Length of day (LOD), a fundamental component of Earth orientation parameters (EOP), reflects variations in Earth's rotation rate. Due to the influenced of atmospheric circulation, ocean currents, hydrological processes, and internal Earth dynamics, LOD exhibits complex nonlinear characteristics, making accurate prediction challenging Current LOD prediction models primarily depend on the high-precision, smoothed EOP C04 series provided by the IERS. However, this series has an inherent delay of approximately 30 days, causing it unsuitable for real-time applications such as interplanetary spacecraft tracking and navigation, GNSS meteorology, and real-time satellite orbit determination. To address these challenges, a novel approach based on a convolutional long short-term memory (ConvLSTM) method was proposed, which captures the time-varying characteristics of LOD by integrating IGS rapid products and effective angular momentum (EAM) datasets to improve the accuracy of near real-time LOD predictions. Results indicate that incorporating GNSS near real-time (NRT) data improves short-term (10–30 days) LOD prediction accuracy by 55.07%. By incorporating GNSS NRT data and EAM datasets, the ConvLSTM model significantly improves LOD prediction accuracy across various time scales. This enhancement not only strengthens Earth's rotation prediction models but also facilitates critical applications in real-time satellite orbit determination, extreme weather forecasting, and so on.

How to cite: Yu, K., Li, Z., Wang, J., and Jiang, W.: A Deep Learning Approach for Improving Near Real-Time LOD Prediction Accuracy by Integrating IGS Rapid Products and EAM Datasets, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4771, https://doi.org/10.5194/egusphere-egu25-4771, 2025.

Modern climate change has triggered large-scale lateral mass transport between land and the oceans. Indeed, satellite observations suggest unprecedented melting of global glaciers and polar ice sheets, large spatiotemporal variability of terrestrial water storage, sustained dwindling of groundwater resources, and rising global and regional sea levels. We have investigated the impact of this climate-driven surface mass redistribution on the planetary-scale phenomenon of Earth’s rotation and reported the key findings in three papers published recently in Nature Geoscience (https://doi.org/10.1038/s41561-024-01478-2), PNAS (https://doi.org/10.1073/pnas.2406930121), and Geophysical Research Letters (https://doi.org/10.1029/2024GL111148). This presentation will showcase these new results, discuss their implications, and underscore the need for continued geodetic observations to advance climate research.

The first part of this presentation is focused on the polar motion—the motion of the Earth’s spin axis relative to the crust—and provides a first cohesive interpretation of the 120-year-long data. Our analysis unravels the critical roles of climatological processes, particularly in modulating the polar motion on interannual to multidecadal timescales. We disentangle polar motion signals to uniquely constrain global-scale hydrological models. We also tease out a systematic anticorrelation between the climatological and core processes, hinting at the two-way coupling between Earth’s surficial and deep-interior processes—an intriguing multidisciplinary topic for further exploration.

Next, we will examine more than 40 years of Earth’s oblateness (J2) data and nearly 3000 years of eclipse data to evaluate the impact of climate change on length of day (LOD) variations. We show that the rate of LOD change in the past two decades (+1.3 milliseconds/century) is the greatest since the onset of modern climate change. Under high-end emission scenarios, this rate could double and surpass the tidal friction contribution (+2.4 milliseconds/century), highlighting the planetary-scale impact of modern climate change. We also derive an independent estimate of the glacial isostatic adjustment signal, which, when added to the tidal friction signal, fully reconciles the secular LOD trend derived from the ancient eclipse data, diminishing the possible contribution of core processes on secular timescales. We show, on the other hand, that in the preindustrial era the role of climatic oscillations was subdominant. In fact, by using archaeomagnetic and more modern geomagnetic data and using the simple principles of magnetohydrodynamics, we demonstrate that fluid motion in the Earth's core explains the decadal and millennial fluctuations observed in LOD record. Our results present a consistent explanation for the long-period polar motion and LOD and have considerable implications for internal and external geodynamics.

How to cite: Kiani Shahvandi, M., Adhikari, S., Dumberry, M., Mishra, S., and Soja, B.: The role of climate change on Earth’s polar motion and the length of day  , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1876, https://doi.org/10.5194/egusphere-egu25-1876, 2025.

We revisit the computation of diurnal and semidiurnal effects of the ocean tide on Polar Motion (PM) and UT1 considering the principal waves of the Ocean Tidal Angular Momentum (OTAM) calculated from the FES 2014, TPXO8 and EOT11 ocean tide atlas. We take into account the recent development of polar motion theory, especially the frequency dependence of the transfer functions in (sub-)diurnal bands. The method of calculating the minor waves is also carefully studied and modified: instead of an interpolation based on neighboring waves, we propose a frequency dependent expression obtained by a linear fit to the admittances and phases of principal waves. Compared in time domain with polar motion (PM) and UT1 derived from Very Long Baseline Interferometry (VLBI) observations, our tables for FES 2014 and TPXO8 perform as well as the recent Desai-Sibois model computed from TPXO8 tidal atlas. The impact of diurnal and semi-diurnal oscillations produced by the luni-solar tidal torque on the asymmetric mean mass distribution of the Earth are observed in the corresponding residuals, which is not the case for the older PM/UT1 model recommended in IERS Convention 2010. More generally, we conclude that tidal modelling of sub-daily terms and corresponding empirical developments are consistent to within 23 μas for PM and 3 μs for UT1. Our tables, calculated from FES 2014 or TPXO8 OTAM, can be truncated to the 48 or 50 terms with amplitudes above 1 μas for PM or 0.1 μs for UT1 to describe those Earth rotation Parameters in a way consistent with their current observation uncertainties.  

How to cite: Bizouard, C. and Cheng, Y.: Diurnal and semi-diurnal effects of ocean tides on polar motion and UT1: an updated assessment, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5769, https://doi.org/10.5194/egusphere-egu25-5769, 2025.

Understanding Earth's rotation is crucial for a wide range of applications, including positioning, satellite navigation, and remote sensing, as variations in Earth's rotational speed and orientation directly impact the accuracy of these technologies. Earth’s periodic orientation changes, known as nutations, are currently evaluated using a model adopted by the international community back in 2000. This work seeks to develop an updated nutation model by integrating the latest geophysical knowledge and refining computational methods. We build on the oceanic corrections computed by Yuting Cheng during her PhD, on the method for determining the updated Basic Earth Parameters (BEPs) from VLBI data developed in Koot et al. (2008), an Bayesian inversion updated in parameterization and sampling method, and on insights gained from the GRACEFUL Synergy ERC grant on core dynamics.

How to cite: Cheng, Y., Dehant, V., Bizouard, C., and Rivoldini, A.: Basic Earth Parameters from VLBI observations: an update, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20278, https://doi.org/10.5194/egusphere-egu25-20278, 2025.

VLBI is the unique space-geodetic technique sensitive to the full set of Earth Orientation Parameters (EOP), i.e., polar motion offsets and rates, UT1–UTC, the length-of-day (LOD) and the nutation offsets. Classically, the Rapid (R1/R4) sessions, scheduled twice a week, are the main contributor to EOP determination as they are processed with highest priority (leading to comparably low latencies). Additionally, Intensive sessions scheduled daily are processed to determine the UT1–UTC offset at short latencies.

However, also other VLBI session types (mainly 24-hour sessions) are regularly observed and processed, but typically with longer latencies, and those sessions are not regularly combined yet. As most of these sessions also have the potential to deliver good EOP estimates, their inclusion into the combination would lead to a densification of the VLBI contribution to combined EOP series. Very recently, the IERS product centers for EOPs emphasized that such a combined IVS contribution would be very valuable to improve the accuracy and reliability of the Earth rotation products according to the user requirements.

This study aims to define a set of criteria to evaluate VLBI sessions with respect to their suitability for EOP determination. These sessions include, but are not limited to, 24-hour sessions with globally well-distributed networks which were initially scheduled for other purposes like the determination of the Terrestrial Reference Frame (TRF) but are also sensitive to EOPs. Besides the distribution of the stations in a geographical sense, the selection criteria also include investigation of the sensitivity of the observations to the parameters estimated within individual sessions and of correlations between these parameters.

The different characteristics of the various VLBI session types could lead to systematic differences in the EOP estimates. We thus will investigate the resulting EOPs in view of systematics and will set up a procedure to regularly monitor the consistency between the different session types. We outline the combination strategy being developed to enable such a flexible combination of pre-selected VLBI session setups for dedicated studies and also on an operational basis, whereby the routines are based on the current operational combination scenario of the BKG/DGFI-TUM IVS Combination Centre.

How to cite: Kehm, A., Bachmann, S., Klemm, L., Modiri, S., and Thaller, D.: Characteristics of different VLBI session types in the view of Earth Orientation Parameter determination, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11002, https://doi.org/10.5194/egusphere-egu25-11002, 2025.

If the rotational equilibrium of a planetary body is disturbed, the rotation pole responds with a cyclical motion. When viewed from space, it is expressed as a wobble of the planet around its rotation axis and the duration of one cycle is referred to as the Chandler period. Because planets are not rigid, the wobble period differs from the  Euler period by the factor (1-k_X/k_f), where k_X/k_f is a ratio of two Love numbers. Here, we perform numerical simulations in which viscoelastic deformation of the planet and the Liouville equation hence polar motion are self-consistently coupled. We show that k_X is not the Love number at the frequency of the Chandler wobble itself, as is commonly assumed, but rather that it is close to k_e, the elastic Love number. This result is important when the Chandler periods of Earth and Mars are interpreted, because the measured frequency is related to the internal rheological structure in a different way than previously thought.

Details of this work are provided in the manuscript by Patočka and Walterová (2025).

References:

Patočka and Walterová (2025): “Formula for the Chandler Period (Free Wobble of Planetary Bodies)”, submitted to GRL, preprint in ESSOAr: 10.22541/essoar.172901323.38157149/v1

How to cite: Walterová, M. and Patočka, V.: Formula for the Chandler Period (Free Wobble of Planetary Bodies), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17394, https://doi.org/10.5194/egusphere-egu25-17394, 2025.

Earth Orientation Parameters (EOP), including polar motion (PM), universal time variations (UT1-UTC), and celestial pole offsets (CPO), play a critical role in the accurate transformation of coordinates between terrestrial and celestial reference frames. Reliable EOP predictions are indispensable for applications in modern geodesy and astronomy, including precise positioning, navigation on Earth and in space, and determining the orbits of satellites.

The Second Earth Orientation Parameters Prediction Comparison Campaign (2^nd EOP PCC), conducted between 2021 and 2022 by CBK PAN Warsaw in collaboration with GFZ Potsdam, provided a platform to evaluate EOP various prediction capabilities. Following the main campaign, a post-operational phase of the 2^nd EOP PCC was initiated in January 2023, offering participants the opportunity to continue submitting and evaluating their EOP forecasts. This extended phase serves as a platform for additional studies on prediction accuracy, reliability, and robustness, while fostering collaboration among participating institutions.

A key element of the post-operational phase is the EOP PML sub-campaign, which explores the application of machine learning (ML) techniques to EOP prediction. Predictions are evaluated under two scenarios: one excluding and the other including Effective Angular Momentum (EAM) data derived from atmospheric, oceanic, hydrological, and sea-level contributions. These predictions are tested over a 10-day horizon using predefined input data, i.e., IERS 20 C04 solutions and EAM forecasts. The EOP PML aims to assess the potential of ML-based approaches in enhancing prediction accuracy under controlled conditions.

This presentation will provide an overview of the post-operational phase of the 2^nd EOP PCC, with a focus on its goals, methodologies, and preliminary results, including insights gained from the EOP PML sub-campaign. By integrating traditional and ML-based approaches, this effort contributes to advancing EOP prediction techniques and their operational applications.

How to cite: Partyka, A., Nastula, J., Śliwińska-Bronowicz, J., Wińska, M., and Michalczak, M.: Insights from the post-operational phase of the Second Earth Orientation Parameters Prediction Comparison Campaign (2nd EOP PCC) and sub-campaign dedicated to machine learning-based prediction approaches (EOP PML), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9631, https://doi.org/10.5194/egusphere-egu25-9631, 2025.