Abstract
The Gravity Recovery and Climate Experiment (GRACE) satellite mission was launched in March 2002 and has an expected 5‐year lifetime. One potential application of GRACE measurements of time‐variable gravity will be to isolate the postglacial rebound signal, which can then be used to estimate the Earth's viscosity structure. In this paper we present a sensitivity analysis of simulated GRACE data, designed to assess the accuracy with which those data can be used to recover a simple model of Earth viscosity. We find that without combining with any other data type, but ignoring complications caused by uncertainties in the global ice loading history, GRACE data alone would allow us to determine the viscosity of a uniform lower mantle layer and an upper mantle/transition zone layer to within ±30–40% and to estimate lithospheric thickness to within ±15–20%. GRACE will have a harder time differentiating between the separate viscosities of the transition zone and upper mantle, but accuracies of within a factor of 2 might still be achievable for those parameters. Errors in the ice loading history could significantly degrade these viscosity estimates, particularly for the transition zone and upper mantle. The accuracy of recovery of the true Earth viscosity will depend in part on how well the model parameterization used for the grid search can represent the true Earth structure. However, combining GRACE data with data from other more traditional measurements of postglacial rebound has the potential of dramatically improving viscosity estimates throughout the Earth, particularly in the lower mantle.
Highlights
[2] Geodetic observations are playing an increasingly important role in constraining postglacial rebound (PGR) of the solid Earth
Instead of modeling the simulated Gravity Recovery and Climate Experiment (GRACE) data as the secular geoid coefficient rates for PGR corresponding to a particular Earth viscosity, we model the coefficient rates as PGR plus present-day secular trends in Antarctic ice mass, Greenland ice mass, and sea level
[43] The comparisons of simulated GRACE measurements and Earth models presented in this paper suggest that by using GRACE data alone, it should be possible to obtain useful information about the Earth’s viscosity structure
Summary
[3] The ongoing PGR process of redistribution of mass deep within the Earth causes temporal variations in the gravity field. [9] To evaluate the accuracy with which GRACE can recover this signal and to explore the implications for estimating the Earth’s viscosity profile, we construct 5 years of synthetic, monthly Stokes’ coefficients Clm and Slm, which include simulated GRACE measurement errors as well as plausible gravitational effects of PGR, present-day ice mass imbalances in Antarctica and Greenland, redistribution of water mass in the ocean and in its storage on continents other than Antarctica and Greenland, and errors in the corrections applied for changes in atmospheric mass. The model generates daily, gridded estimates of soil moisture, snowpack, surface water, and groundwater These are used to construct monthly averaged Stokes’ coefficients, which are included as part of the synthetic GRACE data. In this study we did not impose conservation of total water on the planet
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