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1.
Abstract

During November 1976 to February 1977 near‐surface wind, current and temperature measurements were made at three sites along the Strait of Juan de Fuca. Strong tidal currents and major intrusions of warmer, fresher offshore coastal water were superimposed upon the estuarine circulation of near‐surface seaward flow. The r.m.s. amplitudes of the diurnal and semidiurnal tidal currents were ～30 cms‐1 and 30–47 cm s‐1, respectively. The vector‐mean flow at 4 m‐depth was seaward and decreased in speed from 28 cm s‐1 at 74 km from the entrance to 9 cm s‐1 at 11 km from the entrance. On five occasions intrusions of 1–3 C warmer northeast Pacific coastal water occurred for durations of 1–10 days. The 25 cm s‐1 up‐strait speed of the intrusive lens agreed to within 20% of the gravity current speed computed from Benjamin's (1968) hydraulic model. The near‐surface currents associated with the intrusions and the southerly coastal winds were significantly correlated, indicating that the intrusions were initiated when shoreward Ekman currents advected Pacific coastal water into the Strait. The reversals were not significantly coherent with the along‐strait sea surface slope measured along the north side of the Strait nor were they strongly related to local wind forcing.  相似文献   

2.
A long-term record of surface currents from a high-frequency radar system, along with near-surface hydrographic transects, moored current meter records, and satellite imagery, are analyzed to determine the relative importance of river discharge, wind, and tides in driving the surface flow in the Fraser River plume. The observations show a great deal of oceanographic and instrumental variability. However, averaged quantities yielded robust results. The effect of river flow, which determines buoyancy and inertia near the river mouth, was found by taking a long-term average. The resulting flow field was dominated by a jet with two asymmetric gyres; the anticyclonic gyre to the north had flow speeds consistent with geostrophy. The mean flow speed near the river mouth was 14.3?cm?s–1, while the flow further afield was 5?cm?s–1 or less. Wind stress and surface currents were highly coherent in the subtidal frequency band. Northwesterly winds drive a surface flow to the southeast at speeds of nearly 30?cm?s–1. Southeasterly winds drive a surface flow to the northwest at speeds reaching 20?cm?s–1; however, there is more spatial variability in speed and direction relative to the northwesterly wind case. A harmonic analysis was used to extract the tidally driven flows. Ellipse parameters for the major tidal constituents varied considerably in both alignment and aspect ratio over the radar domain, in direct contrast to a barotropic model which predicted rectilinear flow along the Strait of Georgia. This is a result of water filling and draining the shallow mud flats north of the Fraser's main channel. The M2 velocities at the surface were also weaker than their barotropic counterparts. However, the shallow water constituent MK3 was enhanced at the surface and nearly as strong as the mean flow, implying that non-linear interactions are important to surface dynamics.  相似文献   

3.
Abstract

Using satellite pictures of Baffin Bay and Davis Strait, ice‐floes were tracked in order to give weekly surface velocities for 1978–1979. The approximate location of the edge of the ice sheet was also determined.

In winter the direction of travel was mainly southward in Davis Strait then, as the summer approached, the edge of the ice sheet retreated northward and floe motion became less clearly defined — even going north on occasion in Baffin Bay.

Near shore speeds along Baffin Island exceeded 50 cm s‐1 in Davis Strait during November and February. Typical values in the winter/spring period were 10–15 cm s‐1 between Davis Strait and Hudson Strait. Wind records at nearby shore stations showed directions to be mainly from the northwest, roughly parallel to the Baffin Island coastline.

The study confirms the usefulness of satellite pictures as a data source for modelling surface ice movement and for selecting navigation routes in these northern waters.  相似文献   

4.
Abstract

An extensive set of measurements of currents, winds, subsurface pressures and water properties was undertaken in the summer of 1982 in Queen Charlotte Sound on the west coast of Canada. At most observation sites the summer‐averaged currents are found to be about 10 cm s?1, smaller than the tidal currents but comparable to the standard deviation of the non‐tidal currents. The strongest average flow was the outflow of surface water past Cape St James at the northwestern corner of the Sound. During strong winds from the north or northwest a strong outflow of near‐surface fresher water was also observed over Cook Bank in the south. Eddies dominate the motion in the interior of the Sound, as shown by the behaviour of a near‐surface drifter that remained in mid‐Sound for 40 days before a storm pushed it into Hecate Strait. The disorganized, weak currents in the central Sound will likely allow surface waters or floating material to remain there for periods of several weeks in summer.

Empirical orthogonal function analyses of fluctuating currents, subsurface pressures and winds reveal that a single mode explains most of the wind and pressure variance but not the current variance. The first two pressure modes represent two distinct physical processes. The first mode is a nearly uniform, up‐and‐down pumping of the surface, while the second mode tilts across the basin from east to west, likely due to geostrophic adjustment of wind‐driven currents. This mode also tilts from south to north, owing to along‐strait wind stress. Most contributions to the first mode currents come from meters near shore or the edge of a trough. Coherence is high between these second mode pressures and first mode currents and winds, and lower but still significant between first mode pressures and first mode currents and winds. It is therefore difficult to predict the behaviour of currents in Queen Charlotte Sound in summer from pressure measurements at a single site, but the difference in sea‐level across Hecate Strait is a more reliable indicator.  相似文献   

5.
Abstract

We analyse the trajectories of 24 deep‐drogued, satellite‐tracked drifters launched between 50 and 52°N in the northeast Pacific during June and October 1987. Three aspects of the observed motions at the drogue depths of 100 to 120 m are studied: (i) the spatial structure of the mean and variance velocity fields; (ii) the dispersion and eddy diffusion characteristics of the fluctuating motions; and (iii) the properties of selected mesoscale eddies.

The mean Lagrangian velocity field is consistent with the mean flow pattern derived from the historical dynamic height topography. Fluctuating motions within the region are dominated by mesoscale eddies and meanders. Several instances of persistent O(100 days) westward flowing countercurrents were also observed. Based on the Lagrangian integral time‐ and length scales, drifter motions become decorrelated within a period of 10 days and a separation of 100 km. The mean zonal and meridional integral time‐scales of 4.5 and 3.6 days, respectively, are nearly identical with those obtained by Krauss and Böning (1987) from deep‐drogued drifter tracks in the North Atlantic. Because of the relatively small (<100 cm2 s?2) kinetic energy values in the northeast Pacific, the corresponding mean Lagrangian length scales of 29.4 and 29.9 km are roughly half those for the Atlantic.

The observed drifter dispersion is generally consistent with Taylor's (1921) theory for single‐particle dispersion in homogeneous isotropic turbulence. Estimates obtained using 476 pseudo‐drifter tracks generated from the original records indicate that the dispersion increases linearly with time, t, within the first 3 to 5 days of launch and subsequently increases as t1/2 (the random‐walk regime) within 10 days of launch. The respective peak zonal and meridional eddy diffusion coefficients of 4.1 × and 3.8 × 107 cm2 s?1 are reached within 30 days of deployment. Similar estimates for the peak eddy diffusivities are obtained using dispersion curves for sets of 4 drifters launched at the same location during the June and October deployments. The dispersion of these clusters followed an exponential rather than a t1/2 dependence over the first 70 days after release.

Eddies are predominantly clockwise rotary and are characterized by radii of 26 ± 16 km, periods of rotation of 16.0 ± 5.2 days, and azimuthal current speeds of 12.7 ± 8.6 cm s?1. One eddy was tracked for over 10 months. Oceanographic data collected during the October deployment period showed the eddies have vertical extents of 500 to 700 m and are linked to isotherm depressions of over 100 m in the main pycnocline. All eddies in the bifurcation zone propagate to the west at roughly 1.5 ± 0.4 cm s?1 counter to the prevailing mean flow and winds. These speeds are consistent with the westward phase speeds of first mode baroclinic planetary (Rossby) waves.  相似文献   

6.
Abstract

We present an analysis of current‐meter, sea‐level and hydrographic data collected in the Strait of Belle Isle and the northeastern Gulf of St Lawrence. From an array of moorings in the Strait from July to October 1980, we calculate a net transport into the Gulf of 0.13 × 106 m3 s?1 and show that the mean and eddy fluxes of heat through the Strait represented a net loss of heat to the northeastern Gulf. The estimated rate of loss of heat is less than the long‐term mean computed by Bugden (1981) but becomes comparable if adjusted for interannual changes of transport and water temperature. Moreover, the 1980 data permit the permanent tide‐gauge stations in the Strait at West Ste Modeste and Savage Cove to be levelled relative to one another, thus allowing surface currents to be calculated from sea‐level alone. Hence the long‐term wintertime transport into the Gulf can be calculated after fractional effects on the vertical structure of the flow are considered. During an average winter it appears that advection through the Strait can account for about 35% of the Gulf Intermediate Layer. A multiple regression involving average Intermediate Layer temperatures over 9 years suggests that winter air temperature in the Gulf, representative of atmospheric cooling, and sea‐level difference across the Strait, representative of advection, are equally important variables and together account for 50% of the Layer's temperature variability. Analysis of current‐meter, sea‐level and hydrographic data collected in 1975 supports earlier hypotheses that the strongest inflow of water with ? < 0° C and salinity between 32 and 3 3 should occur in winter. It appears that during the 1975 field program the inflow was about 0.6 × 106 m3 s?1, which is about twice the long‐term average for January to May.  相似文献   

7.
A systematic comparison of wind profiles and momentum exchange at a trade wind site outside Oahu, Hawaii and corresponding data from the Baltic Sea is presented. The trade wind data are to a very high degree swell dominated, whereas the Baltic Sea data include a more varied assortment of wave conditions, ranging from a pure growing sea to swell. In the trade wind region swell waves travel predominantly in the wind direction, while in the Baltic, significant cross-wind swells are also present. Showing the drag coefficient as a function of the 10-m wind speed demonstrates striking differences for unstable conditions with swell for the wind-speed range 2 m s?1 < U 10 < 7 m s?1, where the trade-wind site drag values are significantly larger than the corresponding Baltic Sea values. In striking contrast to this disagreement, other features studied are surprisingly similar between the two sites. Thus, exactly as found previously in Baltic Sea studies during unstable conditions and swell, the wind profile in light winds (3 m s?1) shows a wind maximum at around 7–8 m above the water, with close to constant wind speed above. Also, for slightly higher wind speeds (4 m s?1 < U 10 < 7 m s?1), the similarity between wind profiles is striking, with a strong wind-speed increase below a height of about 7–8 m followed by a layer of virtually constant wind speed above. A consequence of these wind-profile features is that Monin–Obukhov similarity is no longer valid. At the trade-wind site this was observed to be the case even for wind speeds as high as 10 m s?1. The turbulence kinetic energy budget was evaluated for four cases of 8–16 30- min periods at the trade-wind site, giving results that agree very well with corresponding figures from the Baltic Sea.  相似文献   

8.
Abstract

As part of the Canadian Atlantic Storms Program (CASP), near‐bottom current velocity, pressure, light transmission (as a measure of suspended sediment concentration) and water temperature were recorded using a variety of instruments deployed in water depths of 20 to 37 m on the inner Scotian Shelf, during February and March 1986. Detailed mapping of a 12‐km2 area encompassing the instrument mooring sites revealed a variety of bottom types. These include sand and gravel (both forming ripples at various scales), cobble‐boulder lags, and bedrock, resulting in bottom roughness estimates that vary widely (10?4 m < k < 10° m) over short horizontal distances (of the order 102 m). The velocity data provided information on the near‐bottom current response to winter storms anda basis for computations of sediment load and transport rates. The near‐bottom mean flow showed distinct storm‐driven circulation patterns, with velocities roughly parallel to alongshore wind stress but opposed to shore‐normal wind. Wave‐induced oscillatory motions also showed marked increases during storms and frequently dominated the near‐bottom flow. Sediment load (depth‐integrated concentration) and transport were computed using a model in which the load is related to the excess normalized shear stress. The computed mean concentrations were compatible with the optical transmis someter data. These computations yielded estimates ranging up to 0.7 kg m?2 for the mean sediment load and 443 kg m?1 h?1 for the net transport. Hindcast scour rates, of the order of 1 mm h?1 under moderate storm conditions were generally compatible with depths of scour measured by divers.  相似文献   

9.
卫星反演海面风场资料能够弥补海上气象测风资料缺乏的不足,对近海风能资源评估具有重要意义。通过ASCAT(Advanced Scatterometer)风速数据与美国及中国近海岸浮标测风资料的对比分析,结果表明,ASCAT风速的均方根误差为1.27 m·s-1。比较利用近海岸浮标逐小时风速及与其相匹配ASCAT瞬时风速计算的各项风能参数,得出ASCAT与浮标的平均风速和风功率密度的残差分别在±0.5 m·s-1和±50 W·m-2以内,该残差占浮标计算结果的比例分别在±8%和±12%以内。使用ASCAT风速资料拟合的Weibull分布函数与浮标的结果较吻合。因此,ASCAT风速资料也能够为海上风能资源评估提供有用的风能参数信息。最后使用ASCAT瞬时风速数据分析了中国近海10 m及70 m高度处的风能资源的空间分布特征,结果表明,台湾海峡平均风速和风功率密度最大。  相似文献   

10.
The Pacific Atmospheric Sulfur Experiment (PASE) was a field mission that took place aboard the NCAR C-130 airborne laboratory over the equatorial Pacific Ocean near Christmas Island (Kirimati, Republic of Kiribati) during August?CSeptember, 2007. Eddy covariance measurements of the ozone fluxes at various altitudes above the ocean surface, along with simultaneous mapping of the horizontal gradients provided a unique opportunity to observe all of the dynamical components of the ozone budget in this remote marine environment. The results of six daytime and two sunrise flights indicate that vertical transport into the marine boundary layer from above and horizontal advection by the tradewinds are both important source terms, while photochemical destruction consisting of 82% photolysis (leading to OH production), 11% reaction with HO2, and 7% reaction with OH provides the main sink. The overall photochemical lifetime of ozone in the marine boundary layer was found to be 6.5 days. Ocean uptake of ozone was observed to be fairly slow (mean deposition velocity of 0.024?±?0.014 cm s?1) accounting for a diurnally averaged loss rate that was ??30% as large as the net photochemical destruction. From the measurement of deposition velocity an ozone reactivity of ??50 s?1 in seawater is inferred. Due to the unprecedented measurement accuracy of the dynamical budget terms, unobserved photochemistry was able to be deduced, leading to the conclusion that 3.9?±?3.0 ppt (parts per trillion by volume) of NO is present on average in the daytime tropical marine boundary layer, broadly consistent with several previous studies in similar environments. It is estimated, however, that each ppt of BrO hypothetically present would counter each ppt of NO above the requisite 3.9 ppt needed for budget closure. The long-term budget of ozone is further analyzed in the buffer layer, between the boundary layer and free troposphere, and used to derive an entrainment velocity across the trade wind inversion of 0.51 ± 0.38 cm s?1.  相似文献   

11.
一次多回击负地闪放电过程的甚高频辐射和传输特征分析   总被引：1，自引：0，他引：1  
利用短基线时间差甚高频(VHF)辐射源定位系统对一次多回击负地闪放电过程进行详细研究发现, 负地闪的预击穿、梯级先导、直窜先导及回击后云内放电过程伴随有较强烈的VHF辐射。结合同步观测的闪电快、慢电场变化资料, 分析VHF辐射源时空发展特征发现, 预击穿阶段辐射源在云中的放电通道为双向发展, 平均速度均在104 m s-1量级, 预击穿下行分支直接转化为梯级先导, 并产生多个分支通道同时向地面发展, 先导平均速度在105 m s-1量级。继后回击之前先导过程均产生多个分支通道, 直窜先导平均速度在105～106 m s-1量级, 新开辟的梯级先导速度在105 m s-1量级。闪击间及地闪后期云内放电活动较为复杂, 主要表现为辐射源从闪电起始区域发展, 进一步延伸云内闪电通道。地闪后期多次负极性K变化过程(Kitagawa and Kobayashi, 1958)主要表现为负极性流光沿之前的正极性电离通道快速发展, 平均速度在106 m s-1量级。  相似文献   

12.
This study investigated multi-decadal variability in the wind resource over the Republic of Korea using the Weather Research and Forecasting (WRF) mesoscale meteorological model. Mesoscale simulations were performed for the period from November 1981 to November 2010. The typical wind climatology over the Korean Peninsula, which is influenced by both continental and oceanic features, was represented by the physics-based mesoscale simulations. Winter had windier conditions with northwesterly flows, whereas less windy with southwesterly flows appeared in summer. The annual mean wind speeds over the Republic of Korea were approximately 2 m s?1 with strong wind in mountainous areas, coastal areas, and islands. The multi-decadal variability in wind speed during the study period was characterized by significant increases (positive trend) over many parts of the study area, even though the various local trends appeared depending on the station locations. The longterm trend in the spatially averaged wind speed was approximately 0.002 m s?1 yr?1. The annual frequency of daily mean wind speeds over 5 m s?1 at the turbine hub height also increased during the study period throughout the Republic of Korea. The present study demonstrates that multi-decadal mesoscale simulations can be useful for climatological assessment of wind energy potential.  相似文献   

13.
Abstract

The impacts of climate change on surface air temperature (SAT) and winds in the Gulf of St. Lawrence (GSL) are investigated by performing simulations from 1970 to 2099 with the Canadian Regional Climate Model (CRCM), driven by a five-member ensemble. Three members are from Canadian Global Climate Model (CGCM3) simulations following scenario A1B from the Intergovernmental Panel on Climate Change (IPCC); one member is from the Community Climate System Model, version 3 (CCSM3) simulation, also following the A1B scenario; and one member is from the CCSM4 (version 4) simulation following the Representative Concentration Pathway (RCP8.5) scenario. Compared with North America Regional Reanalysis (NARR) data, it is shown that CRCM can reproduce the observed SAT spatial patterns; for example, both CRCM simulations and NARR data show a warm SAT tongue along the eastern Gulf; CRCM simulations also capture the dominant northwesterly winds in January and the southwesterly winds in July. In terms of future climate scenarios, the spatial patterns of SAT show plausible seasonal variations. In January, the warming is 3°–3.5°C in the northern Gulf and 2.5°–3°C near Cabot Strait during 2040–2069, whereas the warming is more uniform during 2070–2099, with SAT increases of 4°–5°C. In summer, the warming gradually decreases from the western side of the GSL to the eastern side because of the different heat capacities between land and water. Moreover, the January winds increase by 0.2–0.4?m?s?1 during 2040–2069, related to weakening stability in the atmospheric planetary boundary layer. However, during 2070–2099, the winds decrease by 0.2–0.4?m?s?1 over the western Gulf, reflecting the northeastward shift in northwest Atlantic storm tracks. In July, enhanced baroclinicity along the east coast of North America dominates the wind changes, with increases of 0.2–0.4?m?s?1. On average, the variance for the SAT changes is about 10% of the SAT increase, and the variance for projected wind changes is the same magnitude as the projected changes, suggesting uncertainty in the latter.  相似文献   

14.
A numerical investigation of wind speed effects on lake-effect storms   总被引：2，自引：0，他引：2  
Observations of lake-effect storms that occur over the Great Lakes region during late autumn and winter indicate a high sensitivity to ambient wind speed and direction. In this paper, a two-dimensional version of the Penn State University/National Center for Atmospheric Research (PSU/NCAR) model is used to investigate the wind speed effects on lake-effect snowstorms that occur over the Great Lakes region.Theoretical initial conditions for stability, relative humidity, wind velocity, and lake/land temperature distribution are specified. Nine different experiments are performed using wind speeds ofU=0, 2, 4,..., 16 m s–1. The perturbation wind, temperature, and moisture fields for each experiment after 36 h of simulation are compared.It is determined that moderate (4–6 m s–1) wind speeds result in maximum precipitation (snowfall) on the lee shore of the model lake. Weak wind speeds (0U<4 m s–1) yield significantly higher snowfall amounts over the lake along with a spatially concentrated and intense response. Strong wind speeds (6<U16 m s–1), yield very little, if any, significant snowfall, although significant increases in cloudiness, temperature, and perturbation wind speed occur hundreds of kilometers downwind from the lake.  相似文献   

15.
The drag coefficient C d (10 m) at the center of shallow Lake Flevo (20-km diam) is evaluated for wind speeds u between 5 and 15 m s?1 independently by three methods. Trivane measurements of eddy-correlation fluxes agree with eddy flux data available for moderate wind speeds from other sites, and can together be represented by C d(10 m) = 0.0007 μ0.3. Additional evaluations of water-surface slope give C d(10 m) ≈ 0.0024, indicating that the stress at the water-surface level may not be entirely accounted for by eddy-correlation measurements well above the waves. Neither the eddy-correlation stress, nor the water-surface stress appears to be accurately estimable from profile measurements of wind, temperature and humidity analyzed without regard to sea state, if u > 10 m s?1.  相似文献   

16.
Abstract

An intercomparison of the Väisälä MicroCora system used in the Automated Shipboard Aerological Program (ASAP) and the Atmospheric Environment Service upper‐air system (GMD/ADRES) was conducted in May‐June 1983. Thirty‐three paired ascents were made. The ASAP system dry‐bulb temperatures averaged 0.3°C warmer. For the lowest 100 mb, the dew‐point temperature difference (ASAP ‐ GMD/ADRES) was near ‐1°C whereas for the 780–500 mb layer, the difference was 1°C. The wind component mean differences averaged were small but with a 4 m s?1 standard deviation.  相似文献   

17.
Abstract

A numerical model, the Parallel Ocean Program (POP) was used to run a 46-year simulation of the North Pacific Ocean beginning in January 1960. The model had a horizontal resolution of 0.25°, 28 vertical levels, and employed spectral nudging that, unlike standard nudging, nudges only specific frequency and wavenumber bands. This simulation was nudged to the mean and monthly Levitus climatology of potential temperature and absolute salinity (SA). The model was forced with the mean monthly winds, sea level pressure, net heat flux, and precipitation from the National Centers for Environmental Prediction (NCEP).

The simulation was used to examine the anomalous intrusions, previously observed from 2001 to 2002, of cooler and fresher (less spicy) water flowing southward along the coast of western North America. The simulated anomaly began in 1999 in the North Pacific, progressed southeastward towards the coast and then southward, at least as far south as southern California. The southward velocity signal, modulated by a strong annual cycle, reached Point Conception in 2000 while the temperature and SA anomalies arrived later, in 2002–03. The simulated velocity anomalies were eastward at about 3?cm s?1 in the northeast Pacific near 47°N in agreement with observations. Simulated coastal southward flow speeds reached 10–20?cm s?1 during the summer from 2000 to 2002.

This intrusion was by far the largest to occur over the entire length of the simulation. It was also the only time during the simulation when the Victoria mode was positive (associated with enhanced flow to the east via the North Pacific Gyre Oscillation (NPGO)) and the Multivariate El Niño-Southern Oscillation (ENSO) Index (MEI) was negative (La Niña conditions), tending to cause a southward flow anomaly along the coast.  相似文献   

18.
《大气与海洋》2012,50(4):27-39
On the basis of Acoustic Doppler Current Profiler (ADCP) measurements of current and hydrographic data obtained in October 2008, a diagnostic model of ocean circulation with a modified inverse method is used to study the circulation in Luzon Strait. Satellite-based geostrophic velocity calculated from the merged absolute dynamic topography is also used and compared with the in situ data. The analyses reveal that during the period of observations there were two branches of the Kuroshio current, and the maximum velocity of the current reached 175 cm s?1 at the surface. The main stream of the Kuroshio was located at 122°10′E to 122°40′E near the southern boundary of the study region and confined to the upper 700 m, while its western branch was located at 121°00′E to 121°35′E and confined to the upper 400 m. The Kuroshio water intruded into the South China Sea through the northern boundary of the study region east of 120°45′E. At 1000 m depth, the flow was dominated by southwestward or westward flow in the area north of 20°30′N, while the flow was mostly southeastward in the area south of 20°30′N. A cyclonic eddy was identified in the region east of Luzon Strait. At 1500 m depth, cyclonic eddies were seen on both sides of Luzon Strait. The volume transport across the longitudinal section 120°45′E between about 20.00°N and 21.20°N south of Taiwan during the period of observations was about 4?×?106 m3 s?1. One Argo float was tracked as it moved across Luzon Strait, reflecting the westward flow at both the surface and 1000 m depth.

RÉSUMÉ?[Traduit par la rédaction] En partant des mesures de courant par profileur de courant à effet Dopler (ADCP) et des données hydrographiques recueillies en octobre 2008, nous étudions la circulation dans le détroit de Luçon en nous servant d'un modèle diagnostique de la circulation de l'océan combiné à une méthode inverse modifiée. Nous nous servons également de la vélocité géostrophique mesurée par satellite, calculée à partir de la topographie dynamique absolue totale, pour la comparer avec les données in situ. Les analyses révèlent que pendant la période d'observation, il y avait deux ramifications du Kuroshio et que la vélocité maximale du courant a atteint 175 cm s?1 à la surface. La principale ramification du Kuroshio était située entre 122°10′E et 122°40′E à proximité de la limite sud de la région à l'étude et elle était confinée aux 700 premiers mètres; sa ramification ouest était située entre 121°00′E et 121°35′E et elle était confinée aux 400 premiers mètres. Le Kuroshio se déversait dans la mer de Chine occidentale en traversant la limite nord de la région à l'étude à l'est de 120°45′E. À 1000 m de profondeur, le courant s'écoulait essentiellement en direction sud-ouest ou ouest dans le secteur au nord de 20°30′N, et en direction sud-est dans la région au sud de 20°30′N. Nous avons identifié un tourbillon cyclonique dans la région à l'est du détroit de Luçon. Nous avons relevé des tourbillons cycloniques à une profondeur de 1500 m de part et d'autre du détroit de Luçon. Le transport volumique dans le profil longitudinal à 120°45′E entre 20.00° N et 21.20° N environ au sud de Taïwan pendant la période d'observation a atteint environ 4?×?106 m3 s?1. Nous avons suivi une bouée Argo dérivant au gré du courant dans le détroit de Luçon, ce qui a permis d’établir qu'il s'écoulait en direction ouest à la surface et à une profondeur de 1000 m.  相似文献   

19.
A detailed climatology of the cyclogenesis over the Southern Atlantic Ocean (SAO) from 1990 to 1999 and how it is simulated by the RegCM3 (Regional Climate Model) is presented here. The simulation used as initial and boundary conditions the National Centers for Environmental Prediction—Department of Energy (NCEP/DOE) reanalysis. The cyclones were identified with an automatic scheme that searches for cyclonic relative vorticity (ζ10) obtained from a 10-m height wind field. All the systems with ζ10 ≤ ?1.5 × 10?5 s?1 and lifetime equal or larger than 24 h were considered in the climatology. Over SAO, in 10 years were detected 2,760 and 2,787 cyclogeneses in the simulation and NCEP, respectively, with an annual mean of 276.0 ± 11.2 and 278.7 ± 11.1. This result suggests that the RegCM3 has a good skill to simulate the cyclogenesis climatology. However, the larger model underestimations (?9.8%) are found for the initially stronger systems (ζ10 ≤ ?2.5 × 10?5 s?1). It was noted that over the SAO the annual cycle of the cyclogenesis depends of its initial intensity. Considering the systems initiate with ζ10 ≤ ?1.5 × 10?5 s?1, the annual cycle is not well defined and the higher frequency occurs in the autumn (summer) in the NCEP (RegCM3). The stronger systems (ζ10 ≤ ?2.5 × 10?5 s?1) have a well-characterized high frequency of cyclogenesis during the winter in both NCEP and RegCM3. This work confirms the existence of three cyclogenetic regions in the west sector of the SAO, near the South America east coast and shows that RegCM3 is able to reproduce the main features of these cyclogenetic areas.  相似文献   

20.
Abstract

The wind generation of transverse thermocline motions in an infinitely long two‐layer channel is studied theoretically. Winds both along and across the channel are considered. Horizontal momentum transfer is parameterized by a constant coefficient of eddy viscosity. For a channel narrow compared with its internal Rossby radius of deformation, the transverse motions are uni‐modal and generated most efficiently by long‐shore winds. Theoretical results in this narrow channel limit agree well with observations made at Babine Lake, British Columbia. For a channel wide compared with its Rossby radius, the response is multi‐modal, especially for cross‐channel winds. For a model Lake Michigan, computed interfacial displacements due to a steady wind either across or along the channel are small compared with the observed displacements. However, a semi‐diurnal wind (in either direction) is in near resonance with the seventh transverse mode. Thus multi‐modal displacements as large as those observed could possibly be generated by semi‐diurnal winds across or along the channel.  相似文献   

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