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  • 1
    Electronic Resource
    Electronic Resource
    Statistical properties of microwave backscattering from laboratory wind-wave surfaces (1992)
    Springer
    Journal of oceanography 48 (1992), S. 139-154 
    Details
    ISSN: 1573-868X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The microwave backscattering from wind-wave surfaces is observed in a windwave tunnel under various conditions of the wind and wind waves, and its statistical features are investigated. The dependence of the backscattered power on the wind speed and the incident angle shows similar features to those predicted by models proposed previously. However, the dependence of the backscattered power on the incident angles also corresponds to the asymmetrical feature of the wind-wave surfaces with respect to the wind direction. The spectral analyses of time series of the backscattered intensity show that the propagating speed of fine structures of the wind-wave surface contributing to the backscattering at large incident angles does not coincide with the phase speed of the freely propagating Braggwaves. Atupwind incidence, the surface structures of wind waves contributing to the backscattering propagates with the dominant waves at their phase speed. This result is inconsistent with the two-scale model in which the Bragg waves are simply superimposed on longer waves, but is consistent with the results of optical observation by Ebuchiet al. (1987). At downwind incidence, the propagating speed is slower than the phase speed of the dominant waves.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02239002
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  • 2
    Electronic Resource
    Electronic Resource
    Comparison of sea surface heights observed by TOPEX altimeter with sea level data at Chichijima (1996)
    Springer
    Journal of oceanography 52 (1996), S. 259-273 
    Details
    ISSN: 1573-868X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The sea surface heights (SSHs) observed by the TOPEX altimeter are compared with tide gauge data at Chichijima in Ogasawara (Bonin) Islands and hydrographic data taken around the islands, in order to quantitatively verify the altimeter observations and oceanic tide corrections by three tide models proposed by Cartwright and Ray (1991), Rayet al. (1994), and Maet al. (1994). First, performance of the new tide models is assessed by comparing tidal variations consisting of diurnal and semi-diurnal constituents with the tide gauge data at Chichijima. The tide model proposed by Rayet al. gives the smallest root-mean-squared (rms) difference of 2.61 cm. Errors in amplitude and phase in each tide model are evaluated by spectral analysis. The TOPEX SSHs corrected by the tide models are compared with sea level data at Chichijima. A long-term variation of a period of about 1 year is found in the residual between the SSHs and the Chichijima sea levels. This variation is also found in the difference between the dynamic height anomalies calculated from hydrographic data around the island and the Chichijima sea levels. By subtracting the long-term variation, the rms difference between the TOPEX SSHs and the Chichijima sea levels is reduced to about 4 cm and the slope of the regression line is improved to unity. The residual shows variations related to aliasing caused by incompleteness of the ocean tide correction with the repeat cycle of the altimeter observation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02235923
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  • 3
    Electronic Resource
    Electronic Resource
    Fine structure of laboratory wind-wave surfaces studied using an optical method (1987)
    Springer
    Boundary layer meteorology 39 (1987), S. 133-151 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The fine structure of laboratory wind-wave surfaces was investigated using an optical method. Several characteristic structures, closely associated with wind speed and the stage of development of the waves, are described. A parallel light, incident on the wind-wave surface, was backscattered by ‘specular facets’ perpendicular to the incident angle. These specular facets, which represented the fine structures, were photographed and quantitatively analyzed by image processing techniques. For wind speeds ranging from 3.6 to 13.6 m s−1, different types of small-scale undulations appeared: a three-dimensional rhombic structure; a train of capillary waves on the forward face with wavelengths gradually decreasing with distance from the crest, and a streaky structure on the backward face in the direction of the wind; and random and wide-spreading irregularities covering the whole wind-wave surface. The spatial scales and temporal variation of the undulations are described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00121871
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  • 4
    Electronic Resource
    Electronic Resource
    Statistical study on the local equilibrium between wind and wind waves by using data from ocean data buoy stations (1992)
    Springer
    Journal of oceanography 48 (1992), S. 77-92 
    Details
    ISSN: 1573-868X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The local equilibrium between the wind and wind waves, which is defined by a range of the coefficient of the 3/2-power law between the non-dimensional significant wave height and period, is statistically investigated by using wind and wave data obtained at four ocean data buoy stations in the seas near Japan. The friction velocity is calculated from the wind speed measured at one height together with the significant wave period by using formulas of the wave dependent drag coefficient proposed by Tobaet al. (1990). The data for small waves or for weak winds indicate that the waves do not satisfy the criterion for the local equilibrium, because they may be affected by changing winds or remotely generated swells. In the seas near Japan, the data which satisfy the local equilibrium are about 6% through a year. Otherwise swells are dominant in most situations. Changing winds also cause deviations from the local equilibrium. The degree of satisfaction of the local equilibrium can be classified by ranges of the significant wave height. As the significant wave height exceeds 4 m, the local equilibrium is more frequently satisfied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02234033
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  • 5
    Electronic Resource
    Electronic Resource
    Growth of Wind Waves with Fetch in the Sea of Japan under Winter Monsoon Investigated Using Data from Satellite Altimeters and Scatterometer (1999)
    Springer
    Journal of oceanography 55 (1999), S. 575-584 
    Details
    ISSN: 1573-868X
    Keywords: Wind wave ; altimeter ; scatterometer ; air-sea interaction ; remote sensing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract By using wind vector fields observed by the NASA Scatterometer (NSCAT) and significant wave heights observed by the TOPEX/POSEIDON and European Remote Sensing Satellite-2 (ERS-2) altimeters, one-dimensional fetch growth of wind waves has been investigated under conditions of strong wind and high waves caused by the East Asian winter monsoon in the Sea of Japan. The evolution of fetch-limited wind waves can be observed by the altimeters along their ground tracks. The fetch is estimated by using vector wind fields observed by NSCAT. The derived growth characteristics of wind waves are compared with empirical relationships between the non-dimensional fetch and significant wave height proposed by previous studies. Good agreement is discernible with Toba's fetch graph formula normalized by the friction velocity, while Wilson's well-known formula normalized by the wind speed at a height of 10 m tends to underestimate the wave height under such severe conditions of high wind and very long fetch. This discrepancy is explained by the wind-speed dependence of the drag coefficient. A simple correction to Wilson's formula for the high wind conditions is proposed and compared with the observed data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007836701387
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  • 6
    Electronic Resource
    Electronic Resource
    Sea-surface roughness length fluctuating in concert with wind and waves (1991)
    Springer
    Journal of oceanography 47 (1991), S. 63-79 
    Details
    ISSN: 1573-868X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract When the nondimensional aerodynamic roughness parameter for the sea surface (gz 0/u * 2,g being the acceleration of gravity,u * the air friction velocity) is plotted as a function of the wave age, the data points in the diagram are distributed mostly in a triangle area between the Charnock formula and the Toba-Koga formula; the nondimensional roughness perameter is not expressed as a unique function of the wave age, but rather there seem to be multiple regimes. In order to investigate the cause of the data point scattering, a reanalysis was made of the 4.5-hour time series of the wind profile and wind-wave statistics which were obtained at an oceanographic tower station under the conditions of a winter monsoon wind having slightly fluctuating speed and steadily growing wind waves. It is concluded that the averaged variation ofz 0 is given by the Toba-Koga formula with a constant of value 0.015. However, as a result of the wind fluctuation on the time scales ranging from several minutes to an hour, data points show a conspicuous fluctuation on the nondimensional roughness parameter-wave age diagram in the direction transverse to the averaged variation. The variation inz 0 directly reflects the degree of over- or under-saturation in the high-frequency range of the wind-wave spectra. Physical interpretation of these variations is also presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02301483
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  • 7
    Electronic Resource
    Electronic Resource
    Evaluation of Vector Winds Observed by NSCAT in the Seas around Japan (2000)
    Springer
    Journal of oceanography 56 (2000), S. 495-505 
    Details
    ISSN: 1573-868X
    Keywords: NSCAT ; scatterometer ; surface wind vectors ; remote sensing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract In order to validate wind vectors derived from the NASA Scatterometer (NSCAT), two NSCAT wind products of different spatial resolutions are compared with observations by buoys and research vessels in the seas around Japan. In general, the NSCAT winds agree well with the wind data from the buoys and vessels. It is shown that the root-mean-square (rms) difference between NSCAT-derived wind speeds and the buoy observations is 1.7 ms−1, which satisfies the mission requirement of accuracy, 2 ms−1. However, the rms difference of wind directions is slightly larger than the mission requirement, 20°. This result does not agree with those of previous studies on validation of the NSCAT-derived wind vectors using buoy observations, and is considered to be due to differences in the buoy observation systems. It is also shown that there are no significant systematic trends of the NSCAT wind speed and direction depending on the wind speed and incidence angle. Comparison with ship winds shows that the NSCAT wind speeds are lower than those observed by the research vessels by about 0.7 ms−1 and this bias is twice as large for data observed by moving ships than by stationary ships. This result suggests that the ship winds may be influenced by errors caused by ship's motion, such as pitching and rolling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1011192725800
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  • 8
    Electronic Resource
    Electronic Resource
    On the wave dependence of sea-surface wind stress (1990)
    Springer
    Journal of oceanography 46 (1990), S. 177-183 
    Details
    ISSN: 1573-868X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Analysis is made of wind and wave data, which were obtained during the passage of Typhoon 8013 at an Ocean Data Buoy Station south of Honshu operated by the Japan Meteorological Agency, in order to investigate the wave dependence of sea-surface roughness parameter in the situation where wind waves are dominant with less significant swells. The data fit better the wave-dependent expression of the wind stress,z 0 σ p/u*=γ, than to Charnock's formula,gz 0/u*2=β, wherez 0 is the roughness length,σ p the angular frequency of the spectral peak of wind waves,u* the friction velocity of air,g the acceleration of gravity,γ andβ are non-dimensional constants. The results are very similar to those of our previous study using data from an oil producing platform in the Bass Strait, Australia, although the type of observation system and the synoptic situation of the winds and wind waves were totally different.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02125578
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  • 9
    Electronic Resource
    Electronic Resource
    Validation of wind speeds and significant wave heights observed by the TOPEX altimeter around Japan (1994)
    Springer
    Journal of oceanography 50 (1994), S. 479-487 
    Details
    ISSN: 1573-868X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The wind speeds and significant wave heights observed by the TOPEX altimeter during the first 30 repeat cycles (for about 10 months) are validated by comparing with the data obtained at Japanese Ocean Data Buoy stations. The values of Kuband σ0 observed by the altimeter show good agreement with those estimated from the buoy wind speed using the modified Chelton-Wentz algorithm. The wind speeds derived from the Ku-band σ0 using the algorithm agree well with the buoy data with an rms difference of 1.99 ms−1. The significant wave heights observed by the altimeter have a systematic bias of 0.3 m.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02234969
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  • 10
    Electronic Resource
    Electronic Resource
    Comparison of surface current variations observed by TOPEX altimeter with TOLEX-ADCP data (1995)
    Springer
    Journal of oceanography 51 (1995), S. 351-362 
    Details
    ISSN: 1573-868X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Variations of surface current velocity derived by the TOPEX altimeter are compared with data from Tokyo-Ogasawara Line Experiment (TOLEX)-Acoustic Doppler Current Profiler (ADCP) monitoring for a period from October 1992 to July 1993. Since the locations of ADCP ship track and TOPEX altimeter ground tracks do not coincide with each other, and the temporal and spatial sampling are also different between the ADCP and altimeter observations, re-sampling, interpolation and smoothing in time and space are needed to the ADCP and altimeter data. First, the interpolated TOPEX sea surface height is compared with sea level data at Chichijima in the Ogasawara Islands. It is found that aliasing caused by the tidal correction error for M2 constituent in the TOPEX data is significant. Therefore, comparison of the TOPEX data with the TOLEX-ADCP data is decided to be made by using cross-track velocity components of the surface current, which are considered to be relatively less affected by the errors in the tidal correction. The cross-track velocity variations derived from the TOPEX sea surface heights agree well with those of the ADCP observations. The altimeterderived velocity deviations associated with transition of the Kuroshio paths coincide with the ADCP data. It is quantitatively confirmed that the TOPEX altimeter is reliable to observe the synoptic variations of surface currents including fluctuations of the Kuroshio axis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02285171
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