Variability of the Gravity-to-Height Ratio Due to Surface Loads

Abstract

We study the ratio between the gravity variation and vertical displacement on the surface of a self-gravitating earth model when a surface load is applied. We adopt a theoretical and numerical point of view, excluding any observations. First, we investigate the spectral behavior of the ratio of the harmonic components of the gravity variation and vertical displacement. Then, we model the gravity-to-height ratio for different surface loads (continental hydrology, atmospheric pressure, ocean tides) using outputs of global numerical models in order to relate the predicted spatial values to theoretical mean values deduced from the spectral domain. For locations inside loaded areas, the ratio is highly variable because of the Newtonian attraction of the local masses and depends on the size of the load. For the hydrological loading (soil moisture and snow), the mean ratio over the continents is -0.87 lGal mm -1 , but increases with decreasing size of the river basins. For the atmospheric loading, assuming an inverted-barometer response of the ocean, the ratio is positive, with larger values for high latitudes (0.49 lGal mm -1 )-particularly on the coasts-than for lower latitudes (0.30 lGal mm -1 ). The ratio, however, is much less variable outside the loaded areas: in desert areas such as the Sahara and Arabia, its mean value is -0.28 lGal mm -1 . For the ocean tidal loading, we find a mean ratio of -0.26 lGal mm -1 over the continents for the diurnal tidal waves. Both results are close to the theoretical mean value of -0.26 lGal mm -1 combining elastic and remote attraction contributions.

Superconducting Gravimetry

“…A similar study combining the analysis of vertical GPS and SG was done for the Strasbourg station by Rosat et al (2009b). More insight on the variability of the ratio of gravity changes and vertical displacement due to surface loads including hydrology can be found in de Linage et al (2007Linage et al ( , 2009a. Although SGs are the best choice to detect gravity changes at interannual and seasonal timescales because of their high precision and low drift, they only deliver point measurements.…”

A comparison of the gravity field over Central Europe from superconducting gravimeters, GRACE and global hydrological models, using EOF analysis

“…The first is local-cell component (which is not the near-zone effect referred to in Section 2.3) for the model grid cell in which the station is located (this is effectively a Bouguer plate effect with the equivalent water height in the cell as thickness) and the second is a non-local (regional and global) contribution from the other cells. The latter arises from the Earth's sphericity; a more detailed description may be found in de Linage et al (2009) andPfeffer et al (2011).…”

Local and global hydrological contributions to time-variable gravity in Southwest Niger

“…Furthermore distant water masses generate Newtonian attraction, enhanced by the sphericity of the Earth (e.g. de Linage et al 2007; de Linage et al 2009). For a better interpretation of our gravimetric measurements, we attempt to correct them for these large‐scale effects using either global hydrological models, or GRACE satellite data.…”

“…Blewitt et al 2001; Bevis et al 2005) and (3) the water mass distributions generate gravity changes by the combination of Newtonian attraction and elasticity effects (e.g. Amalvict et al 2004; de Linage et al 2007; de Linage et al 2009). Llubes et al (2004) quantified the influence of aquifers on gravity variations and evidenced that mass effects are dominant at local scale (<10 km), whereas elastic effects, related to the vertical displacement of the crust and the mass redistribution inside the Earth, are dominant at scales larger than several hundreds of kilometres.…”