31 research outputs found
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Efficient Inverse Modeling of Barotropic Ocean Tides
A computationally efficient relocatable system for generalized inverse (GI) modeling of barotropic ocean tides is described. The GI penalty functional is minimized using a representer method, which requires repeated solution of the forward and adjoint linearized shallow water equations (SWEs). To make representer computations efficient, the SWEs are solved in the frequency domain by factoring the coefficient matrix for a finite-difference discretization of the second-order wave equation in elevation. Once this matrix is factored representers can be calculated rapidly. By retaining the first-order SWE system (defined in terms of both elevations and currents) in the definition of the discretized GI penalty functional, complete generality in the choice of dynamical error covariances is retained. This allows rational assumptions about errors in the SWE, with soft momentum balance constraints (e.g., to account for inaccurate parameterization of dissipation), but holds mass conservation constraints. While the dynamical calculations involve elevations alone, depth-averaged currents can be directly assimilated into the tidal model with this approach. The efficient representer calculation forms the basis for the Oregon State University (OSU) Tidal Inversion Software (OTIS). OTIS includes software for generating grids, prior model covariances, and boundary conditions; for time stepping the nonlinear shallow water equations to generate a first guess or prior solution; for preliminary processing of TOPEX/Poseidon altimeter data; for solution of the GI problem; and for computation of posterior error bars. Approximate GI solution methods, based on using a reduced set of representers, allow very large datasets to be inverted. OTIS regional and local GI tidal modeling (with grids containing up to 105 nodes) require only a few hours on a common desktop workstation. Use of OTIS is illustrated by developing a new regional-scale (1/6°) model of tides in the Indonesian Seas
Constraints on the resistivity of the oceanic lithosphere and asthenosphere from seafloor ocean tidal electromagnetic measurements
Author Posting. © The Author(s), 2019. This is the author's version of the work. It is posted here by permission of Oxford University Press for personal use, not for redistribution. The definitive version was published in Geophysical Journal International, 219(1), (2019): 464-478, doi:10.1093/gji/ggz315.The electromagnetic (EM) field generated by ocean tidal flow is readily detectable in both satellite magnetic field data, and in ocean-bottom measurements of electric and magnetic fields. The availability of accurate charts of tidal currents, constrained by assimilation of modern satellite altimetry data, opens the possibility of using tidal EM fields as a source to image mantle electrical resistivity beneath the ocean basins, as highlighted by the recent success in defining the globally averaged lithosphereâasthenosphere boundary (LAB) with satellite data. In fact, seafloor EM data would be expected to provide better constraints on the structure of resistive oceanic lithosphere, since the toroidal magnetic mode, which can constrain resistive features, is a significant component of the tidal EM field within the ocean, but is absent above the surface (in particular in satellite data). Here we consider this issue in more detail, using a combination of simplified theoretical analysis and 1-D and 3-D numerical modelling to provide a thorough discussion of the sensitivity of satellite and seafloor data to subsurface electrical structure. As part of this effort, and as a step toward 3-D inversion of seafloor tidal data, we have developed a new flexible 3-D spherical-coordinate finite difference scheme for both global and regional scale modelling, with higher resolution models nested in larger scale solutions. We use the new 3-D model, together with Monte Carlo simulations of errors in tidal current estimates, to provide a quantitative assessment of errors in the computed tidal EM signal caused by uncertainty in the tidal source. Over the open ocean this component of error is below 0.01 nT in Bz at satellite height and 0.05 nT in Bx on the seafloor, well below typical signal levels. However, as coastlines are approached error levels can increase substantially. Both analytical and 3-D modelling demonstrate that the seafloor magnetic field is most sensitive to the lithospheric resistance (the product of resistivity and thickness), and is more weakly influenced (primarily in the phase) by resistivity of the underlying asthenosphere. Satellite data, which contain only the poloidal magnetic mode, are more sensitive to the conductive asthenosphere, but have little sensitivity to lithospheric resistance. For both seafloor and satellite dataâs changes due to plausible variations in Earth parameters are well above error levels associated with source uncertainty, at least in the ocean interior. Although the 3-D modelling results are qualitatively consistent with theoretical analysis, the presence of coastlines and bathymetric variations generates a complex response, confirming that quantitative interpretation of ocean tidal EM fields will require a 3-D treatment. As an illustration of the nested 3-D scheme, seafloor data at five magnetic and seven electric stations in the northeastern Pacific (41âN, 165âW) are fit with trial-and-error forward modelling of a local domain. The simulation results indicate that the lithospheric resistance is roughly 7 Ă 108âΩm2. The phase of the seafloor data in this region are inconsistent with a sharp transition between the resistive lithosphere and conductive asthenosphere.This work has been supported by National Natural Science Foundation of China grants 41804072 and 41574104, and NSF grant EAR-1447109. Special thanks to Dr Benjamin Murphy who provided the conductivity-depth profile for 1-D earth model, Dr Min Ding who provided valuable discussion about the oceanic lithosphere and Dr Jeffery Love who provided comments on the stylistics of the manuscript
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Tidal currents on the central Oregon shelf : models, data, and assimilation
Measurements of tidal currents on the central Oregon shelf are available from several sources, including recent high frequency (HF) coastal radar and Acoustic Doppler Profiler (ADP) deployments, and historical current moorings. In this paper we use a generalized inverse (GI) approach to compare these data to, and then assimilate them into, numerical models for the barotropic tides. Harmonic analysis of the data in short time windows using a modified admittance approach reveals that tidal currents on the Oregon shelf are highly variable in time, and can contain significant baroclinic components. Data from the winter months, when waters on the shelf are only weakly stratified, are found to be most nearly barotropic and thus most reasonable for assimilation into the shallow water equations model. The various data sources are used in several different combinations for assimilation and validation. Forcing the prior forward model with normal flow open boundary conditions obtained from a regional barotropic inverse model results in semidiurnal barotropic currents that are consistent (within estimated error limits) with all available data. In contrast, diurnal currents on the shelf are very sensitive to details of the model configuration, and are significantly improved by data assimilation. Very similar solutions result from assimilation of either the HF radar or ADP data sets. The high sensitivity of the diurnal band currents can be understood dynamically in terms of trapped shelf waves. A short (âŒ85 km long) section of shelf off the central Oregon coast is wide enough to allow firstâmode barotropic shelf waves at the subinertial diurnal frequencies. This results in locally resonant large amplitude diurnal tidal currents that are very sensitive to details in the local forcing, and hence quite variable in time
Revised circulation scheme North of the Denmark Strait
Author Posting. © The Author(s), 2013. This is the author's version of the work. It is posted here by permission of Elsevier Ltd. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part I: Oceanographic Research Papers 79 (2013): 20-39, doi:10.1016/j.dsr.2013.05.007.The circulation and water mass transports north of the Denmark Strait are investigated using recently collected and
historical in-situ data along with an idealized numerical model and atmospheric reanalysis fields. Emphasis is placed
on the pathways of dense water feeding theDenmark StraitOverflowWater plume as well as the upper-layer circulation
of freshwater. It is found that the East Greenland Current (EGC) bifurcates at the northern end of the Blosseville
Basin, some 450 km upstream of the Denmark Strait, advecting overflow water and surface freshwater away from the
boundary. This âseparated EGCâ flows southward adjacent to the previously identified North Icelandic Jet, indicating
that approximately 70% of the Denmark Strait Overflow Water approaches the sill along the Iceland continental slope.
Roughly a quarter of the freshwater transport of the EGC is diverted offshore via the bifurcation. Two hypotheses are
examined to explain the existence of the separated EGC. The atmospheric fields demonstrate that flow distortion due
to the orography of Greenland imparts significant vorticity into the ocean in this region. The negative wind stress curl,
together with the closed bathymetric contours of the Blosseville Basin, is conducive for spinning up an anti-cyclonic
gyre whose offshore branch could represent the separated EGC. An idealized numerical simulation suggests instead
that the current is primarily eddy-forced. In particular, baroclinic instability of the model EGC spawns large anticyclones
that migrate offshore and coalesce upon reaching the Iceland continental slope, resulting in the separated
EGC. Regardless of the formation mechanism, the recently obtained shipboard data and historical hydrography both
indicate that the separated EGC is a permanent feature of the circulation north of the Denmark Strait.Support for this work was provided by the Norwegian Research Council (KV), the European Union 7th Framework Programme (FP7 2007-2013)
under grant agreement n.308299 NACLIM Project (KV), US National Science Foundation grants
OCE-0959381 (RP, MS, DT) and OCE-0850416 (MS), and the Natural Sciences and Engineering
Research Council of Canada (KM)
The Atlantic Water boundary current north of Svalbard in late summer
Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 122 (2017): 2269â2290, doi:10.1002/2016JC012486.Data from a shipboard hydrographic/velocity survey carried out in September 2013 of the region north of Svalbard in the Nansen Basin are analyzed to characterize the Atlantic Water (AW) boundary current as it flows eastward along the continental slope. Eight meridional transects across the current, spanning an alongstream distance of 180 km, allow for a detailed description of the current and the regional water masses. During the survey the winds were light and there was no pack-ice. The mean section reveals that the boundary current was O(40 km) wide, surface-intensified, with a maximum velocity of 20 cm/s. Its mean transport during the survey was 3.11â±â0.33 Sv, of which 2.31â±â0.29 Sv was AW. This suggests that the two branches of AW entering the Arctic Ocean via Fram Straitâthe Yermak Plateau branch and the Svalbard branchâhave largely combined into a single current by 30°E. At this location the boundary current meanders with a systematic change in its kinematic structure during offshore excursions. A potential vorticity analysis indicates that the flow is baroclinically unstable, consistent with previous observations of AW anticyclones offshore of the current as well as the presence of a near-field cyclone in this data set. Our survey indicates that only a small portion of the boundary current is diverted into the KvitĂžya Trough (0.17â±â0.08 Sv) and that the AW temperature/salinity signal is quickly eroded within the trough.National Science Foundation Grant Number: ARC-12640982017-09-2
Accuracy Assessment of Global Internal-Tide Models Using Satellite Altimetry
Altimeter measurements are corrected for several geophysical parameters in order to access ocean signals of interest, like mesoscale or sub-mesoscale variability. The ocean tide is one of the most critical corrections due to the amplitude of the tidal elevations and to the aliasing phenomena of high-frequency signals into the lower-frequency band, but the internal-tide signatures at the ocean surface are not yet corrected globally. Internal tides can have a signature of several centimeters at the surface with wavelengths of about 50â250âkm for the first mode and even smaller scales for higher-order modes. The goals of the upcoming Surface Water Ocean Topography (SWOT) mission and other high-resolution ocean measurements make the correction of these small-scale signals a challenge, as the correction of all tidal variability becomes mandatory to access accurate measurements of other oceanic signals. In this context, several scientific teams are working on the development of new internal-tide models, taking advantage of the very long altimeter time series now available, which represent an unprecedented and valuable global ocean database. The internal-tide models presented here focus on the coherent internal-tide signal and they are of three types: empirical models based upon analysis of existing altimeter missions, an assimilative model and a three-dimensional hydrodynamic model. A detailed comparison and validation of these internal-tide models is proposed using existing satellite altimeter databases. The analysis focuses on the four main tidal constituents: M2, K1, O1 and S2. The validation process is based on a statistical analysis of multi-mission altimetry including Jason-2 and Cryosphere Satellite-2 data. The results show a significant altimeter variance reduction when using internal-tide corrections in all ocean regions where internal tides are generating or propagating. A complementary spectral analysis also gives some estimation of the performance of each model as a function of wavelength and some insight into the residual non-stationary part of internal tides in the different regions of interest. This work led to the implementation of a new internal-tide correction (ZARON\u27one) in the next geophysical data records version-F (GDR-F) standards
Altimetry for the future: Building on 25 years of progress
In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the ââGreenâ Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instrumentsâ development and satellite missionsâ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion
Altimetry for the future: building on 25 years of progress
In 2018 we celebrated 25âŻyears of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology.
The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the âGreenâ Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instrumentsâ development and satellite missionsâ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion
LEXICAL VERNACULAR IN THE SPEECH OF LITERARY LANGUAGE USERS RESIDING IN PERM REGION
The article considers the influence of dialectal layer of the languages by means of incorporating
vernaculars into the lexical system of the literary language. It is stated that substandard verbs most frequently get
the status of colloquial verbs due to their expressive semantic content or to their wider area of usage. The material
for the analysis was 24 substandard verbal lexemes recorded in the explanatory and dialectal dictionaries of the
Russian language and found in the speech of native speakers of the literary language. Data on the use of these
units were obtained from recordings of the speech of residents of Perm and cities of Perm Krai (the total duration of
the audio is about 30 hours). The research is based on the description of the semantic and functional-stylistic
potential of vernacular vocabulary. The dynamics of stylistic characteristics of a word is described on the basis of
the data recorded in lexicographic publications of different years. It is shown that the transition of words from one
subsystem of the Russian language to another is a natural and logical process that contributes to the enrichment
of the vocabulary of the Russian language. It has been confirmed that vernacular is a transitional space between
dialects and literary language
Numerical study of the tide and tidal dynamics in the South China Sea
Tides and their dynamic processes in the South China Sea (SCS) are studied by assimilating Topex/Poseidon altimetry data into a barotropic ocean tide model for the eight major constituents (M-2 S-2, K-1 O-1 N-2 K-2 P-1 Q(1)) using a tidal data inversion scheme. High resolution (similar to 10 km) and large model domain are adopted to better resolve the physical processes involved and to minimize the uncertainty from the open boundary condition. The model results, which tire optimized by an inversion scheme, compare well with tidal gauge measurements. The study reveals that the amplitude of the semi-diurnal tide, M2, decreases, while the amplitude of the diurnal tide, K-1, increases similar to the Helmholtz resonance after the tidal waves propagate from the western Pacific into the SCS through the Luzon Strait (LS). Analyses of the energy studies show that the LS is a place where both M2 and K, tidal energy dissipates the most, and strong M, tidal dissipation also occurs in the Taiwan Strait (TS). The work rate of the tidal generating force in the SCS basin is negative for M2 and positive for K1. It is found that the responses of tides in the SCS are largely associated with the propagating directions of the tides in the Pacific, the tidal frequency, the wavelengths, the local geometry and bottom topography. (C) 2007 Elsevier Ltd. All rights reserved