Can we model the effect of observed sea level rise on tides?

The link between secular changes in the lunar semidiurnal ocean tide (M2) and relative sea level rise is examined based on numerical tidal modeling and the analysis of long-term sea level records from Europe, Australia, and the North American Atlantic coasts. The study sets itself apart from previous work by using a 1/12° global tide model that incorporates the effects of self-attraction and loading through time-step-wise spherical harmonic transforms instead of iteration. This novel self-attraction and loading implementation incurs moderate computational overheads (some 50%) and facilitates the simulation of shelf sea tides with a global root mean square error of 14.6 cm in depths shallower than 1,000 m. To reproduce measured tidal changes in recent decades, the model is perturbed with realistic water depth changes, compiled from maps of altimetric sea level trends and postglacial crustal rebound. The M2 response to the adopted sea level rise scenarios exhibits peak sensitivities in the North Atlantic and many marginal seas, with relative magnitudes of 1-5% per century. Comparisons with a collection of 45 tide gauge records reveals that the model reproduces the sign of the observed amplitude trends in 80% of the cases and captures considerable fractions of the absolute M2 variability, specifically for stations in the Gulf of Mexico and the Chesapeake-Delaware Bay system. While measured-to-model disparities remain large in several key locations, such as the European Shelf, the study is deemed a major step toward credible predictions of secular changes in the main components of the ocean tide.</p

High-frequency earth rotation variations deduced from altimetry-based ocean tides

A model of diurnal and semi-diurnal variations in Earth rotation parameters (ERP) is constructed based on altimetry-measured tidal heights from a multi-mission empirical ocean tide solution. Barotropic currents contributing to relative angular momentum changes are estimated for nine major tides in a global inversion algorithm that solves the two-dimensional momentum equations on a regular 0.5^\circ grid with a heavily weighted continuity constraint. The influence of 19 minor tides is accounted for by linear admittance interpolation of ocean tidal angular momentum, although the assumption of smooth admittance variations with frequency appears to be a doubtful concept for semi-diurnal mass terms in particular. A validation of the newly derived model based on post-fit corrections to polar motion and universal time (\Delta UT1) from the analysis of Very Long Baseline Interferometry (VLBI) observations shows a variance reduction for semi-diurnal \Delta UT1 residuals that is significant at the 0.05 level with respect to the conventional ERP model. Improvements are also evident for the explicitly modeled K_1, Q_1, and K_2 tides in individual ERP components, but large residuals of more than 15 \upmu as remain at the principal lunar frequencies of O_1 and M_2. We attribute these shortcomings to uncertainties in the inverted relative angular momentum changes and, to a minor extent, to violation of mass conservation in the empirical ocean tide solution. Further dedicated hydrodynamic modeling efforts of these anomalous constituents are required to meet the accuracy standards of modern space geodesy

Low-frequency dynamic ocean response to barometric-pressure loading

Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(11), (2022): 2627-2641, https://doi.org/10.1175/jpo-d-22-0090.1.Changes in dynamic manometric sea level ζm represent mass-related sea level changes associated with ocean circulation and climate. We use twin model experiments to quantify magnitudes and spatiotemporal scales of ζm variability caused by barometric pressure pa loading at long periods (≳1 month) and large scales (≳300km) relevant to Gravity Recovery and Climate Experiment (GRACE) ocean data. Loading by pa drives basin-scale monthly ζm variability with magnitudes as large as a few centimeters. Largest ζm signals occur over abyssal plains, on the shelf, and in marginal seas. Correlation patterns of modeled ζm are determined by continental coasts and H/f contours (H is ocean depth and f is Coriolis parameter). On average, ζm signals forced by pa represent departures of ≲10% and ≲1% from the inverted-barometer effect ζib on monthly and annual periods, respectively. Basic magnitudes, spatial patterns, and spectral behaviors of ζm from the model are consistent with scaling arguments from barotropic potential vorticity conservation. We also compare ζm from the model driven by pa to ζm from GRACE observations. Modeled and observed ζm are significantly correlated across parts of the tropical and extratropical oceans, on shelf and slope regions, and in marginal seas. Ratios of modeled to observed ζm magnitudes are as large as ∼0.2 (largest in the Arctic Ocean) and qualitatively agree with analytical theory for the gain of the transfer function between ζm forced by pa and wind stress. Results demonstrate that pa loading is a secondary but nevertheless important contributor to monthly mass variability from GRACE over the ocean.The authors acknowledge support from the National Aeronautics and Space Administration through the GRACE Follow-On Science Team (Grant 80NSSC20K0728) and the Sea Level Change Team (Grant 80NSSC20K1241). The contribution from I. F. and O. W. represents research carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (Grant 80NM0018D0004)

The Tides They Are A-Changin': A Comprehensive Review of Past and Future Nonastronomical Changes in Tides, Their Driving Mechanisms, and Future Implications:A comprehensive review of past and future non‐astronomical changes in tides, their driving mechanisms and future implications

Scientists and engineers have observed for some time that tidal amplitudes at many locations are shifting considerably due to non-astronomical factors. Here we review comprehensively these important changes in tidal properties, many of which remain poorly understood. Over long geological time-scales, tectonic processes drive variations in basin size, depth, and shape, and hence the resonant properties of ocean basins. On shorter geological time-scales, changes in oceanic tidal properties are dominated by variations in water depth. A growing number of studies have identified widespread, sometimes regionally-coherent, positive and negative trends in tidal constituents and levels during the 19th, 20th and early 21st centuries. Determining the causes is challenging because a tide measured at a coastal gauge integrates the effects of local, regional, and oceanic changes. Here, we highlight six main factors that can cause changes in measured tidal statistics on local scales, and a further eight possible regional/global driving mechanisms. Since only a few studies have combined observations and models, or modelled at a temporal/spatial resolution capable of resolving both ultra-local and large-scale global changes, the individual contributions from local and regional mechanisms remain uncertain. Nonetheless, modelling studies project that sea-level rise and climate change will continue to alter tides over the next several centuries, with regionally coherent modes of change caused by alterations to coastal morphology and ice sheet extent. Hence, a better understanding of the causes and consequences of tidal variations is needed to help assess the implications for coastal defense, risk assessment, and ecological change

The Tides They are A-Changin\u27: A Comprehensive Review of Past and Future Nonastronomical Changes in Tides, Their Driving Mechanisms, and Future Implications

Scientists and engineers have observed for some time that tidal amplitudes at many locations are shifting considerably due to nonastronomical factors. Here we review comprehensively these important changes in tidal properties, many of which remain poorly understood. Over long geological time scales, tectonic processes drive variations in basin size, depth, and shape and hence the resonant properties of ocean basins. On shorter geological time scales, changes in oceanic tidal properties are dominated by variations in water depth. A growing number of studies have identified widespread, sometimes regionally coherent, positive, and negative trends in tidal constituents and levels during the 19th, 20th, and early 21st centuries. Determining the causes is challenging because a tide measured at a coastal gauge integrates the effects of local, regional, and oceanic changes. Here, we highlight six main factors that can cause changes in measured tidal statistics on local scales and a further eight possible regional/global driving mechanisms. Since only a few studies have combined observations and models, or modeled at a temporal/spatial resolution capable of resolving both ultralocal and large-scale global changes, the individual contributions from local and regional mechanisms remain uncertain. Nonetheless, modeling studies project that sea level rise and climate change will continue to alter tides over the next several centuries, with regionally coherent modes of change caused by alterations to coastal morphology and ice sheet extent. Hence, a better understanding of the causes and consequences of tidal variations is needed to help assess the implications for coastal defense, risk assessment, and ecological change

Long-term Earth-Moon evolution with high-level orbit and ocean tide models

Tides and Earth‐Moon system evolution are coupled over geological time. Tidal energy dissipation on Earth slows [Formula: see text] rotation rate, increases obliquity, lunar orbit semi‐major axis and eccentricity, and decreases lunar inclination. Tidal and core‐mantle boundary dissipation within the Moon decrease inclination, eccentricity and semi‐major axis. Here we integrate the Earth‐Moon system backwards for 4.5 Ga with orbital dynamics and explicit ocean tide models that are “high‐level” (i.e., not idealized). To account for uncertain plate tectonic histories, we employ Monte Carlo simulations, with tidal energy dissipation rates (normalized relative to astronomical forcing parameters) randomly selected from ocean tide simulations with modern ocean basin geometry and with 55, 116, and 252 Ma reconstructed basin paleogeometries. The normalized dissipation rates depend upon basin geometry and [Formula: see text] rotation rate. Faster Earth rotation generally yields lower normalized dissipation rates. The Monte Carlo results provide a spread of possible early values for the Earth‐Moon system parameters. Of consequence for ocean circulation and climate, absolute (un‐normalized) ocean tidal energy dissipation rates on the early Earth may have exceeded [Formula: see text] rate due to a closer Moon. Prior to [Formula: see text] , evolution of inclination and eccentricity is dominated by tidal and core‐mantle boundary dissipation within the Moon, which yield high lunar orbit inclinations in the early Earth‐Moon system. A drawback for our results is that the semi‐major axis does not collapse to near‐zero values at 4.5 Ga, as indicated by most lunar formation models. Additional processes, missing from our current efforts, are discussed as topics for future investigation

Atmosphere-induced short period variations of earth rotation

Adresse des Verl.: 1040 Wien, Gußhausstraße 27-29Austrian Science Fund (FWF)15

Modelling of atmospheric influences on Earth rotation on different time scales

Abweichender Titel laut Übersetzung der Verfasserin/des VerfassersZsfassung in engl. SpracheVariationen des atmosphärischen Drehimpulses werden durch großräumige Massenverlagerungen und Veränderungen des Windfelds der Atmosphäre hervorgerufen. Durch Interaktion mit der darunterliegenden Kruste und dem Mantel beeinflussen derartige atmosphärische Vorgänge auch das Rotationsverhalten der Erde - sie sind so für einen Teil der beobachteten Polbewegung und Tageslängenschwankung (LOD) verantwortlich.In der vorliegenden Diplomarbeit wird versucht, den Einfluss der Atmosphäre auf die Erdrotation anhand der sogenannten Drehimpulsfunktionen zu modellieren. Die Drehimpulsfunktionen werden dabei auf Basis der meteorologischen Daten des ECMWF (European Centre for Medium-Range Weather Forecasts) durch Integration über die Dichte und das Geschwindigkeitsfeld der Atmosphäre berechnet. Die Zeitreihen der geodätisch beobachteten Polbewegung und Tageslängenschwankung entstammen dem C04-Datensatz des IERS (International Earth Rotation and Reference Systems Service) bzw. den GPS- und VLBI-Beobachtungen für die Dauer des Beobachtungsprogrammes CONT08. Je nachdem in welchem Periodenbereich der Einfluss der Atmosphäre in der Erdrotation untersucht wird, sind unterschiedliche Modellierungsansätze zu gebrauchen. Für Effekte mit Perioden von wenigen Tagen bis hin zu mehreren Wochen oder länger ist die Übereinstimmung zwischen geodätischen und atmosphärischen Daten sehr gut, und der Vergleich im Zeitbereich auf Ebene der Drehimpulsfunktionen (Differentiationsansatz) oder auf Ebene der Polbewegung (Integrationsansatz) empfehlenswert. Im täglichen bzw. subtäglichen Bereich müssen in den Gleichungen neben dem Chandler Wobble (CW) auch die Effekte der Free Core Nutation (FCN) miteinbezogen werden. Die Kohärenz zwischen Drehimpulsfunktionen und geodätischen Zeitreihen sinkt für hochfrequente Signale jedoch drastisch, sodass sich der Verfasser auf die Abschätzung der Amplituden in den Spektren der atmosphärisch angeregten Erdrotationsparameter (Polbewegung und LOD) beschränkt.Die verwendeten Drehimpulsfunktionen sind nach verschiedenen Varianten berechnet und besitzen je nach zu behandelnder Zeitskala auch unterschiedliche Auflösung (1 d, 6 h oder 1 h). Zusätzlich stehen die Drehimpulsfunktionen des NCEP (National Centers for Environmental Prediction) zur Verfügung. Im Vergleich mit Erdrotationsparametern ergeben sich beim Differentiationsansatz Korrelationskoeffizienten bis zu 0.80 in der äquatorialen Komponente bzw. 0.99 in LOD. Im Fall des Integrationsansatzes beträgt die Standardabweichung zwischen Polbewegung aus C04 und Polbewegung aus Atmosphärendaten bestenfalls 6.3 mas. Die täglichen und subtäglichen atmosphärischen Effekte besitzen grundsätzlich Amplituden, die kleiner als 10 uas (Polbewegung) bzw. 10 us (LOD) sind.Variations in the angular momentum of the atmosphere are caused by large-scale atmospheric mass redistributions as well as changes in the pattern of winds. By interacting with the underlying mantle, those processes give rise to fluctuations in all three components of the Earth's rotation vector. Certain parts of geodetic polar motion and observed changes in length of day (LOD) can always be attributed to variations of atmospheric angular momentum. The overall goal of this paper is to model the influence of the atmosphere on Earth rotation via the so-called atmospheric angular momentum functions, which are calculated as integrals over density and wind velocities. For this purpose, the meteorological data of the ECMWF (European Centre for Medium-Range Weather Forecasts) are used. Time series for observed polar motion and LOD are taken from the C04-record of the IERS (International Earth Rotation and Reference Systems Service) and from GPS- and VLBI-observations that were accumulated during the geodetic observation program CONT08. In order to study the influence of the atmosphere on Earth rotation, one has to apply different models depending on the time scale examined. For periods of a few days or longer, the correspondence between geodetic and atmospheric time series is very good, and the comparison may be effectively carried out in time domain - either on the level of angular momentum functions (differentiation approach) or on the level of polar motion (integration approach). In the diurnal and semi-diurnal frequency band it is necessary to take into account both eigenmodes of the Earth, Chandler Wobble (CW) and Free Core Nutation (FCN). However, there is a significant drop of coherence between atmospheric angular momentum functions and geodetic observations when examining high frequency signals. As a consequence, only the mean amplitudes of short-periodic atmospheric excitation in polar motion and length of day are estimated.Calculation of the atmospheric angular momentum functions is done in a few different ways. Depending on the frequency band that is looked at, time series with various resolutions are used (1 d, 6 h or 1 h).Additionally, the author includes the angular momentum functions derived from NCEP (National Centers for Environmental Prediction) data. When comparing with geodetic data, the differentiation approach yields correlation coefficients up to 0.80 in the equatorial component and 0.99 for LOD. As for the integration approach, the standard deviation between polar motion from C04 and polar motion from atmospheric excitation is 6.3 mas in the best case. In the diurnal and semi-diurnal frequency band the mean amplitudes of atmospheric signals are generally smaller than 10 uas (polar motion) and 10 us (LOD), respectively.13