The Experts below are selected from a list of 255 Experts worldwide ranked by ideXlab platform
Benjamin F Chao - One of the best experts on this subject based on the ideXlab platform.
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effect of global mass conservation among Geophysical Fluids on the seasonal length of day variation
Journal of Geophysical Research, 2012Co-Authors: Haoming Yan, Benjamin F ChaoAbstract:[1] Geophysical Fluids models for the atmosphere, ocean, and land hydrology usually do not properly enforce the conservation of mass either individually or collectively. Called the global mass balance (GMB) effect, these errors, if not corrected, will significantly affect the determination of the effect of Geophysical Fluids on the variation in the Earth's rotation rate or length of day (LOD). Here we analyze the seasonal budget of the excitation sources for LOD variation in comparison with corresponding observations. We find that (1) the combined mass-induced excitations of LOD variation by Geophysical Fluids are brought to much better agreement with the observed upon accounting for the GMB effect; (2) the above can be further improved to almost perfect closure if the motion term of the atmospheric angular momentum (to be removed from the observed LOD variation in obtaining the mass-induced LOD variation) is magnified by 7%, corroborating the finding of Chao and Yan (2010); and (3) the above quantities all agree remarkably well with the equivalent LOD variation determined via J2 variation from satellite laser ranging observations, indicating the usefulness of the latter as an independent measurement for mass transports in the Geophysical Fluids.
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relation between length of day variation and angular momentum of Geophysical Fluids
Journal of Geophysical Research, 2010Co-Authors: Benjamin F Chao, Haoming YanAbstract:[1] The remarkable relation well observed between variation in the length of day (ΔLOD) and variation in the axial atmospheric angular momentum (ΔAAM) (plus the oceanic counterpart, to a much lesser extent) is a consequence of the conservation of angular momentum on planet Earth. Quantification of the exact ΔLOD-ΔAAM relation, which we seek in the present study, depends significantly on the extent to which the core participates, or is dynamically coupled with the mantle, in transmission of the axial ΔAAM from the mantle to the core. If, after conversion to the equivalent ΔLOD assuming core-mantle decoupling (as in current standard practice), the calculated axial ΔAAM (according to atmospheric general circulation models [GCMs]) is systematically greater than the observed ΔLOD, then we can conclude the presence, and, furthermore, estimate the strength, of the said dynamic core-mantle coupling. However, in this study we find the opposite instead, that the calculated ΔAAM (plus the small oceanic counterpart) is smaller than the observed ΔLOD by 10%–20% consistently across the intraseasonal and seasonal time scales. Our main logical conclusion is that the atmospheric GCMs in general underpredict the ΔAAM, by at least 10%–20% at the mentioned time scales, a fact of importance with respect to the assessment of GCMs. Therefore, the systematic discrepancy found between the ΔAAM-predicted and the observed ΔLOD masks the relevant information on core-mantle coupling that we seek.
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Earth Rotational Variations Excited by Geophysical Fluids
2004Co-Authors: Benjamin F ChaoAbstract:Modern space geodetic measurement of Earth rotation variations, particularly by means of the VLBI technique, has over the years allowed studies of Earth rotation dynamics to advance in ever-increasing precision, accuracy, and temporal resolution. A review will be presented on our understanding of the Geophysical and climatic causes, or "excitations". for length-of-day change, polar motion, and nutations. These excitations sources come from mass transports that constantly take place in the Earth system comprised of the atmosphere, hydrosphere, cryosphere, lithosphere, mantle, and the cores. In this sense, together with other space geodetic measurements of time-variable gravity and geocenter motion, Earth rotation variations become a remote-sensing tool for the integral of all mass transports, providing valuable information about the latter on a wide range of spatial and temporal scales. Future prospects with respect to Geophysical studies with even higher accuracy and resolution will be discussed.
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The Global Geophysical Fluids Center of IERS (and its Special Bureau for Mantle)
2002Co-Authors: Benjamin F ChaoAbstract:The Global Geophysical Fluids Center (GGFC) was established by the International Earth Rotation Service (IERS) on IERS's 10th anniversary day January 1, 1998, in an effort to expand IERS's services to the scientific community. Under the GGFC, eight Special Bureaus (SB) have been selected, each to be responsible for research and data service activities pertaining to mass transports and related Geophysical processes in specific components of the Earth system, or "global Geophysical Fluids," including the atmosphere, oceans, solid Earth, core, and Geophysical processes of gravity, loading, tides and hydrological cycles. GGFC and the SBs have the responsibility of supporting, facilitating, and providing services to the worldwide research community, in areas related to the variations in Earth rotation, gravity field and geocenter that are caused by mass transport in the global Geophysical Fluids. These minute variations have been observed by various space geodetic techniques, as effective remote sensing tools, with ever increasing precision/accuracy and temporal/spatial resolution. The GGFC and SBs have organized dedicated workshops and special sessions at international conferences, published articles, and held regular business meetings. The SBs also maintain individual website for data services and information exchanges. See URL . In particular, the SB for Mantle focuses on large-scale mass redistributions that occur in the mantle in association with various dynamic processes, including seismic activities, the post-glacial rebound, and mantle convections.
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global Geophysical Fluids center of iers
2000Co-Authors: Benjamin F Chao, Veronique Dehant, R S Gross, R D Ray, D A Salstein, M Watkins, Clark R WilsonAbstract:The Global Geophysical Fluids Center (GGFC) and its seven Special Bureaus (SB, for Atmosphere, Oceans, Tides, Hydrology, Mantle, Core and Gravity/Geocenter) were establishes by the International Earth Rotation Service in 1998, to support global geodynamic research. Mass transports in the Geophysical Fluids of the Earth system will cause observable geodynamic effects on a broad time scale.These include (1) variations in the solid Earth's rotation (in length-of-day and polar motion/nutation) via the conservation of angular momentum and effected by torques at the fluid-solid Earth interface; (2) changes in the global gravitational field according to Newton's gravitational law; and (3) motion in the center of mass of the solid Earth relative to that of the whole Earth ("geocenter") via the conservation of linear momentum. These minute signals have become observable by space geodetic techniques, primarily VLBI, SLR, GPS, and DORIS, and new exciting data will be available by space gravity, altimetry, SAR, and magnetic missions. In this sense the precise space geodetic techniques have become effective means of remote sensing of global mass transports. The GGFC and its SBs have the responsibility of supporting, facilitating, and providing services to the worldwide research community in the related research areas. We compute, analyze, compare, archive, and disseminate the time series of the angular momenta and the related torques, gravitational coefficients, and geocenter shift for all Geophysical Fluids, based on global observational data, and/or products from state-of-the-art models some of which assimilate such data. The computed quantities, algorithm and data formats are standardized. This paper reviews our activities, reports the status, and looks forward into the future.
D A Salstein - One of the best experts on this subject based on the ideXlab platform.
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comparison of polar motion excitation series derived from grace and from analyses of Geophysical Fluids
Geophysical Research Letters, 2007Co-Authors: Jolanta Nastula, Rui M Ponte, D A SalsteinAbstract:[1] Three sets of degree-2, order-1 harmonics of the gravity field, derived from the Gravity Recovery and Climate Experiment (GRACE) data processed at the Center for Space Research (CSR), Jet Propulsion Laboratory (JPL) and GeoforschungsZentrum (GFZ), are used to compute polar motion excitation functions χ1 and χ2. The GFZ and JPL excitations and the CSR χ2 excitation compare generally well with geodetically observed excitation after removal of effects of oceanic currents and atmospheric winds. The agreement considerably exceeds that from previous GRACE data releases. For the JPL series, levels of correlation with the geodetic observations and the variance explained are comparable to, but still lower than, those obtained independently from available models and analyses of the atmosphere, ocean, and land hydrology. Improvements in data quality of gravity missions are still needed to deliver even tighter constraints on mass-related excitation of polar motion.
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the global Geophysical Fluids center ggfc of the international earth rotation and reference systems service
ITN, 2003Co-Authors: Ben F Chao, Veronique Dehant, R S Gross, R D Ray, D A Salstein, H P Plag, T Van Dam, T Van Hoolst, M M Watkins, Clark R WilsonAbstract:The International Earth Rotation Service established a Global Geophysical Fluids Center (GGFC) in 1998, as one if its product centers. The purpose is to better support, facilitate, and provide services to the worldwide research community, in areas related to the variations in Earth rotation, gravity field and geocenter that are caused by mass transport in the Geophysical Fluids including the atmosphere, ocean, solid Earth, and core, and Geophysical processes associated with tides, mass loading, and hydrological cycles. These services are administered through GGFC’s Special Bureaus (SB). Today there are eight SBs worldwide; they are SB Atmosphere, SB Oceans, SB Tides, SB Hydrology, SB Mantle, SB Core, SB Gravity/Geocenter, and SB Loading. They maintain individual data archive and services.
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global Geophysical Fluids center of iers
2000Co-Authors: Benjamin F Chao, Veronique Dehant, R S Gross, R D Ray, D A Salstein, M Watkins, Clark R WilsonAbstract:The Global Geophysical Fluids Center (GGFC) and its seven Special Bureaus (SB, for Atmosphere, Oceans, Tides, Hydrology, Mantle, Core and Gravity/Geocenter) were establishes by the International Earth Rotation Service in 1998, to support global geodynamic research. Mass transports in the Geophysical Fluids of the Earth system will cause observable geodynamic effects on a broad time scale.These include (1) variations in the solid Earth's rotation (in length-of-day and polar motion/nutation) via the conservation of angular momentum and effected by torques at the fluid-solid Earth interface; (2) changes in the global gravitational field according to Newton's gravitational law; and (3) motion in the center of mass of the solid Earth relative to that of the whole Earth ("geocenter") via the conservation of linear momentum. These minute signals have become observable by space geodetic techniques, primarily VLBI, SLR, GPS, and DORIS, and new exciting data will be available by space gravity, altimetry, SAR, and magnetic missions. In this sense the precise space geodetic techniques have become effective means of remote sensing of global mass transports. The GGFC and its SBs have the responsibility of supporting, facilitating, and providing services to the worldwide research community in the related research areas. We compute, analyze, compare, archive, and disseminate the time series of the angular momenta and the related torques, gravitational coefficients, and geocenter shift for all Geophysical Fluids, based on global observational data, and/or products from state-of-the-art models some of which assimilate such data. The computed quantities, algorithm and data formats are standardized. This paper reviews our activities, reports the status, and looks forward into the future.
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Space geodesy monitors mass transports in global Geophysical Fluids
Eos Transactions American Geophysical Union, 2000Co-Authors: Ben F Chao, Veronique Dehant, R S Gross, R D Ray, D A Salstein, M M Watkins, Clark R WilsonAbstract:Large-scale mass transports in the Earth system produce variations in Earth's rotation, gravity field, and geocenter. Although relatively small, these global geodynamic effects have been measured by space geodetic techniques to increasing, unprecedented accuracy, opening up important new avenues of research that will lead to a better understanding of global mass transport processes and the Earth's dynamic responses. To take full advantage of these advances, the International Earth Rotation Service (IERS), the organization that monitors the rotational motions of the Earth and related properties, saw the need in 1998 to create an infrastructure to facilitate the link between the space geodetic measurement and the geodynamic “global change” research communities [Dehant et al., 1997]. Hence was born the IERS Global Geophysical Fluids Center (GGFC).
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monitoring global Geophysical Fluids by space geodesy
1999Co-Authors: Benjamin F Chao, Veronique Dehant, R S Gross, R D Ray, D A Salstein, M WatkinsAbstract:Since its establishment on 1/1/1998 by the International Earth Rotation Service, the Coordinating Center for Monitoring Global Geophysical Fluids (MGGF) and its seven Special Bureaus have engaged in an effort to support and facilitate the understanding of the Geophysical Fluids in global geodynamics research. Mass transports in the atmosphere-hydrosphere-solid Earth-core system (the "global Geophysical Fluids") will cause the following geodynamic effects on a broad time scale: (1) variations in the solid Earth's rotation (in length-of-day and polar motion/nutation) via the conservation of angular momentum and effected by torques at the fluid-solid Earth interface; (2) changes in the global gravitational field according to Newton's gravitational law; and (3) motion in the center of mass of the solid Earth relative to that of the whole Earth ("geocenter") via the conservation of linear momentum. These minute signals have become observable by space geodetic techniques, primarily VLBI, SLR, GPS, and DORIS, with ever increasing precision/accuracy and temporal/spatial resolution. Each of the seven Special Bureaus within MGGF is responsible for calculations related to a specific Earth component or aspect -- Atmosphere, Ocean, Hydrology, Ocean Tides, Mantle, Core, and Gravity/Geocenter. Angular momenta and torques, gravitational coefficients, and geocenter shift will be computed for Geophysical Fluids based on global observational data, and from state-of-the-art models, some of which assimilate such data. The computed quantities, algorithm and data formats are standardized. The results are archived and made available to the scientific research community. This paper reports the status of the MGGF activities and current results.
Jeroen Wouters - One of the best experts on this subject based on the ideXlab platform.
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mathematical and physical ideas for climate science
Reviews of Geophysics, 2014Co-Authors: Valerio Lucarini, Richard Blender, Corentin Herbert, Francesco Ragone, Salvatore Pascale, Jeroen WoutersAbstract:The climate is a forced and dissipative nonlinear system featuring nontrivial dynamics on a vast range of spatial and temporal scales. The understanding of the climate's structural and multiscale properties is crucial for the provision of a unifying picture of its dynamics and for the implementation of accurate and efficient numerical models. We present some recent developments at the intersection between climate science, mathematics, and physics, which may prove fruitful in the direction of constructing a more comprehensive account of climate dynamics. We describe the Nambu formulation of fluid dynamics and the potential of such a theory for constructing sophisticated numerical models of Geophysical Fluids. Then, we focus on the statistical mechanics of quasi-equilibrium flows in a rotating environment, which seems crucial for constructing a robust theory of Geophysical turbulence. We then discuss ideas and methods suited for approaching directly the nonequilibrium nature of the climate system. First, we describe some recent findings on the thermodynamics of climate, characterize its energy and entropy budgets, and discuss related methods for intercomparing climate models and for studying tipping points. These ideas can also create a common ground between geophysics and astrophysics by suggesting general tools for studying exoplanetary atmospheres. We conclude by focusing on nonequilibrium statistical mechanics, which allows for a unified framing of problems as different as the climate response to forcings, the effect of altering the boundary conditions or the coupling between Geophysical flows, and the derivation of parametrizations for numerical models.
R S Gross - One of the best experts on this subject based on the ideXlab platform.
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Impact of Geophysical Fluids on UT1
Proceedings of the International Astronomical Union, 2009Co-Authors: R S GrossAbstract:AbstractGeophysical Fluids have a major impact on the Earth's rotation. Tidal variations within the oceans are the predominant cause of subdaily length-of-day (lod) variations while those within the solid body of the Earth are a major source of longer period variations; tidal dissipation within the solid Earth and oceans cause a secular change in lod. Fluctuations of the atmospheric winds are the predominant cause of nontidal lod variations on sub-decadal time scales while decadal variations are caused by interactions between the fluid core and mantle.
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the global Geophysical Fluids center ggfc of the international earth rotation and reference systems service
ITN, 2003Co-Authors: Ben F Chao, Veronique Dehant, R S Gross, R D Ray, D A Salstein, H P Plag, T Van Dam, T Van Hoolst, M M Watkins, Clark R WilsonAbstract:The International Earth Rotation Service established a Global Geophysical Fluids Center (GGFC) in 1998, as one if its product centers. The purpose is to better support, facilitate, and provide services to the worldwide research community, in areas related to the variations in Earth rotation, gravity field and geocenter that are caused by mass transport in the Geophysical Fluids including the atmosphere, ocean, solid Earth, and core, and Geophysical processes associated with tides, mass loading, and hydrological cycles. These services are administered through GGFC’s Special Bureaus (SB). Today there are eight SBs worldwide; they are SB Atmosphere, SB Oceans, SB Tides, SB Hydrology, SB Mantle, SB Core, SB Gravity/Geocenter, and SB Loading. They maintain individual data archive and services.
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global Geophysical Fluids center of iers
2000Co-Authors: Benjamin F Chao, Veronique Dehant, R S Gross, R D Ray, D A Salstein, M Watkins, Clark R WilsonAbstract:The Global Geophysical Fluids Center (GGFC) and its seven Special Bureaus (SB, for Atmosphere, Oceans, Tides, Hydrology, Mantle, Core and Gravity/Geocenter) were establishes by the International Earth Rotation Service in 1998, to support global geodynamic research. Mass transports in the Geophysical Fluids of the Earth system will cause observable geodynamic effects on a broad time scale.These include (1) variations in the solid Earth's rotation (in length-of-day and polar motion/nutation) via the conservation of angular momentum and effected by torques at the fluid-solid Earth interface; (2) changes in the global gravitational field according to Newton's gravitational law; and (3) motion in the center of mass of the solid Earth relative to that of the whole Earth ("geocenter") via the conservation of linear momentum. These minute signals have become observable by space geodetic techniques, primarily VLBI, SLR, GPS, and DORIS, and new exciting data will be available by space gravity, altimetry, SAR, and magnetic missions. In this sense the precise space geodetic techniques have become effective means of remote sensing of global mass transports. The GGFC and its SBs have the responsibility of supporting, facilitating, and providing services to the worldwide research community in the related research areas. We compute, analyze, compare, archive, and disseminate the time series of the angular momenta and the related torques, gravitational coefficients, and geocenter shift for all Geophysical Fluids, based on global observational data, and/or products from state-of-the-art models some of which assimilate such data. The computed quantities, algorithm and data formats are standardized. This paper reviews our activities, reports the status, and looks forward into the future.
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Space geodesy monitors mass transports in global Geophysical Fluids
Eos Transactions American Geophysical Union, 2000Co-Authors: Ben F Chao, Veronique Dehant, R S Gross, R D Ray, D A Salstein, M M Watkins, Clark R WilsonAbstract:Large-scale mass transports in the Earth system produce variations in Earth's rotation, gravity field, and geocenter. Although relatively small, these global geodynamic effects have been measured by space geodetic techniques to increasing, unprecedented accuracy, opening up important new avenues of research that will lead to a better understanding of global mass transport processes and the Earth's dynamic responses. To take full advantage of these advances, the International Earth Rotation Service (IERS), the organization that monitors the rotational motions of the Earth and related properties, saw the need in 1998 to create an infrastructure to facilitate the link between the space geodetic measurement and the geodynamic “global change” research communities [Dehant et al., 1997]. Hence was born the IERS Global Geophysical Fluids Center (GGFC).
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monitoring global Geophysical Fluids by space geodesy
1999Co-Authors: Benjamin F Chao, Veronique Dehant, R S Gross, R D Ray, D A Salstein, M WatkinsAbstract:Since its establishment on 1/1/1998 by the International Earth Rotation Service, the Coordinating Center for Monitoring Global Geophysical Fluids (MGGF) and its seven Special Bureaus have engaged in an effort to support and facilitate the understanding of the Geophysical Fluids in global geodynamics research. Mass transports in the atmosphere-hydrosphere-solid Earth-core system (the "global Geophysical Fluids") will cause the following geodynamic effects on a broad time scale: (1) variations in the solid Earth's rotation (in length-of-day and polar motion/nutation) via the conservation of angular momentum and effected by torques at the fluid-solid Earth interface; (2) changes in the global gravitational field according to Newton's gravitational law; and (3) motion in the center of mass of the solid Earth relative to that of the whole Earth ("geocenter") via the conservation of linear momentum. These minute signals have become observable by space geodetic techniques, primarily VLBI, SLR, GPS, and DORIS, with ever increasing precision/accuracy and temporal/spatial resolution. Each of the seven Special Bureaus within MGGF is responsible for calculations related to a specific Earth component or aspect -- Atmosphere, Ocean, Hydrology, Ocean Tides, Mantle, Core, and Gravity/Geocenter. Angular momenta and torques, gravitational coefficients, and geocenter shift will be computed for Geophysical Fluids based on global observational data, and from state-of-the-art models, some of which assimilate such data. The computed quantities, algorithm and data formats are standardized. The results are archived and made available to the scientific research community. This paper reports the status of the MGGF activities and current results.
Haoming Yan - One of the best experts on this subject based on the ideXlab platform.
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effect of global mass conservation among Geophysical Fluids on the seasonal length of day variation
Journal of Geophysical Research, 2012Co-Authors: Haoming Yan, Benjamin F ChaoAbstract:[1] Geophysical Fluids models for the atmosphere, ocean, and land hydrology usually do not properly enforce the conservation of mass either individually or collectively. Called the global mass balance (GMB) effect, these errors, if not corrected, will significantly affect the determination of the effect of Geophysical Fluids on the variation in the Earth's rotation rate or length of day (LOD). Here we analyze the seasonal budget of the excitation sources for LOD variation in comparison with corresponding observations. We find that (1) the combined mass-induced excitations of LOD variation by Geophysical Fluids are brought to much better agreement with the observed upon accounting for the GMB effect; (2) the above can be further improved to almost perfect closure if the motion term of the atmospheric angular momentum (to be removed from the observed LOD variation in obtaining the mass-induced LOD variation) is magnified by 7%, corroborating the finding of Chao and Yan (2010); and (3) the above quantities all agree remarkably well with the equivalent LOD variation determined via J2 variation from satellite laser ranging observations, indicating the usefulness of the latter as an independent measurement for mass transports in the Geophysical Fluids.
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relation between length of day variation and angular momentum of Geophysical Fluids
Journal of Geophysical Research, 2010Co-Authors: Benjamin F Chao, Haoming YanAbstract:[1] The remarkable relation well observed between variation in the length of day (ΔLOD) and variation in the axial atmospheric angular momentum (ΔAAM) (plus the oceanic counterpart, to a much lesser extent) is a consequence of the conservation of angular momentum on planet Earth. Quantification of the exact ΔLOD-ΔAAM relation, which we seek in the present study, depends significantly on the extent to which the core participates, or is dynamically coupled with the mantle, in transmission of the axial ΔAAM from the mantle to the core. If, after conversion to the equivalent ΔLOD assuming core-mantle decoupling (as in current standard practice), the calculated axial ΔAAM (according to atmospheric general circulation models [GCMs]) is systematically greater than the observed ΔLOD, then we can conclude the presence, and, furthermore, estimate the strength, of the said dynamic core-mantle coupling. However, in this study we find the opposite instead, that the calculated ΔAAM (plus the small oceanic counterpart) is smaller than the observed ΔLOD by 10%–20% consistently across the intraseasonal and seasonal time scales. Our main logical conclusion is that the atmospheric GCMs in general underpredict the ΔAAM, by at least 10%–20% at the mentioned time scales, a fact of importance with respect to the assessment of GCMs. Therefore, the systematic discrepancy found between the ΔAAM-predicted and the observed ΔLOD masks the relevant information on core-mantle coupling that we seek.