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  • Estimating Near-Surface Shear-Wave-Velocity Structures Via Multichannel Analysis of Rayleigh and Love Waves: An Experiment at the Boise Hydrogeophysical Research Site
    Surv. Geophys. (IF 5.226) Pub Date : 2020-01-03
    Binbin Mi, Jianghai Xia, John H. Bradford, Chao Shen

    Surface-wave analysis has been widely used for near-surface geophysical and geotechnical studies by using the dispersive characteristic of surface waves (Rayleigh or Love waves) to determine subsurface model parameters. Unlike Rayleigh waves, the dispersive nature of Love waves is independent of P-wave velocity in 1D models, which makes Love-wave dispersion curve interpretation simpler than Rayleigh waves. This reduces the degree of nonuniqueness leading to more stable inversion of Love-wave dispersion curves. To estimate the near-surface shear-wave velocities (Vs) using multichannel analysis of Rayleigh (MASW) and Love waves (MALW) for hydrologic characterization, we conducted an experiment at the Boise Hydrogeophysical Research Site (BHRS, an experimental well field located near Boise, Idaho, USA). We constructed the pseudo-3D velocity structures at the BHRS using both the MASW and MALW methods and compared the results to borehole measurements. We used the 3D Vs distribution to identify and resolve the extent of a relatively low-velocity anomaly caused by a sand channel. The Vs structure and anomaly boundaries were delineated at the meter scale and confirmed by the ground-penetrating radar surveys. The differences in shear-wave velocity determined by MASW, MALW and borehole measurements were discussed and interpreted to reflect the near-surface anisotropy associated with the hydrologic characteristics at the BHRS. Our results demonstrated that the combination of MALW and MASW can be a powerful tool for near-surface characterization.

    更新日期:2020-01-04
  • Correction to: Uncertainty and Resolution Analysis of 2D and 3D Inversion Models Computed from Geophysical Electromagnetic Data
    Surv. Geophys. (IF 5.226) Pub Date : 2019-12-02
    Zhengyong Ren, Thomas Kalscheuer

    An error has been found and should be corrected.

    更新日期:2020-01-04
  • On the Use of Electromagnetics for Earth Imaging of the Polar Regions
    Surv. Geophys. (IF 5.226) Pub Date : 2019-09-12
    Graham J. Hill

    The polar regions are host to fundamental unresolved challenges in Earth studies. The nature of these regions necessitates the use of geophysics to address these issues, with electromagnetic and, in particular, magnetotelluric studies finding favour and being applied over a number of different scales. The unique geography and climatic conditions of the polar regions means collecting magnetotelluric data at high latitudes, which presents challenges not typically encountered and may result in significant measurement errors. (1) The very high contact resistance between electrodes and the surficial snow and ice cover (commonly MΩ) can interfere with the electric field measurement. This is overcome by using custom-designed amplifiers placed at the active electrodes to buffer their high impedance contacts. (2) The proximity to the geomagnetic poles requires verification of the fundamental assumption in magnetotellurics that the magnetic source field is a vertically propagating, horizontally polarised plane wave. Behaviour of the polar electro-jet must be assessed to identify increased activity (high energy periods) that create strong current systems and may generate non-planar contributions. (3) The generation of ‘blizstatic’, localised random electric fields caused by the spin drift of moving charged snow and ice particles that produce significant noise in the electric fields during periods of strong winds. At wind speeds above ~ 10 m s−1, the effect of the distortion created by the moving snow is broad-band. Station occupation times need to be of sufficient length to ensure data are collected when wind speed is low. (4) Working on glaciated terrain introduces additional safety challenges, e.g., weather, crevasse hazards, etc. Inclusion of a mountaineer in the team, both during the site location planning and onsite operations, allows these hazards to be properly managed. Examples spanning studies covering development and application of novel electromagnetic approaches for the polar regions as well as results from studies addressing a variety of differing geologic questions are presented. Electromagnetic studies focusing on near-surface hydrologic systems, glacial and ice sheet dynamics, as well as large-scale volcanic and tectonic problems are discussed providing an overview of the use of electromagnetic methods to investigate fundamental questions in solid earth studies that have both been completed and are currently ongoing in polar regions.

    更新日期:2020-01-04
  • Uncertainty and Resolution Analysis of 2D and 3D Inversion Models Computed from Geophysical Electromagnetic Data
    Surv. Geophys. (IF 5.226) Pub Date : 2019-09-24
    Zhengyong Ren, Thomas Kalscheuer

    Abstract A meaningful solution to an inversion problem should be composed of the preferred inversion model and its uncertainty and resolution estimates. The model uncertainty estimate describes an equivalent model domain in which each model generates responses which fit the observed data to within a threshold value. The model resolution matrix measures to what extent the unknown true solution maps into the preferred solution. However, most current geophysical electromagnetic (also gravity, magnetic and seismic) inversion studies only offer the preferred inversion model and ignore model uncertainty and resolution estimates, which makes the reliability of the preferred inversion model questionable. This may be caused by the fact that the computation and analysis of an inversion model depend on multiple factors, such as the misfit or objective function, the accuracy of the forward solvers, data coverage and noise, values of trade-off parameters, the initial model, the reference model and the model constraints. Depending on the particular method selected, large computational costs ensue. In this review, we first try to cover linearised model analysis tools such as the sensitivity matrix, the model resolution matrix and the model covariance matrix also providing a partially nonlinear description of the equivalent model domain based on pseudo-hyperellipsoids. Linearised model analysis tools can offer quantitative measures. In particular, the model resolution and covariance matrices measure how far the preferred inversion model is from the true model and how uncertainty in the measurements maps into model uncertainty. We also cover nonlinear model analysis tools including changes to the preferred inversion model (nonlinear sensitivity tests), modifications of the data set (using bootstrap re-sampling and generalised cross-validation), modifications of data uncertainty, variations of model constraints (including changes to the trade-off parameter, reference model and matrix regularisation operator), the edgehog method, most-squares inversion and global searching algorithms. These nonlinear model analysis tools try to explore larger parts of the model domain than linearised model analysis and, hence, may assemble a more comprehensive equivalent model domain. Then, to overcome the bottleneck of computational cost in model analysis, we present several practical algorithms to accelerate the computation. Here, we emphasise linearised model analysis, as efficient computation of nonlinear model uncertainty and resolution estimates is mainly determined by fast forward and inversion solvers. In the last part of our review, we present applications of model analysis to models computed from individual and joint inversions of electromagnetic data; we also describe optimal survey design and inversion grid design as important applications of model analysis. The currently available model uncertainty and resolution analyses are mainly for 1D and 2D problems due to the limitations in computational cost. With significant enhancements of computing power, 3D model analyses are expected to be increasingly used and to help analyse and establish confidence in 3D inversion models.

    更新日期:2020-01-04
  • The Role of Global/Regional Earth Conductivity Models in Natural Geomagnetic Hazard Mitigation
    Surv. Geophys. (IF 5.226) Pub Date : 2019-12-27
    Anna Kelbert

    Abstract Geomagnetic disturbances cause perturbations in the Earth’s magnetic field which, by the principle of electromagnetic induction, in turn cause electric currents to flow in the Earth. These geomagnetically induced currents (GICs) also enter man-made technological conductors that are grounded; notably, telegraph systems, submarine cables and pipelines, and, perhaps most significantly, electric power grids, where transformer groundings at power grid substations serve as entry points for GICs. The strength of the GICs that flow through a transformer depends on multiple factors, including the spatiotemporal signature of the geomagnetic disturbance, the geometry and specifications of the power grid, and the electrical conductivity structure of the Earth’s subsurface. Strong GICs are hazardous to power grids and other infrastructure; for example, they can severely damage transformers and thereby cause extensive blackouts. Extreme space weather is therefore hazardous to man-made technologies. The phenomena of extreme geomagnetic disturbances, including storms and substorms, and their effects on human activity are commonly referred to as geomagnetic hazards. Here, we provide a review of relevant GIC studies from around the world and describe their common and unique features, while focusing especially on the effects that the Earth’s electrical conductivity has on the GICs flowing in the electric power grids.

    更新日期:2020-01-04
  • Topography Least-Squares Reverse-Time Migration Based on Adaptive Unstructured Mesh
    Surv. Geophys. (IF 5.226) Pub Date : 2019-11-13
    Qiancheng Liu, Jianfeng Zhang

    Abstract Least-squares reverse-time migration (LSRTM) attempts to invert the broadband-wavenumber reflectivity image by minimizing the residual between observed and predicted seismograms via linearized inversion. However, rugged topography poses a challenge in front of LSRTM. To tackle this issue, we present an unstructured mesh-based solution to topography LSRTM. As to the forward/adjoint modeling operators in LSRTM, we take a so-called unstructured mesh-based “Grid Method.” Before solving the two-way wave equation with the Grid Method, we prepare for it a velocity-adaptive unstructured mesh using a Delaunay Triangulation plus Centroidal Voronoi Tessellation algorithm. The rugged topography acts as constraint boundaries during mesh generation. Then, by using the adjoint method, we put the observed seismograms to the receivers on the topography for backward propagation to produce the gradient through the cross-correlation imaging condition. We seek the inverted image using the conjugate gradient method during linearized inversion to linearly reduce the data misfit function. Through the 2D SEG Foothill synthetic dataset, we see that our method can handle the LSRTM from rugged topography.

    更新日期:2020-01-04
  • Modelling by Spherical Cap Harmonic Analysis: A Literature Review
    Surv. Geophys. (IF 5.226) Pub Date : 2019-11-06
    J. Miquel Torta

    There is the need for robust alternatives to the widely used spherical harmonic analysis when measurements are restricted to a region, or when high spatial frequency fields with much less parameters are required. Spherical cap harmonic analysis (SCHA) is one of the preferred alternative regional modelling techniques over the last decades. This paper presents a comprehensive and systematic review of the SCHA literature, underlining the respective merits and weaknesses of the ways in which the technique has been used since it was proposed in the context of geomagnetic field modelling. It reflects the multidisciplinary use of this technique and examines the evidences presented mainly in Earth and planetary science journals. Some bibliometric parameters are provided to understand how the technique and the knowledge of its limitations have progressed and improved, and some avenues for future research are highlighted.

    更新日期:2020-01-04
  • Climatology of Transient Luminous Events and Lightning Observed Above Europe and the Mediterranean Sea
    Surv. Geophys. (IF 5.226) Pub Date : 2019-11-04
    Enrico Arnone, József Bór, Olivier Chanrion, Veronika Barta, Stefano Dietrich, Carl-Fredrik Enell, Thomas Farges, Martin Füllekrug, Antti Kero, Roberto Labanti, Antti Mäkelä, Keren Mezuman, Anna Odzimek, Martin Popek, Marco Prevedelli, Marco Ridolfi, Serge Soula, Diego Valeri, Oscar van der Velde, Yoav Yair, Ferruccio Zanotti, Przemyslaw Zoladek, Torsten Neubert

    In 1999, the first sprites were observed above European thunderstorms using sensitive cameras. Since then, Eurosprite campaigns have been conducted to observe sprites and other transient luminous events (TLEs), expanding into a network covering large parts of Europe and coastal areas. In 2009 through 2013, the number of optical observations of TLEs reached a peak of 2000 per year. Because of this unprecedented number of European observations, it was possible to construct a climatology of 8394 TLEs observed above 1018 thunderstorm systems and study for the first time their distribution and seasonal cycle above Europe and parts of the Mediterranean Sea. The number of TLEs per thunderstorm was found to follow a power law, with less than 10 TLEs for 801 thunderstorms and up to 195 TLEs above the most prolific one. The majority of TLEs were classified as sprites, 641 elves, 280 halos, 70 upward lightning, 2 blue jets and 1 gigantic jet. The climatology shows intense TLE activity during summer over continental areas and in late autumn over coastal areas and sea. The two seasons peak, respectively, in August and November, separated by March and April with almost no TLEs, and a relative minimum around September. The observed TLE activity, i.e. mostly sprites, is shown to be largely consistent with lightning activity, with a 1/1000 of observed TLE-to-lightning ratio in regions with most observations. The overall behaviour is consistent among individual years, making the observed seasonal cycle a robust general feature of TLE activity above Europe.

    更新日期:2020-01-04
  • Correction to: Concepts and Terminology for Sea Level: Mean, Variability and Change, Both Local and Global
    Surv. Geophys. (IF 5.226) Pub Date : 2019-07-02
    Jonathan M. Gregory, Stephen M. Griffies, Chris W. Hughes, Jason A. Lowe, John A. Church, Ichiro Fukumori, Natalya Gomez, Robert E. Kopp, Felix Landerer, Gonéri Le Cozannet, Rui M. Ponte, Detlef Stammer, Mark E. Tamisiea, Roderik S. W. van de Wal

    In the author group at the start of the article and in the affiliations section at the end of the article.

    更新日期:2020-01-04
  • Coastal Sea Level and Related Fields from Existing Observing Systems
    Surv. Geophys. (IF 5.226) Pub Date : 2019-02-05
    Marta Marcos, Guy Wöppelmann, Andrew Matthews, Rui M. Ponte, Florence Birol, Fabrice Ardhuin, Giovanni Coco, Alvaro Santamaría-Gómez, Valerie Ballu, Laurent Testut, Don Chambers, Justin E. Stopa

    Abstract We review the status of current sea-level observing systems with a focus on the coastal zone. Tide gauges are the major source of coastal sea-level observations monitoring most of the world coastlines, although with limited extent in Africa and part of South America. The longest tide gauge records, however, are unevenly distributed and mostly concentrated along the European and North American coasts. Tide gauges measure relative sea level but the monitoring of vertical land motion through high-precision GNSS, despite being essential to disentangle land and ocean contributions in tide gauge records, is only available in a limited number of stations. (25% of tide gauges have a GNSS station at less than 10 km.) Other data sources are new in situ observing systems fostered by recent progress in GNSS data processing (e.g., GPS reflectometry, GNSS-towed platforms) and coastal altimetry currently measuring sea level as close as 5 km from the coastline. Understanding observed coastal sea level also requires information on various contributing processes, and we provide an overview of some other relevant observing systems, including those on (offshore and coastal) wind waves and water density and mass changes.

    更新日期:2020-01-04
  • Concepts and Terminology for Sea Level: Mean, Variability and Change, Both Local and Global
    Surv. Geophys. (IF 5.226) Pub Date : 2019-04-29
    Jonathan M. Gregory, Stephen M. Griffies, Chris W. Hughes, Jason A. Lowe, John A. Church, Ichiro Fukimori, Natalya Gomez, Robert E. Kopp, Felix Landerer, Gonéri Le Cozannet, Rui M. Ponte, Detlef Stammer, Mark E. Tamisiea, Roderik S. W. van de Wal

    Changes in sea level lead to some of the most severe impacts of anthropogenic climate change. Consequently, they are a subject of great interest in both scientific research and public policy. This paper defines concepts and terminology associated with sea level and sea-level changes in order to facilitate progress in sea-level science, in which communication is sometimes hindered by inconsistent and unclear language. We identify key terms and clarify their physical and mathematical meanings, make links between concepts and across disciplines, draw distinctions where there is ambiguity, and propose new terminology where it is lacking or where existing terminology is confusing. We include formulae and diagrams to support the definitions.

    更新日期:2020-01-04
  • Interactions Between Mean Sea Level, Tide, Surge, Waves and Flooding: Mechanisms and Contributions to Sea Level Variations at the Coast
    Surv. Geophys. (IF 5.226) Pub Date : 2019-06-26
    Déborah Idier, Xavier Bertin, Philip Thompson, Mark D. Pickering

    Coastal areas epitomize the notion of ‘at-risk’ territory in the context of climate change and sea level rise (SLR). Knowledge of the water level changes at the coast resulting from the mean sea level variability, tide, atmospheric surge and wave setup is critical for coastal flooding assessment. This study investigates how coastal water level can be altered by interactions between SLR, tides, storm surges, waves and flooding. The main mechanisms of interaction are identified, mainly by analyzing the shallow water equations. Based on a literature review, the orders of magnitude of these interactions are estimated in different environments. The investigated interactions exhibit a strong spatiotemporal variability. Depending on the type of environments (e.g., morphology, hydrometeorological context), they can reach several tens of centimeters (positive or negative). As a consequence, probabilistic projections of future coastal water levels and flooding should identify whether interaction processes are of leading order, and, where appropriate, projections should account for these interactions through modeling or statistical methods.

    更新日期:2020-01-04
  • The Ability of Barotropic Models to Simulate Historical Mean Sea Level Changes from Coastal Tide Gauge Data
    Surv. Geophys. (IF 5.226) Pub Date : 2019-05-06
    C. G. Piecuch, F. M. Calafat, S. Dangendorf, G. Jordà

    Abstract The nature of mean sea level variation over the global coastal ocean is considered based on 219 historical tide gauge records and three barotropic ocean circulation models forced by reanalysis surface air pressure and wind stress. The consistency of the models and their ability to reproduce the data are considered on nonseasonal timescales (seasonal cycles and linear trends removed) from bimonthly to multidecadal over 1900–2010. Models consistently simulate stronger sea level variability at higher latitude, higher frequency, between winters, and over broad shallow shelves and semi-enclosed marginal seas; standard deviations in modeled monthly sea level grow from 1–2 cm on average at low latitude (0°–30°) to 5–10 cm at high latitude (60°–90°), with larger values simulated over some shelf areas (e.g., North Sea). Models are more consistent over narrow shelf regions adjacent to deep basins and less consistent along the broad shallow continental shelf. On monthly timescales, discrepancies between models arise mostly from differences in model configuration (e.g., fine vs. coarse horizontal resolution), whereas model configuration and surface forcing (i.e., choice of atmospheric reanalysis) contribute comparably to model differences on annual timescales. Model solutions become more uncertain at earlier times (e.g., prior to 1950). The models show more skill explaining variance in tide gauge data at higher latitude, higher frequency, between winters, and over broad shallow shelves and within semi-enclosed marginal seas; at middle and high latitudes (poleward of 45°), model sea level solutions on average explain 30–50% of the monthly variance and 35–70% of the variance from one winter to the next in the tide gauge data records. Statistically significant relationships between the model solutions and observational data persist on long decadal periods. The relative skill of individual models is sensitive to region and timescale, such that no one model considered here consistently performs better than the others in all cases. Results suggest that barotropic models are useful for reducing noise in tide gauge records for studies of sea level rise and motivate additional model comparison studies in the context of sea level extremes.

    更新日期:2020-01-04
  • Uncertainties in Long-Term Twenty-First Century Process-Based Coastal Sea-Level Projections
    Surv. Geophys. (IF 5.226) Pub Date : 2019-10-21
    R. S. W. van de Wal, X. Zhang, S. Minobe, S. Jevrejeva, R. E. M. Riva, C. Little, K. Richter, M. D. Palmer

    Abstract Many processes affect sea level near the coast. In this paper, we discuss the major uncertainties in coastal sea-level projections from a process-based perspective, at different spatial and temporal scales, and provide an outlook on how these uncertainties may be reduced. Uncertainty in centennial global sea-level rise is dominated by the ice sheet contributions. Geographical variations in projected sea-level change arise mainly from dynamical patterns in the ocean response and other geophysical processes. Finally, the uncertainties in the short-duration extreme sea-level events are controlled by near coastal processes, storms and tides.

    更新日期:2020-01-04
  • Sea Level and the Role of Coastal Trapped Waves in Mediating the Influence of the Open Ocean on the Coast
    Surv. Geophys. (IF 5.226) Pub Date : 2019-05-02
    Chris W. Hughes, Ichiro Fukumori, Stephen M. Griffies, John M. Huthnance, Shoshiro Minobe, Paul Spence, Keith R. Thompson, Anthony Wise

    The fact that ocean currents must flow parallel to the coast leads to the dynamics of coastal sea level being quite different from the dynamics in the open ocean. The coastal influence of open-ocean dynamics (dynamics associated with forcing which occurs in deep water, beyond the continental slope) therefore involves a hand-over between the predominantly geostrophic dynamics of the interior ocean and the ageostrophic dynamics which must occur at the coast. An understanding of how this hand-over occurs can be obtained by considering the combined role of coastal trapped waves and bottom friction. We here review understanding of coastal trapped waves, which propagate cyclonically around ocean basins along the continental shelf and slope, at speeds which are fast compared to those of baroclinic planetary waves and currents in the open ocean (excluding the large-scale barotropic mode). We show that this results in coastal sea-level signals on western boundaries which, compared to the nearby open-ocean signals, are spatially smoothed, reduced in amplitude, and displaced along the coast in the direction of propagation of coastal trapped waves. The open-ocean influence on eastern boundaries is limited to signals propagating polewards from the equatorial waveguide (although a large-scale diffusive influence may also play a role). This body of work is based on linearised equations, but we also discuss the nonlinear case. We suggest that a proper consideration of nonlinear terms may be very important on western boundaries, as the competition between advection by western boundary currents and a counter-propagating influence of coastal trapped waves has the potential to lead to sharp gradients in coastal sea level where the two effects come into balance.

    更新日期:2020-01-04
  • Climate Model Uncertainty and Trend Detection in Regional Sea Level Projections: A Review
    Surv. Geophys. (IF 5.226) Pub Date : 2019-08-10
    Mark Carson, Kewei Lyu, Kristin Richter, Mélanie Becker, Catia M. Domingues, Weiqing Han, Laure Zanna

    Abstract Projections of future sterodynamic sea level change from global climate models are associated with different sources of uncertainty. From a scientific, societal and policy-making perspective, it is relevant to both understand and reduce uncertainty in projections of climate change. Here, we review recent findings which describe, and shed light on, climate model uncertainty focusing particularly on two types of model uncertainty that contribute to the currently large spread in dynamical sea level patterns (i.e., regional sea level relative to the global mean). These uncertainties are: (1) intermodel uncertainty due to differences in models’ responses in a warming climate and (2) internal model variability due to an individual model’s own climate variability. On timescales longer than about 50 years from now, anthropogenic sterodynamic (dynamic plus global mean) sea level trends from middle- and high-end forcing scenarios will be larger than internal model variability. By 2100, these anthropogenic trends will also be larger than intermodel uncertainty when global mean thermosteric sea level rise and/or melting contributions from land ice are considered along with dynamic sea level changes. Furthermore, we discuss projections of future coastal sea level from the perspective of global climate models as well as from downscaled efforts based on regional climate models. Much knowledge and understanding has been achieved in the last decade from intermodel experiments and studies of sea level process-based model; here, the prospects for improving coastal sea level and reducing sea level uncertainty are discussed.

    更新日期:2020-01-04
  • Satellite Altimetry Measurements of Sea Level in the Coastal Zone
    Surv. Geophys. (IF 5.226) Pub Date : 2019-10-16
    Stefano Vignudelli, Florence Birol, Jérôme Benveniste, Lee-Lueng Fu, Nicolas Picot, Matthias Raynal, Hélène Roinard

    Abstract Satellite radar altimetry provides a unique sea level data set that extends over more than 25 years back in time and that has an almost global coverage. However, when approaching the coasts, the extraction of correct sea level estimates is challenging due to corrupted waveforms and to errors in most of the corrections and in some auxiliary information used in the data processing. The development of methods dedicated to the improvement of altimeter data in the coastal zone dates back to the 1990s, but the major progress happened during the last decade thanks to progress in radar technology [e.g., synthetic aperture radar (SAR) mode and Ka-band frequency], improved waveform retracking algorithms, the availability of new/improved corrections (e.g., wet troposphere and tidal models) and processing workflows oriented to the coastal zone. Today, a set of techniques exists for the processing of coastal altimetry data, generally called “coastal altimetry.” They have been used to generate coastal altimetry products. Altimetry is now recognized as part of the integrated observing system devoted to coastal sea level monitoring. In this article, we review the recent technical advances in processing and the new technological capabilities of satellite radar altimetry in the coastal zone. We also illustrate the fast-growing use of coastal altimetry data sets in coastal sea level research and applications, as high-frequency (tides and storm surge) and long-term sea level change studies.

    更新日期:2020-01-04
  • The Contribution of Wind-Generated Waves to Coastal Sea-Level Changes
    Surv. Geophys. (IF 5.226) Pub Date : 2019-07-29
    Guillaume Dodet, Angélique Melet, Fabrice Ardhuin, Xavier Bertin, Déborah Idier, Rafael Almar

    Abstract Surface gravity waves generated by winds are ubiquitous on our oceans and play a primordial role in the dynamics of the ocean–land–atmosphere interfaces. In particular, wind-generated waves cause fluctuations of the sea level at the coast over timescales from a few seconds (individual wave runup) to a few hours (wave-induced setup). These wave-induced processes are of major importance for coastal management as they add up to tides and atmospheric surges during storm events and enhance coastal flooding and erosion. Changes in the atmospheric circulation associated with natural climate cycles or caused by increasing greenhouse gas emissions affect the wave conditions worldwide, which may drive significant changes in the wave-induced coastal hydrodynamics. Since sea-level rise represents a major challenge for sustainable coastal management, particularly in low-lying coastal areas and/or along densely urbanized coastlines, understanding the contribution of wind-generated waves to the long-term budget of coastal sea-level changes is therefore of major importance. In this review, we describe the physical processes by which sea states may affect coastal sea level at several timescales, we present the methods currently used to estimate the wave contribution to coastal sea-level changes, we describe past and future wave climate variability, we discuss the contribution of wave to coastal sea-level changes, and we discuss the limitations and perspectives of this research field.

    更新日期:2020-01-04
  • Impacts of Basin-Scale Climate Modes on Coastal Sea Level: a Review.
    Surv. Geophys. (IF 5.226) Pub Date : 2019-11-12
    Weiqing Han,Detlef Stammer,Philip Thompson,Tal Ezer,Hindu Palanisamy,Xuebin Zhang,Catia M Domingues,Lei Zhang,Dongliang Yuan

    Global sea level rise (SLR) associated with a warming climate exerts significant stress on coastal societies and low-lying island regions. The rates of coastal SLR observed in the past few decades, however, have large spatial and temporal differences from the global mean, which to a large part have been attributed to basin-scale climate modes. In this paper, we review our current state of knowledge about climate modes' impacts on coastal sea level variability from interannual-to-multidecadal timescales. Relevant climate modes, their impacts and associated driving mechanisms through both remote and local processes are elaborated separately for the Pacific, Indian and Atlantic Oceans. This paper also identifies major issues and challenges for future research on climate modes' impacts on coastal sea level. Understanding the effects of climate modes is essential for skillful near-term predictions and reliable uncertainty quantifications for future projections of coastal SLR.

    更新日期:2019-11-01
  • The Importance of Consistent Global Forest Aboveground Biomass Product Validation.
    Surv. Geophys. (IF 5.226) Pub Date : 2019-08-10
    L Duncanson,J Armston,M Disney,V Avitabile,N Barbier,K Calders,S Carter,J Chave,M Herold,T W Crowther,M Falkowski,J R Kellner,N Labrière,R Lucas,N MacBean,R E McRoberts,V Meyer,E Næsset,J E Nickeson,K I Paul,O L Phillips,M Réjou-Méchain,M Román,S Roxburgh,S Saatchi,D Schepaschenko,K Scipal,P R Siqueira,A Whitehurst,M Williams

    Several upcoming satellite missions have core science requirements to produce data for accurate forest aboveground biomass mapping. Largely because of these mission datasets, the number of available biomass products is expected to greatly increase over the coming decade. Despite the recognized importance of biomass mapping for a wide range of science, policy and management applications, there remains no community accepted standard for satellite-based biomass map validation. The Committee on Earth Observing Satellites (CEOS) is developing a protocol to fill this need in advance of the next generation of biomass-relevant satellites, and this paper presents a review of biomass validation practices from a CEOS perspective. We outline the wide range of anticipated user requirements for product accuracy assessment and provide recommendations for the validation of biomass products. These recommendations include the collection of new, high-quality in situ data and the use of airborne lidar biomass maps as tools toward transparent multi-resolution validation. Adoption of community-vetted validation standards and practices will facilitate the uptake of the next generation of biomass products.

    更新日期:2019-11-01
  • New Opportunities for Forest Remote Sensing Through Ultra-High-Density Drone Lidar.
    Surv. Geophys. (IF 5.226) Pub Date : 2019-08-10
    James R Kellner,John Armston,Markus Birrer,K C Cushman,Laura Duncanson,Christoph Eck,Christoph Falleger,Benedikt Imbach,Kamil Král,Martin Krůček,Jan Trochta,Tomáš Vrška,Carlo Zgraggen

    Current and planned space missions will produce aboveground biomass density data products at varying spatial resolution. Calibration and validation of these data products is critically dependent on the existence of field estimates of aboveground biomass and coincident remote sensing data from airborne or terrestrial lidar. There are few places that meet these requirements, and they are mostly in the northern hemisphere and temperate zone. Here we summarize the potential for low-altitude drones to produce new observations in support of mission science. We describe technical requirements for producing high-quality measurements from autonomous platforms and highlight differences among commercially available laser scanners and drone aircraft. We then describe a case study using a heavy-lift autonomous helicopter in a temperate mountain forest in the southern Czech Republic in support of calibration and validation activities for the NASA Global Ecosystem Dynamics Investigation. Low-altitude flight using drones enables the collection of ultra-high-density point clouds using wider laser scan angles than have been possible from traditional airborne platforms. These measurements can be precise and accurate and can achieve measurement densities of thousands of points · m-2. Analysis of surface elevation measurements on a heterogeneous target observed 51 days apart indicates that the realized range accuracy is 2.4 cm. The single-date precision is 2.1-4.5 cm. These estimates are net of all processing artifacts and geolocation errors under fully autonomous flight. The 3D model produced by these data can clearly resolve branch and stem structure that is comparable to terrestrial laser scans and can be acquired rapidly over large landscapes at a fraction of the cost of traditional airborne laser scanning.

    更新日期:2019-11-01
  • Species Matter: Wood Density Influences Tropical Forest Biomass at Multiple Scales.
    Surv. Geophys. (IF 5.226) Pub Date : 2019-08-10
    Oliver L Phillips,Martin J P Sullivan,Tim R Baker,Abel Monteagudo Mendoza,Percy Núñez Vargas,Rodolfo Vásquez

    The mass of carbon contained in trees is governed by the volume and density of their wood. This represents a challenge to most remote sensing technologies, which typically detect surface structure and parameters related to wood volume but not to its density. Since wood density is largely determined by taxonomic identity this challenge is greatest in tropical forests where there are tens of thousands of tree species. Here, using pan-tropical literature and new analyses in Amazonia with plots with reliable identifications we assess the impact that species-related variation in wood density has on biomass estimates of mature tropical forests. We find impacts of species on forest biomass due to wood density at all scales from the individual tree up to the whole biome: variation in tree species composition regulates how much carbon forests can store. Even local differences in composition can cause variation in forest biomass and carbon density of 20% between subtly different local forest types, while additional large-scale floristic variation leads to variation in mean wood density of 10-30% across Amazonia and the tropics. Further, because species composition varies at all scales and even vertically within a stand, our analysis shows that bias and uncertainty always result if individual identity is ignored. Since sufficient inventory-based evidence based on botanical identification now exists to show that species composition matters biome-wide for biomass, we here assemble and provide mean basal-area-weighted wood density values for different forests across the lowand tropical biome. These range widely, from 0.467 to 0.728 g cm-3 with a pan-tropical mean of 0.619 g cm-3. Our analysis shows that mapping tropical ecosystem carbon always benefits from locally validated measurement of tree-by-tree botanical identity combined with tree-by-tree measurement of dimensions. Therefore whenever possible, efforts to map and monitor tropical forest carbon using remote sensing techniques should be combined with tree-level measurement of species identity by botanists working in inventory plots.

    更新日期:2019-11-01
  • Use of Geophysical and Remote Sensing Data for Assessment of Aquifer Depletion and Related Land Deformation.
    Surv. Geophys. (IF 5.226) Pub Date : 2018-01-01
    Abdullah Othman,Mohamed Sultan,Richard Becker,Saleh Alsefry,Talal Alharbi,Esayas Gebremichael,Hassan Alharbi,Karem Abdelmohsen

    An integrated approach [field, Interferometric Synthetic Aperture Radar (InSAR), hydrogeology, geodesy, and spatial analysis] was adopted to identify the nature, intensity, and spatial distribution of deformational features (sinkholes, fissures, differential settling) reported over fossil aquifers in arid lands, their controlling factors, and possible remedies. The Lower Mega Aquifer System (area 2 × 106 km2) in central and northern Arabia was used as a test site. Findings suggest that excessive groundwater extraction from the fossil aquifer is the main cause of deformation: (1) deformational features correlated spatially and/or temporally with increased agricultural development and groundwater extraction, and with a decline in water levels and groundwater storage (- 3.7 ± 0.6 km3/year); (2) earthquake events (years 1985-2016; magnitude 1-5) are largely (65% of reported earthquakes) shallow (1-5 km) and increased from 1 event/year in the early 1980s (extraction 1 km3/year), up to 13 events/year in the 1990s (average annual extraction > 6.4 km3). Results indicate that faults played a role in localizing deformation given that deformational sites and InSAR-based high subsidence rates (- 4 to - 15 mm/year) were largely found within, but not outside of, NW-SE-trending grabens bound by the Kahf fault system. Findings from the analysis of Gravity Recovery and Climate Experiment solutions indicate that sustainable extraction could be attained if groundwater extraction was reduced by 3.5-4 km3/year. This study provides replicable and cost-effective methodologies for optimum utilization of fossil aquifers and for minimizing deformation associated with their use.

    更新日期:2019-11-01
  • The AlpArray Seismic Network: A Large-Scale European Experiment to Image the Alpine Orogen.
    Surv. Geophys. (IF 5.226) Pub Date : 2018-01-01
    György Hetényi,Irene Molinari,John Clinton,Götz Bokelmann,István Bondár,Wayne C Crawford,Jean-Xavier Dessa,Cécile Doubre,Wolfgang Friederich,Florian Fuchs,Domenico Giardini,Zoltán Gráczer,Mark R Handy,Marijan Herak,Yan Jia,Edi Kissling,Heidrun Kopp,Michael Korn,Lucia Margheriti,Thomas Meier,Marco Mucciarelli,Anne Paul,Damiano Pesaresi,Claudia Piromallo,Thomas Plenefisch,Jaroslava Plomerová,Joachim Ritter,Georg Rümpker,Vesna Šipka,Daniele Spallarossa,Christine Thomas,Frederik Tilmann,Joachim Wassermann,Michael Weber,Zoltán Wéber,Viktor Wesztergom,Mladen Živčić,,,

    The AlpArray programme is a multinational, European consortium to advance our understanding of orogenesis and its relationship to mantle dynamics, plate reorganizations, surface processes and seismic hazard in the Alps-Apennines-Carpathians-Dinarides orogenic system. The AlpArray Seismic Network has been deployed with contributions from 36 institutions from 11 countries to map physical properties of the lithosphere and asthenosphere in 3D and thus to obtain new, high-resolution geophysical images of structures from the surface down to the base of the mantle transition zone. With over 600 broadband stations operated for 2 years, this seismic experiment is one of the largest simultaneously operated seismological networks in the academic domain, employing hexagonal coverage with station spacing at less than 52 km. This dense and regularly spaced experiment is made possible by the coordinated coeval deployment of temporary stations from numerous national pools, including ocean-bottom seismometers, which were funded by different national agencies. They combine with permanent networks, which also required the cooperation of many different operators. Together these stations ultimately fill coverage gaps. Following a short overview of previous large-scale seismological experiments in the Alpine region, we here present the goals, construction, deployment, characteristics and data management of the AlpArray Seismic Network, which will provide data that is expected to be unprecedented in quality to image the complex Alpine mountains at depth.

    更新日期:2019-11-01
  • The Earth's Magnetosphere: A Systems Science Overview and Assessment.
    Surv. Geophys. (IF 5.226) Pub Date : 2018-01-01
    Joseph E Borovsky,Juan Alejandro Valdivia

    A systems science examination of the Earth's fully interconnected dynamic magnetosphere is presented. Here the magnetospheric system (a.k.a. the magnetosphere-ionosphere-thermosphere system) is considered to be comprised of 14 interconnected subsystems, where each subsystem is a characteristic particle population: 12 of those particle populations are plasmas and two (the atmosphere and the hydrogen geocorona) are neutrals. For the magnetospheric system, an assessment is made of the applicability of several system descriptors, such as adaptive, nonlinear, dissipative, interdependent, open, irreversible, and complex. The 14 subsystems of the magnetospheric system are cataloged and described, and the various types of magnetospheric waves that couple the behaviors of the subsystems to each other are explained. This yields a roadmap of the connectivity of the magnetospheric system. Various forms of magnetospheric activity beyond geomagnetic activity are reviewed, and four examples of emergent phenomena in the Earth's magnetosphere are presented. Prior systems science investigations of the solar-wind-driven magnetospheric system are discussed: up to the present these investigations have not accounted for the full interconnectedness of the system. This overview and assessment of the Earth's magnetosphere hopes to facilitate (1) future global systems science studies that involve the entire interconnected magnetospheric system with its diverse time and spatial scales and (2) connections of magnetospheric systems science with the broader Earth systems science.

    更新日期:2019-11-01
  • Mechanisms and Model Diversity of Trade-Wind Shallow Cumulus Cloud Feedbacks: A Review.
    Surv. Geophys. (IF 5.226) Pub Date : 2017-12-15
    Jessica Vial,Sandrine Bony,Bjorn Stevens,Raphaela Vogel

    Shallow cumulus clouds in the trade-wind regions are at the heart of the long standing uncertainty in climate sensitivity estimates. In current climate models, cloud feedbacks are strongly influenced by cloud-base cloud amount in the trades. Therefore, understanding the key factors controlling cloudiness near cloud-base in shallow convective regimes has emerged as an important topic of investigation. We review physical understanding of these key controlling factors and discuss the value of the different approaches that have been developed so far, based on global and high-resolution model experimentations and process-oriented analyses across a range of models and for observations. The trade-wind cloud feedbacks appear to depend on two important aspects: (1) how cloudiness near cloud-base is controlled by the local interplay between turbulent, convective and radiative processes; (2) how these processes interact with their surrounding environment and are influenced by mesoscale organization. Our synthesis of studies that have explored these aspects suggests that the large diversity of model responses is related to fundamental differences in how the processes controlling trade cumulus operate in models, notably, whether they are parameterized or resolved. In models with parameterized convection, cloudiness near cloud-base is very sensitive to the vigor of convective mixing in response to changes in environmental conditions. This is in contrast with results from high-resolution models, which suggest that cloudiness near cloud-base is nearly invariant with warming and independent of large-scale environmental changes. Uncertainties are difficult to narrow using current observations, as the trade cumulus variability and its relation to large-scale environmental factors strongly depend on the time and/or spatial scales at which the mechanisms are evaluated. New opportunities for testing physical understanding of the factors controlling shallow cumulus cloud responses using observations and high-resolution modeling on large domains are discussed.

    更新日期:2019-11-01
  • Observation-Based Estimates of Global Glacier Mass Change and Its Contribution to Sea-Level Change.
    Surv. Geophys. (IF 5.226) Pub Date : 2017-02-17
    B Marzeion,N Champollion,W Haeberli,K Langley,P Leclercq,F Paul

    Glaciers have strongly contributed to sea-level rise during the past century and will continue to be an important part of the sea-level budget during the twenty-first century. Here, we review the progress in estimating global glacier mass change from in situ measurements of mass and length changes, remote sensing methods, and mass balance modeling driven by climate observations. For the period before the onset of satellite observations, different strategies to overcome the uncertainty associated with monitoring only a small sample of the world's glaciers have been developed. These methods now yield estimates generally reconcilable with each other within their respective uncertainty margins. Whereas this is also the case for the recent decades, the greatly increased number of estimates obtained from remote sensing reveals that gravimetry-based methods typically arrive at lower mass loss estimates than the other methods. We suggest that strategies for better interconnecting the different methods are needed to ensure progress and to increase the temporal and spatial detail of reliable glacier mass change estimates.

    更新日期:2019-11-01
  • The Global S[Formula: see text] Tide in Earth's Nutation.
    Surv. Geophys. (IF 5.226) Pub Date : 2016-07-30
    Michael Schindelegger,David Einšpigel,David Salstein,Johannes Böhm

    Diurnal S[Formula: see text] tidal oscillations in the coupled atmosphere-ocean system induce small perturbations of Earth's prograde annual nutation, but matching geophysical model estimates of this Sun-synchronous rotation signal with the observed effect in geodetic Very Long Baseline Interferometry (VLBI) data has thus far been elusive. The present study assesses the problem from a geophysical model perspective, using four modern-day atmospheric assimilation systems and a consistently forced barotropic ocean model that dissipates its energy excess in the global abyssal ocean through a parameterized tidal conversion scheme. The use of contemporary meteorological data does, however, not guarantee accurate nutation estimates per se; two of the probed datasets produce atmosphere-ocean-driven S[Formula: see text] terms that deviate by more than 30 [Formula: see text]as (microarcseconds) from the VLBI-observed harmonic of [Formula: see text] [Formula: see text]as. Partial deficiencies of these models in the diurnal band are also borne out by a validation of the air pressure tide against barometric in situ estimates as well as comparisons of simulated sea surface elevations with a global network of S[Formula: see text] tide gauge determinations. Credence is lent to the global S[Formula: see text] tide derived from the Modern-Era Retrospective Analysis for Research and Applications (MERRA) and the operational model of the European Centre for Medium-Range Weather Forecasts (ECMWF). When averaged over a temporal range of 2004 to 2013, their nutation contributions are estimated to be [Formula: see text] [Formula: see text]as (MERRA) and [Formula: see text] [Formula: see text]as (ECMWF operational), thus being virtually equivalent with the VLBI estimate. This remarkably close agreement will likely aid forthcoming nutation theories in their unambiguous a priori account of Earth's prograde annual celestial motion.

    更新日期:2019-11-01
  • Assessing Global Water Storage Variability from GRACE: Trends, Seasonal Cycle, Subseasonal Anomalies and Extremes.
    Surv. Geophys. (IF 5.226) Pub Date : 2016-07-30
    Vincent Humphrey,Lukas Gudmundsson,Sonia I Seneviratne

    Throughout the past decade, the Gravity Recovery and Climate Experiment (GRACE) has given an unprecedented view on global variations in terrestrial water storage. While an increasing number of case studies have provided a rich overview on regional analyses, a global assessment on the dominant features of GRACE variability is still lacking. To address this, we survey key features of temporal variability in the GRACE record by decomposing gridded time series of monthly equivalent water height into linear trends, inter-annual, seasonal, and subseasonal (intra-annual) components. We provide an overview of the relative importance and spatial distribution of these components globally. A correlation analysis with precipitation and temperature reveals that both the inter-annual and subseasonal anomalies are tightly related to fluctuations in the atmospheric forcing. As a novelty, we show that for large regions of the world high-frequency anomalies in the monthly GRACE signal, which have been partly interpreted as noise, can be statistically reconstructed from daily precipitation once an adequate averaging filter is applied. This filter integrates the temporally decaying contribution of precipitation to the storage changes in any given month, including earlier precipitation. Finally, we also survey extreme dry anomalies in the GRACE record and relate them to documented drought events. This global assessment sets regional studies in a broader context and reveals phenomena that had not been documented so far.

    更新日期:2019-11-01
  • A Review of Ionospheric Scintillation Models.
    Surv. Geophys. (IF 5.226) Pub Date : 2015-07-07
    S Priyadarshi

    This is a general review of the existing climatological models of ionospheric radio scintillation for high and equatorial latitudes. Trans-ionospheric communication of radio waves from transmitter to user is affected by the ionosphere which is highly variable and dynamic in both time and space. Scintillation is the term given to irregular amplitude and phase fluctuations of the received signals and related to the electron density irregularities in the ionosphere. Key sources of ionospheric irregularities are plasma instabilities; every irregularities model is based on the theory of radio wave propagation in random media. It is important to understand scintillation phenomena and the approach of different theories. Therefore, we have briefly discussed the theories that are used to interpret ionospheric scintillation data. The global morphology of ionospheric scintillation is also discussed briefly. The most important (in our opinion) analytical and physical models of scintillation are reviewed here.

    更新日期:2019-11-01
  • 4D Arctic: A Glimpse into the Structure and Evolution of the Arctic in the Light of New Geophysical Maps, Plate Tectonics and Tomographic Models.
    Surv. Geophys. (IF 5.226) Pub Date : 2014-01-01
    Carmen Gaina,Sergei Medvedev,Trond H Torsvik,Ivan Koulakov,Stephanie C Werner

    Knowledge about the Arctic tectonic structure has changed in the last decade as a large number of new datasets have been collected and systematized. Here, we review the most updated, publicly available Circum-Arctic digital compilations of magnetic and gravity data together with new models of the Arctic's crust. Available tomographic models have also been scrutinized and evaluated for their potential to reveal the deeper structure of the Arctic region. Although the age and opening mechanisms of the Amerasia Basin are still difficult to establish in detail, interpreted subducted slabs that reside in the High Arctic's lower mantle point to one or two episodes of subduction that consumed crust of possibly Late Cretaceous-Jurassic age. The origin of major igneous activity during the Cretaceous in the central Arctic (the Alpha-Mendeleev Ridge) and in the proximity of rifted margins (the so-called High Arctic Large Igneous Province-HALIP) is still debated. Models of global plate circuits and the connection with the deep mantle are used here to re-evaluate a possible link between Arctic volcanism and mantle plumes.

    更新日期:2019-11-01
  • Computation of Solar Radiative Fluxes by 1D and 3D Methods Using Cloudy Atmospheres Inferred from A-train Satellite Data.
    Surv. Geophys. (IF 5.226) Pub Date : 2012-01-01
    H W Barker,S Kato,T Wehr

    This study used realistic representations of cloudy atmospheres to assess errors in solar flux estimates associated with 1D radiative transfer models. A scene construction algorithm, developed for the EarthCARE mission, was applied to CloudSat, CALIPSO and MODIS satellite data thus producing 3D cloudy atmospheres measuring 61 km wide by 14,000 km long at 1 km grid-spacing. Broadband solar fluxes and radiances were then computed by a Monte Carlo photon transfer model run in both full 3D and 1D independent column approximation modes. Results were averaged into 1,303 (50 km)2 domains. For domains with total cloud fractions Ac < 0.7 top-of-atmosphere (TOA) albedos tend to be largest for 3D transfer with differences increasing with solar zenith angle. Differences are largest for Ac > 0.7 and characterized by small bias yet large random errors. Regardless of Ac , differences between 3D and 1D transfer rarely exceed ±30 W m-2 for net TOA and surface fluxes and ±10 W m-2 for atmospheric absorption. Horizontal fluxes through domain sides depend on Ac with ∼20% of cases exceeding ±30 W m-2; the largest values occur for Ac > 0.7. Conversely, heating rate differences rarely exceed ±20%. As a cursory test of TOA radiative closure, fluxes produced by the 3D model were averaged up to (20 km)2 and compared to values measured by CERES. While relatively little attention was paid to optical properties of ice crystals and surfaces, and aerosols were neglected entirely, ∼30% of the differences between 3D model estimates and measurements fall within ±10 W m-2; this is the target agreement set for EarthCARE. This, coupled with the aforementioned comparison between 3D and 1D transfer, leads to the recommendation that EarthCARE employ a 3D transport model when attempting TOA radiative closure.

    更新日期:2019-11-01
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