scholarly journals The pole tide and its effect on GRACE time-variable gravity measurements: Implications for estimates of surface mass variations

2015 ◽  
Vol 120 (6) ◽  
pp. 4597-4615 ◽  
Author(s):  
John Wahr ◽  
R. Steven Nerem ◽  
Srinivas V. Bettadpur
Keyword(s):  
Time Variable ◽  
Surface Mass ◽  
Pole Tide ◽  
Time Variable Gravity ◽  
Gravity Measurements ◽  
Variable Gravity

scholarly journals Seismologic applications of GRACE time-variable gravity measurements

2014 ◽  
Vol 27 (2) ◽  
pp. 229-245 ◽  
Author(s):  
Jin Li ◽  
Jianli Chen ◽  
Zizhan Zhang
Keyword(s):  
Time Variable ◽  
Time Variable Gravity ◽  
Gravity Measurements ◽  
Variable Gravity

scholarly journals Determination of ellipsoidal surface mass change from GRACE time-variable gravity data

2019 ◽  
Vol 219 (1) ◽  
pp. 248-259
Author(s):  
Khosro Ghobadi-Far ◽  
Michal Šprlák ◽  
Shin-Chan Han
Keyword(s):  
Time Variable ◽  
Mass Change ◽  
Lower Latitude ◽  
Spherical Approximation ◽  
Polar Regions ◽  
Surface Mass ◽  
Time Variable Gravity ◽  
The Earth ◽  
Mass Redistribution ◽  
Variable Gravity

SUMMARY The problem of determining mass redistribution within the Earth system from time-variable gravity (TVG) data is non-unique. Over seasonal and decadal time-scales, mass redistribution likely takes place on the Earth’s surface. By approximating the Earth’s surface by a sphere, surface mass variation can be uniquely determined from TVG data. Recently, using the improved GRACE TVG data, Li et al. and Ditmar found that such spherical approximation is no longer tenable and suggested practical approaches to accommodate the elliptical shape of the Earth. In this study, we develop a rigorous method of determining surface mass change on the Earth’s reference ellipsoid. We derive a unique one-to-one relationship between ellipsoidal spectra of surface mass and gravitational potential for the ellipsoidal geometry. In conjunction with our ellipsoidal formulation, the linear transformation between spherical and ellipsoidal harmonic coefficients of the geopotential field enables us to determine mass redistribution on the ellipsoid from GRACE TVG data. Using the Release 6 of GRACE TVG data to degree 60, we show that the ellipsoidal approach reconciles surface mass change rate significantly better than the spherical computation by 3–4 cm yr−1, equivalent to 10–15  per cent increase of total signal, in Greenland and West Antarctica. We quantify the spherical approximation error over the polar regions using GRACE Level-2 TVG data as well as mascon solutions, and demonstrate that the systematic error increases linearly with the maximum degree used for the synthesis. The terrestrial water storage computation is less affected by the spherical approximation because of geographic location of major river basins (lower latitude) and signal characteristics. The improvement of TVG data from GRACE and its Follow-On necessitates the ellipsoidal computation, particularly for quantifying mass change in polar regions.

scholarly journals Applications and Challenges of GRACE and GRACE Follow-On Satellite Gravimetry

2022 ◽  
Author(s):  
Jianli Chen ◽  
Anny Cazenave ◽  
Christoph Dahle ◽  
William Llovel ◽  
Isabelle Panet ◽  
...  
Keyword(s):  
Solid Earth ◽  
Large Scale ◽  
Time Variable ◽  
Global Ocean ◽  
Earth System ◽  
Satellite Gravimetry ◽  
Time Variable Gravity ◽  
The Earth ◽  
Gravity Measurements ◽  
Variable Gravity

AbstractTime-variable gravity measurements from the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) missions have opened up a new avenue of opportunities for studying large-scale mass redistribution and transport in the Earth system. Over the past 19 years, GRACE/GRACE-FO time-variable gravity measurements have been widely used to study mass variations in different components of the Earth system, including the hydrosphere, ocean, cryosphere, and solid Earth, and significantly improved our understanding of long-term variability of the climate system. We carry out a comprehensive review of GRACE/GRACE-FO satellite gravimetry, time-variable gravity fields, data processing methods, and major applications in several different fields, including terrestrial water storage change, global ocean mass variation, ice sheets and glaciers mass balance, and deformation of the solid Earth. We discuss in detail several major challenges we need to face when using GRACE/GRACE-FO time-variable gravity measurements to study mass changes, and how we should address them. We also discuss the potential of satellite gravimetry in detecting gravitational changes that are believed to originate from the deep Earth. The extended record of GRACE/GRACE-FO gravity series, with expected continuous improvements in the coming years, will lead to a broader range of applications and improve our understanding of both climate change and the Earth system.

scholarly journals Improved Estimates of Geocenter Variability from Time-Variable Gravity and Ocean Model Outputs

2019 ◽  
Vol 11 (18) ◽  
pp. 2108 ◽  
Author(s):  
Tyler C. Sutterley ◽  
Isabella Velicogna
Keyword(s):  
Center Of Mass ◽  
Global Scale ◽  
Ocean Model ◽  
Time Variable ◽  
Time Variable Gravity ◽  
Geocenter Motion ◽  
Gravity Measurements ◽  
Variable Gravity ◽  
Gravity Recovery ◽  
Grace Mission

Geocenter variations relate the motion of the Earth’s center of mass with respect to its center of figure, and represent global-scale redistributions of the Earth’s mass. We investigate different techniques for estimating of geocenter motion from combinations of time-variable gravity measurements from the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On missions, and bottom pressure outputs from ocean models. Here, we provide self-consistent estimates of geocenter variability incorporating the effects of self-attraction and loading, and investigate the effect of uncertainties in atmospheric and oceanic variation. The effects of self-attraction and loading from changes in land water storage and ice mass change affect both the seasonality and long-term trend in geocenter position. Omitting the redistribution of sea level affects the average annual amplitudes of the x, y, and z components by 0.2, 0.1, and 0.3 mm, respectively, and affects geocenter trend estimates by 0.02, 0.04 and 0.05 mm/yr for the the x, y, and z components, respectively. Geocenter estimates from the GRACE Follow-On mission are consistent with estimates from the original GRACE mission.

Geophysics From Terrestrial Time-Variable Gravity Measurements

2017 ◽  
Vol 55 (4) ◽  
pp. 938-992 ◽  
Author(s):  
Michel Van Camp ◽  
Olivier de Viron ◽  
Arnaud Watlet ◽  
Bruno Meurers ◽  
Olivier Francis ◽  
...  
Keyword(s):  
Time Variable ◽  
Time Variable Gravity ◽  
Gravity Measurements ◽  
Variable Gravity

Spherical and ellipsoidal surface mass change from GRACE time-variable gravity data

2020 ◽  
Author(s):  
Michal Šprlák ◽  
Khosro Ghobadi-Far ◽  
Shin-Chan Han ◽  
Pavel Novák
Keyword(s):  
Gravity Field ◽  
Gravitational Potential ◽  
Gravity Data ◽  
Time Variable ◽  
Mass Change ◽  
Spherical Approximation ◽  
Surface Mass ◽  
Time Variable Gravity ◽  
The Earth ◽  
Variable Gravity

<p>The problem of estimating mass redistribution from temporal variations of the Earth’s gravity field, such as those observed by GRACE, is non-unique. By approximating the Earth’s surface by a sphere, surface mass change can be uniquely determined from time-variable gravity data. Conventionally, the spherical approach of Wahr et al. (1998) is employed for computing the surface mass change caused, for example, by terrestrial water and glaciers. The accuracy of the GRACE Level 2 time-variable gravity data has improved due to updated background geophysical models or enhanced data processing. Moreover, time series analysis of ∼15 years of GRACE observations allows for determining inter-annual and seasonal changes with a significantly higher accuracy than individual monthly fields. Thus, the improved time-variable gravity data might not tolerate the spherical approximation introduced by Wahr et al. (1998).</p><p>A spheroid (an ellipsoid of revolution) represents a closer approximation of the Earth than a sphere, particularly in polar regions. Motivated by this fact, we develop a rigorous method for determining surface mass change on a spheroid. Our mathematical treatment is fully ellipsoidal as we concisely use Jacobi ellipsoidal coordinates and exploit the corresponding series expansions of the gravitational potential and of the surface mass. We provide a unique one-to-one relationship between the ellipsoidal spectrum of the surface mass and the ellipsoidal spectrum of the gravitational potential. This ellipsoidal spectral formula is more general and embeds the spherical approach by Wahr et al. (1998) as a special case. We also quantify the differences between the spherical and ellipsoidal approximations numerically by calculating the surface mass change rate in Antarctica and Greenland.</p><p> </p><p>References:</p><p>Wahr J, Molenaar M, Bryan F (1998) Time variability of the Earth’s gravity field: Hydrological and oceanic effects and their possible detection using GRACE. Journal of Geophysical Research: Solid Earth, 103(B12), 30205-30229.</p>

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