Description: Global continental hydrological models use atmospheric weather data like precipitation and evaporation to force the simulation of continental water storage variations and river discharge. The predominant dependency of the modelled hydrological results from the incoming recipitation-evaporation budget is especially obvious when calculating global geodetic parameters such as Earth rotation excitation and gravity field changes. Many geodetically oriented hydrological studies are based on forcing data from the ERA-40 re-analysis of the European Centre for Medium-Range Weather Forecasts (ECMWF). In 2006 ECMWF started to develop a new interim re-analysis system derived from the latest version of their operational system. The ERA-Interim re-analysis starts 1989 and is now available until 2005. Using an improved assimilation background model and additional observation data several of the problems experienced in ERA-40 have been eliminated or significantly reduced in ERA-Interim, most notably the too-strong tropical oceanic precipitation from the early 1990s onwards. Nevertheless precipitation over tropical continental regions like in Africa is still higher than the estimates from the Global Precipitation Climate Centre (GPCC). The differences between ERA-40 and ERA-Interim forcing data significantly change hydrological Earth rotation excitation. The hydrological land surface discharge model LSDM was used to determine these differences in polar motion, length of day and low degree gravity coefficients. The detected biases indicate that the overall continental water storage is reduced, and part of the water masses are shifted between continents and seasons. The trends in excitation time series due to unbalanced precipitation-evaporation budgets vanish, whereas the seasonal timing of regional water storage events remains almost unaffected. Additional results from regional studies like in the Nile basin help to analyse the quality of the new ERA-Interim data and to classify their benefits for geodetic Earth system models.

Description: Operational global mass transport data of the atmosphere and the oceans are widely used for studies of earth rotation excitation and gravity field simulations and are essential for GRACE dealising purposes, too. Seasonal and short periodic variations are also caused by continental water mass redistributions. In order to account for the continental hydrology processes as well and to close the global water cycle, continental water mass storage fields and fluxes are needed in the same operational manner as for the atmosphere and ocean. To simulate continental water mass redistributions a land surface scheme (SLS) is combined with a hydrological discharge model (HDM). The SLS generates components of the land water budget like soil moisture, snow accumulation and evaporation as well as surface fluxes like runoff and drainage. The latter is applied as input data for the HDM simulating the lateral water flow. Both models work on daily time steps. The new extended model combination (LSXM+HDXM) for the operational use, provides daily variations of the global water mass storage and the corresponding water fluxes as well as the hydrological angular momentum functions and low degree gravity coefficients in near real time. Since both, LSXM+HDXM and OMCT, are consistently forced with operational analyses from ECMWF, the complete data set of atmospheric, oceanic and hydrologic mass variations allows a realistic representation of mass transports in the global hydrological cycle.

Description: Over the last 15 years, the Gravity Recovery and Climate Experiment (GRACE) mission has provided measurements of temporal changes in mass redistribution at and within the Earth that affect polar motion. The newest generation of GRACE temporal models, are evaluated by conversion into the equatorial components of hydrological polar motion excitation and compared with the residuals of observed polar motion excitation derived from geodetic measurements of the pole coordinates. We analyze temporal variations of hydrological excitation series and decompose them into linear trends and seasonal and non-seasonal changes, with a particular focus on the spectral bands with periods of 1000–3000, 450–1000, 100–450, and 60–100 days. Hydrological and reduced geodetic excitation series are also analyzed in four separated time periods which are characterized by different accuracy of GRACE measurements. The level of agreement between hydrological and reduced geodetic excitation depends on the frequency band considered and is highest for interannual changes with periods of 1000–3000 days. We find that the CSR RL06, ITSG 2018 and CNES RL04 GRACE solutions provide the best agreement with reduced geodetic excitation for most of the oscillations investigated.

Description: Different Earth orientation parameter (EOP) time series are publicly available that typically arise from the combination of individual space geodetic technique solutions. The applied processing strategies and choices lead to systematically differing signal and noise characteristics particularly at the shortest periods between 2 and 8 days. We investigate the consequences of typical choices by introducing new experimental EOP solutions obtained from combinations at either normal equation level processed by Deutsches Geodätisches Forschungsinstitut at the Technical University of Munich (DGFI‐TUM) and Federal Agency for Cartography and Geodesy (BKG), or observation level processed by European Space Agency (ESA). All those experiments contribute to an effort initiated by ESA to develop an independent capacity for routine EOP processing and prediction in Europe. Results are benchmarked against geophysical model‐based effective angular momentum functions processed by Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences (ESMGFZ). We find, that a multitechnique combination at normal equation level that explicitly aligns a priori station coordinates to the ITRF2014 frequently outperforms the current International Earth Rotation and Reference Systems Service (IERS) standard solution 14C04. A multi‐Global Navigation Satellite System (GNSS)‐only solution already provides very competitive accuracies for the equatorial components. Quite similar results are also obtained from a short combination at observation level experiment using multi‐GNSS solutions and SLR from Sentinel‐3A and Sentinel‐3B to realize space links. For ΔUT1, however, very long baseline interferometry (VLBI) information is known to be critically important so that experiments combining only GNSS and possibly SLR at observation level perform worse than combinations of all techniques at normal equation level. The low noise floor and smooth spectra obtained from the multi‐GNSS solution nevertheless illustrates the potential of this most rigorous combination approach so that further efforts to include in particular VLBI are strongly recommended.

Description: Based on the latest GFZ release 06 of monthly gravity fields from GRACE satellite mission, area-averaged barystatic sea-level is found to rise by 2.02 mm/a during the period April 2002 until August 2016 in the open ocean with a 1000 km coastal buffer zone when low degree coefficients are properly augmented with information from satellite laser ranging. Alternative spherical harmonics solutions from CSR, JPL and TU Graz reveal rates between 1.94 and 2.08 mm/a, thereby demonstrating that systematic differences among the centers are much reduced in the latest release. The results from the direct integration in the open ocean can be aligned to associated solutions of the sea-level equation when fractional leakage derived from two differently filtered global gravity fields is explicitly considered, leading to a global mean sea-level rise of 1.72 mm/a. This result implies that estimates obtained from a 1000 km coastal buffer zone are biased 0.3 mm/a high due the systematic omission of regions with below-average barystatic sea-level rise in regions close to substantial coastal mass losses induced by the reduced gravitational attraction of the remaining continental ice and water masses.

Description: The German Research Centre for Geosciences GFZ provides non-tidal atmospheric and oceanic loading (NTAOL) displacements for tracking stations located on the Earth’s surface based on ECMWF numerical weather models (NWM) and compatible with GRACE atmosphere and ocean de-aliasing products (AOD1B). We apply both, the dynamic (AOD1B) and the geometric (NTAOL) models, to Precise Orbit Determination (POD) of the altimetry missions ENVISAT, Jason-1, and Jason-2 with Satellite Laser Ranging (SLR) and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) observations. Alternatively to the GFZ displacements, those provided by the International Mass Loading Service (IMLS) based on the MERRA NWM are applied also. The differences in POD are qualified in terms of orbital fits, orbit differences and altimeter cross-over differences. It turns out that the major effect comes from AOD1B, that from NTAOL is considerably smaller, but visible and of benefit for POD. Long-term systematics introduced by the loading models can not be detected. Geographicaly correlated systematics important for altimetry show up, however well below the millimeter. The effect of loading on altimeter cross-over results is even smaller and close to the point where sensitivity is lost.

Description: The impact of continental water mass redistributions on Earth rotation is deduced from stand-alone runs with the Hydrological Discharge Model (HDM) forced by ERA40 re-analyses as well as by the unconstrained atmospheric climate model ECHAM5. The HDM is attached in three different approaches to the atmospheric forcing models. First, ECHAM5 and its embedded land surface model generates directly runoff and drainage appropriate for the subsequent processing with HDM, like it is realized in the dynamically coupled model system ECOCTH, too. Second, an intermediate Simplified Land Surface scheme (SLS) is used to separate ERA40 precipitation into runoff, drainage, and evaporation. Third, precipitation and evaporation are used as input for the Land Surface Discharge Model (LSDM), which estimates runoff and drainage internally for its HDM-like discharge scheme. The individual models are validated by observed river discharges. The induced rotational variations represent mainly the different forcing from precipitation-evaporation and trends from inconsistent mass fluxes. The dynamical coupling of atmosphere and ocean has only a subordinated influence.

Description: Geodetic observables as, e.g., changes in the Earth's rotation, its shape and its gravity field, usually reflect the integral effect of various dynamical processes in the Earth's system associated with mass redistributions within and mass exchanges among atmosphere, ocean, cryosphere, continental hydrosphere and the underlying solid Earth. The reliable interpretation and utilization of such measurements therefore require model concepts representing the relevant dynamics in the sub-systems involved as well as consistent energy, mass and momentum fluxes across the sub-system boundaries. A modular Earth system model aspiring these requirements will be introduced which is currently being developed at GFZ Potsdam. By means of two examples, i.e., temporal changes of the global gravity field as observed by the GRACE mission and variations of the Earth's rotation as monitored by VLBI, it will be exemplarily demonstrated how individual effects like ocean bottom pressure anomalies, hydrologic mass re-distribution, continental ice-mass changes and post-glacial rebound are identified in the data and separated with the help of appropriate components of the modular modelling approach in order to provide additional information about the current state of the Earth and its recent changes.