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Author |
Anzhou Cao, Zheng Guo, Xiaoyu Qi, Peiliang Li, Hailun He |
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Title |
Seasonal and nodal variations of predominant tidal constituents in the global ocean |
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Year |
2021 |
Publication |
Continental Shelf Research |
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Volume |
217 |
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Pages |
104372 |
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Keywords |
Fitting Modified two-step harmonic analysis Nodal modulation Seasonal variation Tide gauge Tides |
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Abstract |
Tides are one of the basic types of ocean water motions. Previous studies have reported that the M2 constituent exhibits seasonal variations (annual cycles) in some regions. However, based on the newly proposed method of modified two-step harmonic analysis (HA) and its application at 240 global tide gauges, we find that the M2 constituent as well as the S2 and K1 do not have significant seasonal variations at these tide gauges. The seasonal variations of the M2 constituent reported in previous studies are caused by its satellites, the H1 and H2 constituents, which are not resolved in these studies due to the short time window (one month or three months) used in HA. Because the frequency of the H1 (H2) constituent is equal to that of the M2 minus (plus) the frequency of annual cycles, the superposition of the M2, H1 and H2 constituents with constant amplitudes is equivalent to the M2 constituent with seasonally varying amplitudes. Compared with the new method, some adaptations to traditional HA aiming to capture variations in amplitudes and phase lags of constituents have some limitations, because they either neglect some satellites of the major constitutes or introduce spurious fluctuations resulting from an unreasonably large number of independent points. The nodal modulations of predominant constituents are also explored in this study. On the global scale, the nodal modulations of the M2, K1 and O1 constituents agree with the theoretical predictions, except a cold spot region with reduced nodal modulation in the Gulf of Maine and a hot spot region with enhanced nodal modulation in the South China Sea for the M2. Nodal modulation is also found for the S2 constituent (in theory, the S2 has no nodal modulation), which is 0.8% averaged at 164 tide gauges where the S2 is not too weak. |
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0278-4343 |
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8032 |
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Author |
Alakkat S. Unnikrishnan, Andrew Matthews, Médéric Gravelle, Laurent Testut, Thorkild Aarup, Philip L. Woodworth, B. Ajay Kumar |
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Title |
Tide gauges |
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Book |
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Year |
2019 |
Publication |
Beal, lisa m.; vialard, jérôme; roxy, mathew k., (eds.) full report. indoos-2: a roadmap to sustained observations of the indian ocean for 2020-2030. clivar/ioc-goos indian ocean region panel (iorp) |
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31-34 |
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Tide gauge measurements provide data for routine tidal predictions in ports as well as for extreme events such as storm surges and tsunamis. Along with satellite altimeter measurements, tide gauges also provide measurements used for sea-level rise estimates. This is particularly important for impact assessment in low-lying coastlines of south Asia as well as islands such as the Maldives in the Indian Ocean. |
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8033 |
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David Byrne, Jeff Polton, Colin Bell |
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Title |
Creation of a global tide analysis dataset: Application of NEMO and an offline objective analysis scheme |
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2021 |
Publication |
Journal of Operational Oceanography |
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1-14 |
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The accurate prediction of tides is vital for the operation of many industries, early warning of coastal flooding and scientific understanding of ocean processes. In this paper, we describe the creation method of a global dataset of tidal harmonics using NEMO (Nucleus for European Modelling of the Ocean) for the first time and an offline objective analysis scheme. Data are assimilated as part of a post-processing step, reducing the computational resources required. A reduced ensemble of tidal harmonics is generated, where each member is run for a shorter period of time than a central background state. This ensemble is used to estimate a single background covariance state, which is used for analysis. Output is validated using an ensemble of objective analyses. For each ensemble member, random selections of observations are omitted and validation is performed at these locations. Improvements in both Mean Absolute Error (MAE) and correlation coefficients (R2) are seen across all 6 of the largest diurnal and semi-diurnal constituents. MAEs in amplitude and phase are reduced by up to 78% and 89%, respectively, and correlations by as much as 0.14. In addition, the majority of locations (between 70 and 80%) see significant improvement. |
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688 |
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1755-876X |
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1755-876X |
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yes |
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8338 |
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Author |
Pengcheng Wang, Natacha B. Bernier, Keith R. Thompson, Tsubasa Kodaira |
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Title |
Evaluation of a global total water level model in the presence of radiational S2 tide |
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Year |
2021 |
Publication |
Ocean Modelling |
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Volume |
168 |
Issue |
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Pages |
101893 |
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Keywords |
NEMO Radiational and gravitational tide Storm surge Tidal nudging Total water level |
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Abstract |
The development of a computationally efficient scheme for predicting the global distribution of total water level (TWL) is discussed. The ocean model is barotropic, has a horizontal grid spacing of 1/12°, and is based on the NEMO modeling framework. It is forced by the gravitational potential and hourly atmospheric fields for 2008. Hourly time spacing was required to resolve the S2 tide in global air pressure and wind. The predicted tide in water deeper than 400 m was nudged to TPXO8 “observations” of tidal elevation or current using a scheme called tidal nudging (Kodaira et al., 2019). The benefit of nudging horizontal velocity in the momentum equation, compared to sea level in the continuity equation, is discussed. Tidal nudging is shown to improve tidal predictions of sea level at the coast, particularly at the S2 tidal frequency. The predicted radiational S2 tide in sea level forced solely by the S2 tide in global air pressure reaches amplitudes exceeding 80 cm. Decreasing the time spacing of the air pressure forcing from 1 h to 3 h reduces the S2 amplitude in air pressure by a factor of 0.82, consistent with expectations based on Fourier analysis. This highlights the importance of using hourly atmospheric forcing when predicting the global sea level response to atmospheric forcing. The radiational S2 tide in sea level is subject to strong nonlinear interaction with the gravitational tide, leading to a pronounced attenuation of the radiational S2 tide. The attenuation is explained by an increase in effective bottom friction at the S2 frequency due to the presence of the gravitational tide. Four schemes for predicting TWL are evaluated to quantify the impact of tidal nudging and nonlinear interaction of tide and surge. Using TWLs observed by 304 coastal tide gauges, we show it is necessary to include both tidal nudging and nonlinear interaction. Plans for the further development of an operational flood forecast system for the Canadian coast, based on the above model, are discussed. |
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1463-5003 |
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8356 |
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Tranchant Y.-T., M. Cancet, E. Sahuc, S. Millet, F. Lyard, L. Testut, V. Ballu, C. Chupin, G. Dibarboure, N. Picot, O. Laurain, P. Bonnefond. |
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High-resolution coastal modeling in Kerguelen Island for CAL/VAL activities |
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Peer-reviewed symposium |
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Year |
2020 |
Publication |
Ocean Surface Topography Science Team Meeting (OSTST) meeting, 19-23 October 2020, Virtual |
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688 |
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8371 |
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M. Afroosa, B. Rohith, Arya Paul, Fabien Durand, Romain Bourdallé-Badie, P. V. Sreedevi, Olivier de Viron, Valérie Ballu, S. S. C. Shenoi |
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Madden-Julian oscillation winds excite an intraseasonal see-saw of ocean mass that affects Earth’s polar motion |
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Year |
2021 |
Publication |
Communications Earth & Environment |
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2 |
Issue |
1 |
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1-8 |
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Keywords |
Physical oceanography |
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Abstract |
Strong large-scale winds can relay their energy to the ocean bottom and elicit an almost immediate intraseasonal barotropic (depth independent) response in the ocean. The intense winds associated with the Madden-Julian Oscillation over the Maritime Continent generate significant intraseasonal basin-wide barotropic sea level variability in the tropical Indian Ocean. Here we show, using a numerical model and a network of in-situ bottom pressure recorders, that the concerted barotropic response of the Indian and the Pacific Ocean to these winds leads to an intraseasonal see-saw of oceanic mass in the Indo-Pacific basin. This global-scale mass shift is unexpectedly fast, as we show that the mass field of the entire Indo-Pacific basin is dynamically adjusted to Madden-Julian Oscillation in a few days. We find this large-scale ocean see-saw, induced by the Madden-Julian Oscillation, has a detectable influence on the Earth’s polar axis motion, in particular during the strong see-saw of early 2013. |
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2662-4435 |
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yes |
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8387 |
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Petra Zemunik, Jadranka Šepić, Havu Pellikka, Leon Ćatipović, Ivica Vilibić |
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Title |
Minute Sea-Level Analysis (MISELA): a high-frequency sea-level analysis global dataset |
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Year |
2021 |
Publication |
Earth system science data |
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Volume |
13 |
Issue |
8 |
Pages |
4121-4132 |
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Abstract |
Sea-level observations provide information on a variety of processes occurring over different temporal and spatial scales that may contribute to coastal flooding and hazards. However, global research on sea-level extremes is restricted to hourly datasets, which prevent the quantification and analyses of processes occurring at timescales between a few minutes and a few hours. These shorter-period processes, like seiches, meteotsunamis, infragravity and coastal waves, may even dominate in low tidal basins. Therefore, a new global 1 min sea-level dataset – MISELA (Minute Sea-Level Analysis) – has been developed, encompassing quality-checked records of nonseismic sea-level oscillations at tsunami timescales (T<2 h) obtained from 331 tide-gauge sites (https://doi.org/10.14284/456, Zemunik et al., 2021b). This paper describes data quality control procedures applied to the MISELA dataset, world and regional coverage of tide-gauge sites, and lengths of time series. The dataset is appropriate for global, regional or local research of atmospherically induced high-frequency sea-level oscillations, which should be included in the overall sea-level extremes assessments. |
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1866-3508 |
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yes |
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8392 |
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Author |
Yushiro Fujii, Kenji Satake, Shingo Watada, Tung-Cheng Ho |
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Title |
Re-examination of Slip Distribution of the 2004 Sumatra–Andaman Earthquake (Mw 9.2) by the Inversion of Tsunami Data Using Green’s Functions Corrected for Compressible Seawater Over the Elastic Earth |
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2021 |
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Pure and Applied Geophysics |
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178 |
Issue |
12 |
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4777-4796 |
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2004 Sumatra–Andaman earthquake far-field tsunami waveform phase-corrected Green’s function slip distribution tsunami data inversion |
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We re-examined the slip distribution on faults of the 2004 Sumatra–Andaman (M 9.1 according to USGS) earthquake by the inversion of tsunami data with phase-corrected Green’s functions applied to linear long waves. The correction accounts for the effects of compressibility of seawater, elasticity of solid earth, and gravitational potential variation associated with the motion of mass to reproduce the delayed arrivals and the reversed phase of the first tsunami waves. We used sea surface height (SSH) data from satellite altimetry (SA) measurements along five tracks, and the tsunami waveforms recorded at tide gauges (TGs) and ocean bottom pressure gauges (OBPGs) in and around the Indian Ocean. The inversion results for both data sets for different rupture velocities (Vr) show that the reproducibility of the spatiotemporal SSHs and tsunami waveforms is improved by the phase corrections, although the effects are not so significant within the Indian Ocean. The best slip distribution model from joint inversion of SA, TG and OBPG data with Vr of 1.3 km/s shows the largest slips of 16–25 m off Sumatra Island, large slips of 2–11 m off the Nicobar Islands, and moderate slips of 2–6 m in the Andaman Islands. The inversion results reproduce the far-field tsunami waveforms well at distant stations even more than 13,000–25,000 km from the epicenter. The total source length is about 1400 km and the seismic moment is Mw 9.2, longer and larger than that of our previous estimates based on TG records. |
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1420-9136 |
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yes |
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8411 |
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Téchiné P., L. Testut, M. Calzas, A. Guillot, C. Drezen, C. Brachet, L. Fichen, T. Donal, V. Kérébel. |
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Title |
Réseau d’Observation Subantarctique et Antarctique du niveau de la MEr |
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Peer-reviewed symposium |
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2022 |
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18émes journées scientifiques du CNFRA, 11-12 mai 2022, Toulouse, France |
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8478 |
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Author |
Téchiné P., Testut L. |
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Présentation du SNO SONEL-ROSAME |
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2018 |
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Réunion de présentation des SNO dans le cadre de la visite au LEGOS du directeur-adjoint scientifique océan-atmosphère de l’INSU, 6 février 2018 |
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8490 |
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