scholarly journals A new unified approach to determine geocentre motion using space geodetic and GRACE gravity data

2017 ◽  
Vol 209 (3) ◽  
pp. 1398-1402 ◽  
Author(s):  
Xiaoping Wu ◽  
Jürgen Kusche ◽  
Felix W. Landerer
Keyword(s):  
Mass Transport ◽  
Gravity Data ◽  
Geodetic Network ◽  
Ocean Bottom ◽  
Unified Approach ◽  
Surface Mass ◽  
Continental Scale ◽  
Grace Data ◽  
Mass Transport Process ◽  
Translational Approach

Abstract Geocentre motion between the centre-of-mass of the Earth system and the centre-of-figure of the solid Earth surface is a critical signature of degree-1 components of global surface mass transport process that includes sea level rise, ice mass imbalance and continental-scale hydrological change. To complement GRACE data for complete-spectrum mass transport monitoring, geocentre motion needs to be measured accurately. However, current methods of geodetic translational approach and global inversions of various combinations of geodetic deformation, simulated ocean bottom pressure and GRACE data contain substantial biases and systematic errors. Here, we demonstrate a new and more reliable unified approach to geocentre motion determination using a recently formed satellite laser ranging based geocentric displacement time-series of an expanded geodetic network of all four space geodetic techniques and GRACE gravity data. The unified approach exploits both translational and deformational signatures of the displacement data, while the addition of GRACE's near global coverage significantly reduces biases found in the translational approach and spectral aliasing errors in the inversion.

Antarctic Circumpolar Current Transport Variability during 2003–05 from GRACE

2007 ◽  
Vol 37 (2) ◽  
pp. 230-244 ◽  
Author(s):  
Victor Zlotnicki ◽  
John Wahr ◽  
Ichiro Fukumori ◽  
Yuhe T. Song
Keyword(s):  
Wind Stress ◽  
Gravity Data ◽  
Ocean Model ◽  
Ocean Modeling ◽  
Ocean Bottom ◽  
Data Types ◽  
Annual Peak ◽  
Regional Ocean Model System ◽  
Grace Data ◽  
Circumpolar Current

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 0.6 cmH2O with ECCO), the average over the full southern path peaks (stronger ACC) in the southern winter, on days of year 197 and 97 for the annual and semiannual components, respectively; the Atlantic Ocean annual peak is 20 days earlier. An approximate conversion factor of 3.1 Sv (Sv ≡ 106 m3 s−1) of barotropic transport variability per cmH2O of BP change is estimated. Wind stress data time series from the Quick Scatterometer (QuikSCAT), averaged monthly, zonally, and over the latitude band 40°–65°S, are also constructed and subsampled at the same months as with the GRACE data. The annual and semiannual harmonics of the wind stress peak on days 198 and 82, respectively. A decreasing trend over the 3 yr is observed in the three data types.

Simple regional analyses are still possible once correlated errors are removed

2021 ◽  
Author(s):  
John Crowley ◽  
Jianliang Huang
Keyword(s):  
Great Lakes ◽  
Data Centers ◽  
Least Squares Method ◽  
Temporal Structure ◽  
Harmonic Coefficient ◽  
Water Levels ◽  
Correlated Errors ◽  
Average Technique ◽  
Surface Mass ◽  
Grace Data

<p>Correlated errors in the monthly spherical harmonic coefficient (SHC) solutions provided by the GRACE data centers are estimated and removed using the destriping method of Crowley and Huang (2020). Regional estimates for mass change are calculated across Canada using the simple basin average technique of Swenson and Wahr (2002) as well as a simple mascon approach developed by the Canadian Geodetic Survey. A comparison with mascon solutions from the GRACE data centers demonstrates excellent agreement and in some cases reveals larger amplitudes and added temporal structure. This approach does not require additional constraints/dependencies, smoothing, normalizations or scaling factors and can easily be applied to any regional geometry without the need to calculate a global solution. Solutions tend to agree well when data quality is good and diverge when errors are larger. This is expected and demonstrates the underlying uncertainties that remain. The similarity in solutions using such different methodologies provides confidence in the time series solutions. We conclude with a regional validation that uses water level changes in the Great Lakes of North America to demonstrate the effectiveness of the method. The Great Lakes are large enough that GRACE clearly detects changes in their water levels. At the same time, the lakes are close enough to each other that distinguishing signals between adjacent lakes remains a challenge for any method.</p><p>References:</p><p>Crowley, J.W., and J Huang, A least-squares method for estimating the correlated error of GRACE models, Geophysical Journal International, Volume 221, Issue 3, June 2020, Pages 1736–1749, https://doi.org/10.1093/gji/ggaa104.</p><p>Swenson, S., and J. Wahr, Methods for inferring regional surface-mass anomalies from Gravity Recovery and Climate Experiment (GRACE) measurements of time-variable gravity, J. Geophys. Res., 107(B9), 2193, doi:10.1029/2001JB000576, 2002.</p>

Electrochemical Removal of Copper and Lead from Industrial Wastewater: Mass Transport Enhancement

2009 ◽  
Vol 44 (2) ◽  
pp. 183-188 ◽  
Author(s):  
Asim Yaqub ◽  
Huma Ajab ◽  
Saqib Khan ◽  
Sajjad Khan ◽  
Robina Farooq
Keyword(s):  
Mass Transfer ◽  
Energy Consumption ◽  
Mass Transport ◽  
Diffusion Layer ◽  
Industrial Wastewater ◽  
Lead Nitrate ◽  
Electrochemical Treatment ◽  
Bulk Solution ◽  
Metallic Ions ◽  
Mass Transport Process

Abstract The effects of ultrasonic frequencies on both the mass transport process and diffusion layer were investigated during electrochemical treatment. The rates of mass transfer at a stainless steel cathode were measured for copper and lead in dilute acidified copper sulphate and lead nitrate solutions at different ultrasonic frequencies. Concentrations in bulk solution were determined by atomic absorption spectrophotometer. By increasing frequencies from 40 to 100 kHz, a high value for the mass transfer coefficient and an effective thinning of the diffusion layer were observed. Higher rates of mass transfer reduced energy consumption. Use of ultrasound with electrochemical processes can provide valuable contributions to remove metallic ions from industrial wastewater without using extra chemicals. The process has efficiently reduced the cost of energy consumption and deposition time.

scholarly journals Observation of the process of snow accumulation on the Antarctic Plateau by time lapse laser scanning

2019 ◽  
Vol 13 (7) ◽  
pp. 1983-1999 ◽  
Author(s):  
Ghislain Picard ◽  
Laurent Arnaud ◽  
Romain Caneill ◽  
Eric Lefebvre ◽  
Maxim Lamare
Keyword(s):  
Mass Balance ◽  
Laser Scanning ◽  
Laser Scanner ◽  
Ice Cores ◽  
Surface Heterogeneity ◽  
Time Lapse ◽  
Snow Accumulation ◽  
Surface Energy Budget ◽  
Surface Mass ◽  
Continental Scale

Abstract. Snow accumulation is the main positive component of the mass balance in Antarctica. In contrast to the major efforts deployed to estimate its overall value on a continental scale – to assess the contribution of the ice sheet to sea level rise – knowledge about the accumulation process itself is relatively poor, although many complex phenomena occur between snowfall and the definitive settling of the snow particles on the snowpack. Here we exploit a dataset of near-daily surface elevation maps recorded over 3 years at Dome C using an automatic laser scanner sampling 40–100 m2 in area. We find that the averaged accumulation is relatively regular over the 3 years at a rate of +8.7 cm yr−1. Despite this overall regularity, the surface changes very frequently (every 3 d on average) due to snow erosion and heterogeneous snow deposition that we call accumulation by “patches”. Most of these patches (60 %–85 %) are ephemeral but can survive a few weeks before being eroded. As a result, the surface is continuously rough (6–8 cm root-mean-square height) featuring meter-scale dunes aligned along the wind and larger, decameter-scale undulations. Additionally, we deduce the age of the snow present at a given time on the surface from elevation time series and find that snow age spans over more than a year. Some of the patches ultimately settle, leading to a heterogeneous internal structure which reflects the surface heterogeneity, with many snowfall events missing at a given point, whilst many others are overrepresented. These findings have important consequences for several research topics including surface mass balance, surface energy budget, photochemistry, snowpack evolution, and the interpretation of the signals archived in ice cores.

Fluctuations of Step Edges: Revelations About Atomic Processes Underlying Surface Mass Transport

1998 ◽  
Vol 528 ◽  
Author(s):  
T. L. Einstein ◽  
S. V. Khare ◽  
O. Pierre-Louis
Keyword(s):  
Mass Transport ◽  
A Priori ◽  
Single Layer ◽  
Atomic Processes ◽  
Vicinal Surfaces ◽  
Surface Mass ◽  
Kinetic Coefficients ◽  
Surface Mass Transport ◽  
Mass Transport Mechanisms

AbstractExperimental advances in recent years make possible quantitative observations of step-edge fluctuations. By applying a capillary-wave analysis to these fluctuations, one can extract characteristic times, from which one learns about the mass-transport mechanisms that underlie the motion as well as the associated kinetic coefficients [1-3]. The latter do not require a priori insight about the microscopic energy barriers and can be applied to situations away from equilibrium. We have studied a large number of limiting cases and, by means of a unified formalism, the crossover between many of these cases[4]. Monte Carlo simulations have been used to corroborate these ideas. We have considered both isolated steps and vicinal surfaces; illustrations will be drawn from noble-metal systems, though semiconductors have also been studied. Attachment asymmetries associated with Ehrlich-Schwoebel barriers play a role in this behavior. We have adapted the formalism for nearly straight steps to nearly circular steps in order to describe the Brownian motion of single-layer clusters of adatoms or vacancies on metal surfaces, again in concert with active experimental activity [3,5]. We are investigating the role of external influences, particularly electromigration, on the fluctuations.

scholarly journals An ice flow modeling perspective on bedrock adjustment patterns of the Greenland ice sheet

2012 ◽  
Vol 6 (6) ◽  
pp. 1263-1274 ◽  
Author(s):  
M. Olaizola ◽  
R. S. W. van de Wal ◽  
M. M. Helsen ◽  
B. de Boer
Keyword(s):  
Mass Balance ◽  
Maximum Yield ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Elastic Response ◽  
Delayed Response ◽  
Surface Mass ◽  
Grace Data ◽  
Grace Satellites ◽  
Gravity Recovery

Abstract. Since the launch in 2002 of the Gravity Recovery and Climate Experiment (GRACE) satellites, several estimates of the mass balance of the Greenland ice sheet (GrIS) have been produced. To obtain ice mass changes, the GRACE data need to be corrected for the effect of deformation changes of the Earth's crust. Recently, a new method has been proposed where ice mass changes and bedrock changes are simultaneously solved. Results show bedrock subsidence over almost the entirety of Greenland in combination with ice mass loss which is only half of the currently standing estimates. This subsidence can be an elastic response, but it may however also be a delayed response to past changes. In this study we test whether these subsidence patterns are consistent with ice dynamical modeling results. We use a 3-D ice sheet–bedrock model with a surface mass balance forcing based on a mass balance gradient approach to study the pattern and magnitude of bedrock changes in Greenland. Different mass balance forcings are used. Simulations since the Last Glacial Maximum yield a bedrock delay with respect to the mass balance forcing of nearly 3000 yr and an average uplift at present of 0.3 mm yr−1. The spatial pattern of bedrock changes shows a small central subsidence as well as more intense uplift in the south. These results are not compatible with the gravity based reconstructions showing a subsidence with a maximum in central Greenland, thereby questioning whether the claim of halving of the ice mass change is justified.

Sign in / Sign up

Export Citation Format

Share Document