Search

The density jump at the inner core boundary of the Earth is poorly constrained by seismic data. One sensitive measure of the jump is the eigenperiod of the inner core wobble (ICW). Although theoretical studies on the ICW have been ongoing for decades, no observed ICW signal has been reported. To increase the detection level, here we use a recently proposed AR‐z method to analyze the 1960–2017 polar motion time series. We finally identify a +8.7 ± 0.2 year prograde motion with an ~2.67 ± 0.04 milliarcsecond amplitude. After confirming that this signal is almost a stationary oscillation and that atmospheric/oceanic/hydrological effects cannot seem to excite this signal, we carefully suggest that this ~8.7 year signal is possibly the ICW. According to this suggestion, we reconstruct a new 1‐D density model with a 507 ± 15 kg/m3 inner core boundary density jump. This new model can also provide a better fit than Preliminary Reference Earth model to the seismic overtone 2S1. Plain Language Summary: The eigenperiod of the ICW is directly related to the density jump at the inner core boundary (ICB) (which is still poorly known). Although theoretical studies on the ICW have been ongoing for decades, only Guo et al. (2005) have tried unsuccessfully to detect the ICW in the PM time series. In this study, we use the AR‐z spectrum, which has significantly higher sensitivity and frequency resolution than the Fourier (and maximum‐entropy) spectrum, especially when the signal‐to‐noise ratio is low. We identify a +8.7 ± 0.2 year prograde motion from the PM as the possible ICW. Our results provide useful constraints on the density jump at the ICB and can further strengthen the understanding of Earth's deep structure and dynamics. Key Points: The AR‐z spectrum method is used to search for the inner core wobble (ICW) in the polar motionA +8.7 ± 0.2 year prograde motion, with an ~2.67 ± 0.04 mas amplitude, is suggested as the possible ICWA modified core density profile is estimated by the suggested ICW period [ABSTRACT FROM AUTHOR]

We investigate a possible link between polar motion and (i) seismic energy release and (ii) timing and intensity of eruptions at Mount Etna (Italy) for which a dense observational database is available. Our study suggests that the seismicity around Mount Etna increases during the largest excursions of the Earth rotation pole, which result from the constructive interference of the climate‐driven seasonal and Chandler wobbles. To a lesser extent, a similar link is detected between the pole tide and the erupted volume of magma. We infer that, by creating periodic changes in the state of stress in the crust through a variable centrifugal force and a periodic vertical displacement (pole tide), variations in polar motion influence eruption timing and magnitude and the rate of seismic energy release from volcanoes. This study provides new evidences on the sensitivity of volcanoes to external forcing. Plain Language Summary: The Earth surface is continuously deformed by a wide range of phenomena including lunisolar tides and centrifugal forces due to changes in the Earth's rotation rate and in the direction of its rotation axis. The latter class of deformations is typically of a centimeter on interannual timescales. On another side, some volcanoes appear to be sensitive to small perturbations of the crustal stress. We detected similar variability in the centrifugal forces arising from the Earth's rotation axis direction variability and Mount Etna seismicity and erupted magma volume. This suggests that the variation of the Earth's rotation axis direction plays a significant role as modulator of the activity of Mount Etna. Key Points: Seismicity and eruption timing and magnitudes at Mount Etna show interannual variations in phase with the solid Earth pole tideEarth's Chandler and annual wobbles may alter the state of stress of the Earth's crust at interannual to decadal timescales [ABSTRACT FROM AUTHOR]

At seasonal and shorter time scales, polar motion and length‐of‐day (LOD) change are dominated by mass redistribution in the Earth climate system, including the atmosphere, oceans, and hydrosphere. Long‐term polar motion and LOD change are believed to be forced by solid Earth geophysical process, such as glacial isostatic adjustment. Decadal LOD variations are also connected to core‐mantle coupling. This study provides a comprehensive analysis of interannual oscillations in all three components of Earth rotation using accurately measured polar motion and LOD time series, and geophysical excitations computed from atmospheric, oceanic, and hydrological models over the period 1962 to 2018. Strong interannual oscillations remain in all three components after detrending and band‐pass filtering to retain variations at periods between 2 and 8 years. Polar motion Y is dominated by a 3.65‐year oscillation, plus others at periods of 2.5 and 5.9 years. Polar motion X shows a strong oscillation near 5.9 years, plus smaller variations at shorter periods. A 5.9‐year LOD variation has been recognized in earlier studies, but oscillations at periods of 2.36, 3.65, and 4.9 years are also observed. Atmosphere, ocean, and hydrosphere (AOH) sources largely account for 2.5‐ and 3.65‐year components in polar motion Y, but not for the 5.9‐year component in polar motion X and Y. The 2.36‐, 3.65‐, and 4.9‐year components in LOD can largely be accounted for by AOH sources. The 5.9‐year LOD component becomes more prominent after AOH sources have been subtracted. The presence of a 5.9‐year variation in all three components of Earth rotation suggests a source in Earth's interior, probably from the core. Key Points: We provide a comprehensive analysis of interannual oscillations in all three components of Earth rotation over the period 1962–2018This is the first study to have identified a 5.9‐year oscillation in all three components of Earth rotation, polar motion (X and Y), and LODThe presence of a 5.9‐year variation in all three components of Earth rotation suggests a source from the core and mantle [ABSTRACT FROM AUTHOR]

We use numerical integration of Brzeziński's broad-band Liouville equations with the new atmospheric/oceanic excitations provided by GFZ Potsdam to calculate their effect on polar motion. There exist several studies hinting that geomagnetic jerks, sudden changes of intensity of geomagnetic field, can also affect polar motion. We concentrate our efforts to study possible influence of geomagnetic jerks on temporal changes of polar motion. We demonstrate that the fit between integrated and polar motion observed by space geodesy improves substantially, if the influence of geomagnetic jerks is added to excitations by geophysical fluids. We also applied additional excitations due to the continental hydrosphere and barystatic sea-level variations. Although these effects complete the geophysical fluids system, their adding could not improve the agreement between integrated and observed polar motion. [ABSTRACT FROM AUTHOR]

Abstract A study of the uncertainty propagation in ITRS/GCRS transformation is presented in this work. General law of propagation of variances is applied to the ITRS/GCRS transformation matrix, deriving the analytical expressions to compute GCRS position uncertainty. This evaluation is based on EOP uncertainties provided by IERS long-term series and formal uncertainties of ITRS-compatible coordinates. Numerical results for the period 1998–2016 are shown and discussed for ITRS positions in different altitudes and latitudes, providing graphical and numerical insights of the mapping of EOP uncertainties to transformed coordinates. Eventually, an analysis of short-term evolution of the Celestial Intermediate Pole coordinates in the GCRS provided by the IAU2006/2000A precession-nutation model is carried out, in order to assess the feasibility to potentially broadcast these parameters in GNSS navigation message. This approach would facilitate the dissemination of terrestrial-celestial transformation parameters for real time users, given that polar motion and UT1-UTC are already foreseen in GPS interface specification. The results presented in this work confirm the feasibility of this idea. [ABSTRACT FROM AUTHOR]

Abstract We investigate the contribution of continental hydrology signals to polar motion excitation resulting from changes in mass distribution associated with terrestrial water and snow/ice based on a variety of datasets. The impact of the former is less well known than that of other geophysical fluids, namely atmospheric and oceanic angular momentum signals, especially for oscillations over shorter-than-annual periods. The geodetic excitation function of polar motion can be determined from observations, while the hydrological excitation function can be estimated either from global models of the land-based hydrosphere or from indirect observations of variations in the Earth's gravity field. With more than 15 years of data, the pair of GRACE satellites has provided valid datasets for studying interannual polar motion excitation. Recent results are promising and indicate agreement between GRACE-derived interannual hydrological excitations and the corresponding geodetic observations. Our work focuses on the non-seasonal spectral range, and compares hydrological excitations based on recent GRACE solutions from different centres with signals from climate models, and as a residual from geodetic observations. [ABSTRACT FROM AUTHOR]

In this contribution, it is shown that GPS orbits are able to absorb some diurnal signals in polar motion. The arising implications for the influence of the subdaily pole model on GPS solutions are discussed. Two signals in polar motion can be absorbed by GPS orbits: a retrograde signal with a period of a sidereal day (23 h 56 min 4 s) and a prograde signal with a period matching the revolution period of the GPS satellites in the terrestrial reference frame (23 h 55 min 56 s). We show that the retrograde signal contributes to the absolute orientation of the orbital planes in space and the prograde signal, due to coincidence of its period with the period of revolution of the GPS satellites, contributes to the position of the geocenter for each individual satellite. It is known from previous studies that there are systematic differences between orbital parameters from GPS solutions computed with different subdaily pole models. We show in this paper that this behavior can be explained by the absorption effects in 1-day GPS orbits. Diurnal signals cannot be spectrally separated over a time interval of 1  day. Adjustment of any diurnal prograde or retrograde signal to a subdaily pole time series given by a subdaily model over 24 h will lead to an estimated signal with a nonzero amplitude. Thus, any subdaily pole model used in the processing of space geodetic observations contains a part which corresponds numerically to the discussed prograde signal and a part which corresponds to the retrograde diurnal signal. Different pole models show different amplitudes of the diurnal signals which will be absorbed by the orbits. As a result, GPS orbits computed with different subdaily pole models have systematically different orientation and position in space. Using 1-day GPS solutions over a time span of 13 years (1994-2007), we show that the systematic variations in orbit position and orientation caused by individual tidal terms in polar motion can be well predicted and explained by the suggested mechanism. [ABSTRACT FROM AUTHOR]

The role of continental water in polar motion excitation can be illustrated by determining Hydrological Angular Momentum calculated from terrestrial water storage (TWS). In this paper we compare global and regional changes in TWS computed using Coupled Model Intercomparison Project Phase 5 climate models, Global Land Data Assimilation System (GLDAS) land hydrology models and observations from the Gravity Recovery and Climate Experiment (GRACE) satellite mission. We also compare hydrological excitation functions derived from models with those obtained from the GRACE mission and the hydrological signal in observed polar motion excitation (the so-called geodetic residuals). The results confirm that GLDAS models of seasonal and non-seasonal TWS change are more consistent with GRACE data than climate models; on the other hand, none of the considered models are fully consistent with GRACE data or geodetic residuals. In turn, GRACE observations are most consistent with the non-seasonal hydrological signal in observed excitation. A detailed study of the contribution of different TWS components to the hydrological excitation function shows that soil moisture dominates. [ABSTRACT FROM AUTHOR]

In this work, we study the Earth Orientation Parameters (EOP) estimated from the continuous VLBI campaign CONT17. This campaign consisted of two station networks observing in parallel for 15 days, allowing for interesting comparison of the results. We find that the WRMS differences between the EOP estimated from the two networks are in the range 40-70 µas. Similar agreement is found with the polar motion estimated from GNSS. We also investigate the high frequency EOP variations and confirm earlier findings that the current IERS model for high frequency EOP variations needs to be updated. [ABSTRACT FROM AUTHOR]

Changes in Terrestrial Water Storage (TWS) due to seasonal changes in soil moisture, ice and snow loading and melting influence the Earth's inertia tensor. Quantitative assessment of hydrological effects of polar motion remains unclear because of the lack of the observations and differences between various atmospheric and ocean models. We compare the effects of several hydrological excitation functions computed as the difference between the excitation function of polar motion Geodetic Angular Momentum (GAM) and joint atmospheric plus oceanic excitation functions, called geodetic residuals. Geodetic residuals are computed for different Atmospheric Angular Momentum (AAM) and Oceanic Angular Momentum (OAM) models and are analyzed and compared with the hydrological excitation function determined from the Land Surface Discharge Model. They are analyzed on decadal, interannual, seasonal and non-seasonal time scales. The equatorial components of hydrological geodetic excitation functions χ1 and χ2 are decomposed into prograde and retrograde time series by applying Complex Fourier Transform Models. The agreement between hydrological geodetic residuals and excitation functions is validated using Taylor diagrams. This shows that agreement is highly dependent on AAM and OAM models. Errors in these models affect the resulting geodetic residuals and have a strong impact on the Earth's angular momentum budget. [ABSTRACT FROM AUTHOR]

Earth's polar motion predictions are essential in near real-time applications including spacecraft navigation and satellite orbit determinations and are also important for geophysics studies. It has previously been demonstrated that the basic problem in predicting a polar motion time-series is to treat separately its low- and high-frequency components. In this paper, this problem is solved by the combination of wavelet transform with the least-squares (LS) extrapolation and autoregressive (AR) method. Wavelet transform is first employed to separate the deterministic low-frequency components including the Chandler and annual wobbles and irregular short-period high-frequency components of a polar motion time-series. Then the deterministic parts are predicted using LS extrapolation of models for the linear trend, Chandler and annual wobbles, while the remaining irregular parts together with LS residuals are forecasted using the AR stochastic method. The polar motion predictions are computed as a combination of the LS extrapolation and AR prediction. The results show that the polar motion predictions up to 360 days in the future obtained by this approach can be remarkably enhanced due to the use of the wavelet-based preprocessing procedure. We conclude that the separate treatment of low- and high-frequency components is of use to enhance polar motion predictions. [ABSTRACT FROM AUTHOR]

Northern Eurasian continent has been regarded to contribute as the major source area, of which seasonal atmospheric pressure loading and unloading cycle leads to the annual wobble of the Earth. In the early days when reliable data of global coverage were not accessible, this dominance has remained as only a hypothesis. Nowadays, however, European Centre for Medium-Range Weather Forecasts and National Centers for Environmental Prediction produce reliable datasets, therefore, such unique feature has become clearer with quantitative evidences. Having both the Earth's polar motion and the global atmospheric state known with unprecedented accuracy, we hereby identify and scrutinize whether Siberia and Manchuria dominate the annual polar motion of the Earth. [ABSTRACT FROM AUTHOR]

Abstract Astrometric and geodetic measurements show that the mean position of Earth's spin axis drifted through the solid crust toward Labrador, Canada at an average speed of 10.5 ± 0.9 cm/yr during the 20th century. Understanding the origins of this secular polar motion (SPM) has significance for modeling the global climate, as it provides a link to ice mass balance and sea-level rise. A perplexing issue, however, is that while glacial isostatic adjustment (GIA) models satisfactorily explain the direction of SPM, the associated prediction of the amplitude is insufficient. Our Bayesian GIA analysis, with constraints from relative sea-level and vertical land motion data, reveals that this process only accounts for 33 ± 18 % of the observed SPM amplitude. This shortfall motivates a more broadly scoped reassessment of SPM drivers. To address this, we assemble a complete reconstruction of Earth's surface mass transport derived from recent advancements in modeling the global 20th century cryospheric, hydrologic, oceanic, and seismogenic mass exchange. The summed signals, nonetheless, cannot fully reconcile the observed SPM, even when considering the error statistics of each driver. We investigate an additional excitation source: changes in Earth's inertia tensor caused by mantle convection. Sophisticated models have recently been advanced in tectonic plate reconstructions, in conjunction with geoid and seismic tomographic models. Here we use these models to compute new estimates of SPM. While the convection-driven SPM has considerable uncertainty, the average direction of 283 recent models aligns with the residual SPM (within 2.7 ∘ ± 14.8 ∘), significantly reducing the gap between observation and prediction. We assert that one key mechanism for driving 20th century SPM is long-term mass movement due to mantle convection. Highlights • Earth's spin axis drifted along ∼74°W at a speed of ∼10.5 cm/yr during the 20th century. • Glacial isostatic adjustment (GIA) explains 33 ± 18 % of the observed polar motion. • Environmental processes plus GIA cannot fully reconcile the observation. • Contribution from mantle convection (MC) is essential to close the budget. • Polar motion based joint GIA/MC inversion may help constrain lower mantle viscosity. [ABSTRACT FROM AUTHOR]

Large polar motions are observed in the apparent polar wander paths of several continents during the Ediacaran. Among various hypotheses proposed in the literature, one consists of the occurrence of two successive fast and large true polar wander (TPW) episodes, from 615 to 590 Ma and then between 575 and 565 Ma. In this study, we explored the effect of the reactivation of a girdle of subduction to produce such TPW. First, we performed a reconstruction of the main continents between 615 and 520 Ma including Laurentia, Baltica, west and central Gondwana, and Australia‐Antarctica. We then implemented this paleogeography into a simple mantle dynamic model to calculate the TPW during the Ediacaran. Our results show that the reactivation of a girdle of subduction surrounding the continents along with a reduced effect of the return flow rising from the lower mantle can produce two TPW episodes consistent with the paleomagnetic observations. This mechanism is possible if the sinking velocities associated with the girdle of subduction drastically decrease between 635 and 730 Ma. Such a large geodynamic event is consistent with the detrital zircon age distribution of the Neoproterozoic supporting a low subduction activity during the Cryogenian and a boost during the Ediacaran. Decrease of subduction‐related stress induced on the lithosphere may have interrupted the rifting of the supercontinent Rodinia for 100 Ma. Finally, the weakening in subduction magmatism might have strongly reduced the CO2 flux into the atmosphere and played a major role in driving the Neoproterozoic global‐scale glaciations. Key Points: The starting of a girdle of subduction can generate two successive TPW events consistent with the Ediacaran paleomagnetic observationsThis mechanism is possible if the sinking velocities associated with the girdle of subduction drastically decrease between 635 and 730 MaThe global detrital zircon age distribution supports a low subduction activity during the Cryogenian and a boost during the Ediacaran [ABSTRACT FROM AUTHOR]

Previous studies on the relationship between polar motion and water mass change have mainly concentrated on the excitation of polar motion via global terrestrial water storage changes (TWSC). In view of the uneven distribution of global terrestrial water storage, the relationship between regional water mass change and polar motion needs to be further explored owing to the lack of documented results. In addition, given the uncertainty in the estimation of TWSC, it is required to develop appropriate indices to describe water mass change from different perspectives. The Amazon River basin (referred to Amazon hereafter), containing the world’s largest river, located at around the 90°W longitude, is selected as the study area. Water vapor flux, precipitation, runoff and TWSC are selected as the indices of water mass changes to reveal the relationship between polar motion and water mass change in this giant basin. The Mann-Kendall (M-K) method, the accumulated anomaly analysis method and the curvature method are used to identify the abrupt change points; the least squares method is used to estimate the trends, and the Fast Fourier Transform (FFT) and the Ensemble Empirical Mode Decomposition (EEMD) are used to perform a periodic analysis, for all the above indices. It is shown that, of all the indices from 1948 to 2011, water vapor flux is the most closely related index to polar motion. In detail, precipitation and water vapor flux contain beat periods of polar motion; water vapor flux, precipitation and polar motion have a common M-K test abrupt change point (occurring in ca. 1968) at the 0.05 significance level; water vapor flux has a similar accumulated anomaly curve with that of polar motion; and water vapor flux is more highly correlated with polar motion than most other indexes. It is found, just like global TWSC, the χ2 component of the excitation via water vapor flux and water storage change in the Amazon follows that of observed polar motion; χ1 does not follow. However, the pattern in the Amazon that the χ2 component of the excitation by water follows that of observed polar motion is at a more significant level than in global. Finally, the new index termed Location of Vapor-based InterTropical Convergence Zone (LVITCZ) we proposed to describe the annual mean latitudinal location of water mass change shows a more close and visual relationship between water mass change and polar motion than other chosen indices do. [ABSTRACT FROM AUTHOR]

Observation of the rotation of synchronously rotating satellites can help to probe their interior. Previous studies mostly assume that these large icy satellites are in hydrostatic equilibrium, although several measurements indicate that they deviate from such a state. Here we investigate the effect of non-hydrostatic equilibrium and of flow in the subsurface ocean on the rotation of Titan. We consider the variations in rotation rate and the polar motion due to (1) the gravitational force exerted by Saturn at orbital period and (2) exchanges of angular momentum between the seasonally varying atmosphere and the solid surface. The deviation of the mass distribution from hydrostaticity can significantly increase the diurnal libration and decrease the amplitude of the seasonal libration. The effect of the non-hydrostatic mass distribution is less important for polar motion, which is more sensitive to flow in the subsurface ocean. By including a large spectrum of atmospheric perturbations, the smaller than synchronous rotation rate measured by Cassini in the 2004–2009 period (Meriggiola et al., 2016) could be explained by the atmospheric forcing. If our interpretation is correct, we predict a larger than synchronous rotation rate in the 2009–2014 period. [ABSTRACT FROM AUTHOR]

This study employs a combination of weighted least-squares extrapolation and an autoregressive model to produce medium-term predictions of polar motion (PM) parameters. The precisions of PM parameters extracted from earth orientation parameter (EOP) products are applied to determine the weight matrix. This study employs the EOP products released by the analysis center of the ‘International Global Navigation Satellite System Service and International Earth Rotation and Reference Systems Service’ needs to be modified to ‘International Global Navigation Satellite System Service (IGS) and International Earth Rotation and Reference Systems Service (IERS)’ as primary data. The polar motion parameters and their precisions are extracted from the EOP products to predict the changes in polar motion over spans of 1-360 days. Compared with the combination of least-squares and autoregressive model, this method shows considerable improvement in the prediction of PM parameters. [ABSTRACT FROM AUTHOR]

The modification of spectral analysis especially intended for studying the disturbing functions of the atmosphere and ocean, as well as the observed polar motion (Wiener-Liouville spectrum), is used. The time series of the atmospheric disturbing functions obtained by the U.S. National Centers for Environmental Prediction (NCEP) of the International Earth Rotation and Reference Systems Service (IERS) for the period from January 1, 1980 to June 20, 2014 (http://www.iers.org/.cs1?pid=43-1100116) are analyzed. It is shown that the baric disturbing function contains a regular mode with a period of ~16 months; the contribution of this mode in the polar motion is estimated. [ABSTRACT FROM AUTHOR]

By a number of test cases using different sample numbers and sample lengths, we obtain a Radial Basis Function Neural Network (RBFNN) model that is suitable for the short-term forecast of polar motion, especially for the ultra-short-term forecast. By using the same data sample of Earth’s polar motion, this RBFNN model can achieve better short-term prediction accuracy than the least-squares+autoregressive (LS+AR) method, and better ultra-short-term prediction accuracy than the LS+AR+Kalman method. Using this model to forecast the polar motion data from January 1, 2002 to December 30, 2007 and from January 1, 2010 to December 30, 2016, respectively, experimental results show that the ultra-short-term forecast accuracy of this RBFNN model is within a precision of 3.15 and 3.08 milliseconds of arc (mas) in polar motion x direction, 2.02 and 2.04 mas in polar motion y direction; the short-term forecast accuracy of RBFNN model is within a precision of 8.83 and 8.69 mas in polar motion x direction, and 5.59 and 5.85 mas in polar motion y direction. As is stated above, this RBFNN model is well capable of forecasting the short-term of polar motion, especially the ultra-short-term. [ABSTRACT FROM AUTHOR]

To meet the need for real-time and high-accuracy predictions of polar motion (PM), the singular spectrum analysis (SSA) and the autoregressive moving average (ARMA) model are combined for short- and long-term PM prediction. According to the SSA results for PM and the SSA prediction algorithm, the principal components of PM were predicted by SSA, and the remaining components were predicted by the ARMA model. In applying this proposed method, multiple sets of PM predictions were made with lead times of two years, based on an IERS 08 C04 series. The observations and predictions of the principal components correlated well, and the SSA + ARMA model effectively predicted the PM. For 360-day lead time predictions, the root-mean-square errors (RMSEs) of PMx and PMy were 20.67 and 20.42 mas, respectively, which were less than the 24.46 and 24.78 mas predicted by IERS Bulletin A. The RMSEs of PMx and PMy in the 720-day lead time predictions were 28.61 and 27.95 mas, respectively. [ABSTRACT FROM AUTHOR]

This paper studies the connection between the subdaily model for polar motion used in the processing of very long baseline interferometry (VLBI) observations and the estimated nutation offsets. By convention accepted by the International Earth Rotation Service, the subdaily model for polar motion recommended for routine processing of geodetic observations does not contain any daily retrograde terms due to their one-to-one correlation with the nutation. Nevertheless, for a 24-h VLBI solution a part of the signal contained in the polar motion given by the used subdaily model is numerically mistaken for a retrograde daily sidereal signal. This fictitious retrograde daily signal contributes to the estimated nutation, leading to systematic differences between the nutation offsets from VLBI solutions computed with different subdaily polar motion models. We demonstrate this effect using solutions for all suitable 24-h VLBI sessions over a time span of 11 years (2000-2011). By changing the amplitudes of one tidal term in the underlying subdaily model for polar motion and comparing the estimated parameters to the solutions computed with the unchanged subdaily model, the paper shows and explains theoretically the effects produced by the individual subdaily terms on the VLBI nutation estimates. [ABSTRACT FROM AUTHOR]

Continental hydrological loading by land water, snow and ice is a process that is important for the full understanding of the excitation of polar motion. In this study, we compute different estimations of hydrological excitation functions of polar motion (as hydrological angular momentum, HAM) using various variables from the Global Land Data Assimilation System (GLDAS) models of the land-based hydrosphere. The main aim of this study is to show the influence of variables from different hydrological processes including evapotranspiration, runoff, snowmelt and soil moisture, on polar motion excitations at annual and short-term timescales. Hydrological excitation functions of polar motion are determined using selected variables of these GLDAS realizations. Furthermore, we use time-variable gravity field solutions from the Gravity Recovery and Climate Experiment (GRACE) to determine the hydrological mass effects on polar motion excitation. We first conduct an intercomparison of the maps of variations of regional hydrological excitation functions, timing and phase diagrams of different regional and global HAMs. Next, we estimate the hydrological signal in geodetically observed polar motion excitation as a residual by subtracting the contributions of atmospheric angular momentum and oceanic angular momentum. Finally, the hydrological excitations are compared with those hydrological signals determined from residuals of the observed polar motion excitation series. The results will help us understand the relative importance of polar motion excitation within the individual hydrological processes, based on hydrological modeling. This method will allow us to estimate how well the polar motion excitation budget in the seasonal and inter-annual spectral ranges can be closed. [ABSTRACT FROM AUTHOR]

Many objects in the solar system are suspected to have experienced reorientation of their spin axes. As their rotation rates are slow and their shapes are nearly spherical, the formation of mass anomalies, by either endogenic or exogenic processes, can change objects’ moments of inertia. Therefore, the objects reorient to align their largest moment of inertia with their spin axis. Such a phenomenon is called True Polar Wander (TPW). Here we report the discovery of a global series of topographic lows on Saturn's satellite Enceladus that we interpret to show that this synchronously locked moon has undergone TPW by ∼55° about the tidal axis. We use improved topographic data from the spherical harmonic expansion of Cassini limb and stereogrammetric measurements to characterize regional topography over the surface of Enceladus. We identify a group of nearly antipodal basins orthogonal to a basin chain tracing a non-equatorial circumglobal belt across Enceladus' surface. We argue that the belt and the antipodal regions are fossil remnants of earlier equator and poles, respectively. We argue that these lows arise from isostasic compensation and that their pattern reflects spatial variations in internal dynamics of the ice shell. Our hypothesis is consistent with a variety of geological features visible in Cassini images. [ABSTRACT FROM AUTHOR]

The position of a Martian lander is affected by different aspects of Mars' rotational motions: the nutations, the precession, the length-of-day variations and the polar motion. These various motions have a different signature in a Doppler observable between the Earth and a lander on Mars’ surface. Knowing the correlations between these signatures and the moments when these signatures are not null during one day or on a longer timescale is important to identify strategies that maximize the geophysical return of observations with a geodesy experiment, in particular for the ones on-board the future NASA InSight or ESA-Roscosmos ExoMars2020 missions. We provide first-order formulations of the signature of the rotation parameters in the Doppler and range observables. These expressions are functions of the diurnal rotation of Mars, the lander position, the planet radius and the rotation parameter. Additionally, the nutation signature in the Doppler observable is proportional to the Earth declination with respect to Mars. For a lander on Mars close to the equator, the motions with the largest signature in the Doppler observable are due to the length-of-day variations, the precession rate and the rigid nutations. The polar motion and the liquid core signatures have a much smaller amplitude. For a lander closer to the pole, the polar motion signature is enhanced while the other signatures decrease. We also numerically evaluate the amplitudes of the rotation parameters signature in the Doppler observable for landers on other planets or moons. [ABSTRACT FROM AUTHOR]

We present results from the generation of 10-year-long continuous time series of the Earth's polar motion at 15-min temporal resolution using Global Positioning System ground data. From our results, we infer an overall noise level in our high-rate polar motion time series of 60 $$\upmu \hbox {as}$$ (RMS). However, a spectral decomposition of our estimates indicates a noise floor of 4 $$\upmu \hbox {as}$$ at periods shorter than 2 days, which enables recovery of diurnal and semidiurnal tidally induced polar motion. We deliberately place no constraints on retrograde diurnal polar motion despite its inherent ambiguity with long-period nutation. With this approach, we are able to resolve damped manifestations of the effects of the diurnal ocean tides on retrograde polar motion. As such, our approach is at least capable of discriminating between a historical background nutation model that excludes the effects of the diurnal ocean tides and modern models that include those effects. To assess the quality of our polar motion solution outside of the retrograde diurnal frequency band, we focus on its capability to recover tidally driven and non-tidal variations manifesting at the ultra-rapid (intra-daily) and rapid (characterized by periods ranging from 2 to 20 days) periods. We find that our best estimates of diurnal and semidiurnal tidally induced polar motion result from an approach that adopts, at the observation level, a reasonable background model of these effects. We also demonstrate that our high-rate polar motion estimates yield similar results to daily-resolved polar motion estimates, and therefore do not compromise the ability to resolve polar motion at periods of 2-20 days. [ABSTRACT FROM AUTHOR]

Continuous (CONT) VLBI campaigns have been carried out about every 3 years since 2002. The basic idea of these campaigns is to acquire state-of-the-art VLBI data over a continuous time period of about 2 weeks to demonstrate the highest accuracy of which the current VLBI system is capable. In addition, these campaigns support scientific studies such as investigations of high-resolution Earth rotation, reference frame stability, and daily to sub-daily site motions. The size of the CONT networks and the observing data rate have increased steadily since 1994. Performance of these networks based on reference frame scale precision and polar motion/LOD comparison with global navigation satellite system (GNSS) earth orientation parameters (EOP) has been substantially better than the weekly operational R1 and R4 series. The precisions of CONT EOP and scale have improved by more than a factor of two since 2002. Polar motion precision based on the WRMS difference between VLBI and GNSS for the most recent CONT campaigns is at the 30 $$\upmu $$ as level, which is comparable to that of GNSS. The CONT campaigns are a natural precursor to the planned future VLBI observing networks, which are expected to observe continuously. We compare the performance of the most recent CONT campaigns in 2011 and 2014 with the expected performance of the future VLBI global observing system network using simulations. These simulations indicate that the expected future precision of scale and EOP will be at least 3 times better than the current CONT precision. [ABSTRACT FROM AUTHOR]

The ring laser gyroscope (RLG) technique has been investigated for about 20 years as a potential complement to space geodetic techniques in measuring variations of Earth rotation. The technique is of great interest, especially in the context of monitoring rapid changes of rotation with sub-daily resolution. In this paper, we review how the known high frequency signals in Earth rotation parameters, including the so-called diurnal polar motion, diurnal and semidiurnal ocean tide effects in polar motion and UT1 and librations, prograde diurnal in polar motion and semidiurnal in UT1, contribute to the RLG observable, the Sagnac frequency. Our results suggest that at the current accuracy level of the technique, the signals coming from diurnal polar motion and ocean tides should be taken into account in analysis while the influence of libration can be neglected. We also point out that the contributing signals are superimposed upon each other and can hardly be separated from the data from a single instrument. Our computations are done taking parameters of the RLG at the Wettzell Observatory in Germany. However, we also consider how the strength of a particular signal depends on the geographic location of a horizontally mounted instrument. Finally, we discuss the relationship between the geographical location and terrestrial orientation of RLG and its consequence for the observed Sagnac signal. [ABSTRACT FROM AUTHOR]

We extend previous work to derive a non-linear rotational stability theory governing true polar wander (TPW) of terrestrial planets with viscoelastic lithospheres. We demonstrate, analytically and using numerical examples, that our expressions are consistent with previous results in the limiting cases of low and infinite (i.e., purely elastic) viscosity lithospheres. To illustrate the stability theory, we compute TPW on Mars driven by a simple, prescribed mass loading. Our calculations demonstrate that on short time scales relative to the relaxation time of the viscoelastic lithosphere, the rotation axis follows a constrained path that reflects stabilization by remnant strength in the lithosphere, but that on long times scales this stabilization disappears and the load ultimately reaches the equator. Earlier work based on the assumption of a permanent remnant bulge in the case of a purely elastic lithosphere has suggested that Martian TPW would not persist for any significant time after a load is emplaced, and thus an equilibrium stability theory is sufficient to model long-term (order 1 Myr or longer) polar motion of the planet. Our results suggest, in contrast, that TPW on Mars can continue over time scales on the order of the relaxation time of the lithosphere after load emplacement; for sufficiently high lithospheric viscosities, this time scale may be comparable to the age of the planet. [ABSTRACT FROM AUTHOR]

We examine Earth’s polar motion (PM) for the years 1979–2010 to understand climate related sources of PM excitation at periods longer than a year, and to investigate Antarctic and Greenland ice mass balance contributions to long period PM. There is particular interest in years prior to the GRACE mission (prior to 2002). Although long period PM is dominantly a measure of changes in two spherical harmonic Stokes coefficients (ΔC 21 and ΔS 21 ), we remove excitations due to winds and currents by estimating them from ERA-Interim winds and GECCO2 currents. PM estimates of ΔC 21 and ΔS 21 are compared with model estimates of contributions from the atmosphere, oceans, water stored on the continents, and polar ice sheets. We also include contributions from groundwater depletion and mountain glaciers. PM Stokes coefficient variations agree very well with model estimates over inter-annual time scales. For ΔC 21 we find good agreement at long periods, with a common long-period (quadratic) variation, but not for ΔS 21 . This suggests deficiencies in understanding long period ice mass variations in Antarctica and/or groundwater mass changes in Eurasia and North America. [ABSTRACT FROM AUTHOR]

Based on SDSS data, we have considered the spatial environment of galaxies with extended polar rings. We used two approaches: estimating the projected distance to the nearest companion and counting the number of companions as a function of the distance to the galaxy. Both approaches have shown that the spatial environment of polar-ring galaxies on scales of hundreds of kiloparsecs is, on average, less dense than that of galaxies without polar structures. Apparently, one of the main causes of this effect is that the polar structures in a denser environment are destroyed more often during encounters and mergers with other galaxies. [ABSTRACT FROM AUTHOR]

Accurate real-time polar motion parameters play an important role in satellite navigation and positioning and spacecraft tracking. To meet the needs for real-time and high-accuracy polar motion prediction, a hybrid model that integrated singular spectrum analysis (SSA), least-squares (LS) extrapolation and an autoregressive moving average (ARMA) model was proposed. SSA was applied to separate the trend, the annual and the Chandler components from a given polar motion time series. LS extrapolation models were constructed for the separated trend, annual and Chandler components. An ARMA model was established for a synthetic sequence that contained the remaining SSA component and the residual series of LS fitting. In applying this hybrid model, multiple sets of polar motion predictions with lead times of 360 days were made based on an IERS 08 C04 series. The results showed that the proposed method could effectively predict the polar motion parameters. [ABSTRACT FROM AUTHOR]

We present results of the DORIS data processing for the ITRF2014 carried out in the Institute of Astronomy, Russian Academy of Sciences (short INA) for the time period 1993.0–2015.0. The evaluated SINEX free-network (inawd08) weekly solutions for station positions and polar motion have been submitted to the IDS Combination Center. We applied the upgraded models of the gravity field, troposphere, and used corrected data for SPOT-5 satellite which permitted us to improve the result precision for Helmert transformation parameters and EOP. The agreement with the IERS C04 solution turns out better than 0.1 mas with a dispersion of 1 mas. The evaluated amplitudes of annual geocenter variations derived from inawd08 weekly solutions are 3.4 ± 0.5 mm, 4.4 ± 0.5 mm, and 3.3 ± 1.0 mm for X , Y , and Z components, respectively. The recovered amplitudes and phases are in a good agreement with the geophysical models. The results of two single satellite campaigns related to the scale increase in 2012 and 1994 for IDS combination are studied. Unlike other Analysis Centers, we did not apply a phase center law for ground antennas. It was shown that the correction for the phase center variation (PCV) of ground DORIS antennas results in the shift of the mean scale factor by 1.24 ppb (i.e., ∼8 mm) with respect to the case without correction. The PCV model and the satellites HY-2A and SARAL are included into the INA latest solutions (inawd10) after the submission for the ITRF2014. The future work is discussed. [ABSTRACT FROM AUTHOR]

The International DORIS Service (IDS) submitted input data for the most recent realization of the International Terrestrial Reference System (ITRS), the International Terrestrial Reference Frame 2014 (ITRF2014). As one of the ITRS Combination Centers, DGFI-TUM is in charge to analyze and assess the quality of the submitted data and to compute a combined global TRF solution (called DTRF2014) using observations of the four geodetic space techniques GNSS, VLBI, SLR and DORIS. The combination methodology used at DGFI-TUM is based on the combination of datum-free normal equations. Together with station coordinates and velocities, terrestrial pole coordinates are estimated in one common adjustment. The paper presents the analysis results of the most recent DORIS submission IDS-d09 and evaluates its quality w.r.t. the DTRF2008 (IDS-only) solution. In the most recent version of the analysis, we introduce in total 55 station discontinuities and reduce 15 stations due to a too short time span or too few observations. Time series of weekly IDS solutions are computed and validated w.r.t. DTRF2008. The transformation parameter time series and the station residuals are discussed in detail. Especially the scale parameter time series shows a significant improvement compared to the DTRF2008 input data. The scatter of the x - and y -translation is significantly reduced to 5.7 mm and 7.1 mm compared to 6.6 mm and 8.1 mm for the DTRF2008 (IDS-only) solution. The z -translation time series still shows a high correlation with solar activity. 10% of all station residuals are significantly affected by spectral peaks at draconitic period harmonics of the altimetry satellites Jason and TOPEX/Poseidon and up to 48% of all station residual time series contain significantly determined frequencies with a 14 day period. The multi-year IDS solution is validated w.r.t. DTRF2008 and the consistently estimated terrestrial pole coordinates are analyzed and compared to IERS 08 C04. The x-pole spectra comprises prominent peaks at various draconitic frequencies. [ABSTRACT FROM AUTHOR]

Based on a numerical-analytical model of the terrestrial pole oscillations, we investigate the effects of fluctuation-dissipation perturbations due to the pole tide. We consider the fluctuation perturbations at a frequency close to the Chandler one using the sea level data as an example. Allowance for the small irregular perturbations in tidal processes is shown to lead to variations in the Chandler component of the oscillations. We note that the amplitude of the Chandler pole oscillations is sensitive to the difference of the Chandler frequency and a frequency close to it and to the dissipation coefficients. [ABSTRACT FROM AUTHOR]

The hydrological contribution to decadal, inter-annual and multi-annual suppress polar motion derived from climate model as well as from GRACE (Gravity Recovery and Climate Experiment) data is discussed here for the period 2002.3-2016.0. The data set used here are Earth Orientation Parameters Combined 04 (EOP C04), Flexible Global Ocean-Atmosphere-Land System Model: Grid-point Version 2 (FGOAL-g2) and Global Land Data Assimilation System (GLDAS) climate models and GRACE CSR RL05 data for polar motion, hydrological and gravimetric excitation, respectively. Several Hydrological Angular Momentum (HAM) functions are calculated here from the selected variables: precipitation, evaporation, runoff, soil moisture, accumulated snow of the FGOALS and GLDAS climate models as well as from the global mass change fields from GRACE data provided by the International Earth Rotation and Reference System Service (IERS) Global Geophysical Fluids Center (GGFC). The contribution of different HAM excitation functions to achieve the full agreement between geodetic observations and geophysical excitation functions of polar motion is studied here. [ABSTRACT FROM AUTHOR]

The complex demodulation (CD) algorithm is an efficient tool for extracting the diurnal and subdiurnal components of Earth rotation from the routine VLBI observations (). This algorithm was implemented by into a dedicated version of the VLBI analysis software VieVs. The authors processed around 3700 geodetic 24-hour observing sessions in 1984.0-2010.5 and estimated simultaneously the time series of the long period components as well as diurnal, semidiurnal, terdiurnal and quarterdiurnal components of polar motion (PM) and universal time UT1. This paper describes the tests of the CD algorithm by checking consistency of the low frequency components of PM and UT1 estimated by VieVS CD and those from the IERS and IVS combined solutions. Moreover, the retrograde diurnal component of PM demodulated from VLBI observations has been compared to the celestial pole offsets series included in the IERS and IVS solutions. We found for all three components a good agreement of the results based on the CD approach and those based on the standard parameterization recommended by the IERS Conventions () and applied by the IERS and IVS. We conclude that an application of the CD parameterization in VLBI data analysis does not change those components of EOP which are included in the standard adjustment, while enabling simultaneous estimation of the high frequency components from the routine VLBI observations. Moreover, we deem that the CD algorithm can also be implemented in analysis of other space geodetic observations, like GNSS or SLR, enabling retrieval of subdiurnal signals in EOP from the past data. [ABSTRACT FROM AUTHOR]

The Chandler wobble (CW) and annual wobble (AW) are the two main components of polar motion, which are difficult to separate because of their very close periods. In the light of Fourier dictionary and basis pursuit method, a Fourier basis pursuit (FBP) spectrum is developed, which can reduce spectral smearing and leakage caused by the finite length of the time series. Further, a band-pass filtering method based on FBP spectrum (FBPBPF), which can effectively suppress the edge effect, is proposed in this paper. The simulation test results show that the FBPBPF method can effectively suppress the edge effect caused by spectral smearing and leakage and that its reconstruction accuracy at the boundary is approximately three times higher than the Fourier transform band-pass filtering method, which is based on Hamming windowed FFT spectrum, in extracting quasi-harmonic signals. The FBPBPF method is then applied to Earth's polar motion data during 1900-2015. Through analyzing the amplitude and period variations of CW and AW, and calculating the eccentricity variation of the AW, we found that: (1) the amplitude of the CW is currently at a historic minimum level, and it is even possible to diminish further until a complete stop; and (2) the eccentricity of the AW has a gradually decreased fluctuation during the last 116 years. [ABSTRACT FROM AUTHOR]

Continental hydrology has a large influence on the excitation of polar motion (PM). However, these effects are far from being completely understood. Current global water storage models differ significantly from one another and are unable to completely represent the complex hydrological cycle, particularly at interannual scales. A promising alternative to study hydrological effects on PM is given by the GRACE satellite mission. In this study, we assess the ability of GRACE to investigate interannual hydrological PM excitations. For this purpose, we use the latest GRACE Release-05 data from three different processing centers (CSR, GFZ, JPL) that we convert into estimates of hydrological PM excitation, χ 1 H and χ 2 H . In addition to these gravimetric excitations, we also consider geodetic hydrological excitations, which we calculate by removing modelled atmospheric and oceanic effects from precise observations of full PM excitations. We remove signals with frequencies ≥1 cpy from the series and compare the resulting estimates of interannual hydrological excitations for the period 2004.5–2014.5. The comparison between geodetic and gravimetric excitations reveals some discrepancies for χ 1 H , likely to be related to inadequately modelled atmospheric and oceanic effects. On the other hand, good agreement is observed for χ 2 H . For both components, the best agreement between geodetic and gravimetric excitations is obtained for the estimate from CSR. Very good agreement is obtained between GRACE-derived excitations from different processing centers, in particular for CSR and JPL. Both the comparisons between geodetic and gravimetric, and the comparisons between the different gravimetric excitations give substantially better results for χ 2 H than for χ 1 H , leading to the conclusion that geodetic and gravimetric χ 2 H can be more reliably determined than χ 1 H . Although there are still some discrepancies between geodetic and gravimetric interannual hydrological excitations, we conclude that GRACE and potential follow-on missions are valuable tools to study the interannual effects of continental hydrology on the excitation of PM. [ABSTRACT FROM AUTHOR]

Asynchronous polars (APs) are accreting white dwarfs (WDs) that have different WD and orbital angular velocities, unlike the rest of the known polars, which rotate synchronously (i.e. their WD and orbital angular velocities are the same). Past nova eruptions are the predicted cause of the asynchronicity, in part due to the fact that one of the APs, V1500 Cyg, was observed to undergo a nova eruption in 1975. We used the Southern African Large Telescope 10 m class telescope and the MDM 2.4 m Hiltner telescope to search for nova shells around three of the remaining four APs (V1432 Aql, BY Cam, and CD Ind) as well as one Intermediate Polar with a high asynchronicity (EX Hya). We found no evidence of nova shells in any of our images. We therefore cannot say that any of the systems besides V1500 Cyg had nova eruptions, but because not all post-nova systems have detectable shells, we also cannot exclude the possibility of a nova eruption occurring in any of these systems and knocking the rotation out of sync. [ABSTRACT FROM AUTHOR]

We challenge the perspective that seismicity could contribute to polar motion by arguing quantitatively that, in first approximation and on the average, interseismic deformations can compensate for it. This point is important because what we must simulate and observe in Earth Orientation Parameter time-series over intermediate timescales of decades or centuries is the residual polar motion resulting from the two opposing processes of coseismic and interseismic deformations. In this framework, we first simulate the polar motion caused by only coseismic deformations during the longest period available of instrumental seismicity, from 1900 to present, using both the CMT and ISC-GEM catalogues. The instrumental seismicity covering a little longer than one century does not represent yet the average seismicity that we should expect on the long term. Indeed, although the simulation shows a tendency to move the Earth rotation pole towards 133°E at the average rate of 16.5mm yr-1, this trend is still sensitive to individual megathrust earthquakes, particularly to the 1960 Chile and 1964 Alaska earthquakes. In order tofurther investigate this issue, we develop a global seismicity model (GSM) that is independent from any earthquake catalogue and that describes the average seismicity along plate boundaries on the long term by combining information about presentday plate kinematics with the Anderson theory of faulting, the seismic moment conservation principle and a few other assumptions. Within this framework, we obtain a secular polar motion of 8mm yr-1 towards 112.5°E that is comparable with that estimated from 1900 to present using the earthquake catalogues, although smaller by a factor of 2 in amplitude and different by 20° in direction. Afterwards, in order to reconcile the idea of a secular polar motion caused by earthquakes with our simplest understanding of the seismic cycle, we adapt the GSM in order to account for interseismic deformations and we use it to quantify, for the first time ever, their contribution to polar motion. Taken together, coseismic and interseismic deformations make the rotation pole wander around the north pole with maximum polar excursions of about 1 m. In particular, the rotation pole moves towards about Newfoundland when the interseismic contribution dominates over the coseismic ones (i.e. during phases of low seismicity or, equivalently, when most of the fault system associated with plate boundaries is locked). When megathrust earthquakes occur, instead, the rotation pole is suddenly shifted in an almost opposite direction, towards about 133°E. [ABSTRACT FROM AUTHOR]

Because of its geophysical interpretation, Earth's polar motion excitation is generally decomposed into prograde (counter-clockwise) and retrograde (clockwise) circular terms at fixed frequency. Yet, these later are commonly considered as specific to the frequency and to the underlying geophysical process, and no study has raised the possibility that they could share features independent from frequency. Complex Fourier Transform permits to determine retrograde and prograde circular terms of the observed excitation and of its atmospheric, oceanic and hydrological counterparts. The total prograde and retrograde parts of these excitations are reconstructed in time domain. Then, complex linear correlation between retrograde and conjugate prograde parts is observed for both the geodetic excitation and the matter term of the hydro-atmospheric excitation. In frequency domain, the ratio of the retrograde circular terms with their corresponding conjugate prograde terms favours specific values: the amplitude ratio follows a probabilistic gamma distribution centred around 1.5 (maximum for 1), and the argument ratio obeys a distribution close to a normal law centred around $$2 \alpha = 160^{\circ }$$ . These frequency and time domain characteristics mean an elliptical polarisation towards $$\alpha ={\sim } 80^{\circ }$$ East with an ellipticity of 0.8, mostly resulting from the matter term of the hydro-atmospheric excitation. Whatsoever the frequency band above 0.4 cpd, the hydro-atmospheric matter term tends to be maximal in the geographic areas surrounding the great meridian circle of longitude $${\sim }80^{\circ }$$ or $${\sim } 260^{\circ }$$ East. The favoured retrograde/prograde amplitude ratio around 1.5 or equivalently the ellipticity of 0.8 can result from the amplification of pressure waves propagating towards the west by the normal atmospheric mode $$\Psi _3^1$$ around 10 days. [ABSTRACT FROM AUTHOR]

The impact of continental hydrological loading from land water, snow and ice on polar motion excitation, calculated as hydrological angular momentum (HAM), is difficult to estimate, and not as much is known about it as about atmospheric angular momentum (AAM) and oceanic angular momentum (OAM). In this paper, regional hydrological excitations to polar motion are investigated using monthly terrestrial water storage data derived from the Gravity Recovery and Climate Experiment (GRACE) mission and from the five models of land hydrology. The results show that the areas where the variance shows large variability are similar for the different models of land hydrology and for the GRACE data. Areas which have a small amplitude on the maps make an important contribution to the global hydrological excitation function of polar motion. The comparison of geodetic residuals and global hydrological excitation functions of polar motion shows that none of the hydrological excitation has enough energy to significantly improve the agreement between the observed geodetic excitation and geophysical ones. [ABSTRACT FROM AUTHOR]

Current-quark masses are compared to the rest masses allowed by the Helmholtz equation in a polar model. Within the uncertainty of the current u quark mass determination, the current quark mass coincides with the rest mass allowed by the Helmholtz equation in the polar model in accordance with the second root of the zero Neumann function. Current d quark mass coincides with the rest mass calculated in accordance with the third root of the Bessel zero function. The basis for the comparison of these results with the results obtained earlier for ordinary real particles u and d quarks stability is discussed. [ABSTRACT FROM AUTHOR]

Based on celestial-mechanics concepts, we provide an amplitude-frequency analysis of the intraday Earth pole oscillations in terms of classical mechanics. An approximate analytical model for real trajectory measurements of the polar motion in a near-day time interval has been identified. [ABSTRACT FROM AUTHOR]

Satellite altimeter sea surface height observations include the geocentric displacements caused by the pole tide, namely the response of the solid Earth and oceans to polar motion. Most users of these data remove these effects using a model that was developed more than 20 years ago. We describe two improvements to the pole tide model for satellite altimeter measurements. Firstly, we recommend an approach that improves the model for the response of the oceans by including the effects of self-gravitation, loading, and mass conservation. Our recommended approach also specifically includes the previously ignored displacement of the solid Earth due to the load of the ocean response, and includes the effects of geocenter motion. Altogether, this improvement amplifies the modeled geocentric pole tide by 15 %, or up to 2 mm of sea surface height displacement. We validate this improvement using two decades of satellite altimeter measurements. Secondly, we recommend that the altimetry pole tide model exclude geocentric sea surface displacements resulting from the long-term drift in polar motion. The response to this particular component of polar motion requires a more rigorous approach than is used by conventional models. We show that erroneously including the response to this component of polar motion in the pole tide model impacts interpretation of regional sea level rise by $$\pm $$ 0.25 mm/year. [ABSTRACT FROM AUTHOR]

This study firstly employs the calculation of base sequence with different length, in 1–90 day predictions of EOP (the UT1-UTC and polar motion), by the combined method of least squares and autoregressive model, and find the base sequence with best result for different prediction spans, which we call as “predictions over optimized data intervals”. Compared to the EOP predictions with fixed base data intervals, the “predictions over optimized data intervals” performs better for the prediction of UT1-UTC, and shows a significant improvement for the prediction of polar motion, and particularly promotes our competitive level in the international activity of Earth Orientation Parameters Combination of Prediction Pilot Project. [ABSTRACT FROM AUTHOR]

The effect of irregularities in the earth's rotation (precession and nutation of the earth's axis of rotation, oscillations in the modulus of the angular velocity, periodic deviations in the line of the poles, and the angular momentum of the globe) on the frequency and time of high-stability atomic clocks are examined in terms of the theory of relativity. It is shown that the relative shift in frequency and time owing to these effects can exceed 5·10. [ABSTRACT FROM AUTHOR]

The fine dynamic effects that make it possible to improve the accuracy of predicting the trajectory of pole motion are revealed by using a numerically analytical approach in modeling the pole oscillatory motion, the key component of which is the Chandler component. [ABSTRACT FROM AUTHOR]

We use the Empirical Mode Decomposition (EMD) method to study the decadal variations in polar motion and its long-term trend since year 1900. The existence of the so-called 'Markowitz wobble', a multidecadal fluctuation of the mean pole of rotation whose nature has long been debated since its discovery in 1960, is confirmed. In the EMD approach, the Markowitz wobble naturally arises as an empirical oscillatory term in polar motion, showing significant amplitude variations and a period of approximately 3 decades. The path of the time-averaged, non-cyclic component of polar motion matches the results of previous investigations based on classical spectral methods. However, our analysis also reveals previously unnoticed steep variations (change points) in the rate and the direction of secular polar motion. [ABSTRACT FROM AUTHOR]

From the maps of regional contribution to atmospheric angular momentum (AAM) over the period 1948–2011 (NCEP/NCAR reanalysis data) time domain excitation in Chandler frequency band was extracted by Panteleev’s filtering method. This permits us to investigate the evolution of the regional atmospheric influence on Chandler wobble. It appears that the temperate latitudes bring the strongest inputs. For pressure term they are limited to continents, and highlight the role of Europe. For the wind term they mostly result from ocean area, encompassing in particular North Atlantic. A quasi-20 year cycle is found in the regional patterns of the atmospheric excitation. The integrated AAM is finally compared with the geodetic excitation reconstructed from the observed polar motion. [ABSTRACT FROM AUTHOR]