Description: The accurate knowledge of the Earth’s orientation and rotation in space is essential for a broad variety of scientific and societal applications. Among others, these include global positioning, near-Earth and deep-space navigation, the realisation of precise reference and time systems as well as studies of geodynamics and global change phenomena. In this paper, we present a refined strategy for processing and combining Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), Global Navigation Satellite Systems (GNSS), and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) observations at the normal equation level and formulate recommendations for a consistent processing of the space-geodetic input data. Based on the developed strategy, we determine final and rapid Earth rotation parameter (ERP) solutions with low latency that also serve as the basis for a subsequent prediction of ERPs involving effective angular momentum data. Realising final ERPs on an accuracy level comparable to the final ERP benchmark solutions IERS 14C04 and JPL COMB2018, our strategy allows to enhance the consistency between final, rapid and predicted ERPs in terms of RMS differences by up to 50% compared to existing solutions. The findings of the study thus support the ambitious goals of the Global Geodetic Observing System (GGOS) in providing highly accurate and consistent time series of geodetic parameters for science and applications.

Description: The Earth System Modelling Group of GeoForschungsZentrum Potsdam (ESMGFZ) provides geodetic products for gravity variations, Earth rotation excitations, and Earth surface deformations related to mass redistributions and mass loads in the atmosphere, ocean, and terrestrial water storage. Earth rotation excitation compiled as effective angular momentum (EAM) functions for each Earth subsystem (atmosphere, ocean, continental hydrology) are important for Earth rotation prediction. Especially the 6-day forecasts extending the model analysis runs offer essential information for the improvement of ultra-short-term Earth rotation predictions. In addition to the individual effective angular momentum function of each subsystem, ESMGFZ calculates a combined EAM prediction product. Adjusted to the official Earth orientation parameter (EOP) products IERS 14C04 and Bulletin A, this EAM prediction product allows to extrapolate the polar motion and Length-of-Day parameter time series for 90 days into the future via the Liouville equation. ESMGFZ submits such an EOP prediction to the 2nd EOPPCC campaign.

Description: The Atmosphere and Ocean De-Aliasing Level-1B (AOD1B) Product provides a priori information about temporal variations in the Earth's gravity field caused by global mass variability in atmosphere and ocean.'It is based on analysis and forecast data of the operational high-resolution global numerical weather prediction (NWP) model from the European Centre for Medium-Range Weather Forecasts (ECMWF) such as ERA5 and ocean bottom pressure from an unconstrained simulation with a global ocean general circulation model that is consistently forced with ECMWF atmospheric data.

Description: We assess the impact of varying the mass anomaly sources on the calculation of atmospheric tidal displacement harmonics. Atmospheric mass anomalies are obtained from five state-of-the-art numerical weather models (NWM): DWD’s ICON-Global, ECMWF’s IFS, JMA’s JRA55, ECMWF’s ERA5, and NASA’s MERRA2. To evaluate how the atmospheric tides’ representation in the different models displaces Earth’s crust, we calculate mass harmonics based on a fixed time span (2019.0–2022.0). To evaluate how temporally variable atmospheric tide manifestations are, we also applied a square-root-information filter on displacements spanning seven decades of ERA5. In addition, the variable harmonic atmospheric forcing is used to excite harmonic sea-surface variations employing the barotropic model TiME. The results from the analysis of the five numerical weather models as well as the monthly updated states of ERA5 harmonics are compared. We find that inter-model differences are larger than temporal harmonic modulations for all waves beating at frequencies higher than 1 cpd. We have confirmed that significant modulations are not an artefact in NWM but rather a true effect, and accounting for them might become of relevance for space geodesy at some point as soon as observations increase in spatio-temporal density and accuracy. The global RMS of radial displacements is 0.07 mm (SNR of 16.2 dB) for the “epoch” ensemble and 0.10 mm (SNR of 8.9 dB) for the “NWM” ensemble. We find discrepancies as large as 0.28 mm between harmonics from MERRA2 and early ERA5 batches, which we attribute to data sparsity in the in situ data assimilated into the NWM during the earlier years of the atmospheric reanalysis.

Description: The Atmosphere and Ocean non-tidal De-aliasing Level-1B (AOD1B) product is widely used in satellite gravimetry to correct for transient effects of atmosphere-ocean mass variability that would otherwise alias into monthly-mean global gravity fields. The most recent release is based on the global ERA5 reanalysis and ECMWF operational data together with simulations from the general ocean circulation model MPIOM consistently forced with fields of the same atmospheric data-set. As background models are inevitably imperfect, residual errors due to aliasing remain. Accounting for the uncertainties of the background model data has, however, proven to be a useful approach to mitigate the impact of residual aliasing. In light of the changes made in the new release of AOD1B, previous uncertainty assessments are deemed too pessimistic and need to be revisited. We here present a new time-series of true errors adapted for AOD1B RL07 for the application in satellite gravity field processing and simulation studies. It is based on model differences between state-of-the-art atmospheric reanalysis and an oceanic ensemble simulation using MPIOM to account for differences in forced as well as intrinsic oceanic variability.

Description: The GRACE Atmosphere and Ocean Level-1B (AOD1B) product is routinely applied in the processing of satellite gravimetry data to mitigate the impact of temporal aliasing. Spurious trends, low-frequency signals or bias jumps in the background model data can, if unaccounted for, introduce biases into the global gravity solutions which might be interpreted erroneously in subsequent geophysical analyses. Here, we examine the most recent release, RL07, of AOD1B for such artefacts. A focus is placed on the transition from the atmospheric reanalysis ERA5 to operational weather model data, in January 2018, which coincides with the gap between the missions GRACE and GRACE-FO. We find that linear trends computed from 1975 to 2020 are well below 30 Pa/a for all components of RL07. The assessment of 3-hourly tendencies gives no indication of bias jumps and shows that the transition in atmospheric data does not have an adverse effect on the consistency of RL07. We conclude with a comparison of the variability of both AOD1B RL06 and RL07 in the context of their application in satellite gravimetry.

Description: The Atmosphere and Ocean De-Aliasing Level-1B (AOD1B) product provides a priori information about temporal variations in the Earth's gravity field induced by non-tidal circulation processes in atmosphere and ocean. It is routinely applied as a background model in the Gravity Recovery and Climate Experiment (GRACE)/GRACE Follow-On (GRACE-FO) satellite gravimetry data processing. We here present three new datasets in preparation for the upcoming release RL07 of AOD1B, that are based on either the global ERA5 reanalysis or the ECMWF operational data together with simulations from the Max-Planck-Institute for Meteorology general circulation model forced consistently with the fields of the same atmospheric data set. The oceanic simulations newly include an updated bathymetry around Antarctica including cavities under the ice shelves, the explicit implementation of the feedback effects of self-attraction and loading to ocean dynamics as well as a refined harmonic tidal analysis. Comparison to the current release of AOD1B in terms of GRACE-FO K-band range-acceleration pre-fit residuals, LRI line-of-sight gravity differences and band-pass filtered altimetry data reveals an overall improvement in the representation of the high-frequency mass variability. Potential benefits of enhancing the temporal resolution remain inconclusive so that the upcoming release 07 will be sampled again every 3 hr.

Description: Accurate quantification of the atmospheric state is achieved by assimilating numerous and disperse observations into numerical weather models (NWM). The spatio-temporal atmospheric density distribution, a derivative of essential meteorological variables, affects among others how electromagnetic signals traverse Earth’s atmosphere and how satellites orbit through Earth’s gravity field. Atmospheric refraction in the electrically neutral atmosphere is quantified e.g., during the GNSS data analysis, and holds valuable information about the water vapor distribution in the vicinity of the ground stations. Satellite gravimetry as realized by the GRACE and GRACE-FO missions is sensitive to mass redistribution within Earth’s fluid envelope, including but not limited to the atmosphere and the terrestrial water storage, and to high-frequency variations stemming from the time-integrated effect of precipitation and evapotranspiration. In this work we employ two state-of-the-art meso-beta scale NWM (ECMWF’s latest reanalysis ERA5 and DWD’s operational model ICON-global) as well as ERA5‘s ensemble members to demonstrate that tropospheric moisture distribution and net atmospheric freshwater fluxes are quite uncertain in modern NWM in comparison to other quantities such as hydrostatic atmospheric mass and that certain space geodetic observing systems such as GNSS and GRACE-FO are appropriate tools to monitor them, thus enhancing the accuracy of numerical weather prediction.

Description: This dataset contains predictions of Earth orientation parameters (EOP) submitted during the Second Earth Orientation Parameters Prediction Comparison Campaign (2nd EOP PCC). The 2nd EOP PCC has been carried out by Centrum Badań Kosmicznych Polskiej Akademii Nauk CBK PAN in Warsaw in cooperation with the GFZ German Research Centre for Geosciences in Potsdam (Germany) and under the auspices of the International Earth Rotation and Reference Systems Service (IERS) within the IERS Working Group on the 2nd EOP PCC. The purpose of the campaign was to re-assess the current capabilities of EOP forecasting and to find most reliable prediction approaches. The operational part of the campaign lasted between September 1, 2021 and December 28, 2022. Throughout the duration of the 2nd EOP PCC, registered campaign participants submitted forecasts for all EOP parameters, including dX, dY, dPsi, dEps (components of celestial pole offsets), polar motion, differences between universal time and coordinated universal time, and its time-derivative length-of-day change. These submissions were made to the EOP PCC Office every Wednesday before the 20:00 UTC deadline. The predictions were then evaluated once the geodetic final EOP observations from the forecasted period became available. Each participant could register more than one method, and each registered method was assigned an individual ID, which was used, e.g., for file naming. The dataset contains text files with predicted parameters as submitted by campaign participants and MATLAB file which is a database with all correct predictions from each participant loaded into a structure.

Description: Modern geodetic observations of the Earth's shape, external gravity field, and orientation in space reflect temporal variations of those quantities that are caused by a wide range of dynamics acting at the surface of our planet as well as deep within the Earth's interior. Global numerical models of those processes which initially are independent from geodetic observations are critically important for the utilization of geodetic data in the other branches of physical Earth sciences. By means of dedicated examples from the Earth System Modelling group at GFZ, we show how (i) a priori information about global ocean tides including minor tides reduces temporal aliasing artefacts; (ii) machine learning techniques guided by land-surface model output can help to downscale coarse resolution satellite data; and (iii) the joint consideration of expertise from both solid Earth geophysics and large-scale hydrosphere dynamics can help to discriminate between gravity field changes induced by glacial isostatic adjustment and nearby terrestrial water storage changes. We will also highlight various model-based data products specifically designed for geodetic applications that are routinely updated at GFZ and provided to the scientific community free of charge as a contribution to the international geodetic data infrastructure. Those data products include crustal deformations due to tidal and non-tidal surface loads; time-variations in gravity induced by mass redistributions in atmosphere and oceans; as well as effective angular momentum functions that characterize changes in the Earth's orientation.