Session G3.3

[Programme]

G3.3 | Earth Rotation: Theoretical aspects, temporal variability, physical interpretation, and prediction

Earth Rotation: Theoretical aspects, temporal variability, physical interpretation, and prediction

Convener: Justyna Śliwińska-BronowiczECSECS | Co-conveners: Sigrid Böhm, Alberto Escapa, David Salstein, Florian Seitz

Orals

| Tue, 16 Apr, 10:45–12:30 (CEST)

Room -2.91

Posters on site

| Attendance Tue, 16 Apr, 16:15–18:00 (CEST) | Display Tue, 16 Apr, 14:00–18:00

Hall X2

Accurate modeling and prediction of Earth rotation is important for geodesy, astronomy and navigation, and relates to the variability of the circulation of the fluid components of the planet. Over the past years geodetic observation systems have made significant advances in monitoring Earth rotational motion and its variability, which must be accompanied by an enhancement of theories and models.
We are interested in the progress in the theory of Earth rotation. We seek contributions that are consistent internally with the accurate observations at the mm-level, to meet the requirements of Global Geodetic Observing System and respond to IAG 2019 Res. 5 and IAU 2021 Res. B2. We invite presentations within the scope of the IAU/IAG JWG Improving Theories and Models of the Earth’s Rotation.
We welcome contributions that highlight new determinations and analyses of Earth Orientation Parameters (EOP), including combinations of different geodetic and astrometric observational techniques for deriving UT1/length-of-day variations and polar motion. We welcome discussions of EOP solutions in conjunction with a consistent determination of terrestrial and celestial frames, as tackled in the IAG/IAU/IERS JWG Consistent Realization of TRF, CRF and EOP. We are interested in the latest achievements in EOP forecasting, especially reports exploring the potential of innovative techniques in improving forecast accuracy.
We invite contributions of both the dynamical basis for links between Earth rotation, geophysical fluids, and other geodetic quantities, such as the Earth gravity field or surface deformation, and of explanations for the physical excitations of Earth rotation. Besides tidal influences from outside the Earth, the principal causes for variable EOP appear to be related to angular momentum exchange from variable motions and mass redistribution of the fluid portions of the planet.
We welcome contributions about the relationship between EOP variability and the variability in fluids due to climate variation or global change signals. Forecasts of these quantities are important especially for the operational determination of EOP and the effort to improve predictions is an important topic. We also welcome input on the modeling, variability, and excitations of the rotation of other planetary bodies.

Session assets

Session materials

Orals: Tue, 16 Apr | Room -2.91

Chairpersons: Justyna Śliwińska-Bronowicz, Florian Seitz, David Salstein

10:45–10:50

5-minute convener introduction

10:50–11:00

EGU24-4521

On-site presentation

Multidisciplinary Implications from the post-2015 Chandler Wobble Anomaly

Masato Furuya and Ryuji Yamaguchi

Given the disappearance of the 6-year beat in recent polar motion data, we have pointed out that the Chandler Wobble (CW) has not been excited since 2015 and further examined if the presently available Earth-system-modeling data can explain the anomaly (Yamaguchi and Furuya 2024, doi:10.1186/s40623-023-01944-y). Here we discuss its implications from meteorological and geodynamical points of view.

We confirmed that two independent atmospheric angular momentum (AAM) data from ERA5 and JRA-55 were almost in perfect match with each other in terms of their persistently smaller contributions to the CW excitations in recent years. We thus examined the temporal changes in the regional contributions to the global AAM, using JRA-55 reanalysis data. While the mass term exhibited no significant changes in any latitude zones throughout the analysis period, the motion term in some latitude zones exhibited larger amplitudes since 2015 than before. We speculate its possible connections to the recent anomalies of the quasi-biennial-oscillation in 2015/2016 and 2019/2020.

Another important conclusion in Yamaguchi and Furuya (2024) is that the quality factor (Q) of the CW is not as high as 100, which has been preferred in previous studies, whereas there have been a couple of times differences even in the recent Q estimates; e.g., from 49 by Furuya and Chao (1996), 97 by Seitz et al (2012), 127 by Nastula and Gross (2015). While Smith and Dahlen (1981) preferred Q~100 and quantitatively interpreted the period and Q in terms of a frequency-dependent mantle anelasticity, the lower Q than previously thought will suggest a need to revise the theory and have an implication for the lower-mantle rheology.

How to cite: Furuya, M. and Yamaguchi, R.: Multidisciplinary Implications from the post-2015 Chandler Wobble Anomaly, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4521, https://doi.org/10.5194/egusphere-egu24-4521, 2024.

11:00–11:10

EGU24-6342

ECS

On-site presentation

The excitation of free core nutation: a reappraisal

Mostafa Kiani Shahvandi, Michael Schindelegger, Lara Börger, Siddhartha Mishra, and Benedikt Soja

Free Core Nutation (FCN) is a rotational normal mode of the Earth arising from the misalignment of the rotation vectors of the mantle and the fluid outer core. There has long been suggestive evidence that this mode is excited against dissipation by variations in Atmospheric and Oceanic Angular Momentum (AAM and OAM, respectively), but efforts to reconcile model-based AAM and OAM estimates with the FCN in geodetic data (the Celestial Pole Offsets, CPO) have remained futile. In particular, prior assessments suggest that the power of geophysical excitation from AAM/OAM data exceeds the power of geodetic excitation at the FCN frequency by a factor of 10 or more. Here we reassess the geophysical excitation of FCN using 3-hourly AAM and OAM series from two latest-generation atmospheric reanalyses and consistently forced ocean forward models, called MERRA-2. We focus on the pressure terms and transform them to the celestial frame by complex demodulation. In addition, we use the latest CPO series of the International Earth Rotation and Reference Systems Service (IERS 20 C04) and convert it to geodetic excitation using a digital filter based on the broad-band Liouville equation. By filtering the geodetic and geophysical excitation series near the FCN frequency band (approximately –440 to –420 days in the celestial frame) we show that the agreement between these two series is improved relative to previous studies, such that the ratio of the power spectrum of geophysical to geodetic excitations is ~4.6. Moreover, we find clear similarities between observed and modeled (excitation) time series in the FCN band. Among the different drivers, the impact of AAM is at least 3 times larger than that of OAM. Our results represent progress in finding the cause of continuous FCN excitation, which is most probably the variability of atmospheric pressure over continental landmasses.

How to cite: Kiani Shahvandi, M., Schindelegger, M., Börger, L., Mishra, S., and Soja, B.: The excitation of free core nutation: a reappraisal, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6342, https://doi.org/10.5194/egusphere-egu24-6342, 2024.

11:10–11:30

EGU24-1271

solicited

Highlight

On-site presentation

Understanding sea level rise using polar motion from 1979 to 2010

Ki-Weon Seo, Dongryeol Ryu, Kookhyeon Youm, Jianli Chen, and Clark Wilson

Sea level rise is one of the most significant consequences of the warming climate. GRACE and GRACE Follow-On satellites have been providing critical clues about the primary contributor to recent sea level rise, such as the melting ice sheets and mountain glaciers, and the depletion of terrestrial water storage. However, due to the limited availability of satellite gravity data (only since 2002) and other direct observations, understanding changes in ocean mass during the 20th century had to rely on global hydrological or Earth systems modeling.

On the other hand, efforts have been made to understand the past sea level rise using a combination of optical/microwave satellite imagery of polar regions, along with glaciological and geodetic data for mountain glaciers, global databases for large dams, and climate models for terrestrial water storage. Despite these efforts, verifying the accuracy of the combined estimates requires independent long-term observational evidence.

In this presentation, we show that studying Earth’s polar motion presents a unique opportunity to comprehend historical sea level rises predating the GRACE satellite era. Observed polar motion data from 1979 to 2010 agree well with estimates derived from various observations and climate models. During this period, the total increase in ocean mass is estimated to 52.94 mm (equivalent to 1.65 mm per year), encompassing contributions from ice melting in Antarctica (9.11 mm), Greenland (8.95 mm), mountain glaciers (20.16 mm), and the depletion of terrestrial water storage (13.72 mm). This approach utilizing polar motion offers a valuable means for historical sea level rise assessments, filling gaps in our understanding before the advent of the GRACE satellite missions.

How to cite: Seo, K.-W., Ryu, D., Youm, K., Chen, J., and Wilson, C.: Understanding sea level rise using polar motion from 1979 to 2010, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1271, https://doi.org/10.5194/egusphere-egu24-1271, 2024.

11:30–11:40

EGU24-10644

ECS

On-site presentation

Chaotic oceanic excitation of low-frequency polar motion variability

Lara Börger, Michael Schindelegger, Mengnan Zhao, Rui M. Ponte, Anno Löcher, Bernd Uebbing, Jean-Marc Molines, and Thierry Penduff

Studies of Earth rotation variations generally assume that changes in non-tidal oceanic angular momentum (OAM) manifest the ocean's forced response to atmospheric pressure, wind, and heat and freshwater fluxes. However, on monthly and longer time scales, changes in OAM may also arise from chaotic intrinsic ocean variability, which has its origin in local non-linear (e.g., mesoscale) dynamics that can further map into mass fluctuations at basin scales. To examine whether or not such chaotic mass redistributions appreciably affect Earth’s polar motion, we compute monthly OAM anomalies from a 50-member ensemble of eddy-permitting global ocean/sea-ice simulations that sample intrinsic variability through a perturbation approach on model initial conditions. The resulting OAM (i.e., excitation) functions are compared both amongst each member and with Earth rotation data from 1995 to 2015. We find that intrinsic variability plays an important role in the excitation of the Chandler wobble, where it modulates the band-integrated excitation power due to forced OAM changes (2.5 mas² over 1995–2015, mas = milliarcseconds) by up to ±2 mas². At interannual frequencies below the Chandler band, intrinsic signals (ensemble spread) account for 16–36% of the variability in the total equatorial oceanic excitation, with contributions being split almost equally between mass and motion terms. More than half of the variance in the mass term contribution is associated with one mode of intrinsic bottom pressure variability, which has opposite polarity between the Atlantic and the Southern Ocean and largest amplitudes around Drake Passage. Overall, chaotic oceanic excitation represents a factor to consider when interpreting low-frequency polar motion changes in terms of natural climate oscillations or core-mantle interactions.

How to cite: Börger, L., Schindelegger, M., Zhao, M., Ponte, R. M., Löcher, A., Uebbing, B., Molines, J.-M., and Penduff, T.: Chaotic oceanic excitation of low-frequency polar motion variability, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10644, https://doi.org/10.5194/egusphere-egu24-10644, 2024.

11:40–11:50

EGU24-12573

Virtual presentation

Polar Motion Prediction with Derivative Information

Marcin Ligas, Maciej Michalczak, Santiago Belda, Jose M. Ferrandiz, and Sadegh Modiri

Our study introduces a hybrid model that combines least-squares (LS) extrapolation of a linear trend and periodic components with a vector autoregression applied to LS residuals in an attempt of enhancing polar motion (x, y) predictions through incorporating its rates (derivatives; x^', y^'). We used the historical daily sampled final IERS EOP 20 C04 time series available on https://www.iers.org as a reference for all computations. The prediction experiment covers 10 years, 01.03.2013 – 01.03.2023. Within this period, 1000 random samples with a length of one year were generated, with the starting modified Julian date (MJD) of each yearly sample randomized. Within each sample, a 30-day forecast was performed every 7 days, resulting in a total of 48 forecasts in each random trial. Polar motion rates were incorporated to the prediction procedure in various combinations, i.e., {x, x^'}, {y, y^'}, {x, y, x^'}, {x, y, y^'}, {x, y, x^', y^'} and the prediction results based on them were compared to the predictions obtained from the reference data combination {x, y}, which does not include derivative information. As a basic measure of prediction accuracy, we used the mean absolute prediction error (MAPE) as well as a number of measures indicating improvement through incorporating rates into the prediction procedure. The results indicate a noticeable gain in prediction accuracy with the use of derivatives, although not substantial, it is systematic. This improvement is particularly apparent for the first few days of the forecast, which might indicate its potential use in ultra-short-term prediction. This promising data combination (and prediction method) is worth further analysis and an attempt of adapting it for operational settings (real time forecast).

How to cite: Ligas, M., Michalczak, M., Belda, S., Ferrandiz, J. M., and Modiri, S.: Polar Motion Prediction with Derivative Information, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12573, https://doi.org/10.5194/egusphere-egu24-12573, 2024.

11:50–12:00

EGU24-8834

ECS

Virtual presentation

Dynamic Mode Decomposition-based short-term prediction of UT1-UTC and LOD using Atmospheric Angular Momentum time series.

Maciej Michalczak, Marcin Ligas, Henryk Dobslaw, and Robert Dill

We present preliminary results of ultra-short-term prediction (10-day forecast horizon) of UT1-UTC and LOD. Forecast procedure is based on Dynamic Mode Decomposition (DMD) and uses IERS EOP 14 C04 as a reference as well as Atmospheric Angular Momentum (AAM) as auxiliary data (AAM come from GFZ Potsdam and ETH Zurich).

Two main prediction experiments (using different types of input data) were conducted: the ideal and the operational case. The ideal one was based on final (historical) data (both C04 and AAM); predictions performed within one year time span starting on a random MJD with 7 day step between subsequent 10 day forecasts, each yearly time span includes 51 10-day predictions. The operational case was based on operational data, covers the period of the 2nd Earth Orientation Parameters Prediction Comparison Campaign, each variant of this case includes 69 10-day predictions.

Within each experiment and for each considered EOP we prepared some additional analysis. In case of LOD, we conducted predictions using 2 types of input LOD time series: directly on published IERS EOP 14 C04 time series and computed as a derivative of IERS EOP 14 C04 UT1-UTC time series. The final UT1-UTC predictions vary depending on the method of determining the constant of integration restoring the proper scale of UT1-UTC.

In the ideal case the mean absolute prediction errors for UT1-UTC vary from 0.009 ms – 0.036 ms for the 1st day and 0.224 ms – 0.292 ms for the 10th day of prediction, whilst those values vary from 0.016 ms – 0.028 ms and 0.045 ms – 0.063 ms for LOD prediction. Corresponding values in the operational case are within the range of 0.058 ms – 0.065 ms and 0.438 ms – 0.463 ms for UT1-UTC, whilst for LOD these values are 0.032 ms – 0.040 ms and 0.093 ms – 0.099 ms.

In operational settings of UT1-UTC prediction, we can observe that our results are slightly worse than the accuracy of IERS predictions (Bulletin A), while comparable to the accuracy of the forecast of methods from 2nd EOPPCC. The results demonstrate that the proposed techniques can efficiently forecast UT1-UTC and LOD. Nevertheless, a deeper analysis is needed on efficient incorporation of Effective Angular Momentum Functions information to improve presented prediction procedure.

How to cite: Michalczak, M., Ligas, M., Dobslaw, H., and Dill, R.: Dynamic Mode Decomposition-based short-term prediction of UT1-UTC and LOD using Atmospheric Angular Momentum time series., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8834, https://doi.org/10.5194/egusphere-egu24-8834, 2024.

12:00–12:10

EGU24-18774

On-site presentation

Analysis of the impact of enhanced predicted EOP on satellite orbit prediction

Leonor Cui Domingo Centeno, Víctor Puente García, José Carlos Rodríguez Pérez, Santiago Belda, and Sadegh Modiri

Earth Orientation Parameters (EOP) constitute the set of parameters that describe the rotation of the Earth with respect to an inertial reference frame. Apart from proper force modelling, EOP are also needed in orbit prediction to calculate the position and velocity of satellites in space. The accuracy of EOP prediction is essential for orbit determination since any error in its computation will propagate to the predicted state vector of the satellite.

The magnitude of the impact of EOP prediction errors depends on the type of orbit and the time interval over which the predictions are made. These EOP prediction inaccuracies can lead to significant position errors as small errors in the EOP accumulate rapidly, thus resulting in larger deviations from the nominal satellite position. Therefore, this effect can be significant and become a concern for applications requiring high precision, such as positioning.

In this contribution, we present numerical results of the discrepancies in the GNSS orbit prediction found when propagating the satellite orbits employing different time series of EOP predicted values. We show a comparison and assessment of the EOP values obtained by different prediction methods used in the 2nd Earth Orientation Parameters Prediction Comparison Campaign (2nd EOP PCC), aiming to study the validation of those EOP that yield the most accurate results in the GNSS orbit prediction.

How to cite: Domingo Centeno, L. C., Puente García, V., Rodríguez Pérez, J. C., Belda, S., and Modiri, S.: Analysis of the impact of enhanced predicted EOP on satellite orbit prediction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18774, https://doi.org/10.5194/egusphere-egu24-18774, 2024.

12:10–12:20

EGU24-9603

On-site presentation

Accurate Inertial Earth Rotation Measurements

Karl Ulrich Schreiber and Jan Kodet

12:20–12:30

Discussion

Posters on site: Tue, 16 Apr, 16:15–18:00 | Hall X2

Display time: Tue, 16 Apr, 14:00–Tue, 16 Apr, 18:00

Chairpersons: Sigrid Böhm, Florian Seitz, Justyna Śliwińska-Bronowicz

Earth rotation theory, observations & prediction

X2.26

EGU24-15752

Status of the update of the Earth's rotation theory and precession-nutation models

(withdrawn)

José M. Ferrándiz, Cheng-li Huang, Alberto Escapa, Maria Karbon, Santiago Belda, and Tomás Baenas

X2.27

EGU24-9457

ECS

Consistently combined Earth Rotation Parameters at BKG - Adding SLR data to VLBI and GNSS

Lisa Klemm, Daniela Thaller, Daniel König, Claudia Flohrer, and Anastasiia Walenta

We present BKG´s current activities in the field of combined data processing of different space-geodetic techniques. The primary goal of the combined analyses is the improvement of the consistency between the techniques through common parameters, mainly Earth Rotation Parameters (ERP), and thereby to improve also the resulting ERPs. In previous studies, we have investigated different combination approaches using VLBI and GNSS data and generated ERP series with latencies of about 1-2 or 14 days, depending on the input data used. In this way, we achieved a significant improvement in accuracy, especially for the dUT1 series, compared to the individual technique-specific solutions. The processing is based on datum-free normal equations (provided via SINEX files), which allow a rigorous combination on the normal equation level instead of the observation level.

Our current activities in the area of multi-technique combination are focused on augmenting the combination of GNSS and VLBI data with SLR data. It is expected that the SLR technique has the potential to improve the combined ERP solution, especially the highly variable dUT1 parameter, by providing a stable LOD contribution. Due to its short latency of about 1 day, the SLR-DAILY product is basically well suited to expand the database of our Rapid EOP series, which is currently only based on GNSS Rapid and VLBI Intensives data. However, the official SLR-DAILY product of the ILRS is a 7-day solution that explicitly contains polar motion (only as constant offsets over 24 hours) and LOD, but no dUT1 parameters and no polar motion rates. Therefore, this solution is not optimal for our combination approach because the parameterization of the ERPs is not identical to the other techniques that uses offsets and rates for all ERPs. However, the in-house ILRS Analysis Center allows us to generate a customized SLR solution that has an improved parameterization of the ERPs and, thus, is optimized for the multi-technique combination. We investigated the SLR data with respect to the quality of the resulting ERP series and integrated the data into our combination process. We present the impact of SLR on the combined ERP product and the challenges of extending the combination with this data.

How to cite: Klemm, L., Thaller, D., König, D., Flohrer, C., and Walenta, A.: Consistently combined Earth Rotation Parameters at BKG - Adding SLR data to VLBI and GNSS, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9457, https://doi.org/10.5194/egusphere-egu24-9457, 2024.

X2.28

EGU24-14969

Current deficiencies and potential for improvement in the realisation of consistently combined Earth Orientation Parameter time series

Florian Seitz, Alexander Kehm, Mathis Bloßfeld, Bingbing Duan, Urs Hugentobler, and Robert Dill

Accurate knowledge of the Earth’s orientation and rotation in space is essential for a broad variety of scientific and societal applications such as near-Earth and deep space navigation, global positioning and satellite orbit determination as well as monitoring geodynamics and climate change phenomena. Consequently, an essential basis for any of the above-mentioned applications is the accurate determination and prediction of Earth Orientation Parameters (EOP), which describe the instantaneous relation between reference frames fixed to the Earth and to inertial space at any epoch. High-precision EOP are determined by combining the observations of four different geodetic space techniques.

Due to different standards for the processing of the observations – most notably the parameterisation of the EOP in the observation-type-specific processing softwares – current EOP combination approaches lack consistency. Such inconsistencies represent a major limiting factor of today’s accuracy of determined EOP as well as of short-term EOP predictions, which are an essential prerequisite for any application in (near-)real time.

This study identifies current deficiencies that limit the consistency and achievable accuracy of combined EOP series. It provides recommendations on how to improve the parameterisation and processing standards of the technique-specific input, and it outlines strategies to achieve a more consistent and accurate EOP combination. The proposed processing strategies shall serve as a basis for improved EOP prediction algorithms in a later stage of the study.

How to cite: Seitz, F., Kehm, A., Bloßfeld, M., Duan, B., Hugentobler, U., and Dill, R.: Current deficiencies and potential for improvement in the realisation of consistently combined Earth Orientation Parameter time series, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14969, https://doi.org/10.5194/egusphere-egu24-14969, 2024.

X2.29

EGU24-16150

Consistency assessment of EOP estimated by different VLBI correlators

Santiago Belda Palazón, Maria Karbon, Alberto Escapa, José M. Ferrándiz, Esther Azcue, Mariana Moreira, and Sadegh Modiri

The VLBI technique provides an extremely precise measurement of the geometric relationship between the receiving radio observatory and the celestial target. It utilizes methods of recording the signals at each antenna. These recordings are physically brought together and played back into a processing device, known as a correlator, which combines the signals in such a way that delivers the fundamental observables of geodetic VLBI, the time delays between signals arriving at the individual antennas as a function of time. Nowadays, numerous correlator software and strategies are employed which may result in inconsistencies on the geodetic products.

In this study, we empirically assess the consistency between the different correlators by analyzing the R1/R4 VLBI sessions from 2002 to 2022 to reflect the impact on the EOP estimates. To compare the different pairs of EOP time series estimates, we calculated the Weighted Mean (WM) of the differences and the Weighted Root Mean Square (WRMS) differences between each of them. Besides, we empirically evaluate the consistency, systematics, and deviations of the IAU 2006/2000A precession-nutation model using several CPO time series derived from the different correlators, providing a new set of empirical corrections to the precession offsets and rates, and to the amplitudes included in the nutation models. Finally, we study the impact on the estimation of new free core nutation (FCN) models.

This research was supported partially by Generalitat Valenciana (SEJIGENT/2021/001) and the European Union—NextGenerationEU (ZAMBRANO 21-04); and also by Spanish Projects PID2020-119383GB-I00 funded by Ministerio de Ciencia e Innovación (MCIN/AEI/10.13039/501100011033/) and PROMETEO/2021/030 funded by Generalitat Valenciana.

How to cite: Belda Palazón, S., Karbon, M., Escapa, A., Ferrándiz, J. M., Azcue, E., Moreira, M., and Modiri, S.: Consistency assessment of EOP estimated by different VLBI correlators, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16150, https://doi.org/10.5194/egusphere-egu24-16150, 2024.

X2.30

EGU24-9388

ECS

Exploring the effect of different VLBI Networks on EOPs estimation.

Lucía D. del Nido Herranz, Santiago Belda, Maria Karbon, Esther Azcue, Víctor Puente, and José M. Ferrándiz

One of the key determinants influencing the accuracy and reliability of Earth Orientation Parameters (EOP) is the network Very Long Baseline Interferometry (VLBI) geometry. VLBI is a high-precision radio astronomy technique that involves multiple radio telescopes spread across the globe, working together as a network. The geometric configuration of these telescopes plays a crucial role in the quality of the data collected and, consequently, the accuracy of EOP measurements. The distribution and arrangement of the VLBI network antennas impact the triangulation process used to determine the positions of celestial radio sources, contributing to the calculation of Earth's rotation parameters. An optimal VLBI geometry ensures a well-constrained and robust observational setup, leading to more precise EOP results crucial for many scientific applications.

In this study, we analyze the impact of using different VLBI networks on the EOP estimation. Due to its nature the Continuous VLBI Campaigns (CONT) give a good basis to investigate these effects. For this purpose, we artificially create different networks with distinct configurations (e.g. removing VLBI antennas located in the northern hemisphere and vice versa, taking out the longest north-south baselines or the east-west baselines…). This sensitivity analysis will contribute to the refinement of the EOP and will help to fulfill the stringent GGOS targets (i.e. a frame with accuracy at epoch of 1 mm or better and a stability of 0.1 mm/y).

Acknowledgment. This research was supported partially by Spanish Projects PID2020-119383GB-I00 funded by Ministerio de Ciencia e Innovación (MCIN/AEI/10.13039/501100011033); PROMETEO/2021/030 and SEJIGENT/2021/001, funded by Generalitat Valenciana; and the European Union—NextGenerationEU (ZAMBRANO 21-04).

How to cite: del Nido Herranz, L. D., Belda, S., Karbon, M., Azcue, E., Puente, V., and Ferrándiz, J. M.: Exploring the effect of different VLBI Networks on EOPs estimation., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9388, https://doi.org/10.5194/egusphere-egu24-9388, 2024.

X2.31

EGU24-15551

ECS

Advancing EOP Prediction: Bridging the Gaps

Sadegh Modiri, Daniela Thaller, Santiago Belda, Dzana Halilovic, Lisa Klem, Daniel König, Sabine Bachmann, Claudia Flohrer, and Anastasiia Walenta

Understanding Earth's orientation parameters (EOP) is paramount for unraveling intricate mass redistribution, gravitational interactions, and geodynamic processes within the Earth's system. With a growing interest in EOP across diverse scientific disciplines such as Earth science, astronomy, and climate change studies, the demand for accurate and timely real-time information has become increasingly crucial. This is particularly evident in applications like satellite navigation, interplanetary spacecraft tracking, and weather forecasting. Despite the precision enabled by modern space geodetic techniques (e.g., Very Long Baseline Interferometry - VLBI, Global Navigation Satellite Systems - GNSS, and Satellite Laser Ranging - SLR), the complexity of data processing and associated delays necessitates significant progress in EOP prediction, especially for applications requiring timely information.

This study addresses these challenges by introducing a redesigned prediction package that effectively bridges the gap between observational data and final estimated products. Utilizing a sophisticated combination of deterministic and stochastic methods, our prediction algorithm is applied to both the official International Earth Rotation and Reference Systems Service (IERS) EOP series and the Federal Agency for Cartography and Geodesy (BKG) single-specific and combined technique time series.

The results of this study make a significant contribution to efforts that aim to enhance the accuracy of predicted Earth Orientation Parameters (EOP). By thoroughly exploring the selection of input data and prediction methods, our research strives to improve the dependability of EOP forecasts, especially for short-term predictions. By tackling crucial challenges in the field, this work not only deepens our understanding of Earth's dynamic processes but also opens doors for more accurate and timely applications across various scientific disciplines that rely on EOP data.

How to cite: Modiri, S., Thaller, D., Belda, S., Halilovic, D., Klem, L., König, D., Bachmann, S., Flohrer, C., and Walenta, A.: Advancing EOP Prediction: Bridging the Gaps, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15551, https://doi.org/10.5194/egusphere-egu24-15551, 2024.

Links between Earth rotation and geophysical processes

X2.32

EGU24-3582

Using Optimal Estimation and Robust Curve-Fitting Tools to Enhance Predicted Earth Angular Momentum for Earth Orientation

Nicholas Stamatakos, Dennis McCarthy, David Salstein, Mark Psiaki, and Jessica Page

X2.33

EGU24-19345

New Data Set of Hydrological Angular Momentum With its Associated 6 Days-Long Forecasts

Robert Dill, Laura Jensen, and Henryk Dobslaw

Since more than 15 years, GFZ routinely provides daily updated hydrological effective angular momentum functions (HAM) and its 6 days-long forecasts for the study of Earth orientation parameter variability and for improving polar motion and UT1-UTC predictions. GFZ’s HAM time series are part of a consistent set of effective angular momentum functions (EAM) covering the Earth’s major subsystems atmosphere, oceans, and the terrestrial hydrosphere. In addition, all EAM products are consistent with the GRACE/GRACE-FO atmosphere-ocean dealiasing product AOD1B release 06 which is used for gravity field processing and precise orbit determination.

For the new HAM data set we switch our hydrological model setup from the Land Surface Discharge Model (LSDM) to the open source, high-resolution hydrological rainfall-runoff-routing model LISFLOOD (https://ec-jrc.github.io/lisflood/). We slightly adapted the latest LISFLOOD 0.05° version for geodetic applications by modifying the snow melting parameterization, the soil depth parameterization, and implementing a seasonal snow storage model for Antarctica to optimize the agreement of simulated terrestrial water storage with mass anomalies from the satellite gravimetry missions GRACE and GRACE-FO on different spatial and temporal scales. Due to (I) up-to-date surface parameter maps; (ii) increased temporal resolution of 3 hours; (iii) enhanced parameterization of hydrological processes such as evapotranspiration, soil infiltration, snow accumulation and dynamic river routing; and (iv) a much more extensive set of atmospheric forcing parameters from ECMWF’s latest global atmospheric reanalysis ERA5, the derived HAM time series could be substantially improved in terms of long-term stability, seasonal amplitudes, sub-seasonal and episodic variations, and short-term forecasts. Furthermore, the new HAM data set is consistent with the new AOD1B release 07.

How to cite: Dill, R., Jensen, L., and Dobslaw, H.: New Data Set of Hydrological Angular Momentum With its Associated 6 Days-Long Forecasts, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19345, https://doi.org/10.5194/egusphere-egu24-19345, 2024.

X2.34

EGU24-5858

Atmospheric excitation of the annual wobble over the 21st-century from CMIP6 predictions under different scenarios

Sigrid Böhm, Anne Strümpf, and David Salstein

The annual wobble is the second distinct feature of polar motion after the Chandler wobble. It is a seasonally forced oscillation driven mainly by significant pressure differences between boreal winter and summer over Siberia. In this study, we investigate the future evolution of the annual wobble amplitude from 21^st-century model projections of atmospheric pressure and wind velocities. The model variables are provided within the Coupled Model Intercomparison Project Phase 6 (CMIP6) for different scenarios that simulate possible future anthropogenic drivers of climate change. We use the simulations of 11 models for five such scenarios, which range from very mild to quite extreme future climate changes. The 21^st-century simulations span 85 years, from 2015 to 2100. Our analysis focuses on the temporal evolution of the amplitude of the annual oscillation in equatorial atmospheric angular momentum functions. More intense scenarios involving more substantial global warming show an increase in the magnitude of the annual wobble towards the end of the century. More extreme annual pressure anomalies over the North Asian landmass probably cause the rising amplitudes.

How to cite: Böhm, S., Strümpf, A., and Salstein, D.: Atmospheric excitation of the annual wobble over the 21st-century from CMIP6 predictions under different scenarios, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5858, https://doi.org/10.5194/egusphere-egu24-5858, 2024.

X2.35

EGU24-8315

Exploiting the SLR+GRACE/GRACE-FO Hybrid Solutions to Determine Gravimetric Excitations of Polar Motion

Jolanta Nastula, Justyna Śliwińska-Bronowicz, Małgorzata Wińska, and Aleksander Partyka

In this study, we investigate the excitation of polar motion (PM) caused by changes in the distribution of hydrosphere mass. This phenomenon is expressed through hydrological angular momentum (HAM) series, which can be estimated using global models of the continental hydrosphere, Earth's gravity field variations, and numerical climate models.

The Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) missions have provided crucial data for understanding the time-variable gravity field affected by changes in global mass distribution. These missions also reveal how mass variations in the continental hydrosphere and cryosphere affect PM. However, it has been identified that GRACE/GRACE-FO solutions have certain limitations when determining geopotential coefficients of lower degrees. As a remedy, it has become standard practice to replace the C₂₀values obtained from GRACE/GRACE-FO solutions with corresponding estimates from Satellite Laser Ranging (SLR). Similar substitutions are also recommended for the C₂₁ and S₂₁ coefficients.

In our study, we employ hybrid SLR+GRACE/GRACE-FO time-variable gravity solutions, made available by the Institute of Geodesy at Graz University of Technology (ITSG) and Centre National D'Etudes Spatiales (CNES), to determine hydrological/gravimetric angular momentum (HAM). To evaluate the SLR+GRACE/GRACE-FO-based HAM series, we compare them with the hydrological signal in observed PM excitation, referred to as geodetic residuals (or GAO). Additionally, we compare these series with HAM derived from GRACE/GRACE-FO data, focusing on seasonal and non-seasonal variations.

Our findings indicate that the excitation functions derived from the hybrid solution closely align with the GAO. In fact, they are similar or even better consistent with GAO than the series derived from the GRACE/GRACE-FO data.

How to cite: Nastula, J., Śliwińska-Bronowicz, J., Wińska, M., and Partyka, A.: Exploiting the SLR+GRACE/GRACE-FO Hybrid Solutions to Determine Gravimetric Excitations of Polar Motion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8315, https://doi.org/10.5194/egusphere-egu24-8315, 2024.

X2.36

EGU24-9835

ECS

Revisiting excitation of length-of-day using recent GRACE/GRACE-FO, SLR, SLR+GRACE/GRACE-FO gravity solutions and geophysical models

Justyna Śliwińska-Bronowicz, Jolanta Nastula, Małgorzata Wińska, and Aleksander Partyka

Variations in Earth’s rotation, encompassing polar motion (PM) and the length-of-day (LOD) changes, result from a variety of factors influencing mass distribution and movement. These factors include the redistribution of air and water masses within the climate system and the solid Earth, and exchanges of angular momentum between the core and mantle. The ability to differentiate between these diverse sources is crucial for comprehending processes occurring at or near the Earth's surface, as well as within its interior.

Fluctuations in the low-degree spherical harmonic coefficients of Earth's gravitational potential are linked to the redistribution of mass on a large scale within and on the planet. Observing changes in these coefficients provides a means to investigate the movement of mass within the Earth system. The degree-2 order-0 coefficient (C₂₀) of geopotential holds particular significance for Earth rotation studies since C₂₀variations (ΔC₂₀) are directly linked to the corresponding excitations of LOD. ΔC₂₀ can be determined from various methods, of which Satellite Laser Ranging (SLR) measurements have the longest tradition. Launching Gravity Recovery and Climate Experiment (GRACE) in 2002 and GRACE Follow-On (GRACE-FO) in 2018 brought new measurements of changes in the Earth's gravitational field, including estimates of the ΔC₂₀. However, estimates of ΔC₂₀ from GRACE/GRACE-FO have limitations due to orbital geometry, the relatively short distance between the two satellites, and tide-like aliases. In practice, GRACE/GRACE-FO computing centres replace ΔC₂₀with an estimate from SLR measurements. Combining GRACE/GRACE-FO and SLR observations could enhance the accuracy of determining low-degree coefficients of geopotential, including ΔC₂₀, ΔC₂₁, and ΔS₂₁.

In this study, we reassess the excitation of LOD over the period 2002–2023, estimated from five different data sources: SLR, GRACE/GRACE-FO, a combination of SLR+GRACE/GRACE-FO, geodetic observations, and geophysical fluid models. To each of the time series we apply the same processing to isolate long-period, seasonal and non-seasonal short-term fluctuations. For every component, we conduct a comparative analysis aiming to evaluate the consistency among various estimates and identify discrepancies between the series. We show that combining GRACE/GRACE-FO with SLR data improves the consistency between ΔC₂₀-derived and observed LOD excitation for the studied oscillations.

How to cite: Śliwińska-Bronowicz, J., Nastula, J., Wińska, M., and Partyka, A.: Revisiting excitation of length-of-day using recent GRACE/GRACE-FO, SLR, SLR+GRACE/GRACE-FO gravity solutions and geophysical models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9835, https://doi.org/10.5194/egusphere-egu24-9835, 2024.

X2.37

EGU24-11706

El Niño 2023-24: a rotational signature?

(withdrawn)

Sébastien Lambert

X2.38

EGU24-3096

Effects of topographic coupling at core-mantle boundary in rotation and orientation changes of the Earth.

Véronique Dehant, Jeremy Rekier, Mihaela Puica, Marta Folgueira, and Tim Van Hoolst

We study coupling mechanisms at the core-mantle boundary (CMB) of the Earth in the frame of nutations and Length-of-Day (LOD) variations. The CMB is usually considered to have a smooth spherical or elliptical shape inducing a Poincaré flow in the nutation case and a global rotation in the LOD case. However, in reality, the CMB is bumpy and there are mountains and valleys representing local height differences of the order of a kilometer. The existence of a topography induces inertial waves that need to be considered in the flow of the core. This is in addition to the Poincaré fluid motion when the nutations are computed and in addition to a relative rotation of the fluid opposite and of the same amplitude as that of the mantle for LOD variations. The additional pressure and the topographic torque depend on the shape of the CMB and can be related to the spherical harmonic coefficients of the CMB topography. We follow the philosophy of the computation of Wu and Wahr [Geophys. J. Int., 128(1), 18-42, 1997] and determine the coefficients of the velocity field in the core at the CMB in terms of the topography coefficients. We used an analytical approach instead of a numerical one. We confirm that some topography coefficients may enhance length-of-day variations and nutations at selected frequencies, and show that these increased rotation variations and nutations are due to resonance effects with inertial waves in the incremental core flow. While they could be at a detectable level for LOD, they are very small for nutations (except for the flattening of the core), enhancing the importance of the electromagnetic coupling at the CMB.

How to cite: Dehant, V., Rekier, J., Puica, M., Folgueira, M., and Van Hoolst, T.: Effects of topographic coupling at core-mantle boundary in rotation and orientation changes of the Earth., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3096, https://doi.org/10.5194/egusphere-egu24-3096, 2024.