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

the benchmark glacier concept does it work lessons from the north cascade range usa benchmark glaciers were established in many alpine areas during the 1960s as part of the international hydrological decade to represent typical mass and energy processes on glaciers in different climatic regions around the world these glaciers have received new interest in the past decade because they are used to infer the contribution of alpine glacier wastage to global sea level rise we compare south cascade glacier the benchmark glacier for the northwest contiguous usa and four other secondary glaciers against the topographic area and mass changes of 321 glaciers in the surrounding region results show that south cascade glacier is unusually large of lower slope and much larger area and had mass losses greater than most other glaciers in the region three of the four secondary glaciers were much more typical year to year variations in mass balance were highly correlated between all five glaciers and any of these glaciers including the benchmark glacier could be used to infer temporal mass variations in the region however the use of south cascade glacier to estimate area mass losses for the region would result in overestimating the area mass changes by a factor of three local differences in the magnitude of annual glacier mass balance control cumulative mass changes and area changes there appears to be no way to select a representative glacier a priori and knowledge of changes over the region is required therefore there may be great uncertainty in estimates of sea level rise from the wastage of alpine glaciers based on the benchmark approach we recommend re evaluation of regional glacier mass changes inferred from benchmark glaciers in critical regions

sea level changes in a back arc foreland transition the late carboniferous permian karoo basin of south africa abstract the late carboniferous to early permian succession in the karoo basin consists in ascending stratigraphic order of diamictites mudrocks greywackes and immature sandstones the diamictites are interpreted as glacigene deposits laid down by a marine ice sheet on a shelf post glacial suspension settling of predominantly mud occurred on the basin floor during open marine and later brackish conditions basin floor fan deposits accumulated in the foredeep whereas deltaic mud silt and sand finally infilled the basin glacigene sedimentation occurred in a back arc basin during the late carboniferous and early permian the post glacial succession accumulated in a foreland basin in which the rising orogenic belt was the predominant sediment source relative sea levels following the major namurian regression apparently remained low during the extensive gondwana glaciation marine ice sheets are highly sensitive to sea level fluctuations and minor sea level rises probably climatically controlled were recorded as interglacials when parts of the marine ice sheet collapsed final collapse of the marine ice sheet was associated with a major transgression post glacial mudrock deposition was characterised by relatively high sea levels except for the period of basin floor fan deposition when there was a sea level lowstand final infilling of the basin by prograding deltas was accompanied by a major regression the late carboniferous to early permian sea level fluctuations in the karoo basin show correspondence with global eustatic cycles reflecting low tectonic interference with sea level patterns however late permian sea levels were predominantly tectonically controlled as a result of foreland basin evolution possible global eustatic events complemented apparent sea level changes within the basin during this period

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

a comparison of in situ bottom pressure array measurements with grace estimates in the kuroshio extension 1 ocean bottom pressure estimates from gravity recovery and climate experiment grace have been validated by comparisons with an array of in situ bottom pressure measurements the 600 km by 600 km array comprised 46 bottom pressure sensors that were part of the kuroshio extension system study kess validations in other ocean regions have been limited by available data to pointwise bottom pressure measurements spatially averaged monthly mean bottom pressure over the kess array is highly correlated with grace bottom pressure estimated at the center of the array the correlations are nearly equally high for three standard choices of spatial smoothing radius applied to grace estimates 300 500 and 750 km in contrast pointwise comparisons between grace and individual bottom pressures are high or low in sub regions of kess depending partially upon the local variance of deep mesoscale eddies whose energetic length scales are shorter than 300 km kess is a suitable validation experiment for the grace estimates at monthly scales with 300 to 750 km spatial radius of smoothing

contribution of small glaciers to global sea level observed long term changes in glacier volume and hydrometeorological mass balance models yield data on the transfer of water from glaciers excluding those in greenland and antarctica to the oceans the average observed volume change for the period 1900 to 1961 is scaled to a global average by use of the seasonal amplitude of the mass balance these data are used to calibrate the models to estimate the changing contribution of glaciers to sea level for the period 1884 to 1975 although the error band is large these glaciers appear to account for a third to half of observed rise in sea level approximately that fraction not explained by thermal expansion of the ocean

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

recent earth oblateness variations unraveling climate and postglacial rebound effects earth9s dynamic oblateness j2 has been decreasing due to postglacial rebound pgr however j2 began to increase in 1997 indicating a pronounced global scale mass redistribution within earth9s system we have determined that the observed increases in j2 are caused primarily by a recent surge in subpolar glacial melting and by mass shifts in the southern pacific and indian oceans when these effects are removed the residual trend in j2 2 9 x 10 11 year 1 becomes consistent with previous estimates of pgr from satellite and eclipse data the climatic significance of these rapid shifts in glacial and oceanic mass however remains to be investigated

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

a method of inferring changes in deep ocean currents from satellite measurements of time variable gravity 1 the nasa deutsches zentrum fur luft und raumfahrt dlr satellite gravity mission gravity recovery and climate experiment grace launched in march 2002 will map the earth s gravity field at scales of a few hundred kilometers and greater every 30 days we describe a method of using those gravity measurements to estimate temporal variations in deep ocean currents we examine the probable accuracy of the current estimates by constructing synthetic grace data based in part on output from an ocean general circulation model we ignore the possible contamination caused by short period gravity signals aliasing into the 30 day solutions we conclude that in the absence of aliasing grace should be able to recover the 30 day variability of midlatitude currents at a depth of 2 km with an error of about 6 15 in variance when smoothed with 500 700 km averaging radii

analysis of large scale ocean bottom pressure variability in the north pacific 1 we use the leading empirical orthogonal functions eofs of ocean bottom pressure obp derived from an ocean model and the technique of eof reconstruction to reduce noise in the large scale obp variations derived from the gravity recovery and climate experiment grace the subsequent obp variations from the model and grace are then examined in the north pacific between january 2003 and may 2007 although annual and semiannual variations are similar grace observes large interannual fluctuations poleward of 30 where obp increases from a low of nearly 3 cm below normal in early 2003 to normal throughout 2004 and 2005 then an increase of nearly the same magnitude in 2006 these fluctuations have also been observed in obp inferred from satellite altimetry corrected for steric variations computed from argo float data since grace and steric corrected altimetry are completely independent observations of obp we conclude that the model has errors or deficiencies in predicting the interannual obp fluctuations in the north pacific

earth s variable rotation recent improvements in geodetic data and practical meteorology have advanced research on fluctuations in the earth9s rotation theinterpretation of these fluctuations is inextricably linked with studies of the dynamics of the earth moon system and dynamical processes in the liquid metallic core of the earth where the geomagnetic field originates other parts of the earth9s interior and the hydrosphere and atmosphere fluctuations in the length of the day occurring on decadal time scales have implications for the topography of the core mantle boundary and the electrical magnetic and other properties of the core and lower mantle investigations of more rapid fluctuations bear on meteorological studies of interannual seasonal and intraseasonal variations in the general circulation of the atmosphere and the response of the oceans to such variations

depositional environments of the lower permian dwyka diamictite and prince albert shale inferred from the geochemistry of early diagenetic concretions southwest karoo basin south africa abstract the upper dwyka and lower ecca groups in the karoo basin of south africa document the climatic and palaeoenvironmental changes associated with the final permo carboniferous deglaciation of the gondwana supercontinent the depositional environments of these groups have until recently been interpreted on the basis of sedimentological and palaeontological evidence here we use the geochemistry of early diagenetic concretions septarian calcite concretions from the upper dwyka group and phosphatic chert concretions and beds from the lower ecca group to infer the depositional environment of these rocks in the southwestern karoo basin 18o values 7 8 to 8 9 smow suggest that the calcite concretions precipitated from a mixture of meteoric and glacial melt waters rather than permian seawater 13c values 15 to 3 pdb indicate that the carbon was derived from a mixture of craton derived calcareous material and organic matter bacterially degraded in the lower sulphate reduction to upper methanogenesis zones during early burial diagenesis the rare earth element ree patterns sr concentrations and 87sr 86sr ratios 0 716 0 737 significantly greater than permian seawater 0 708 together also support the interpretation that calcite and phosphatic concretions formed in glacial fresh water sediments

oceanic effects on polar motion determined from an ocean model and satellite altimetry 1993 2001 1 mass redistribution and motion in the oceans are major driving forces of geodetic variations including polar motion length of day geocenter and gravity field changes we examine oceanic contribution to polar motion using estimates from a data assimilating ocean general circulation model and satellite radar altimeter observations the data include model estimates of variations in oceanic mass obp and meridional and zonal velocities sea level anomalies from topex poseidon t p satellite altimeter measurements and steric sea surface height changes deduced from the model are also used to estimate obp effects estimated oceanic contributions from both the model and t p show considerably better agreement with polar motion observations compared with results from previous studies the improvement is particularly significant at intraseasonal timescales both obp and ocean current variations provide important contributions to polar motion at intraseasonal timescales the oceans appear to be a dominant contributor to residual polar motion not accounted for by the atmosphere the oceans also play an important role in seasonal excitation combined obp and ocean current contributions explain much of the residual semiannual variability

bacterial origin of east australian continental margin phosphorites many models of the origin of marine phosphorites require a sediment rich in organic matter which by decomposition releases phosphorus for the precipitation of carbonate fluorapatite1 7 this concept is useful in explaining contemporary phosphorite in areas of very high productivity off the coasts of peru chile and south west africa8 10 where there are high organic matter fluxes to the sea floor4 7 11 it does not explain the origin of marine phosphorite deposits which formed in regions of limited oceanic upwelling and productivity12 14 the east australian continental margin an area of phosphogenesis throughout the late pleistocene and holocene13 14 is a modern analogue of an east coast phosphogenic province15 17 with low productivity over the upper slope region where the most recent phosphorites have been found18 evidence is reported here for the carbonate fluorapatite in the east australian phosphorites being located within bacterial cellular structures and a model proposed for the origin of these deposits through the slow bacterial assimilation of phosphorus from seawater in an area of restricted sedimentation

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

combination of gravimetric and altimetric space observations for estimating oceanic polar motion excitations 1 global dynamic processes cause variations in the earth s rotation which are monitored by various geometric observation techniques such as global navigation satellite systems gnss satellite laser ranging slr and very long baseline interferometry vlbi with millimeter accuracy the integral effect on earth rotation of mass displacements and motion is therefore precisely known but the separation of contributions from particular geodynamic processes remains a challenge here we show that the oceanic mass effect on earth rotation can be derived from both time variable gravity field solutions from the gravity recovery and climate experiment grace and sea level anomalies sla observed from satellite altimeter missions the grace solutions require filtering and the application of an ocean mask whereas the sla need to be corrected for the steric effect as polar motion is only affected by mass redistributions we assess the accuracy of our oceanic polar motion excitations by using grace and sla solutions from different processing centers in addition we compare polar motion excitations from grace satellite altimeter data and their combinations with excitations estimated from ocean models we show that the combination of gravimetric and altimetric solutions reduces systematic errors of the individual solutions the combined solutions are about 2 times more accurate than ocean model results and about 3 times more accurate than the so called reduced geodetic excitation functions we anticipate our analysis to be valuable input for improved modeling of oceanic mass redistributions

interannual atmospheric torque and el nino southern oscillation where is the polar motion signal 1 in this paper we investigate the atmospheric excitation of polar motion pm associated with the el nino southern oscillation enso phenomenon enso effects on length of day due to changes in the axial component of atmospheric angular momentum aam have long been recognized but identification of pm excitation with enso induced equatorial aam anomalies has proved more elusive here we use an appropriately modified form of the inverted barometer ib assumption to study enso related atmospheric torques arising from pressure loading on the earth s ellipsoidal bulge and mountains and from frictional wind stress over the earth s land and ocean covered surface the resulting dissipation torques which accommodate adjustment of the oceanic mass distribution to time variable atmospheric loading are found to be small the ellipsoidal torques have the largest amplitude reflecting the order of magnitude discrepancy between the height departures of the earth s bulge 20 km and its surface orography 2 km because of relatively uniform pressure covariances with the southern oscillation index over the continents for the largely land based x component and the uniform ib response for the largely ocean based y component however the enso related pm excitation arising from the ellipsoidal torques is reduced to an amplitude comparable with the sum of regional mountain torques from the individual continents the largest of these are generated over asia and antarctica arising from efficient coupling of enso related surface pressure anomalies with large scale orographic features the geometrical mitigation of the ellipsoidal torques classically expected to dominate equatorial aam forcing accounts for the lack of a detectable atmosphere driven polar motion response to enso

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

the oceanic contribution to the earth s seasonal angular momentum budget seasonal variations in the speed of the earth s rotation manifest themselves as fluctuations in the length of the day lod with an amplitude of about 1000 microseconds s we know from previous work that at least 95 of these variations can be accounted for in terms of angular momentum exchanged between the atmosphere and the solid earth here we examine the respective contributions of the antarctic circumpolar current acc and the global oceans to the earth s seasonal angular momentum budget using in situ data from the drake passage and results from both the oceanic regional model fine resolution antarctic model fram of webb et al 1991 and the global oceanic model of maier reimer et al 1993 as analyzed by brosche et al 1990 the estimated annual contribution of the acc 2 4 s is much smaller than the total variation in the oceanic models or the existing lod aam residual both 15 20 s the estimated semi annual acc contribution 3 8 s is offset by counter currents further north in both oceanic models which exhibit larger semi annual variations in planetary angular momentum further refinements in the earth s seasonal angular momentum budget therefore will require the full planetary plus relative contribution of the global oceans in addition to that of the acc

hydrological excitations of polar motion 1993 2002 summary changes in continental water storage obtained from an advanced land data assimilation system ldas are employed to compute hydrological excitations of polar motion for the 10 yr period of 1993 2002 the results are compared with observed excitations of polar motion and contributions from the atmosphere and ocean and with results from previous studies there is remarkably good agreement between ldas derived results and remaining observed excitations i e after atmospheric and oceanic effects are removed from the observations ldas predicted hydrological excitations play a major role in closing the excitation budget for prograde and retrograde annual wobble especially for the prograde component and show considerably better agreement with observations than previous results ldas predicted results show significantly larger interannual variability and also agree well with observed excitations not accounted for by the atmosphere and ocean as demonstrated in this study ldas shows major improvement in modelling large scale change in land water storage at both seasonal and interannual timescales 1i n t r o duction under the conservation of angular momentum any change in the earth s inertia tensor due to redistribution of mass will cause changes in the earth s rotation variations of atmospheric angular momentum aam or oceanic angular momentum oam will also change the earth s rotation via exchange of angular momentum between the solid earth and its geophysical fluid envelope at interannual or shorter timescales redistribution of air and water mass and movement within the earth system including the atmosphere ocean and hydrosphere plus snow ice sheet are primary driving forces behind changes in the earth s rotation while redistribution of mass within the core and mantle plays a more important role at decadal or longer timescales

glaciogenic banded phosphorites from permian sedimentary rocks numerous bands of lower permian marine sedimentary phosphorite have been discovered in a cyrogenic diamictite as well as in a late glacial fissile shale sequence in the natal part of the great karoo basin in south africa these thin 1 30 cm bands are extensive range in p 2 o 5 content from 3 to 29 percent and average 12 5 percent the bands are presumed to have formed authigenically by direct precipitation of micron sized francolite carbonate fluorapatite microsphorite that is optically pseudoisotropic and contains an average of 1 1 percent co super 2 3 that replaces po super 3 4 in its structure lithic associates include quartz clay minerals and dropstones of varied composition in both the fissile shale and the diamictite the phosphorite bands formed within 60 degrees to 75 degrees south paleolatitude in a restricted epicontinental basin at the onset of a marine transgression following the melting and recession of continental ice sheets the occurrence of phosphorite within the glacial diamictite as well as in the fissile shale sequence in which scattered dropstones indicate continued glacial influence suggest polar to cold climatic conditions during phosphorite deposition phosphogenesis therefore seems to have taken place in an environment which is characteristically different in its climate and latitude setting from those described for major marine sedimentary phosphorite deposits of special interest is the banded morphology which is not characteristic of post cambrian deposits

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

causes of rapid motions of the earth s pole analysis of new highly accurate geodetic data reveals rapid motions of the earth s pole with peak to peak variations of 0 002 to 0 020 seconds of arc fluctuating on timescales between two weeks and several months comparison with meteorological excitation estimates shows that these motions are at least partially driven by surface air pressure changes as modified by the response of sea level to atmospheric loading such geodetic measurements thus potentially provide a novel means of observing the dynamics of the atmosphere and oceans at very low spatial wavenumbers

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

atmospheric and oceanic excitation of the earth s wobbles during 1980 2000 1 because of the action of various geophysical excitation mechanisms the earth does not rotate about its figure axis so it wobbles as it rotates here the effectiveness of atmospheric and oceanic processes in exciting the earth s wobbles during 1980 2000 is evaluated using estimates of atmospheric angular momentum from the national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis project and estimates of oceanic angular momentum from the estimating the circulation and climate of the ocean ecco consortium s simulation of the general circulation of the oceans on intraseasonal timescales atmospheric surface pressure changes are found to be the single most effective process exciting the earth s wobbles explaining about twice as much of the observed variance as do either atmospheric wind or ocean bottom pressure changes and nearly 4 times as much of the observed variance as do oceanic currents however on interannual timescales ocean bottom pressure changes are found to be the single most effective process exciting the earth s wobbles explaining more than 5 times as much of the observed variance as do atmospheric wind and pressure changes combined and more than twice as much of the observed variance as do oceanic currents within the chandler band it is found that during 1980 2000 atmospheric and oceanic processes have enough power to excite the chandler wobble and are significantly coherent with it the single most important mechanism exciting the chandler wobble is found to be ocean bottom pressure variations atmospheric and oceanic processes do not appear to have enough power to excite the earth s wobbles to their observed levels on pentadal and longer timescales although series longer than the 21 yearlong series used here need to be studied in order to obtain greater statistical significance of this result

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

rapid ocean signals in polar motion and length of day 1 non tidal variability in ocean currents and bottom pressure is substantial at short periods but relating the associated signals in ocean angular momentum oam to observed polar motion and length of day fluctuations has been difficult our simulations using a barotropic ocean model reveal a clear connection between the estimated oam signals and both polar motion and length of day at periods of 3 10 days the dynamic response of the oceans to barometric pressure plays an important role in the excitation of rapid rotation signals the impact of oam variability is most clear when using gps based earth orientation measurements with little temporal smoothing using the gps series and accounting for oam in addition to atmospheric effects yields substantial improvements in the excitation budget for rapid polar motion and length of day the comparisons with earth rotation data provide a useful check on the rapid ocean variability simulated by the barotropic model

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

oceanic excitations on polar motion a cross comparison among models recent studies based on various ocean general circulation models ogcms demonstrate that the oceans are a major contributor to polar motion excitations in this paper we analyse and compare observed non atmospheric polar motion excitations with oceanic angular momentum oam variations determined from four ogcms which include the parallel ocean climate model pocm a barotropic ocean model bom the estimating the circulation and climate of the ocean ecco non data assimilating model ecco nda and the ecco data assimilating model ecco da the data to be analysed span a 5 yr overlapped period from 1993 to 1997 at annual timescale considerable discrepancies exist between pocm and the other three models which result mainly from differences in annual components of the forcing wind fields at semi annual timescale however pocm shows better phase agreement with observed non atmospheric polar motion excitation than the other three ocean models at intraseasonal timescales ecco da yields better agreement with observations and reduces the variance of non atmospheric excitations by similar to 60 per cent 10 20 per cent more than those explained by the other three models however at the very short periods of 4 20 days the bom estimates could explain about half of the observed variance twice as much as that by ecco nda and also shows considerably better correlation with observations due to different modelling schemes and methods significant discrepancies could arise with respect to the quality of modelling large scale oceanic mass redistribution and current variation a complete understanding of global oceanic contributions to polar motion excitation still remains a challenge

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

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

observing ocean heat content using satellite gravity and altimetry 1 a method for combining satellite altimetry observations with satellite measurements of the earth s time varying gravity to give improved estimates of the ocean s heat storage is presented over the ocean the time variable component of the geoid can be related to the time varying bottom pressure the methodology of estimating the ocean s time varying heat storage using altimetric observations alone is modified to include observations of bottom pressure a detailed error analysis of the methodology is undertaken it is found that the inclusion of bottom pressure improves the ocean heat storage estimates the improvement comes from a better estimation of the steric sea surface height by the inclusion of bottom pressure in the calculation over using the altimeter observed sea surface height alone on timescales of the annual cycle and shorter the method works particularly well however long timescale changes in the heat storage are poorly reproduced because of deficiencies in the methodology and the presence of contaminating signals in the bottom pressure observations index terms 4556 oceanography physical sea level variations 1223 geodesy and gravity ocean earth atmosphere interactions 3339 1227 geodesy and gravity planetary geodesy and gravity 5420 5714 6019 1243 geodesy and gravity space geodetic surveys 4275 oceanography general remote sensing and electromagnetic processes 0689 keywords ocean heat content altimetry satellite gravity steric height remote sensing

recent trends in arctic ocean mass distribution revealed by grace 1 measurements of ocean bottom pressure by the gravity recovery and climate experiment grace and new in situ bottom pressure measurements confirm the accuracy and utility of grace measurements in the arctic ocean they reveal a declining trend in bottom pressure that corresponds to mass changes due to decreasing upper ocean salinities near the north pole and in the makarov basin the spatial distribution and magnitude of these trends suggest the arctic ocean is reverting from the cyclonic state characterizing the 1990s to the anticyclonic state that was prevalent prior to the 1990s

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

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

oceanic signals in observed motions of the earth s pole of rotation motion of the earth s pole of rotation relative to its crust commonly referred to as polar motion can be excited by a variety of geophysical mechanisms1 in particular changes in atmospheric wind and mass fields have been linked to polar motion over a wide range of timescales but substantial discrepancies remain between the atmospheric and geodetic observations1 2 3 4 here we present results from a nearly global ocean model which indicate that oceanic circulation and mass field variability play important roles in the excitation of seasonal to fortnightly polar motion the joint oceanic and atmospheric excitation provides a better agreement with the observed polar motion than atmospheric excitation alone geodetic measurements may therefore be used to provide a global consistency check on the quality of simulated large scale oceanic fields

global surface water induced seasonal variations in the earth s rotation and gravitational field summary the seasonal cycle in continental surface water storage is modelled first using a global meteorological data set of precipitation snow and rain and evapotranspiration compiled by willmott et af its effects on the annual wobble excitation y and the seaonal variations in the length of day lod and low degree zonal gravitational coefficients ji are then computed the resulting y agrees well with the widely referenced estimate by van hylckama however these results are questionable because an anatomy of the computation indicates a near complete east west longitudinal cancellation ia the snow contribution in contradiction to the satellite remote sensing data study by chao et af the problem arises from a chronic underestimation of asian snow mass by conventional methods in order to obtain an optimal estimate of y under present circumstances we combine the contribution of rainfall and evapotranspiration computed from willmott et af s data set with the snow load contribution computed by chao et al from satellite data the result indicates a great deal of cancellation between these two contributions especially in the prograde component because of their opposite seasonal cycles and the similar quantities of water mass involved the surface water contribution to y is thus far smaller than previously computed the seasonal variations in j2 j3 j4 and lod are similarly estimated because of the zonal nature of their weighting functions they suffer no longitudinal cancellation so that the chronic underestimation of asian snow is less of a problem furthermore their rainfall and snow load contributions largely reinforce each other quantitatively the surface water induced variation may prove to be a significant contributor to the overall seasonal non tidal variations in low degree ji coefficients and lod this study excludes greenland and antarctica where no pertinent hydrological data are available at present