Global time-variations of hydrological signals from GRACE satellite gravimetry

SUMMARY Successfully launched in 2002 mid-March, the goal of the Gravity Recovery And Climate Experiment (GRACE) satellite mission is to measure the spatio-temporal variations of the gravity field of the Earth to high accuracy (∼1 cm in terms of geoid height) and a spatial resolution of ∼200–300 km, for a nominal period of 5 yr. The unprecedented precision of the GRACE mission will enable us to detect tiny time variations of the gravity field related to global redistributions of water and air mass inside fluid envelops at the surface of the Earth. In this paper, we present a new approach based on linear inverse methods to separate the different contributions of the main surface fluid reservoirs (oceans, atmosphere, total continental water storage including snow, soil wetness, ground water and ice caps) from monthly synthetic GRACE geoids. The synthetic geoids were computed from outputs of global models of different climatic fields. Because of the non-uniqueness of the classical inverse problems in gravimetry, independent information was added before inverting the synthetic geoids. Geoid solutions associated with each fluid contribution were then converted into water-equivalent thickness maps. Validation of the continental water storage solutions was performed by comparing total soil water estimates [soil moisture (SM) plus groundwater] with predictions of a global hydrological model in 71 different drainage basins of the world. Analysis of the a posteriori errors of the solutions suggests that the inversion method developed in this study allows recovering monthly water mass changes with a cm precision.

[1]  S. Swenson,et al.  Methods for inferring regional surface‐mass anomalies from Gravity Recovery and Climate Experiment (GRACE) measurements of time‐variable gravity , 2002 .

[2]  Matthew Rodell,et al.  The potential for satellite-based monitoring of groundwater storage changes using GRACE: the High Plains aquifer, Central US , 2002 .

[3]  Tracy K. P. Gregg,et al.  Volcanic eruptions on mid‐ocean ridges: New evidence from the superfast spreading East Pacific Rise, 17°–19°S , 2002 .

[4]  P. Milly,et al.  Global Modeling of Land Water and Energy Balances. Part I: The Land Dynamics (LaD) Model , 2002 .

[5]  William H. Press,et al.  Numerical recipes in C , 2002 .

[6]  J. Wahr,et al.  Can surface pressure be used to remove atmospheric , 2001 .

[7]  Matthew Rodell,et al.  An analysis of terrestrial water storage variations in Illinois with implications for the Gravity Recovery and Climate Experiment (GRACE) , 2001 .

[8]  Entry, Flux, and Exit of Potential Vorticity in Ocean Circulation , 2001 .

[9]  Matthew Rodell,et al.  Detectability of variations in continental water storage from satellite observations of the time dependent gravity field , 1999 .

[10]  Johan Nilsson,et al.  Reconciling thermodynamic and dynamic methods of computation of water-mass transformation rates , 1999 .

[11]  D. Giard,et al.  Global Soil Wetness Project: Forecast and Assimilation Experiments Performed at Météo-France@@@フランス気象局における予報と同化実験 , 1999 .

[12]  F. Bryan,et al.  Time variability of the Earth's gravity field: Hydrological and oceanic effects and their possible detection using GRACE , 1998 .

[13]  L. Perelman,et al.  Hydrostatic, quasi‐hydrostatic, and nonhydrostatic ocean modeling , 1997 .

[14]  L. Perelman,et al.  A finite-volume, incompressible Navier Stokes model for studies of the ocean on parallel computers , 1997 .

[15]  R. Tokmakian.  Comparisons of time series from two global models with tide‐gauge data , 1996 .

[16]  C. Wunsch,et al.  How well does a 1/4° global circulation model simulate large-scale oceanic observations? , 1996 .

[17]  Huug van den Dool,et al.  Analysis of model-calculated soil moisture over the United States (1931-1993) and applications to long-range temperature forecasts , 1996 .

[18]  Gurvan Madec,et al.  A global ocean mesh to overcome the North Pole singularity , 1996 .

[19]  R. Blakely.  Potential theory in gravity and magnetic applications , 1996 .

[20]  F. Perosanz.  Utilisation des mesures GPS pour la restitution dynamique précise d'orbites et l'amélioration des modèles globaux de champ de gravité terrestre : application au satellite TOPEX/POSEIDON et à la simulation des performances des futures missions géodésiques , 1995 .

[21]  R. Greatbatch.  A note on the representation of steric sea level in models that conserve volume rather than mass , 1994 .

[22]  Robert M. Chervin,et al.  Ocean general circulation from a global eddy‐resolving model , 1992 .

[23]  S. Planton,et al.  A Simple Parameterization of Land Surface Processes for Meteorological Models , 1989 .

[24]  B. Chao,et al.  Snow load effect on the Earth's rotation and gravitational field, 1979–1985 , 1987 .

[25]  C. Jekeli.  Alternative methods to smooth the Earth's gravity field , 1981 .