Time-variable gravity field models derived from observations of the Gravity Recovery and Climate Experiment (GRACE) mission, whose science operations phase ended in June 2017 after more than 15 years, enabled a multitude of studies of Earth’s surface mass transport processes and climate change. The German Research Centre for Geosciences (GFZ), routinely processing such monthly gravity fields as part of the GRACE Science Data System, has reprocessed the complete GRACE mission and released an improved GFZ GRACE RL06 monthly gravity field time series. This study provides an insight into the processing strategy of GFZ RL06 which has been considerably changed with respect to previous GFZ GRACE releases, and modifications relative to the precursor GFZ RL05a are described. The quality of the RL06 gravity field models is analyzed and discussed both in the spectral and spatial domain in comparison to the RL05a time series. All results indicate significant improvements of about 40% in terms of reduced noise. It is also shown that the GFZ RL06 time series is a step forward in terms of consistency, and that errors of the gravity field coefficients are more realistic. These findings are confirmed as well by independent validation of the monthly GRACE models, as done in this work by means of ocean bottom pressure in situ observations and orbit tests with the GOCE satellite. Thus, the GFZ GRACE RL06 time series allows for a better quantification of mass changes in the Earth system.
Signatures of ocean tidal dynamics are omnipresent in oceanographic and geodetic observations taken either on the ground or from space. This includes periodic variations in ocean currents registered by moored instruments or acoustic tomography (Dushaw et al., 1997;Luyten & Stommel, 1991;Ray, 2001) as well as by induced secondary magnetic fields (Maus & Kuvshinov, 2004;Saynisch et al., 2018), sea surface height changes measured from tide gauges and satellite altimetry (Doodson, 1928;Schrama & Ray, 1994), and global bottom pressure variations from pelagic pressure recorders and gravimetric satellite missions (Wiese et al., 2016). More recently, even tiny variations in sea surface temperature (Hsu et al., 2020) and tropical precipitation observations (Kohyama & Wallace, 2016) were related to ocean tidal dynamics.Separating tidal and transient signals in satellite records is not trivial due to the complicated spatiotemporal sampling of observations taken from satellites in non-geostationary orbits. The repeat orbit of the TOPEX/Poseidon (T/P) satellite altimetry mission (Fu & Cazenave, 2000) has been carefully selected in a way that aliases the major ocean tidal constituents into periods that are well distinct from naturally occurring periodicities, thereby providing tidal charts based on observations that cover the open ocean in a regular spatial pattern (Shum et al., 1997
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