Displays

In this investigation, we identify optimal locations for VGOS radio telescopes to estimate Earth orientation parameters (EOP) with a new method based on bulk schedule generation and large-scale Monte-Carlo simulations. Thereby, we focus on a high number of simulations and a proper consideration of scheduling to minimize these undesired error sources.

The location of the telescope is varied over 477 possible locations, homogeneously distributed over land areas on the globe. The antenna is added to a fixed network of 6, 12 and 18 existing and upcoming VGOS stations. The optimal location is defined through the minimal resulting repeatabilities of the simulated EOP. In this study, a special focus was laid on the generation of high-quality observing plans to minimize the effects of scheduling combined with a high number of simulations to minimize their randomness. To remove the unintended effects caused by scheduling over 93 thousand schedules were iteratively generated. Each schedule is further simulated 1000 times leading to over 5 trillion simulated and analyzed observations. Besides showing our results for the best telescope location, we will highlight how scheduling and the number of simulations affects the repeatability of the estimated EOP. This will help further simulation studies to improve their results.

The optimal telescope location depends on the EOP of interest and the existing network. For simple network geometries, such as the 6 station network which consists of antennas in Europe and North America, the importance of east-west baselines can be seen for the determination of dUT1 while the importance of north-south baselines can be seen for the determination of polar motion and nutation. For more complex network geometries and an increasing number of VGOS stations, the lack of southern stations becomes more prominent. For the 12 and 18 station network, the location of an additional antenna in south America can significantly improve the accuracy of the EOP by up to 60%.

How to cite: Schartner, M., Böhm, J., and Nothnagel, A.: Optimal VGOS telescope location for the estimation of Earth orientation parameters, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13484, https://doi.org/10.5194/egusphere-egu2020-13484, 2020.

The over four decades long record of Satellite Laser Ranging (SLR) observations to a variety of historical geodetic spherical satellites makes it possible to directly observe the long-term (seasonal to decadal time scales) displacement of the Earth’s mean axis of maximum inertia, namely its principal figure axis, with respect to the crust, through the determination of the degree-2 order-1 geopotential coefficients over the 34-year period 1984—2017.

On the other hand, the pole coordinate time series (mainly from GPS and VLBI data), yield the motion of the rotation pole with even a greater accuracy.

The time-dependent nature of the response of the Earth’s mantle to external forces, where it behaves either elastically on short time scales (seconds) or like a viscous fluid over geological time scales (millions of years), is poorly constrained at decadal periods. Here we propose to relate oscillations of the figure axis to those of the Earth’s rotation pole (through the Euler-Liouville equations) to study the mass-related excitation of polar motion and provide global constraints on the rheological properties of the deep Earth.

How to cite: Couhert, A., Bizouard, C., Mercier, F., Chanard, K., Greff, M., and Exertier, P.: Constraints on the Rheology of the Earth's Deep Mantle from Decadal Observations of the Earth's Figure Axis and Rotation Pole, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18545, https://doi.org/10.5194/egusphere-egu2020-18545, 2020.

The current IAU2000 nutation theory considers the Earth’s dynamical ellipticity as a constant, whereas the IAU2006 precession theory uses a linear model for it. Apart from the problems of consistency between the two theories, whose full solution was proposed recently, the fundamental issue, namely whether the observed time variation of the Earth’s gravity field can affect the Earth’s rotation to a non-negligible extent or not, remains untreated.

This presentation is intended to share some preliminary results concerning precession and nutation. The variation of the Earth’s dynamical ellipticity is modelled from one of the time series providing the time-varying Stokes coefficients, and its effects on the longitude are computed following a new method introduced by the authors to that purpose. The found variations are above the accuracy goals of GGOS, the Global Geodetic Observing System of the International Association of Geodesy, adopted by its Joint Working Group on Improving theories and models of the Earth rotation (JWG ITMER).

How to cite: Ferrándiz, J. M., Escapa, A., Baenas, T., Belda, S., and Vigo, M. I.: Effects of the observed Earth’s oblateness variation on precession-nutation: A first assessment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16509, https://doi.org/10.5194/egusphere-egu2020-16509, 2020.

The availability of highly accurate, up-to-date Earth Orientation Parameters is of major importance for all positioning and navigation applications on Earth, Sea, Air and also in Space. This is equally true for ESA missions and the EU space programs, e.g. Galileo, EGNOS and Copernicus.

In the frame of its responsibility to provide the Geodetic reference for ESA missions, ESA’s Navigation Support Office at ESOC is already contributing to the realisation of the International Terrestrial Reference Frame (ITRF) and the combined Earth Orientation Parameters provided by the International Earth Rotation Service (IERS). The contribution is realised through individual contributions to international services such as the International GNSS Service (IGS), the International Laser Ranging Services (ILRS), the International DORIS Service (IDS), the International Earth Rotation Service (IERS) and in the future also to the International VLBI Service (IVS).

For the combination and the long-term predictions of the Earth orientation products ESA is still relying on the International Earth Rotation Service (IERS). Over the past years, ESA repeatedly experienced problems with outdated or missing predictions of the Earth orientation parameters (Bulletin A). Considering the importance of up-to-date Earth orientation parameters, the dependence on a single source outside Europe is considered a risk for European industry, for ESA missions and for EU programmes. For this reason, ESA initiated in 2017 a study with the target to develop independent ESA Earth Orientation parameter products. This study, executed by a consortium led by the Deutsches Geodätisches Forschungsinstitut (DGFI-TUM), is expected to finish in the course of this year.

In this presentation we will give an overview of ESAs up-to-date reference products and discuss their quality. It will outline the combination approach and discuss the way forward to an fully operational provision of the ESA Earth Orientation Parameter products.

How to cite: Schoenemann, E., Springer, T., Otten, M., Mayer, V., Bruni, S., Enderle, W., and Zandbergen, R.: Status of ESA’s independent Earth Orientation Parameter products, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17154, https://doi.org/10.5194/egusphere-egu2020-17154, 2020.

Over almost 20 last years, observations from the Gravity Recovery and Climate Experiment (GRACE) mission have become invaluable as means to examine Earth global mass change. Since 2002, the relative along track motions between two identical satellites have been used to derive Earth’s time variable gravity field. The great success and scientific sound of the mission, which ended in 2017, contributed to the launch of its successor, GRACE Follow-On (GFO) in May 2018. Until now, monthly time series of GFO-based geopotential models have been made available to the users by official GRACE data centres at Center for Space Research (CSR), Jet Propulsion Laboratory (JPL) and GeoForschungsZentrum (GFZ). This data enables the continuation of many researches which started with the beginning of the GRACE mission. Such applications included monitoring of land water storage changes, drought event identification, flood prediction, ice mass loss detection, groundwater level change analysis, and more.

In geodesy, a crucial application of GRACE/GFO mission observations is the study of polar motion (PM) changes due to mass redistribution of the Earth’s surficial fluids (atmosphere, ocean, land hydrosphere). PM represents two out of five Earth Orientation Parameters (EOP), that describe the rotation of our Planet and link the terrestrial reference frame with the corresponding celestial reference frame. The use of C₂₁, S₂₁ coefficients of GRACE/GFO-based geopotential models is a common method for determining polar motion excitation.

In this study, we present the first estimates of hydrological polar motion excitation functions (Hydrological Angular Momentum, HAM) computed from GFO data which were provided by CSR, JPL and GFZ teams. The HAM are calculated using (1) C₂₁, S₂₁ coefficients of geopotential (GFO Level-2 data) as well as (2) gridded terrestrial water storage (TWS) anomalies (GFO Level-3 data). We compare and evaluate the two methods of HAM estimation and examine the compatibility between CSR, JPL and GFZ solutions. We also validate different HAM estimations using precise geodetic measurements of the pole coordinates.

Our analyses show that the highest internal agreement between different GFO solutions can be obtained when comparing CSR and JPL. Notably, GFZ estimates differ slightly from the other GFO models. The highest agreement between different GFO-based HAM, and between GFO-based HAM and reference data is obtained when GFO Level-3 data are used. We also demonstrate that the current accuracy of HAM from GRACE Follow-On mission meets the expectations and is comparable with the accuracy of HAM from GRACE Release-6 (RL06) data.

How to cite: Śliwińska, J., Wińska, M., and Nastula, J.: Preliminary hydrological polar motion excitation estimates from the GRACE Follow-On mission, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-174, https://doi.org/10.5194/egusphere-egu2020-174, 2020.

We decompose the well known LOD time series provided by IERS, that shows so-called decadal variations, in fluctuations at several timescales, namely: sub-centennial (60-90 years), inter-decadal (20-35 years), decennial (~11 years) and intra-decennial (~6 years). A Hodrick and Prescott (1977) type of analysis is used, followed by the decomposition of the trend and oscillatory parts at the mentioned timescales using Butterworth filtering. Comparing the results to previously (e.g. Dobrica et al., 2018) known oscillations of the geomagnetic field (dD/dt), and carrying out a similar analysis for parameters describing the evolution of the magnetospheric ring current, suggest the latter is the ultimate driver of both geomagnetic and LOD variations. The probable mechanisms are discussed as well: Alfvén torsional oscillations in the outer core, triggered by variations in the magnetospheric ring current, or a direct control of geomagnetic declination by variations in the magnetospheric ring current. While the first one is long accepted for the long-term variations in D and LOD, a similar possibility for the 6-year variation is out of question due to the implied value of the geomagnetic field within the outer core (Gillet et al., 2010); for the latter we suggest the second mechanism.       

How to cite: Demetrescu, C. and Dobrica, V.: Length of day fluctuations at long and short timescales. Geomagnetic drivers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13127, https://doi.org/10.5194/egusphere-egu2020-13127, 2020.

Time-variations in the orientation of the solid Earth are largely governed by the exchange of angular momentum with the surface geophysical fluids of atmosphere, oceans, and the land surface. Modelled fields of atmospheric winds, atmospheric surface pressure, ocean currents, ocean bottom pressure, and terrestrial water storage allow calculating effective angular momentum (EAM) functions that can be compared to geodetic angular momentum functions (GAM) derived from observed Earth Orientation Parameters (EOP) via the Liouville equation. Especially in the high-frequency range, currently available global geophysical fluid models provide highly reliable information about angular momentum transfers that determine the orientation changes of the Earth.

In this contribution, we investigate the extent to which the modelled Earth rotation angular momentum functions processed at GFZ can be used to evaluate time series of EOP processed from different geodetic space techniques at periods between 2 and 60 days. We therefore compare the time series from various sources that are based on individual techniques (e.g., VLBI[TD1], GNSS, SLR, and DORIS) only, and also combined solutions that are processed at different institutions (e.g., JPL, GFZ, BKG[TD2], DGFI-TUM) or published by international services (e.g., IERS, IGS, IVS[TD3] ). By calculating differences from all possible pairs of EAM and GAM and by utilizing both band-pass filtering and spectral analysis techniques, we will elaborate the systematic differences between excitation functions from different sources that are expected to help identifying deficits in geodetic data processing and/or numerical modelling.

How to cite: Dill, R., Dobslaw, H., Thomas, M., Hendrik, H., Daniela, T., Mathis, B., Alexander, K., and Florian, S.: Validation of Earth rotation time series by comparison of their sub-daily to sub-monthly excitation signal with simulated geophysical fluid model excitations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4530, https://doi.org/10.5194/egusphere-egu2020-4530, 2020.

Inertial modes are natural oscillations in the fluid parts of planets which are caused by the restoring action of the Coriolis force. The relation between these modes, as they appear in the liquid core of planets, and the well-known rotational modes – the Free (Inner) Core Nutation (FCN & FICN) and the Chandler and Inner Core Wobble (CW & IW) – is not well understood, with the FCN often being mistakenly identified to the simplest inertial mode, the Spin-Over (SO). In this work, we clarify this relation using a new formalism to compute the rotational modes of a two-layer triaxial planet with a rigid mantle and an inviscid fluid core to all order in the eccentricity. We confirm the validity of our model through comparison with the results from direct numerical integration of the equations of motion. Using this technique, we demonstrate how the SO is the only inertial mode affecting the rotation of the planet and we show how this mode identifies with the FCN only in the limit of vanishing eccentricity.

How to cite: Rekier, J., Triana, S., Trinh, A., and Dehant, V.: The relation between the rotational and inertial modes of a triaxial planet, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18882, https://doi.org/10.5194/egusphere-egu2020-18882, 2020.

Skorobogatykh I.V., Myo Zaw Aung

About the calculation of the frequencies of lunar-solar tides

in the model of viscoelastic Earth

The problem of calculating the Earth tidal deformations under the influence of gravity of the Moon and the Sun is considered. The Earth is assumed to be a viscoelastic body that is axisymmetric in an undeformed state and has an axisymmetric absolutely solid core. The elastic displacements at the boundary of the viscoelastic part and the solid core equal to zero, and another boundary is free. Viscoelastic material is assumed to move according to the Kelvin - Voigt model. The center of mass of the Earth – Moon system moves in a slowly changing elliptical orbit around the Sun under the influence of gravitational forces from the Sun and the Moon. For this problem the Sun and the Moon are considered as material points. Previously, this problem was considered in [1], with a significant number of simplifications and assumptions. 

The equations that describe the Earth's deformations, are obtained from the d’Alembert-Lagrange variational principle [2].Also,  according to the modal approach, the displacement vector is represented as an infinite series of eigenforms of the elastic part’s free oscillations. As a result, for modal variables an infinite system of ordinary differential equations of the second order is written The system can be simplified using the physical observation, that under the influence of viscous friction in the free oscillations in the material are damped and therefore the deformations occur in a quasi-static way [2], which allows us to discard the inertial terms in the equations.  As a result, in the obtained simplified system it can be noted that only the equations for the first four forms contain the non-zero right-hand sides, which means that the deformations of the remaining forms are (under quasi-static condition) small and can be neglected. As a result, we have a system of eight equations. The right-hand sides of these equations are due to the gravitational interactions between the  Earth and the Sun and between the Earth and the Moon which means that they depend on their radius vectors. Therefore they can are expressed through the angles that determine these radius vectors, as well as the angles that determine the orientation of the Earth in space. By expanding the right-hand sides of the equations as a series in powers of a small parameter (which is taken as the ratio of the Earth's radius to the distance from the Earth to the Moon), we can represent them as series containing sines and cosines of the combinations of aforementioned angles. Since the angles can be considered as uniformly changing over not too long time periods, this allows us to approximate the frequency of the Earth tidal deformations.

References

1. Skorobogatykh I.V., Do Chung Bo “On the frequencies of the lunar-solar tides of the deformed Earth” Kosmonavtika i Raketostroyeniye, 2015, issue 1 (80), pp. 106-113.
2. Vilke V.G. “Analytical and qualitative methods in the mechanics of systems with an infinite number of degrees of freedom” M.: Moscow Publishing House. University, 1986. 192 p.

How to cite: zaw aung, M. and Vladimirovich, S.: About the calculation of the frequencies of lunar-solar tides in the model of viscoelastic Earth, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10201, https://doi.org/10.5194/egusphere-egu2020-10201, 2020.

As other relevant quantities related to the Earth dynamics, the Earth dynamical ellipticity is influenced by tidal effects. In particular, it is affected by the permanent tide due to the time independent part of the Earth redistribution tidal potential. Hence, it is necessary to distinguish between its tide-free and non tide-free values (e.g., Burša 1995) when determining it from observations (e.g., Marchenko & Lopushanskyi 2018). This question is seldom considered in Earth rotation studies. For example, neither IAU2000/AIU2006 nutation/precession model nor IERS Conventions specify explicitly whether the dynamical ellipticity is a zero-tide parameter or not. However, current accuracy goals might be sensitive to that difference.

Within the framework of a Hamiltonian approach (Baenas, Escapa, & Ferrándiz 2019), we present a consistent treatment of the influence of the permanent tide on the dynamical ellipticity. In particular, we develop an analytical expression of the redistribution tidal potential based on Andoyer canonical variables and a semi-analytical theory of the orbital motions of the Moon and the Sun, following the same procedure as that given in Kinoshita (1977).

This method allows obtaining an expression of the zero frequency term of the redistribution tidal potential that updates that of Zadro & Marussi (1973), usually employed in reporting parameters of common relevance to Astronomy, Geodesy, & Geodynamics (e.g., Burša 1995, Groten 2004). In addition, it clarifies the procedure that must be followed in order that the dynamical ellipticity, fitted to the observations, contains the effects of the permanent tide avoiding in this way potential inconsistencies.

How to cite: Escapa, A., Baenas, T., and Ferrándiz, J. M.: On the permanent tide and the Earth dynamical ellipticity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21410, https://doi.org/10.5194/egusphere-egu2020-21410, 2020.

Accounting for non-stationary effects in the model of the Earth’s pole motion

Wai Yan Soe, Rumyantsev D.S., Perepelkin V.V.

Nowadays the problem of constructing a model of the Earth pole motion is relevant both in theoretical and in applied aspects. The main difficulty of accurately describing the Earth pole motion is that it has non-stationary perturbations leading to the changes in both the average parameters of its motion and the motion as a whole.

The main process of the Earth pole coordinates fluctuations is the sum of the quasi periodic Chandler component and annual one. The approximation of the Earth pole motion is generally accepted to be a few parametric two-frequency model with constant coefficients. Relatively slow changes in the parameters of the Chandler and annual components make it possible to use this approximation in the time intervals of 6–7 years, that is, during the period of the Chandler and annual components modulation. This model has low algorithmic complexity and describes the main process of pole oscillations with acceptable accuracy.

However, due to the non-stationary perturbations there are effects in the Chandler and annual components that are not typical for a simple dynamical system that is described by linear differential equations with constant coefficients. Such changes can also be observed in the dissipative systems with not only with the amplitude variations but also when oscillation process is in steady-state condition [1].

In this work the effect of changing in the Earth pole oscillatory mode is revealed, which consists in a jump-like shift in the average frequency of the pole around the midpoint (the motion of the Earth pole midpoint is a pole trend of a long-period and secular nature), which leads to a change in the average speed of its motion.

A method is proposed to determine the moment when the average frequency is shifted, which is important for refining the forecast model of the Earth pole motion. Using this method a modified model of pole motion is developed and the dynamic effects in its motion are considered, caused by the change in the amplitudes ratio of the Chandler and annual harmonics.

References

[1] Barkin M.Yu., Krylov S.S., Perepelkin V.V. Modeling and analysis of the Earth pole motion with nonstationary perturbations. IOP Conf. Series: Journal of Physics: Conf. Series 1301 (2019) 012005; doi:10.1088/1742-6596/1301/1/012005

How to cite: Wai, Y.: Accounting for non-stationary effects in the model of the Earth’s pole motion, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9954, https://doi.org/10.5194/egusphere-egu2020-9954, 2020.

A significant 6-year oscillation (SYO) signal existing in the length-of-day (LOD) variations may reflect the fast dynamics of the Earth cores. The time-varying characteristic (TVC) of this signal may reveal the relevant details on the geophysical excitation process. However, it is still debate about the TVC of the SYO. Our previous works indicated that the SYO signal was showing an obviously decaying trend during 1962~2012 based on the normal Morlet wavelet transform (NMWT) method, while other works did not show the similar decaying result based on the other methods (e.g., the least square fitting- LSF). Here, in order to solve this controversial issue, we revisit the SYO and its TVC. Through a lot of numerical simulation tests, NMWT method is further confirmed to be a good approach to quantitatively recover the target damped harmonic signals from the complex background noises, but the classical LSF method can destroy the original harmonic signal. This work indicates that the unattenuated SYO result obtained by the LSF method is not reliable. In addition, this work further analyzes the LOD data during a longer span (i.e., 1840~2018) and extracts the SYO result in the time domain, the result of which  shows: 1) the amplitude modulation phenomenon of the SYO itself on the longer time span, revealing the relevant excitation information within the Earth system; 2) a decreasing trend of the SYO signal in its amplitude after 1960s, which further supports the current SYO decaying result during 1962~2019. This recovered SYO result during a longer time-span obtained by this work is significant to understand the nature of the SYO change and its excitation process.

How to cite: Duan, P., Xu, C., Xu, X., and Huang, C.: On the time-varying characteristic of the 6-year oscillation signal in length-of-day, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8295, https://doi.org/10.5194/egusphere-egu2020-8295, 2020.

The Chandler wobble (CW) and Annual wobble (AW) are the main components of the Earth’s Polar motion, which play an important role in our understanding of their excitations. The Fourier Basis Pursuit Band-Pass Filtering (FBPBPF) method, which can effectively suppress the edge effect, are applied to extract the CW and AW in Earth's polar motion during 1900-2016. Through analyze the variation of CW extracted by the FBPBPF method, we find that the amplitude of the CW has been diminishing since 1995. However, the amplitude of the CW had stopped decline in the last year, and start to increase at now.

How to cite: Wang, G., Liu, L., Liu, J., and Tu, Y.: The status of Chandler wobble, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2996, https://doi.org/10.5194/egusphere-egu2020-2996, 2020.

How to cite: Bizouard, C., Nurul Huda, I., and Lambert, S.: Study of the Earth rheological properties from polar motion, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19240, https://doi.org/10.5194/egusphere-egu2020-19240, 2020.

Budgeting geophysical fluid excitations against space-geodetic observations of polar motion reveals non-negligible residuals on sub-monthly time scales, typically 1−2 cm when projected onto the Earth's surface. A possible source for these discrepancies are imperfections in the hydrodynamic models used to derive the required ocean excitation functions. To guide future model improvements, we present a systematic assessment of the oceanic component of sub-monthly polar motion based on three global time-stepping models which are forced by the same atmospheric data but considerably differ in their numerical setup and physical parameterizations. In particular, we use ocean bottom pressure output and angular momenta from (i) the finite-element 2 Dimensions Gravity Wave Model (Mog2D), (ii) the baroclinic Max-Planck-Institute Ocean Model (MPIOM) at 1° horizontal resolution, representing the current industry standard, and (iii) a more experimental, eddy-permitting setup of the MITgcm (MIT General Circulation Model). Validations of data from 2007 to 2008 are performed against observed polar motion and daily GRACE (Gravity Recovery and Climate Experiment) solutions, which resolve the broad scales of ocean bottom pressure variability relevant for angular momentum considerations. No definite quantitative results are available at the time of this writing, but a specific question we aim to answer is whether the MITgcm run outperforms the other models in our validations, given its higher resolution and partial representation of flow interactions with major topographic features.

How to cite: Schindelegger, M., Harker, A., Salstein, D., and Dobslaw, H.: A multi-model assessment of sub-monthly polar motion and the associated ocean bottom pressure variability, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7621, https://doi.org/10.5194/egusphere-egu2020-7621, 2020.

The Coupled Model Intercomparison Project (CMIP) is an effort to investigate the past, present and future state of a number of Earth system variables, using a variety of models developed by research centers around the globe. This broad initiative aims at understanding climate signals due to both natural variability and in response to changing radiative forcing. One of the so-called endorsed MIPs of the CMIP phase 6, the ScenarioMIP, is dedicated to providing multi-model climate projections based on alternative scenarios of future emissions and land use changes linked to socioeconomic factors. The climate of the 21^st century is simulated based on different forcings, which are defined from a combination of possible future pathways of societal development, the Shared Socioeconomic Pathways (SSPs), and the Representative Concentration Pathways (RCPs), identified by what radiative forcing level might exist in 2100.

Our study will examine the integrated effect of atmosphere and ocean variability on the Earth rotation speed, represented as changes in the length of day (LOD). Angular momentum variations due to mass and motion terms will be calculated from different models for the four most prominent scenarios as well as for historical simulations. We will also analyze spatial patterns of the respective variables in order to identify those regions in the atmosphere and oceans that contribute the most to LOD excitation. Finally, we will compare trends in the total axial angular momentum functions among each other and to trends in the global temperature to show the influence of global warming on the rotation rate.

How to cite: Böhm, S. and Salstein, D.: Climate impact on Earth rotation speed from CMIP6 model simulations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7088, https://doi.org/10.5194/egusphere-egu2020-7088, 2020.

Polar motion is caused by mass redistribution and motion within the Earth system. The GRACE satellite mission observed variations of the Earth’s gravity field which are caused by mass redistribution. Therefore GRACE time variable gravity field models are a valuable source to estimate individual geophysical mass-related excitations of polar motion. Since GRACE observations contain erroneous meridional stripes, filtering is essential in order to retrieve meaningful information about mass redistribution within the Earth system. However filtering reduces not only the noise but also smooths the signal and induces leakage of neighboring subsystems into each other.

We present a novel approach to reduce these filter effects in GRACE-derived equivalent water heights and polar motion excitation functions which is based on once and twice filtered gravity field solutions. The advantages of this method are that it is independent from geophysical model information, works on global grid point scale and can therefore be used for mass variation estimations of several subsystems of the Earth (e.g. continental hydrosphere, oceans, Antarctica and Greenland). In order to validate this new method, we perform a closed-loop simulation based on a realistic orbit scenario and error assumptions for instruments and background models, apply it to real GRACE data (GFZ RL06) and show comparisons with ocean model results from ECCO and MPIOM.

How to cite: Göttl, F., Murböck, M., Schmidt, M., and Seitz, F.: Reducing filter effects in GRACE-derived polar motion excitations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7444, https://doi.org/10.5194/egusphere-egu2020-7444, 2020.

The dynamic interactions that occur between the solid Earth and surficial fluids are related globally by conservation of angular momentum in the Earth system. Owing to this condition, the surficial fluids have shown to be main excitation sources of the Earth’s variable rotation on timescales between a few days and several years. Likewise, the Mars’ rotation changes due to variations of atmospheric circulation and surface pressure, and the variable Martian polar ice caps associated with the CO₂ sublimation/condensation effects. Investigations of the Earth and Mars’ rotations by surficial fluids may further our understandings of the Earth and planetary global dynamics. Here, we present our recent progresses on excitations of the Earth and Mars’ rotational variations on multiple time scales: (1) differences between the NCEP/NCAR and ECMWF atmospheric excitation functions of the Earth’s rotation, and (2) the Mars’ rotational variations and the dust cycles during the Mars Years 24-31.

How to cite: Zhou, Y., Xu, X., Xu, C., Chen, J., and Salstein, D.: Excitations of the Earth and Mars’ Variable Rotations by Surficial Fluids, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1908, https://doi.org/10.5194/egusphere-egu2020-1908, 2020.

The rotation rate of Ganymede, the largest satellite of Jupiter, is on average equal to its orbital mean motion but cannot be constant on orbital time scale as a result of the gravitational torque exerted by Jupiter on the moon. Here we discuss small deviations from the average rotation rate, evaluate polar motion, and discuss Ganymede's obliquity. We examine different time scales, from diurnal to long-period, and assess the potential of using rotation as probes of the interior structure.

The ESA JUICE (JUpiter ICy moons Explorer) mission will accurately measure the rotation of Ganymede during its orbital phase around the satellite starting in 2032. We report on different theoretical aspects of the rotation for realistic models of the interior of Ganymede, include tidal deformations and take into account the low-degree gravity field and topography of Ganymede. We assess the advantages of a joint use of rotation and tides to constrain the satellite's interior structure, in particular its ice shell and ocean.

How to cite: Van Hoolst, T., Baland, R.-M., Coyette, A., and Yseboodt, M.: The rotation and interior of Ganymede, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13749, https://doi.org/10.5194/egusphere-egu2020-13749, 2020.

The accuracy of near real-time estimates and short-term predictions of Earth orientation parameters (EOPs) can be enhanced by the use of Atmospheric Angular Momentum (AAM) and Ocean Angular Momentum (OAM) information, by accounting for the global conservation of angular momentum in the Earth system. The US Navy analysis and forecast scheme is named the Navy Earth System Prediction Capability (NAVY ESPC)  and is comprised of the Navy Global Environmental Model (NAVGEM) atmospheric and Hybrid Coordinate Ocean Model (HYCOM) ocean systems (along with ice forecasts). GOFS is being improved continually, and the resultant motion and mass fields are potentially useful for operational Earth orientation applications.  Consistency between the NAVGEM and HYCOM fields is required for calculations of the total angular momentum of the combined system of geophysical fluids. However, they might not include land-based Hydrological Angular Momentum functions (HAM) and the additional amount due to sea-level variability, the Sea-Level Angular Momentum (SLAM), both of which may be accounted for separately. We investigate various combination and optimal estimation processes using these data series, in conjunction with existing EOP observations to improve accuracy and robustness of short-term EOP predictions. Results are compared with those from other fluid models, particularly from those of the GeoForschungsZentrum (GFZ), the German Research Center for Geosciences. We also estimate power spectral density as a measure of error, for NAVGEM and HYCOM-based AAM/OAM series and similar series from other centers, comparing them to equivalent measures calculated from Earth orientation parameters.

How to cite: Stamatakos, N., Salstein, D., and McCarthy, D.: IERS Rapid Service/Prediction Center Use of Atmospheric and Ocean Angular Momentum for Earth Orientation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3738, https://doi.org/10.5194/egusphere-egu2020-3738, 2020.

GINGER (Gyroscopes IN General Relativity) is a proposal aiming at measuring the Lense-Thirring effect with an experiment based on Earth. It is based on an array of ring lasers, at present the most sensitive inertial sensors to measure the rotation rate of the Earth.

Rotation and angular measurements are of great importance for various fields of science: General Relativity predicts rotation terms originated from the kinetic term, Earth Science studies the Earth's angular velocity with its variations, the tides and related perturbations, the normal modes of the Earth, the angular perturbations associated to the movement of the plates, the deformations of hydrological nature, without neglecting the rotational signals produced by the earthquakes. A ring laser integral to the Earth's surface is sensitive not only to the angular rotation of the planet, but also to global and local rotational signals. For this reason GINGER is relevant for geophysics.

GINGERINO is a ring laser prototype installed inside the underground laboratory of the Gran Sasso. Its typical sensitivity is well below 0.1 nrad/s in 1 second measurement, and it is acquiring data on a continuous basis since several years. The most recent data of GINGERINO and the results relevant for geoscience are discussed.

How to cite: Di Virgilio, A. D. V.: GINGERINO and the GINGER Project, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21959, https://doi.org/10.5194/egusphere-egu2020-21959, 2020.