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11.
On recording sea surface elevation with accelerometer buoys: lessons from ITOP (2010) 总被引：2，自引：2，他引：0
Measurements of significant wave height are made routinely throughout the world’s oceans, but a record of the sea surface elevation (η) is rarely kept. This is mostly due to memory limitations on data, but also, it is thought that buoy measurements of sea surface elevation are not as accurate as wave gauges mounted on stationary platforms. Accurate records of η which contain rogue waves (defined here as an individual wave at least twice the significant wave height) are of great interest to scientists and engineers. Using field data, procedures for tilt correcting and double integrating accelerometer data to produce a consistent record of η are given in this study. The data in this study are from experimental buoys deployed in the recent Impact of Typhoons on the Ocean in the Pacific (ITOP) field experiment which occurred in 2010. The statistics from the ITOP buoys is under that predicted by Rayleigh theory, but matches the distributions of Boccotti and others (Tayfun and Fedele) (Ocean Eng 34:1631-1649, 2007). Rogue waves were recorded throughout the experiment under various sea state conditions. Recommendations, as a result of lessons learned during ITOP, are made for the routine recording of η which may not add significantly to the existing data burden. The hope is that we might one day collect a worldwide database of rogue waves from the existing buoy network, which would progress our understanding of the rogue wave phenomenon and make work at sea safer. 相似文献
12.
Reishi Takashima Hiroshi Nishi Toshiro Yamanaka Keiichi Hayashi Amane Waseda Akiko Obuse Takashige Tomosugi Naoki Deguchi Sunao Mochizuki 《Earth and Planetary Science Letters》2010,289(3-4):570-582
Making Upper Cretaceous biostratigraphic correlations between the Northwest Pacific and Tethyan–Atlantic sections have been difficult because of rare frequencies of age-diagnostic macro- and microfossils in the sequences in the Northwest Pacific region. In order to correlate these sections precisely, an integrated planktic foraminiferal and bulk wood carbon-isotope stratigraphy from the upper Cenomanian to the lower Campanian succession (the middle–upper part of the Yezo Group) of Hokkaido, northern Japan is established with an average resolution of 50 k.y. The δ13C curves from bulk wood of the Yezo Group and from bulk carbonate of English Chalk show remarkably similar patterns of isotopic fluctuation, allowing the correlation of 22 carbon isotopic events between these sections. This high-resolution correlation greatly improves the previous micro- and macrofossil biostratigraphic schemes in the Northwest Pacific region, and reveals that global events, such as the oxygen depletion at the OAE 2 horizon, the constant decrease in pCO2 during the Late Cretaceous, and the eustatic sea-level falls in the late middle Turonian, Santonian/Campanian Boundary and early Campanian, are recorded in the Upper Cretaceous sequence of the Northwest Pacific. 相似文献
13.
Benaissa Rhouta Ezzouhra Zatile Lahcen Bouna Omar Lakbita Francis Maury Lahcen Daoudi Marie Christine Lafont M’Barek Amjoud François Senocq Amane Jada Ahmed Aït Aghzzaf 《Physics and Chemistry of Minerals》2013,40(5):411-424
This study is devoted to the physicochemical and mineralogical characterizations of palygorskite from Marrakech High Atlas, Morocco. The raw clay and its Na+-saturated <2 μm fraction were characterized using chemical, structural, and thermal analytical techniques. Measurements of specific surface area and porous volume are reported. The clay fraction was found to be made up of 95 % of palygorskite and 5 % of sepiolite. An original feature of this palygorskite is its deficiency in zeolitic H2O. The half-cell structural formula of its dehydrated form was determined on the basis of 21 oxygens to be (Si7.92Al0.08)(Mg2.15Al1.4Fe0.4Ti0.05 $ \square_{1} $ )(Ca0.03Na0.08K0.04)O21, while the hydrated form could be formulated as (Si7.97Al0.03)(Mg2.17Al1.46Fe0.40Ti0.05)(Ca0.03Na0.07K0,03)O20.18(OH)1.94(OH2)3.88·2.43 H2O. These formulas show that the (Al3++Fe3+)/Mg2+ ratio is around 0.84, revealing a pronounced dioctahedral character. Further, inside its octahedral sheet, it was determined that the inner M1 sites are occupied by vacancies, whereas the M2 sites are shared between 90 % of trivalent cations (78 % for Al3+ and 22 % for Fe3+), 7.5 % of Mg2+, and 2.5 % of Ti4+, all of them linked to 1.94 of structural hydroxyls. The two remaining Mg2+ by half-cell occupy edge M3 sites and are coordinated to 3.88 molecules of OH2. Channels of this palygorskite are deficient in zeolitic H2O since they contain only 2.43 H2O molecules. A correlation was found between these results and the observation of very intense and well-resolved FTIR bands arising from dioctahedral domains (mainly Al2OH, Fe2OH, and AlFeOH) along with very small responses from a trioctahedral domain (Mg3OH). Accordingly, a schematic representation of the composition of the octahedral sheet was proposed. The cation exchange capacity, specific surface area, and total pore volume were also assessed to be ca. 21.2 meq/100 g, 116 m2/g, and 0.458 cm3/g, respectively. 相似文献
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15.
Abstract. Geochemical studies for gas hydrate, gas and organic matter collected from gas hydrate research wells drilled at the landward side of the eastern Nankai Trough, offshore Tokai, Japan, are reported. Organic matter in the 2355 m marine sediments drilled to Eocene is mainly composed of Type III kerogen with both marine and terrigenous organic input. The gas hydrate-bearing shallow sediments are immature for hydrocarbon generation, whereas the sediments below 2100 mbsf are thermally mature. The origins of gases change from microbial to thermogenic at around 1500 mbsf.
Carbon isotope compositions of CH4 and CO2 , and hydrocarbon compositions consistently suggest that the CH4 in the gas hydrate-bearing sediments is generated by microbial reduction of CO2 . The δ13 C depth-profiles of CH4 and CO2 suggest that the microbial methanogenesis is less active in the Nankai Trough sediments compared with other gas hydrate-bearing sediments where solid gas hydrate samples of microbial origin were recovered. Since in situ generative-potential of microbial methane in the Nankai Trough sediments is interpreted to be low due to the low total organic carbon content (0.5 % on the average) in the gas hydrate-bearing shallow sediments, upward migration of microbial methane and selective accumulation into permeable sands should be necessary for the high concentration of gas hydrate in discrete sand layers. 相似文献
Carbon isotope compositions of CH
16.
Abstract Six oil samples collected from the Sagara oil field, Shizuoka Prefecture, were geochemically analyzed. Unlike the Niigata oils, the Sagara oils: (i) are low-sulphur light oils dominated by gasoline and kerosene fractions; (ii) have low values of environment index in light hydrocarbon compositions; (iii) have high Pr/ n -C17 and low Ph/ n -C18 ratios and high oleanane/hopane ratios; (iv) have high relative abundance of C29 and low relative abundance of C28 regular steranes; and (v) have 'light' stable carbon isotope compositions. These characteristics show that the source rocks of the Sagara oils contain mainly marine organic matter, but with more input of terrigenous organic matter deposited under more oxic conditions compared to those of the Niigata oils. The light carbon isotope compositions and the low relative abundance of C28 regular steranes of the Sagara oils suggest that their source rock is not Miocene, but probably Paleogene in age. The Sagara oils probably migrated along faults from deeper parts of the basin. 相似文献
17.
Takuji Waseda Leland Jameson Humio Mitsudera Max Yaremchuk 《Journal of Oceanography》2003,59(2):187-200
Wavelet Analysis provides a new orthogonal basis set which is localized in both physical space and Fourier transform space.
Empirical Orthogonal Functions (EOFs), on the other hand, provide a global representation of data sets. Here we investigate
the various ways in which one can combine these basis sets for optimal representation of data. EOFs represent the global large
scale information and wavelet analysis are used to supplement this large scale information with local fine scale information.
Here we begin to explore the application of these two basis sets for outputs from an Ocean General Circulation Model and we
explore various applications, including data assimilation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
18.
The Tsugaru Strait, which connects the Sea of Japan with the Pacific Ocean, is characterized by the eastward Tsugaru Warm Current (TWC) and oscillating tidal currents of similar magnitude. A 15-day current observation was conducted in one of the two narrow channels in the strait, at the northwest tip of the Shimokita Peninsula. The observation revealed that the spectral energy of the semidiurnal current exceeds that of the diurnal current, contrary to the conventional view. The Tsugaru Strait regional model was developed to study the mechanism of this spectral energy reversal (140–141.5° E, 40.4–42.6° N, 500?m grid resolution). At the eastern and western open boundaries, the model was driven by the constant Tsugaru warm current and tidal elevation, which was adjusted by comparing the model with tidal gauge observations within the channel. The relative magnitude of the spectral energies differed from that of the observation when the model was driven by tide only. However, the spectral energy levels were reversed when the model was driven by both tide and current. The nonlinear interaction of periodic tidal currents and the steady TWC was explained by the vorticity equation, which describes the production and advection of residual currents from tidal currents. According to the model results, flow separation and advection of vorticity by the TWC was the most prominent factor in this phenomenon. Because of the strong nonlinearities, flow separation around the headland occurred during the tidal period with dominant current magnitude and furnished the main difference between the diurnal and semidiurnal interactions. These phenomena were enhanced by the complex topography, and demonstrate the importance of scale interaction, especially when developing high-resolution regional models. 相似文献
19.
The development of ocean waves under explosive cyclones (ECs) is investigated in the Northwestern Pacific Ocean using a hindcast wave simulation around Japan during the period 1994 through 2014. A composite analysis of the ocean wave fields under ECs is used to investigate how the spatial patterns of the spectral wave parameters develop over time. Using dual criteria of a drop in sea level pressure below 980 hPa at the center of a cyclone and a decrease of at least 12 hPa over a 12-h period, ECs are identified in atmospheric reanalysis data. Two areas under an EC were identified with narrow directional spectra: the cold side of a warm front and the right-hand side of an EC (relative to the propagating direction). Because ECs are associated with atmospheric fronts, ocean waves develop very differently under ECs than they do under tropical cyclones. Moreover, ECs evolve very rapidly such that the development of the ocean wave field lags behind the peak wind speed by hours. In a case study of an EC that occurred in January 2013, the wave spectrum indicates that a warm front played a critical role in generating distinct ocean wave systems in the warm and cold zones along the warm front. Both the warm and cold zones have narrow directional and frequency spectra. In contrast, the ocean wave field in the third quadrant (rear left area relative to the propagation direction) of the EC is composed of swell and wind sea systems propagating in different directions. 相似文献
20.
Takehiko Nose Adrean Webb Takuji Waseda Jun Inoue Kazutoshi Sato 《Ocean Dynamics》2018,68(10):1383-1402
A predictability study on wave forecast of the Arctic Ocean is necessary to help identify hazardous areas and ensure sustainable shipping along the trans-Arctic routes. To assist with validation of the Arctic Ocean wave model, two drifting wave buoys were deployed off Point Barrow, Alaska for two months in September 2016. Both buoys measured significant wave heights exceeding 4 m during two different storm events on 19 September and 22 October. The NOAA-WAVEWATCH III? model with 16-km resolution was forced using wind and sea ice reanalysis data and obtained general agreement with the observation. The September storm was reproduced well; however, model accuracy deteriorated in October with a negative wave height bias of around 1 m during the October storm. Utilising reanalysis data, including the most up-to-date ERA5, this study investigated the cause: grid resolution, wind and ice forcing, and in situ sea level pressure observations assimilated for reanalysis. The analysis has found that there is a 20% reduction of in situ SLP observations in the area of interest, presumably due to fewer ships and deployment options during the sea ice advance period. The 63-member atmospheric ensemble reanalysis, ALERA2, has shown that this led to a larger ensemble spread in the October monthly mean wind field compared to September. Since atmospheric physics is complex during sea ice advance, it is speculated that the elevated uncertainty of synoptic-scale wind caused the negative wave model bias. This has implications for wave hindcasts and forecasts in the Arctic Ocean. 相似文献