首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 625 毫秒
1.
The relationship between the RMS amplitudes of the wind wave spectral components and the wind speed has been studied at ten frequencies in the band of 0.65–23 Hz. To measure the parameters of the high-frequenci waves, a resistance elevation wave gauge was operated, which was deployed in the Black See on an oceanographic platform near Katsively. The correlation between the wave amplitudes and the wind velocity at high frequencies of 5–23 Hz, corresponding to gravitation-capillary ripples, was found to reach a value of 0.8. At lower frequencies of 0.65–4.3 Hz, corresponding to short gravity waves, it dropped to 0.5–0.7. The response of spectral components to the wind speed variations in the gravity-capillary range is higher than in the range of short gravity waves. The results obtained differ from Phillips' idea about a saturated range for the frequency form of the spectrum of high-frequency gravity waves, since a linear dependence of the spectral amplitudes on the wind speed is established at a wind of force 1–8.Translated by Mikhail M. Trufanov.  相似文献   

2.
The variability of the sea surface wind and wind waves in the coastal area of the Eastern Tsushima Strait was investigated based on the hourly data from 1990 to 1997 obtained at a station 2 km off Tsuyazaki, Fukuoka. The annual mean wind speed was 4.84 m s−1, with strong northwesterly monsoon in winter and weak southwesterly wind in summer. Significant wave heights and wave periods showed similar sinusoidal seasonal cycles around their annual means of 0.608 m and 4.77 s, respectively. The seasonal variability relative to the annual mean is maximum for wave heights, medium for wind speeds, and minimum for wave periods. Significant wave heights off Tsuyazaki turned out to be bounded by a criterion, which is proportional to the square of the significant wave period corresponding to a constant steepness, irrespective of the season or the wind speed. For terms shorter than a month, the significant wave height and the wave period were found to have the same spectral form as the inshore wind velocity: white for frequencies less than 0.2 day−1 and proportional to the frequency to the −5/3 power for higher frequencies, where the latter corresponds to the inertial subrange of turbulence. The spectral levels of wave heights and wave periods in that inertial range were also correlated with those of the inshore wind velocity, though the scatter was large. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

3.
The structure of the turbulent boundary layer underneath laboratory wind waves was studied by using a combination of a high-sensitivity thermometer array with a two-component sonic flowmeter. The temperature fluctuations are used to detect movements of water parcels, with temperature as a passive quantity. The turbulence energy was dominant in the frequency range (0.01 0.1 Hz), which was much smaller than the wind-wave frequency (2 5 Hz), and in which the turbulence was anisotropic. There was a frequency range (0.2 2 Hz for velocity, 0.2 5 Hz for temperature fluctuation) where the turbulence was isotropic and had a –5/3 slope in the energy spectrum. These points are the same as those in previous works. However, by analyses of the time series by using a variable-interval time-averaging technique (VITA), it has been found that conspicuous events in this main turbulence energy band are the downward bursting from the vicinity of the water surface. Thus the structure of the water layer underneath the wind waves has characters which are similar to the familiar turbulent boundary layer over a rough solid wall, as already conceived. It has been found that, at the same time, the turbulence energy can be related to quantities of the wind waves (the root mean squared water level fluctuation and the wave peak frequency), for different wind and wave conditions. That is, the turbulence underneath the wind waves develops under a close coupling with the wind waves.  相似文献   

4.
A submarine-launched wave measuring buoy   总被引：1，自引：0，他引：1  
A wave buoy, the Submarine Deployed Sea State Sensor (SUDSS), was developed to directly measure surface waves from a submerged moving submarine. The SUDSS is adapted from the Submarine Launched Expendable Bathythermograph (SSXBT) by replacing its temperature probe with a vertical sensing accelerometer. The SUDSS, launched from the aft signal ejector, utilizes the SSXBT cylinder, its lifting body, and filament wire spool-out mechanisms. Upon surfacing it oscillates vertically in phase with waves of frequencies below 0.5 Hz producing a voltage signal that is conducted via the filament wire back to the submarine and processed to produce a 10–12 minute wave record. On-board data analysis determines spectra, sea state, and the partial variance of spectral energy which between 0.2–0.5 Hz estimates the local wind speed.An accelerometer calibrator for wave frequencies was assembled consisting of a computer-controlled motor-driven swing arm which rotates an accelerometer as a simple harmonic oscillator; different rotation rates providing a variety of frequencies. Absolute accelerations are determined from the arm radius and its angular velocity. Wilcoxen accelerometers were chosen, providing a linear output of 1 v/g0 (sensitivity) for simulated waves from 0.09–0.25 Hz (4–11 s periods).The SUDSS fitted with a buoyant tether signal cable, can be deployed from a surface ship for rapid wave/sea state measurements.  相似文献   

5.
When considering physical mechanisms for decadal-timescale climate variability in the North Pacific, it is useful to describe in detail the expected response of the ocean to the chaotic atmospheric forcing. The expected response to this white-noise forcing includes strongly enhanced power in the decadal frequency band relative to higher frequencies, pronounced changes in basin-wide climate that resemble regime shifts, preferred patterns of spatial variability, and a depth-dependent profile that includes variability with a standard deviation of 0.2–0.4°C over the top 50–100 m. Weak spectral peaks are also possible, given ocean dynamics. Detecting coupled ocean–atmosphere modes of variability in the real climate system is difficult against the spectral and spatial structure of this ‘null-hypothesis’ of how the ocean and atmosphere interact, especially given the impossibility of experimentally decoupling the ocean from the atmosphere. Turning to coupled ocean–atmosphere models to address this question, a method for identifying coupled modes by using models of increasing physical complexity is illustrated. It is found that a coupled ocean–atmosphere mode accounts for enhanced variability with a time scale of 20 years/cycle in the Kuroshio extension region of the model's North Pacific. The observed Pacific Decadal Oscillation (PDO) has many similarities to the expected noise-forced response and few similarities to the model's coupled ocean–atmosphere variability. However, model deficiencies and some analyses of observations by other workers indicate that the possibility that part of the PDO arises from a coupled ocean–atmosphere mode cannot be ruled out.  相似文献   

6.
The results of hourly measurements of sea roughness and hydrometeorological parameters, which were automatically taken from special buoys over a long period of time, were used. These buoys were located in the open regions of both the Atlantic and Pacific oceans in different climatic zones; the mean water-surface temperature around the buoys varies from 1–3°C to 26–28°C. In addition to measurement results, the tables contain data on the spectral density of sea roughness for a wide range of frequencies. An analysis of these data, which was made for a short-wave region of the wind-wave spectrum, for the first time revealed a noticeable watertemperature dependence of the spectral density of wind waves within the frequency range 0.30–0.40 Hz, which corresponds to wave lengths of 9-4 m. The presence of such dependence is explained by a rapid temperature change in kinematic sea-water viscosity. Earlier, we indicated the temperature dependence of only very short spectral components that relate to a centimetric wavelength range. The statistical significance of the watertemperature effect on the spectral density of waves of the indicated frequency is supported by the results of a variance analysis. Temperature variations in the parameter of sea-surface roughness, which is determined, first of all, by the energy of the spectral shortwave region, are estimated. Altimetry is the basic method which is used in remotely determining the velocity of near-water wind. This method allows one to obtain records of deviations of the sea surface from the geoid surface and to calculate (on the basis of these records) the spectral density of wave components of almost any frequency. It is known that the wave-spectrum components in the region of low frequencies are almost always affected by ripple. Consequently, the energy of these components is determined not only by wind forcing, and only the components in the range of frequencies exceeding approximately 0.3 Hz are purely windy. Therefore, using the results of sea-surface altimetry in order to determine the velocity of near-water wind, one should use the spectral densities of wave components in this frequency region. The water-temperature dependence of the spectral density of short wind waves is manifested only in a certain frequency interval, which supports this recommendation.  相似文献   

7.
Estimation of the leeway drift of small craft   总被引：1，自引：0，他引：1  
Small craft (<6·4 m) leeway is determined as a function of the wind speed in the range of 5–20 knots (3·6–10·3 m/sec). Leeway is calculated relative to the surface current by measurement of the separation distance of the small craft from a dyed patch of surface water at sea, using time-sequenced aerial photography. Leeway increases linearly with wind speed for small craft equipped with or without a sea anchor in the wind range studied. Leeway for small craft without sea anchor can be calculated from the equation UL = 0.07 UW + 0.04 where UW is the wind speed at 2 m elevation. Leeway for small craft drifted off the be calculated from the equation ULD = 0·05 UW − 0·12. The small craft drifted off the downwind direction in about 80% of the experiments. The drift angle is variable and difficult to predict.  相似文献   

8.
The high frequency part (10 Hz50 Hz) of the one-dimensional wave spectrum was measured in a wind-wave channel under accurately controlled conditions. The results are compared with the spectral forms for the capillary range that have been proposed recently byPierson andStacy (1973) andToba (1973). In a general sense, fairly good agreement is found between the present results and those ofPierson andStacy (1973) and ofToba (1973). The spectrum in the capillary range is clearly wind speed dependent, and the spectral density in that range increases with increasing wind speed.However, closer examination shows systematic deviations of the present results from those previously proposed, particularly for high speed winds.  相似文献   

9.
基于浮标实测数据的WindSat海洋反演产品精度分析   总被引：1，自引：1，他引：0  
To evaluate the ocean surface wind vector and the sea surface temperature obtained from Wind Sat, we compare these quantities over the time period from January 2004 to December 2013 with moored buoy measurements. The mean bias between the Wind Sat wind speed and the buoy wind speed is low for the low frequency wind speed product(WSPD_LF), ranging from –0.07 to 0.08 m/s in different selected areas. The overall RMS error is 0.98 m/s for WSPD_LF, ranging from 0.82 to 1.16 m/s in different selected regions. The wind speed retrieval result in the tropical Ocean is better than that of the coastal and offshore waters of the United States. In addition, the wind speed retrieval accuracy of WSPD_LF is better than that of the medium frequency wind speed product. The crosstalk analysis indicates that the Wind Sat wind speed retrieval contains some cross influences from the other geophysical parameters, such as sea surface temperature, water vapor and cloud liquid water. The mean bias between the Wind Sat wind direction and the buoy wind direction ranges from –0.46° to 1.19° in different selected regions. The overall RMS error is 19.59° when the wind speed is greater than 6 m/s. Measurements of the tropical ocean region have a better accuracy than those of the US west and east coasts. Very good agreement is obtained between sea surface temperatures of Wind Sat and buoy measurements in the tropical Pacific Ocean; the overall RMS error is only 0.36°C, and the retrieval accuracy of the low latitudes is better than that of the middle and high latitudes.  相似文献   

10.
Seasonal and interannual variations of the mixed layer properties in the Antarctic Zone (AZ) south of Tasmania are described using 7 WOCE/SR3 CTD sections and 8 years of summertime SURVOSTRAL XBT and thermosalinograph measurements between Tasmania and Antarctica. The AZ, which extends from the Polar Front (PF) to the Southern Antarctic Circumpolar Current Front (SACCF), is characterized by a 150 m deep layer of cold Winter Water (WW) overlayed in summer by warmer, fresher water mass known as Antarctic Surface Water (AASW). South of Tasmania, two branches of the PF divide the AZ into northern and southern zones with distinct water properties and variability. In the northern AZ (between the northern and southern branches of the PF), the mixed layer depth (MLD) is fairly constant in latitude, being 150 m deep in winter and around 40–60 m in summer. In the southern AZ, the winter MLD decreases from 150 m at the S-PF to 80 m at the SACCF and from 60 to 35 m in summer. Shallower mixed layers in the AZ-S are due to the decrease in the wind speed and stronger upwelling near the Antarctic Divergence. The WW MLD oscillates by ±15 m around its mean value and modest interannual changes are driven by winter wind stress anomalies.The mixed layer is on annual average 1.7 °C warmer, 0.06 fresher and 0.2 kg m−3 lighter in the northern AZ than in the southern AZ. The Levitus (1998) climatology is in agreement with the observed mean summer mixed layer temperature and salinity along the SURVOSTRAL line but underestimates the MLD by 10–20 m. The winter MLD in the climatology is also closed to that observed, but is 0.15 saltier than the observations along the AZ-N of the SR3 line. MLD, temperature and density show a strong seasonal cycle through the AZ while the mixed layer salinity is nearly constant throughout the year. During winter, the AZ MLD is associated with a halocline while during summer it coincides with a thermocline.Interannual variability of the AZ summer mixed layer is partly influenced by large scale processes such as the circumpolar wave which produces a warm anomaly during the summer 1996–1997, and partly by local mechanisms such as the retroflection of the S-PF which introduces cold water across the AZ-N.  相似文献   

11.
Surface winds from the UK Meteorological Office mesoscale (12 km grid) atmospheric model have been used to define the wind at a location in Liverpool Bay during 1997–2001. Winds from the SW (centred on 240°) with a speed of about 10 m/s (20 knots) were the most frequent, although weaker winds from the SE were also common. The wind spectra were red in character and showed no evidence for a peak at the synoptic (2–5 day) time scale; however, a zero-up-crossing analysis suggested a dominant periodicity at 3.1 days, and at this time scale the winds were spatially coherent over a distance of 300 km. A wind direction transition matrix was derived to quantify the probability with which the wind changed between two specified directions. This information was then used with an estimate of the mean duration of a wind event to compute a stochastic wind time series that contained a similar energy level, periodicity, and direction variability to the archived wind data. The archived and stochastic winds were then used in 1000 oil spill contingency simulations during which estimates of the mean and minimum times taken for oil to reach the coastline, and the percentage of the oil impacting selected sites were computed. The stochastic winds provided more realistic results, when compared against those derived using the wind archive, than those obtained using a wind rose representation of the winds. The derivation and use of a stochastic wind time series has application to a range of modelling studies.  相似文献   

12.
The surface waves in the Baltic Sea are hindcast with the spectral wave model HYPAS during a 12-month period. The model results show a strong temporal and spatial variation in the wave field due to the physical dimensions of the different basins and the predominant wind field. The highest waves in the area are found in the outer part of Skagerrak, as well as in the central and southern parts of the Baltic Proper. To get significant waves above 6 m high, strong winds (15–20 m/s) must have been blowing for 6 to 24 h from a favourable direction over a deep area.  相似文献   

13.
The BIO Mark 8 thrust anemometer measures the drag of the wind on a perforated table tennis ball mounted on a vertical beam. The tri-axial displacement of the beam is sensed by eddy current proximity sensors. This anemometer has a flat frequency response from 0 to 10 Hz and can measure wind from 0 to 28 m s−1 at temperature from − 19 to + 28°C. It is designed for remote operation for extended periods of time such as on stable towers at sea.  相似文献   

14.
3种海面风场资料在台湾海峡的比较和评估   总被引：7，自引：3，他引：4  
本文对3种海面风场资料(CCMP、NCEP、ERA)在台湾海峡风场的平面分布和时间变化特征进行了相互比较,并应用2011年浮标观测的风速和风向资料分别对3种风场的误差进行了分析及评估。主要结论如下:(1)3种资料风场的平面分布、季节变化和年际变化特征基本一致,差异主要表现在冬季NCEP资料在海峡中部和南部的风速相对CCMP和ERA资料较大;(2)CCMP资料的风速偏差、风速均方根误差和风向均方根误差分别为-0.62m/s、1.67m/s和31°,NCEP分别为0.15m/s、1.64m/s和31°,ERA分别为-1.36m/s、2.4m/s和33°;NCEP资料的风速整体略偏大、CCMP略偏小、ERA偏小明显,CCMP和NCEP资料比ERA资料更接近观测;(3)在西南季风影响期以及风速较小时(风速不大于10m/s)CCMP资料的风速可信度较高、NCEP资料的风速偏大;在东北季风影响期以及风速较大时(大于10m/s)NCEP资料的风速可信度较高、CCMP资料的风速偏小;(4)3种资料的风向误差接近,均在低风速时(风速小于5m/s)误差较大。本文的结论可以为台湾海峡的海洋和大气科学研究选择合适的海面风场资料提供借鉴和参考。  相似文献   

15.
The ocean bottom seismograph (OBS) of the Institut für Geophysik, Hamburg (IfG) is designed for refraction seismic experiments and for recording microseismic noise. Hydrophone signals are recorded directly on a casette tape recorder with a band width of 3–60 Hz. Signals from three component 1 Hz seismometers are recorded on a 2nd casette tape recorder in FM for a frequency range of 0.1–1 Hz. A telemetering buoy at the surface is connected with the OBS by a polypropylene rope.  相似文献   

16.
ROMS with horizontal grid spacing of 3.5 km for the region off Central California was compared to RAFOS float observations and satellite altimetry on meso/submesoscales. The approach introduced and used two new metrics for model-data comparison, as well as suggested how to calculate these metrics for different spatio-temporal scales. The first metric consisted of the first two moments of exit time and was used to compare ROMS against RAFOS float observations at mid-depths (between 300 m and 350 m). Exit time is the time a float launched at a point takes to leave a domain for the first time. The second metric was spectral entropy and was used to estimate how well ROMS reproduced variability of the sea surface height (SSH) anomaly field extracted from an AVISO data set (1992–2007) for specified temporal and spatial scales. Calculations showed that ROMS reproduced the mid-depth mesoscale/submesoscale currents next to the coast in a very accurate manner (low-order exit time statistics of floats were reproduced by ROMS with an accuracy better than 95%); but ROMS overestimated the speed of westward drift of floats by as much as 20–30% at distances greater than 350 km from the coastline. ROMS predicted the variability of the mesoscale (100–400 km) SSH anomaly field for temporal scales of 1–12 months with a reasonable accuracy. A wavelet transform modulus maxima technique applied to the spectral entropy of SSH anomaly also demonstrated good agreement between ROMS and satellite altimetry for mesoscales characterized by singular exponents and multi-fractal spectra for 1–12 month time scales.  相似文献   

17.
This paper considers the results of the numerical simulation of the steady currents and waves field structures in the Vistula Lagoon under constant wind forcing. The currents?? structure is essentially 3-dimensional. The direction of the near-shore drift is determined by the wind and shore orientation, but the currents involve two layers in the deeper part of the basin: the upper layer downwind current and the upwind compensative current in the underlying layer. The wind waves depend upon the wind speed, fetch, and depth until the wind speed is less than 6?C8 m/s. As the wind increases, the fetch??s dependence disappears. The wind height depends only on the wind??s magnitude, and, under stormy conditions (when the wind??s speed exceeds 15 m/s), the waves are limited by the water depth alone.  相似文献   

18.
A long term simulation of the barotropic circulation in the Río de la Plata estuary was performed with the aim of identifying the characteristic patterns of sea surface height (SSH) variability from synoptic to inter-annual time scales and their forcing mechanisms. Hamburg Shelf Ocean Model (HamSOM), forced by tides, monthly mean runoffs and 4-daily 10 m winds and surface atmospheric pressure from the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis was run. The solution was analyzed for the period 1965–2004. Inter-annual variability accounts for almost 10% of the variance. The first EOF mode of SSH variability on this time scale is associated with a mean anomaly of approximately 0.25 m at the upper estuary forced by both runoff and winds, which seems to be strongly associated with the ENSO cycles. Other two modes, with periodicities around 2.5 and 10 years were also found. Even though they are linked to weaker SSH anomalies, they are consistent with inter-annual modes of wind variability reported by other authors. Those modes are important, particularly if they act in phase, because they can provide a background for stronger surges. In contrast with the salinity field, SSH variability on seasonal time scales accounts for a very small percentage of variance and it is the combination of an annual and a semi-annual signal forced by winds and runoff, respectively. Approximately 90% of the variance is due to wind driven variability on sub-annual time scales. The most significant SSH anomalies in this band are associated with cyclogenetic events in the atmosphere, occurring either over Uruguay or over the Patagonian Shelf, whereas the strengthening or weakening of the semi-permanent South Atlantic anticyclone displays a relatively smaller influence. In agreement with previous publications, the estuary's spatial patterns in response to short-scale wind variability seem to be determined by wind direction more than by wind speed.  相似文献   

19.
Sea-surface acoustic backscattering measurements at moderate to high frequencies were performed in the shallow water of the south Yellow Sea, using omnidirectional spherical sources and omnidirectional hydrophones. Sea-surface backscattering data for frequencies in the 6–25 k Hz range and wind speeds of(3.0±0.5)and(4.5±1.0) m/s were obtained from two adjacent experimental sites, respectively. Computation of sea-surface backscattering strength using bistatic transducer is described. Finally, we calculated sea-surface backscattering strengths at grazing angles in the range of 16°–85°. We find that the measured backscattering strengths agree reasonably well with those predicted by using second order small-roughness perturbation approximation method with "PM" roughness spectrum for all frequencies at grazing angles ranged from 40° to 80°. The backscattering strengths varied slightly at grazing angles of 16°–40°, and were much stronger than roughness scattering. It is speculated that scattering from bubbles dominates the backscattering strengths at high wind speeds and small grazing angles. At the same frequencies and moderate to high grazing angles, the results show that the backscattering strengths at a wind speed of(4.5±1.0) m/s were approximately 5 d B higher than those at a wind speed of(3.0±0.5) m/s. However, the discrepancies of backscattering strength at low grazing angles were more than 10 d B. Furthermore the backscattering strengths exhibited no significant frequency dependence at 3 m/s wind speed. At a wind speed of 4.5 m/s, the scattering strengths increased at low grazing angles but decreased at high grazing angles with increasing grazing angle.  相似文献   

20.
Wind and wind-generated waves were measured in a wind-wave tank. A clear transition was found in the relation between the wind speed U 10 and the wind friction velocity u * near u * = 0.2 m/s, where U 10 is the wind speed at 10 m height extrapolated from the measured wind profile in a logarithmic layer, and u * = 0.2 m/s corresponds roughly to U 10 = 8 m/s in the present measurement. Quite a similar transition was found in the relation between the spectral density of high frequency wind waves and u *. These results suggest the existence of the critical wind speed for air–sea boundary processes, which was proposed by Munk (J Marine Res 6:203–218, 1947) more than half a century ago. His original idea of the critical wind speed was based on the discontinuities in such phenomena as white caps, wind stress, and evaporation, which commonly appear at a wind speed near 7 m/s. On the basis of the results of our present study and those of earlier studies, we discuss the phenomena which are relevant to the critical wind speed for the air–sea boundary processes. The conclusion is that the critical wind speed exists and it is attributed to the start of wave breaking rather than the Kelvin–Helmholtz instability, but the air–sea boundary processes are not discontinuous at a particular wind speed; because of the stochastic nature of breaking waves, the changes occur over a range of wind speeds. Detailed discussions are presented on the dynamical processes associated with the critical wind speed such as wind-induced change of sea surface roughness and high frequency wave spectrum. Future studies are required, however, to clarify the dynamical processes quantitatively. In particular, there is a need to further examine the gradual change of breaking patterns of wind waves with the increase of wind speed, and the associated change of the structure of the wind over wind waves, such as separation of the airflow at the crest of wind waves, the turbulent stress, and wave-induced stress. Studies on the dynamical structure of the high frequency wave spectrum are also needed.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号