Seasonal gravity field variations from GRACE and hydrological models

Abstract

This study present an investigation of the newly released 18 monthly gravity field solutions from the GRACE twin space-crafts with emphasis on the global scale annual gravity field variations observed from GRACE and modeled from hydrological models as annual changes in terrestrial water storage. Four global hydrological models covering the same period in 2002-2003 as the GRACE observations were investigated to for their mutual consistency in estimates of annual variation in terrestrial water storage and related temporal changes in gravity field. The hydrological models differ by a maximum of 2 μGal or nearly 5 cm equivalent water storage in selected regions. Integrated over all land masses the standard deviation among the annual signal from the four hydrological models are 0.6 μGal equivalent to around 1.4 cm in equivalent water layer thickness. The estimated accuracy of the annual variation in gravity from GRACE is around 0.4 μGal (0.9 cm water layer thickness) on 2000 km length scales. This makes the GRACE observations of terrestrial water storage on global annual scales more accurate than present-day hydrological models.