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: 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.

Description: The core-mantle interaction was included in a numerical, non-linear three-layered model of the Earth's rotation, based on the angular momentum balance. We investigated the dynamical behavior of a fluid outer core and a solid inner core inside the Earth, related to the mantle by inertial coupling torques. The comparison of model results for the Free Core Nutation, the Free Inner Core Nutation and the Chandler Wobble with the observed and expected rotation parameters of the Earth gives insights on the core-mantle and inner core coupling torques as well as on damping properties due to rotational deformation. The model also allows for a detailed investigation of the dynamic motion of the solid inner core inside the liquid outer core. We present results obtained for various forcing and damping conditions including rotational deformation.

Description: Global hydrological models are dedicated to the simulation of world wide continental hydrological processes on the basis of a reduced set of global available input parameters. The land surface discharge model (LSDM) is especially optimized for the representation of the global water mass cycle in a consistent combination with an ocean model and an atmospheric model. Such Earth system models are essential for the generation of global geodetic parameters like Earth rotation variations and gravity field changes. LSDM itself can principally be divided into two parts. One part is modelling the vertical water budget from the incoming precipitation up to the excess runoff and drainage within a grid cell. The other is the discharge part modelling the horizontal water transport from the surface runoff via the river network down to the freshwater flow into the ocean. Designed as global model the flow processes in LSDM are based on a simplified representation using a twoparameter linear cascade approach which can be easily adapted world wide. Since water flow processes depend on a complex set of surface parameters the challenging task is to reduce the high quantity of available Earth observation data to the physically relevant parameters of the cascade model. Surface data have been analyzed concerning their availability, their influence on flow retention and their integration into the parameterization of the global model LSDM. At this the geoinformation part was generally realized using the open source geoinformation software GRASS. The objective is to transfer relationships between surface parameters and the modelled flow process found in regional catchment analyses to the whole earth’s surface. The integration of complex land surface data into the global hydrological model LSDM improves the geodetic model results significantly and provides the opportunity to consider time varying influences of the land surface due to easily updatable parameters.

Description: Data of global continental water mass redistribution is widely used for studies of Earth rotation excitation and gravity field simulations. They could be also useful for de-aliasing purposes of the GRACE gravity mission. The global hydrological land surface discharge model (LSDM) is oriented towards the simulation of a closed hydrological cycle conserving the total water masses in a consistent integrated Earth system model. In contrast to regional models, LSDM is optimized for globally distributed near real-time input data from the European Centre for edium-Range Weather Forecasts (ECMWF) generating the influence on integrated geodetic parameters like polar motion, length of day variations, and low degree gravity field changes on a routinely basis. To be independent of the restricted availability of a detailed local parameterization and time variable calibration LSDM works without regional or local tuning. This approach has also the advantage that the model processes remain physically interpretable. Regional results from LSDM, like river discharges, have been analyzed in detail to locate error sources coming along with this global focussing and associated simplifications. Especially for the Nile catchment we identify three necessary refinements. Since the hydrological discharge depends strongly on the precipitation input the overestimated tropical rain in Middle-East Africa of the ECMWF meteorological data has to be corrected before any further analysis. Even the improved ERA-Interim data has to be scaled to the monthly mean level provided by the Global Precipitation Climate Centre (GPCC), to obtain comparable river discharges. Evaporation estimates from the ECMWF have to be enhanced according to local effects from swamps and flooded regions like the Sudd. Anthropogenic influences such as dams and irrigation were incorporated to realistically absorb the high seasonal variability in rainfall. The regionally improved LSDM still keeps a global operational model generating now comparable river discharges for the Nile basin. The regional improvements lead also to noticeable variations in the global geodetic parameters, mainly due to the corrected precipitation-evaporation budget. Furthermore the results provide indirectly clear indications for deficiencies of the ECMWF precipitation/evaporation estimates in the tropical and sub-tropical Africa region.