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Spatio-temporal variations of land water storage

by LEGOS last modified Feb 04, 2014 10:47 AM


Scientific context

The GRACE mission (Gravity Recovery & Climate Experiment) was launched in March 2002. This mission is dedicated to very high resolution (~200-400 km) global mapping of the spatio-temporal variations of the Earth's gravity field (or geoid) over time scales ranging from one month to a decade. The results produced by GRACE for a given time period represent the sum of the vertically integrated mass variations inside the solid and fluid envelopes. Most of these mass redistributions result from change in land water storage in the continental reservoirs (soil water, underground water and snow pack), mass variations of the ice sheets, and ocean mass changes.

Some results

G. Ramillien (Ramillien et al., 2004) has developed a robust approach to separate the various contributions of the major surface reservoirs (atmosphere, oceans, land water reservoirs, ice sheets) from monthly GRACE geoids (available since April 2002) provided by the GRACE project (GFZ, CSR, GRGS/Toulouse). This iterative approach, based on inverse (generalised least-squares) methods, is applied to extract the variations in land water storage. Figure 1 and 2 show that the inverse method damps significantly the noise of the raw geoids. Temporal maps of the geographical variations in total liquid water and snow mass have been produced since April 2002. GRACE solutions have also been used at river basin scale to determine temporal series of integrated water volume on the basin area (Ramillien et al., 2005a, Schmidt et al., 2006, Ramillien et al., 2007).

Gravimétrie spatiale c1-fig1


Figure 1 : Example of raw geoid solution from GFZ (November 2003).

Gravimétrie spatiale c1-fig2

Figure 2 : Inverse method solution for land water storage using the geoid solution shown in figure 1 (November 2003).

Ice sheets mass balance from GRACE

In a recent study (Ramillien et al., 2006), the GOHS team used GRACE data 3 years ago to determine the mass balance of Greenland and Antarctica. The results confirm the trends provided by other space techniques. This is illustrated by the following map, that shows the geographical distribution of ice volume variations of the two ice sheets, using GRACE between mid-2002 and mid-2003. The corresponding contributions to sea level are ~0.3 mm/yr for Greenland and ~0.2 mm/yr for Antarctica.

ice volume variations


Contacts : R. Ramillien, F. Frappart, A. Cazenave

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