 2006 combined improvements in data and filtering techniques allow observation of ice loss in the northern antarctic peninsula ap and along the coast of the west and central amundsen sea embayment ase in west antarctica there is also evidence of ice loss along the coast near the stancomb wills sta and jutulstraumen jut glaciers in queen maud land apparent rates are adjusted for influences of limited spatial resolution filtering and estimated postglacial rebound pgr to obtain ice loss rates for the northern ap coastal ase and sta jut of 28 8 7 9 81 17 and 16 7 9 7 km3 yr respectively this is the first estimate for the northern ap from satellite gravity data the ase estimate 81 17 km3 yr is consistent with a previous value 77 14 km3 yr using an earlier grace data release these results indicate significant improvement in grace data quality increased spatial resolution and applicability of grace data to a wider class of problems than previously possible

microfossil evidence for land movements associated with the ad 1964 alaska earthquake microfossil diatom and pollen data from a number of cores at coastal marshes at girdwood flats and kenai flats in cook inlet alaska suggest that there was a phase of gradual land subsidence prior to the main shock of the ad 1964 earthquake this phase followed a long period of gradual land uplift since the last large earthquake which occurred about 730 900 years ago caesium 137cs records indicate that subsidence started approximately 15 years before the 1964 earthquake this pre seismic subsidence is evident in the coastal marsh sediment sequences in changes in diatom and pollen assemblages that indicate changes in tidal marsh environments or a change from raised bog to marsh conditions the microfossil evidence indicates 0 15 m pre seismic land subsidence at both girdwood flats and kenai flats and co seismic subsidence of 1 8 m and 0 2 m respectively

optimized smoothing of gravity recovery and climate experiment grace time variable gravity observations 1 high degree and high order spherical harmonics of time variable gravity fields observed by the gravity recovery and climate experiment grace gravity mission are dominated by noise we develop two smoothing methods that suppress these high degree and high order errors with results superior to more commonly used gaussian smoothing these optimized smoothing methods considerably improve signal to noise levels of grace terrestrial water storage estimates relative to residual signal and noise over the oceans and show significantly better spatial resolution and lower leakage error on the basis of analysis using an advanced land surface model the equivalent spatial resolution from these optimized smoothing estimates is about 500 km compared to the roughly 800 1000 km gaussian smoothing that is required to suppress high degree noise in the grace fields

application of avhrr imagery and grace measurements for calculation of actual evapotranspiration over the quaternary aquifer lake chad basin and validation of groundwater models the paper presents an application of noaa avhrr and grace data for studying the regional hydrogeology of the quaternary aquifer in the lake chad basin the actual evapotranspiration et over the phreatic aquifer is computed using the s sebi algorithm and then compared to the et estimates derived from the grace land water solutions both the grace solutions and the s sebi results are similar in description of the actual et over the lake chad basin avhrr data helped to overcome non uniqueness in the modelling of the piezometry anomalies particularly in regional groundwater models the harr piezometric dome appeared to be an area of relatively high effective recharge while the chari baguirmi and the kadzell piezometric depressions and bahr el gahzal were probably areas of excess et over recharge

hillslope soils and vegetation abstract assessing how vegetation controls hillslope soil processes is a challenging problem as few abiotic landscapes exist as observational controls here we identify five avenues to examine how actively eroding hillslope soils and processes would differ without vegetation and we explore some potential feedbacks that may result in landscape resilience on vegetated hillslopes the various approaches suggest that a plant free world would be characterized by largely soil free hillslopes that plants may control the maximum thickness of soils on slopes that vegetated landforms erode at rates about one order of magnitude faster than plant free outcrops in comparable settings and that vegetated hillslope soils generally maintain long residence times such that both n and p sufficiency for ecosystems is the norm we conclude that quantitatively parameterizing biota within process based hillslope models needs to be a priority in order to project how human activity may further impact the soil mantle

comparison of observed and modeled seasonal crustal vertical displacements derived from multi institution gps and grace solutions eleven gps crustal vertical displacement cvd solutions for 110 igs08 igs14 core stations provided by the international global navigation satellite systems service analysis centers are compared with seven gravity recovery and climate experiment grace modeled cvd solutions the results of the internal comparison of the gps solutions from multiple institutions imply large uncertainty in the gps postprocessing there is also evidence that grace solutions from both different institutions and different processing approaches mascon and traditional spherical harmonic coefficients show similar results suggesting that grace can provide cvd results of good internal consistency when the uncertainty of the gps data is accounted for the grace data can explain as much as 50 of the actual signals and more than 80 of the gps annual signals our study strongly indicates that grace data have great potential to correct the nontidal loading in gps time series

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

a comparison of annual vertical crustal displacements from gps and gravity recovery and climate experiment grace over europe 1 we compare approximately 3 years of gps height residuals with respect to the international terrestrial reference frame with predictions of vertical surface displacements derived from the gravity recovery and climate experiment grace gravity fields for stations in europe an annual signal fit to the residual monthly heights corrected for atmospheric pressure and barotropic ocean loading effects should primarily represent surface displacements due to long wavelength variations in water storage a comparison of the annual height signal from gps and grace over europe indicates that at most sites the annual signals do not agree in amplitude or phase we find that unlike the annual signal predicted from grace the annual signal in the gps heights is not coherent over the region displaying significant variability from site to site confidence in the grace data and the unlikely possibility of large amplitude small scale features in the load field not captured by the grace data leads us to conclude that some of the discrepancy between the gps and grace observations is due to technique errors in the gps data processing this is evidenced by the fact that the disagreement between gps and grace is largest at coastal sites where mismodeling of the semidiurnal ocean tidal loading signal can result in spurious annual signals