Effects of the observed Earth’s oblateness variation on precession-nutation: A first assessment

2020 ◽  
Author(s):  
José M. Ferrándiz ◽  
Alberto Escapa ◽  
Tomás Baenas ◽  
Santiago Belda ◽  
M. Isabel Vigo
Keyword(s):  
Time Series ◽  
Gravity Field ◽  
Time Variation ◽  
Earth Rotation ◽  
Working Group ◽  
International Association ◽  
Time Varying ◽  
Fundamental Issue ◽  
The Earth ◽  
Full Solution

<p>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.</p><p>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).</p>

The Global Geodetic Observing System (GGOS) – infrastructure underpinning Earth science

2021 ◽  
Author(s):  
Basara Miyahara ◽  
Laura Sánchez ◽  
Martin Sehnal
Keyword(s):  
Mass Transport ◽  
Gravity Field ◽  
Reference Frames ◽  
Earth Science ◽  
International Association ◽  
Analytical Techniques ◽  
Temporal Variations ◽  
Core Element ◽  
The Earth ◽  
Surface Kinematics

<p>The Global Geodetic Observing System (GGOS) is the contribution of Geodesy to the observation and monitoring of the Earth System. Geodesy is the science of determining and representing the shape of the Earth, its gravity field and its rotation as a function of time. A core element to reach this goal are stable and consistent geodetic reference frames, which provide the fundamental layer for the determination of time-dependent coordinates of points or objects, and for describing the motion of the Earth in space. Traditionally, geodetic reference frames have been used for surveying, mapping, and space-based positioning and navigation. With modern instrumentation and analytical techniques, Geodesy is now capable of detecting time variations ranging from large and secular scales to very small and transient deformations with increasing spatial and temporal resolution, high accuracy, and decreasing latency. GGOS has been working closely with components of International Association of Geodesy (IAG) to provide consistent and openly available observations of the spatial and temporal changes of the shape and gravity field of the Earth, as well as the temporal variations of the Earth’s rotation. These efforts make available a global picture of the surface kinematics of our planet, including the ocean, ice cover, continental water, and land surfaces, as well as estimates of mass anomalies, mass transport, and mass exchange in the System Earth. Surface kinematics and mass transport together are the key to global mass balance determination, and are an important contribution to understanding the energy budget of our planet. In order to play its vital role, GGOS has following missions; a) to provide the observations needed to monitor, map, and understand changes in the Earth’s shape, rotation, and mass distribution, b) to provide the global geodetic frame of reference that is the fundamental backbone for measuring and consistently interpreting key global change processes and for many other scientific and societal applications, c) to benefit science and society by providing the foundation upon which advances in Earth and planetary system science and applications are built. For the mission, GGOS works tighter with components of the IAG, more specifically, IAG Services, IAG Commissions and IAG Inter-Commission Committees. The IAG Services provide the infrastructure and products on which all contributions of GGOS are based, and the IAG Commissions and IAG Inter-Commission Committees provide expertise and support to address key scientific issues within GGOS. Together with the IAG components, GGOS provides the fundamental infrastructure underpinning Earth sciences and their applications.</p>

scholarly journals Review of the achievements of project MERIT for the intercomparison of techniques for monitoring the rotation of the Earth

1988 ◽  
Vol 128 ◽  
pp. 227-232
Author(s):  
G. A. Wilkins
Keyword(s):  
Earth Rotation ◽  
Working Group ◽  
New Techniques ◽  
New Methods ◽  
The Earth ◽  
Terrestrial Reference System ◽  
Rotation Of The Earth ◽  
Analyse Data ◽  
Set Up ◽  
International Services

It is generally recognised that the Working Group on the Rotation of the Earth that was set up after IAU Symposium No. 82 has successfully achieved its principal objectives, namely: “to make recommendations on … future international services on earth-rotation” and “to obtain and analyse data on earth-rotation by both current and new methods …”. In particular, by organising Project MERIT, it has stimulated the development and use of new techniques and it has brought together in fruitful collaboration scientists from many countries and disciplines. Other subsidiary objectives have also been achieved and the project has been extended through cooperation with the COTES Working Group on the terrestrial reference system. The possible reasons for this success are also reviewed in the expectation that the conclusions will be relevant to other future projects.

Recovering climate-related mass transport signals by current and next-generation gravity missions

2020 ◽  
Author(s):  
Roland Pail ◽  
Henryk Dobslaw ◽  
Annette Eicker ◽  
Laura Jensen
Keyword(s):  
Climate Change ◽  
Time Series ◽  
Mass Transport ◽  
Gravity Field ◽  
Transport Processes ◽  
Measuring System ◽  
Climate Projections ◽  
Earth System ◽  
Next Generation ◽  
The Earth

<p>Gravity field missions are a unique geodetic measuring system to directly observe mass transport processes in the Earth system. Past and current gravity missions such as CHAMP, GRACE, GOCE and GRACE-Follow On have improved our understanding of large-scale mass changes, such as the global water cycle, melting of continental ice sheets and mountain glaciers, changes in ocean mass that are closely related to the mass-related component of sea level rise, which are subtle indicators of climate change, on global to regional scale. Therefore, mass transport observations are also very valuable for long-term climate applications. Next Generation Gravity Missions (NGGMs) expected to be launched in the midterm future have set high anticipations for an enhanced monitoring of mass transport in the Earth system with significantly improved spatial and temporal resolution and accuracy. This contribution will present results from numerical satellite mission performance simulations designed to evaluate the usefulness of gravity field missions operating over several decades for climate-related applications. The study is based on modelled of mass transport time series obtained from future climate projections until the year 2100 following the representative emission pathway RCP8.5 Numerical closed-loop simulations will assess the recoverability of mass variability signals by means of different NGGM concepts, e.g. GRACE-type in-line single-pair missions, Bender double-pair mission being composed of a polar and an inclined satellite pair, or high-precision high-low tracking missions following the MOBILE concept, assuming realistic noise levels for the key payload. In the evaluation and interpretation of the results, special emphasis shall be given to the identification of (natural or anthropogenic) climate change signals in dependence of the length of the measurement time series, and the quantification of robustness of derived trends and systematic changes.</p>

The International DORIS Service is preparing the future

2020 ◽  
Author(s):  
Pascale Ferrage ◽  
Laurent Soudarin ◽  
Frank Lemoine
Keyword(s):  
Earth Rotation ◽  
International Association ◽  
Tracking System ◽  
Tectonic Plate ◽  
Plate Motions ◽  
The Earth ◽  
Earth Rotation Parameters ◽  
The Future ◽  
Rotation Parameters

<p>The DORIS system recorded its first measurement on February 3rd, 1990, from the SPOT-2 remote sensing satellite. 30 years after, the system is at its best. DORIS has proven greatly valuable for geodesy and geophysics applications: measuring tectonic plate motions, determination of the rotation and the gravity parameters of the Earth, contributing to the international reference system. Technological and methodological improvements have allowed the improvement in the estimates of the positions of the DORIS tracking ground stations, the Earth rotation parameters and other geodetic variables such as the geocenter and the scale of the ITRF.<br>The International DORIS Service (IDS) was created in 2003 under the umbrella of the International Association of Geodesy (IAG) to foster scientific research related to the French DORIS tracking system and to deliver scientific products, mostly related to the International Earth rotation and Reference systems Service (IERS). Since its start, the organization has continuously evolved, leading to additional and improved operational products from an expanded set of DORIS Analysis Centers. IDS is now based on a reinforced structure with two Data Centers, six Analysis Centers, four Associate Analysis Centers, and a Combination Center. Using the experience gained in the preparation of the ITRFs, many improvements were made all along both in data analysis and on technical aspects. After the IDS Retreat held in June 2018, the IDS GB worked on the development of a strategic plan for the IDS. In the coming years, IDS will focus on growing the community, extending the DORIS applications, and improving the technology, the infrastructure and the processing.<br>This presentation addresses the recent achievements made by IDS and how the service is preparing the future.</p>

The GGOS Bureau of Products and Standards

2020 ◽  
Author(s):  
Detlef Angermann ◽  
Thomas Gruber ◽  
Michael Gerstl ◽  
Urs Hugentobler ◽  
Laura Sanchez ◽  
...  
Keyword(s):  
Organizational Structure ◽  
Gravity Field ◽  
Working Group ◽  
System Modeling ◽  
Earth System ◽  
Earth System Modeling ◽  
The Earth ◽  
External Stakeholders ◽  
Definition Of

<p>The Bureau of Products and Standards (BPS) supports GGOS in its goal to obtain consistent products describing the geometry, rotation and gravity field of the Earth. A key objective of the BPS is to keep track of adopted geodetic standards and conventions across all IAG components as a fundamental basis for the generation of consistent geometric and gravimetric products. This poster gives an overview about the organizational structure, the objectives and activities of the BPS. In its present structure, the two Committees “Earth System Modeling” and “Essential Geodetic Variables” as well as the newly established Working Group “Towards a consistent set of parameters for the definition of a new GRS” are associated to the BPS. Recently the updated 2<sup>nd</sup> version of the BPS inventory on standards and conventions used for the generation of IAG products has been compiled. Other activities of the Bureau include the integration of geometric and gravimetric observations towards the development of integrated products (e.g., GGRF, IHRF, atmosphere products) in cooperation with the IAG Services and the GGOS Focus Areas, the contribution to the re-writing of the IERS Conventions as Chapter Expert for Chapter 1 “General definitions and numerical standards”, the interaction with external stakeholders regarding standards and conventions (e.g., ISO, IAU, BIPM, CODATA) as well as contributions to the Working Group “Data Sharing and Development of Geodetic Standards” within the UN GGIM Subcommittee on Geodesy.</p>

scholarly journals Simulation of the time-variable gravity field by means of coupled geophysical models

2011 ◽  
Vol 4 (1) ◽  
pp. 27-70 ◽  
Author(s):  
Th. Gruber ◽  
J. L. Bamber ◽  
M. F. P. Bierkens ◽  
H. Dobslaw ◽  
M. Murböck ◽  
...  
Keyword(s):  
Time Series ◽  
Gravity Field ◽  
Mass Distribution ◽  
Time Variable ◽  
Data Sets ◽  
Earth System ◽  
Time Variable Gravity ◽  
The Earth ◽  
Gravity Fields ◽  
Variable Gravity

Abstract. Time variable gravity fields, reflecting variations of mass distribution in the system Earth is one of the key parameters to understand the changing Earth. Mass variations are caused either by redistribution of mass in, on or above the Earth's surface or by geophysical processes in the Earth's interior. The first set of observations of monthly variations of the Earth gravity field was provided by the US/German GRACE satellite mission beginning in 2002. This mission is still providing valuable information to the science community. However, as GRACE has outlived its expected lifetime, the geoscience community is currently seeking successor missions in order to maintain the long time series of climate change that was begun by GRACE. Several studies on science requirements and technical feasibility have been conducted in the recent years. These studies required a realistic model of the time variable gravity field in order to perform simulation studies on sensitivity of satellites and their instrumentation. This was the primary reason for the European Space Agency (ESA) to initiate a study on "Monitoring and Modelling individual Sources of Mass Distribution and Transport in the Earth System by Means of Satellites". The goal of this interdisciplinary study was to create as realistic as possible simulated time variable gravity fields based on coupled geophysical models, which could be used in the simulation processes in a controlled environment. For this purpose global atmosphere, ocean, continental hydrology and ice models were used. The coupling was performed by using consistent forcing throughout the models and by including water flow between the different domains of the Earth system. In addition gravity field changes due to solid Earth processes like continuous glacial isostatic adjustment (GIA) and a sudden earthquake with co-seismic and post-seismic signals were modelled. All individual model results were combined and converted to gravity field spherical harmonic series, which is the quantity commonly used to describe the Earth's global gravity field. The result of this study is a twelve-year time-series of 6-hourly time variable gravity field spherical harmonics up to degree and order 180 corresponding to a global spatial resolution of 1 degree in latitude and longitude. In this paper, we outline the input data sets and the process of combining these data sets into a coherent model of temporal gravity field changes. The resulting time series was used in some follow-on studies and is available to anybody interested via a Website.

scholarly journals COMMISSION 19: ROTATION OF THE EARTH

2008 ◽  
Vol 4 (T27A) ◽  
pp. 37-49
Author(s):  
Aleksander Brzezinski ◽  
Chopo Ma ◽  
Véronique Dehant ◽  
Pascale Defraigne ◽  
Jean O. Dickey ◽  
...  
Keyword(s):  
Earth Rotation ◽  
Reference Frames ◽  
International Association ◽  
Vice President ◽  
Past President ◽  
Scientific Investigations ◽  
The Earth ◽  
International Vlbi Service ◽  
Commission President ◽  
Rotation Of The Earth

The Commission supports and coordinates scientific investigations in the Earth rotation and related reference frames. Several changes had been introduced to the structure of Commission 19 since the IAU XXVI General Assembly in Prague, 2006. The Organizing Committee of Commission 19 has been substantially reduced. It consists now of six ex-officio members, the Commission president, vice-president, past president and representatives from the International Association of Geodesy (IAG), International Earth Rotation and Reference Systems Service (IERS), International VLBI Service for Geodesy and Astrometry (IVS), and five members at-large who are nominated by the OC, selected by the Commission members and elected by the IAU GA for a maximum of two terms. The modified terms of reference of Commission 19, the list of members and other details can be found at the Commission website <iau-comm19.cbk.waw.pl/>.

scholarly journals INTRODUCTION TO TIME-VARYING MODELING WITH MACROECONOMIC AND FINANCIAL DATA

2012 ◽  
Vol 16 (S2) ◽  
pp. 167-175 ◽  
Author(s):  
Fredj Jawadi
Keyword(s):  
Time Series ◽  
Time Variation ◽  
Moving Average ◽  
Statistical Properties ◽  
Financial Data ◽  
Time Varying ◽  
Arch Model ◽  
Financial Variables ◽  
Short And Long Term

The dynamics of macroeconomic and financial series has evolved swiftly and asymmetrically since the end of the 1970s, and their statistical properties have also changed over time, suggesting complex relationships between economic and financial variables. The transformations can be explained by considerable changes in householder's behavior, market structures, and economic systems and by the alternation of exogenous shocks and financial crises that have affected the economic cycle, with significant evidence of time variation in the major economic variables. Hence, there is a need for new econometric protocols to take such changes into consideration. The introduction of ARMA (autoregressive moving average models) by Box and Jenkins (1970) led to the development of time-series econometrics, which had a major impact on the conceptual analysis of economic and financial data. This type of modeling offered a transition from a static setup to a new modeling process that reproduces the time-varying features of macroeconomic and financial series. However, the ARMA modeling system retains the constancy of the first and second moments, limits the phases of a cycle to symmetrical instances, and only reproduces the dynamics of stationary variables. It thus fails to adequately reproduce the nonstationary relationships between major economic and financial variables. Abrupt changes in economies and financial systems have given evidence of nonstationary series whose statistical properties are also time-varying, making it necessary to develop new econometric tools to capture the time variation of economic and financial series in the mean and in the variance, and to apprehend their dynamics in the short and long term. Among the most important and influential studies in the 1980s' econometrics literature were therefore those that dealt with the introduction of the ARCH (autoregressive conditional heteroskedasticity) model by Engle (1982) and the cointegration theory by Engle and Granger (1987). The ARCH model, which focuses on the time-varying features of volatility structure, was a major breakthrough, as it highlighted the importance of the second moment of time series, while the cointegration framework enabled the short- and long-term dynamics of nonstationary variables to be modeled.

Assessing recently improved precession-nutation models 

2021 ◽  
Author(s):  
José M. Ferrándiz ◽  
Miguel A. Juárez ◽  
Santiago Belda ◽  
Tomás Baenas ◽  
Sadegh Modiri ◽  
...  
Keyword(s):  
Working Group ◽  
International Association ◽  
General Assembly ◽  
Fall Meeting ◽  
Individual Analysis ◽  
The Earth ◽  
Joint Working Group ◽  
Semi Empirical

&lt;p&gt;In 2020 new estimations of nutation amplitudes or precession parameters have been published or presented at main meetings. The derivation of corrections to improve the current precession-nutation models was encouraged by Resolution 5 of the 2019 General Assembly of the International Association of Geodesy (IAG). Besides, the GGOS/IERS Unified Analysis Workshop held in October 2019 recommended that effort to be prioritized among the tasks of the current IAU/IAG Joint Working Group on Improving Theories and Models of the Earth&amp;#8217;s rotation (JWG ITMER).&lt;/p&gt;&lt;p&gt;This presentation is intended to present comparisons of some of those new semi-empirical and semi-theorical precession-nutation models developed by different authors from either VLBI solutions of individual analysis centers or combinations of them. The models recently introduced by the authors that were reported at the AGU 2020 Fall Meeting are included in this assessment.&lt;/p&gt;

GRACEFUL: Probing the deep Earth interior by synergistic use of observations of the magnetic and gravity fields, and of the rotation of the Earth

2020 ◽  
Author(s):  
Mioara Mandea ◽  
Veronique Dehant ◽  
Anny Cazenave
Keyword(s):  
Magnetic Field ◽  
Gravity Field ◽  
Time Scales ◽  
Earth Rotation ◽  
Outer Core ◽  
Time Dependent ◽  
Mantle Boundary ◽  
Core Mantle Boundary ◽  
The Core ◽  
The Earth

&lt;div&gt; &lt;p&gt;To understand the processes involved in the deep interior of the Earth and explaining its evolution, in particular the dynamics of the Earth&amp;#8217;s fluid iron-rich outer core, only indirect satellite and ground observations are available. They each provide invaluable information about the core flow but are incomplete on their own:&lt;/p&gt; &lt;p&gt;-&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160; The time dependent magnetic field, originating mainly within the core, can be used to infer the motions of the fluid at the top of the core on decadal and subdecadal time scales.&lt;/p&gt; &lt;p&gt;-&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160; The time dependent gravity field variations that reflect changes in the mass distribution within the Earth and at its surface occur on a broad range of time scales. Decadal and interannual variations include the signature of the flow inside the core, though they are largely dominated by surface contributions related to the global water cycle and climate-driven land ice loss.&lt;/p&gt; &lt;p&gt;-&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160; Earth rotation changes (or variations in the length of the day) also occur on these time scales, and are largely related to the core fluid motions through exchange of angular momentum between the core and the mantle at the core-mantle boundary.&lt;/p&gt; &lt;p&gt;Here, we present the main activities proposed in the frame of the GRACEFUL ERC project, which aims to combine information about the core deduced from the gravity field, from the magnetic field and from the Earth rotation in synergy, in order to examine in unprecedented depth the dynamical processes occurring inside the core and at the core-mantle boundary.&lt;/p&gt; &lt;/div&gt;

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