A Global Vertical Reference Frame Based on Four Regional Vertical Datums

A Global Vertical Reference Frame (GVRF) has been realized by means of several regional and local vertical datums (LVD) distributed world-wide: the North American Vertical Datum 1988 (NAVD 88), Australian Height Datum 1971 (AHD 71), LVD France, Institute Géographique National 1969 (IGN 69) and Brazilian Height Datum 1957 (BHD 57). The vertical shifts of the above LVD origins have been related to the adopted reference geopotential value W ₀ = (62 636 856.0 ± 0.5) m²s^–2 and they were determined at the 5 cm level. However, the W ₀ reference value can be chosen arbitrarily, the methodology, which was developed here, does not require that the above value be adopted.     

地球参考框架的发展现状和未来展望

地球参考框架是国家重要的空间基础设施,是地球上人类所有活动的空间参考基准。本文首先阐述了国际地球参考框架（International Terrestrial Reference Frame,ITRF）的发展现状,重点评述了ITRF的建立与维持,针对ITRF的发展现状提出了存在的问题;其次,以ITRF与2000国家大地坐标系（China Geodetic Coordinate System 2000,CGCS2000）的关系及现状为切入点,探讨了我国建立北斗坐标系的必要性,介绍了建立北斗坐标系的基本思路以及初始实现;最后,对地球参考框架的未来发展进行了展望。     

Local hydrology, the Global Geodynamics Project and CHAMP/GRACE perspective: some case studies

We first quantify the influence of aquifers on gravity variations by considering local, regional and continental scales. We show that locally only the direct attraction of the underlying aquifer has to be taken into account. At continental (or global scales), the underground water masses act by direct attraction (due to the earth curvature), loading flexure and potential redistribution. We show that at the intermediate regional scale (saying a few kilometres to a few hundreds of kilometres), groundwater contributions can be neglected in practice. Afterwards, we illustrate the difficulties in tackling the local hydrological context by studying comparatively the geological and hydrogeological surroundings of three European Global Geodynamics Project (GGP) superconducting gravimeter stations (Strasbourg, Moxa, and Vienna). Finally, it appears clearly that hydrological variability and cycle characterisations constitute the up-to-date challenge while studying gravity variations in a large spectral range. That is why, gravity is used to quantify hydrological transfers, and overall when seeking for small signals from the Earth's deep interior or other environmental signals (atmosphere, oceans) where groundwater influence can be seen as a disturbance.     

Seismicity,Tectonics, and GPS Geodynamics of the Caucasus

Izvestiya, Physics of the Solid Earth - The style of the seismotectonic deformation of the Earth’s crust in the Caucasus and its immediate surroundings corresponds to the thrust setting with...     

Solar Influence on Global and Regional Climates

The literature relevant to how solar variability influences climate is vast—but much has been based on inadequate statistics and non-robust procedures. The common pitfalls are outlined in this review. The best estimates of the solar influence on the global mean air surface temperature show relatively small effects, compared with the response to anthropogenic changes (and broadly in line with their respective radiative forcings). However, the situation is more interesting when one looks at regional and season variations around the global means. In particular, recent research indicates that winters in Eurasia may have some dependence on the Sun, with more cold winters occurring when the solar activity is low. Advances in modelling “top-down” mechanisms, whereby stratospheric changes influence the underlying troposphere, offer promising explanations of the observed phenomena. In contrast, the suggested modulation of low-altitude clouds by galactic cosmic rays provides an increasingly inadequate explanation of observations.     

A Comparison of Global and Regional GRACE Models for Land Hydrology

When using GRACE as a tool for hydrology, many different gravity field model products are now available to the end user. The traditional spherical harmonics solutions produced from GRACE are typically obtained through an optimization of the gravity field data at the global scale, and are generated by a number of processing centers around the world. Alternatives to this global approach include so-called regional techniques, for which many variants exist, but whose common trait is that they only use the gravity data collected over the area of interest to generate the solution. To determine whether these regional solutions hold any advantage over the global techniques in terms of overall accuracy, a range of comparisons were made using some of the more widely used regional and global methods currently available. The regional techniques tested made use of either spherical radial basis functions or single layer densities (i.e., mascons), with the global solutions having been obtained from the various major processing centers. The solutions were evaluated using a range of computed statistics over a selection of major river basins, which were globally distributed and ranged in size from 1 to 6 million km². For one of the basins tested, the Zambezi, additional validation tests were conducted through comparisons against a custom designed regional hydrology model of the region. We could not prove that current regional models perform better than global ones. Monthly mean water storage variations agree at the level of 0.02 m equivalent water height. The differences in terms of monthly mean water storage variations between regional and global solutions are comparable with the differences among only global or regional solutions. Typically they reach values of 0.02 m equivalent water heights, which seems to be the level of accuracy of current GRACE solutions for river basins above 1 million km². The amplitudes of the seasonal mass variations agree at the sub-centimetre level. Evident from all of the comparisons shown is the importance that the choice of regularization, or spatial filtering, can have on the solution quality. This was found to be true for global as well as regional techniques.     

AGrav—The New International Absolute Gravity Database of BGI and BKG and its benefit for the Global Geodynamics Project (GGP)

A new database for absolute gravity (AG) measurements has been implemented at BGI and BKG and is operational now for storing absolute gravity data either in the form of metadata or as detailed measurement results. The database development was proposed by the IGFS (International Gravity Field Service) and is expected to have a great importance for the GGOS (Global Geodetic Observing System) initiative. This database will provide an overview about AG stations and observations and by this improve the cooperation between gravity groups and foster the combination with other geodetic observation techniques. The international community of absolute gravimeter users is asked to contribute to this database.In addition to its primary purposes, demonstration of the global site distribution and information about available observations, the database could also provide an important contribution to the Global Geodynamics Project (GGP). Precise repeated absolute gravity measurements at the superconducting gravimeter (SG) sites are necessary for the determination of SG drift parameters and can be used for checking SG instrument calibration factors. The AGrav database is capable of storing the necessary AG observations at the SG location in detail up to the “single drop level” and provides this information for the combination with SG time series. An example for a selected station is presented. It is proposed to establish an interface between the AGrav and GGP databases.     

Geodetic evidence for rifting in afar, 2. Vertical displacements

In a previous paper we have proposed a two-dimensional elastic model which accounts for the horizontal displacements measured for the rifting episode which occurred in November 1978 in Afar. In this paper we demonstrate that the same model accounts for the measured vertical displacements as well as for the horizontal ones when the thickness of the lithosphere is introduced in the model as a new parameter. After comparison with similar data obtained in recent years in Iceland, we propose a global interpretation for the rifting phenomenon.     

Satellite Altimetry-Based Sea Level at Global and Regional Scales

Since the beginning of the 1990s, sea level is routinely measured using high-precision satellite altimetry. Over the past ~25 years, several groups worldwide involved in processing the satellite altimetry data regularly provide updates of sea level time series at global and regional scales. Here we present an ongoing effort supported by the European Space Agency (ESA) Climate Change Initiative Programme for improving the altimetry-based sea level products. Two main objectives characterize this enterprise: (1) to make use of ESA missions (ERS-1 and 2 and Envisat) in addition to the so-called ‘reference’ missions like TOPEX/Poseidon and the Jason series in the computation of the sea level time series, and (2) to improve all processing steps in order to meet the Global Climate Observing System (GCOS) accuracy requirements defined for a set of 50 Essential Climate Variables, sea level being one of them. We show that improved geophysical corrections, dedicated processing algorithms, reduction of instrumental bias and drifts, and careful linkage between missions led to improved sea level products. Regarding the long-term trend, the new global mean sea level record accuracy now approaches the GCOS requirements (of ~0.3 mm/year). Regional trend uncertainty has been reduced by a factor of ~2, but orbital and wet tropospheric corrections errors still prevent fully reaching the GCOS accuracy requirement. Similarly at the interannual time scale, the global mean sea level still displays 2–4 mm errors that are not yet fully understood. The recent launch of new altimetry missions (Sentinel-3, Jason-3) and the inclusion of data from currently flying missions (e.g., CryoSat, SARAL/AltiKa) may provide further improvements to this important climate record.     

Global and Regional Electricity Components in Undisturbed Midlatitude Lower Atmosphere

The physical mechanisms determining the variability of the vertical profiles of electrical conductivity, space charge density, and electric field in the undisturbed midlatitude lower atmosphere are discussed. The influence of the global and local mesoscale processes on the variability of electrical conductivity and the main component of the atmospheric electric field is estimated. The sunrise effect is studied, estimates are obtained for the charge accumulation rate in the column of the lower atmosphere and the corresponding growth rate of the field strength close to the ground. It is shown that the increase in the average charge density is mainly due to the breakdown of the stable stratification of the atmospheric boundary layer and transformation of the vertical profile of electrical conductivity following the convective mixing of a radon and its daughter products.     

A Review of Recent Updates of Sea-Level Projections at Global and Regional Scales

Sea-level change (SLC) is a much-studied topic in the area of climate research, integrating a range of climate science disciplines, and is expected to impact coastal communities around the world. As a result, this field is rapidly moving, and the knowledge and understanding of processes contributing to SLC is increasing. Here, we discuss noteworthy recent developments in the projection of SLC contributions and in the global mean and regional sea-level projections. For the Greenland Ice Sheet contribution to SLC, earlier estimates have been confirmed in recent research, but part of the source of this contribution has shifted from dynamics to surface melting. New insights into dynamic discharge processes and the onset of marine ice sheet instability increase the projected range for the Antarctic contribution by the end of the century. The contribution from both ice sheets is projected to increase further in the coming centuries to millennia. Recent updates of the global glacier outline database and new global glacier models have led to slightly lower projections for the glacier contribution to SLC (7–17 cm by 2100), but still project the glaciers to be an important contribution. For global mean sea-level projections, the focus has shifted to better estimating the uncertainty distributions of the projection time series, which may not necessarily follow a normal distribution. Instead, recent studies use skewed distributions with longer tails to higher uncertainties. Regional projections have been used to study regional uncertainty distributions, and regional projections are increasingly being applied to specific regions, countries, and coastal areas.     

Geodetic and seismic constraints on recent activity at Long Valley Caldera,California: evidence for viscoelastic rheology

Long Valley Caldera is an active volcanic region in east central California. Surface deformation on the resurgent dome within the caldera was an order of magnitude higher for the five-month period September 1997 through January 1998 compared to the previous three-year average. However, the location of the immediate (shallow) source of deformation remained essentially constant, 5–7 km beneath the dome, near the top of a region of probable magma accumulation defined by seismic data. Similarly, although the rate of seismic moment release increased dramatically, earthquake locations remained similar to earlier periods. The rate of deformation increased exponentially between April–May 1997 and late November 1997 with a time constant of ∼55–65 days, after which it decreased exponentially with about the same time constant. We develop a model consistent with these observations and also consistent with independent constraints on sub-surface rheology from thermal, geochemical and laboratory data. Deformation at sites on the resurgent dome most sensitive to the shallow deformation source are well fit by a model with a single pressure source at 6 km depth which experienced a pressure pulse that began in late 1996, peaked in November 1997, close to the time of major seismic moment release, and essentially ended in mid-1999. The pressure source in our model is surrounded by a 1 km thick “shell” of Maxwell viscoelastic material (shell viscosity 10¹⁶ Pa s) within an elastic half space, and has peak values that are much lower than corresponding purely elastic half space models. The shell viscosity is characteristic of a weak, deformable solid, e.g. quartz-bearing country rock surrounding the magma chamber at temperatures in the range 500–600°C, i.e. above the brittle–ductile transition, and/or largely crystallized rhyolite near its solidus temperature of ∼670°C, material that probably exists near the top of the zoned magma chamber at Long Valley.     

Modeling Groundwater Depletion at Regional and Global Scales: Present State and Future Prospects

Except for frozen water in ice and glaciers, groundwater is the world’s largest distributed store of freshwater and has strategic importance to global food and water security. In this paper, the most recent advances quantifying groundwater depletion (GWD) are comprehensively reviewed. This paper critically evaluates the recently advanced modeling approaches estimating GWD at regional and global scales, and the evidence of feedbacks to the Earth system including sea-level rise associated with GWD. Finally, critical challenges and opportunities in the use of groundwater are identified for the adaption to growing food demand and uncertain climate.     

Cenozoic Tectonic Deformation and Related Geodynamics in the Western Part of Sichuan and Yunnan,Southwest China

Tectonic deformation of Cenozoic strata,youthful tectonontorphology,and high seismicity in the western part of Sichuan and Yunnan(Southwest China)marked intensive tectonism there during the Ceno7oic.It is a good place for studying the continental geodynamics because it is far away from those active plate boundaries surrounding the East Asian continent but near the southeastern margin of the Qinghai-Xizang(Tibet)plateau.The present study discriminated two phases of tectonic deformation with quite different styles in Cenozoic.Early compression deformation,expressed by folds,thrust,and even nappe structure,mainly occurred between the middle and late Eocene.Late extension deformation expressed by block-faulting started at least in the late Pliocene.Nonconformity,absence of strata,nonsuccessive tectonism,and inverse movement of the faults in late stages illustrated that two different deformation phases should be caused by different geodynamic processes.The early compression deformation would be related to Ar     

日本1999年到2002年测地学与地球物理学活动报告

日本是测地学与地球物理学国际联合会(IUG)最开始的9个成员国之一。IUGG成立于919年,现在有66个成员国。日本测地学与地球物理学国家委员会是作为日本科学委员会180个联络委员会的一个成员而成立的,其作用是为了商讨地学的重要性,为了执行在测地学和地球物理学方面的科学研究的国际合作和协调方面的决定。     

1998年7～9月的全球地震动态

１９９８年第三季度,全球地震活动仍为中等水平,新几内亚北部近海和厄瓜多尔近海各发生一次７级以上地震,亚速尔群岛发生一次６级以上的地震,全球中等以上地震活动无异常现象。