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1.
Semidiurnal tidal currents on the outer shelf of the Mackenzie Shelf in the Beaufort Sea were found to be strongly influenced by the locally generated baroclinic tide. Two primary factors are involved in this process: (1) the sharp shelf break along the northeastern Mackenzie Shelf, promoting the generation of vigorous internal tidal waves; and (2) the proximity to critical latitudes for M2 and N2 motions locking these waves and preventing them from leaving the source region. As a result, internal tides are resonantly trapped between the shelf and critical latitudes. The physical properties and temporal variations of tidal motions were examined using current meter measurements obtained from 1987–1988 at four sites (SS1, SS2, SS3, and SS4) offshore of the shelf break at depths of ∼200 m. Each mooring had Aanderaa RCM4s positioned at ∼35 m below the surface and ∼50 m above the bottom. Complex demodulation was used to compute the envelopes (amplitude modulation) of these components. A striking difference in the variability of clockwise (CW) and counterclockwise (CCW) tidal currents was found. The CW tides are highly variable, have greater amplitude, exhibit a burst-like character associated with wind events and contain about 80% of the total energy of the semidiurnal tidal currents. In contrast, the CCW components have a more regular temporal regime with distinct monthly, fortnightly and 10-day modulation at astronomical periodicities associated with frequency differences M2–N2 (0.03629 cpd), S2–M2 (0.06773 cpd), and S2–N2 (0.10402 cpd). Significant horizontal correlation of the CW current envelopes was found only between stations near the northeast Mackenzie Shelf, indicating this to be the main area of baroclinic internal wave generation.  相似文献   

2.
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3.
Observations at 8 sites in the outer central Great Barrier Reef show M2, S2, K1, and O1 tidal currents flow directly off-shelf (northeast), when the corresponding tide at Townsville is at zero height and falling, with typical amplitudes of 12, 6, 3, and 2 cm s?1. On the slope (at 300 m depth), the vertically averaged long-shelf component was small. On the shelf, the eccentricity of the tidal ellipses decreases shoreward and the tidal ellipses rotate anticlockwise. The major axes of the tidal ellipses tilt left of cross-shelf, especially for the diurnal constituents. There is satisfactory agreement between the observed and modelled cross-shelf currents. The long-shelf velocity is sensitive to the long-shelf changes in amplitude and phase of the tide heights and high quality tidal data for open boundary conditions will be required if numerical models are to model these currents satisfactorily.  相似文献   

4.
Incoherent internal tidal currents in the deep ocean   总被引：2，自引：0，他引：2  
Eleven months current meter observations from the deep Bay of Biscay were examined for the residual (incoherent internal tidal; icIT) signal, left after harmonic analysis using eight tidal constituents (large-scale barotropic or coherent baroclinic signal) within the semidiurnal band. This residual signal comprised 30% of the total tidal kinetic energy and, due to its flat spectral appearance, it was responsible for typically 5–7 days intermittency. Although icIT was part of the red noise internal wave band continuum, it was not attributable to instrumental noise. It consisted of quasi-harmonics at non-tidal harmonic frequencies having amplitudes larger than N2, the third largest semidiurnal tidal constituent. It is suggested that the kinetic energy at these non-tidal frequencies reflects interaction between semidiurnal tidal motions and the slowly varying background conditions.Responsible Editor: Roger Proctor  相似文献   

5.
Bottom-mounted ADV and ADCP instruments in combination with CTD profiling measurements taken along the Chinese coast of the East China Sea were used to study the vertical structure of temperature, salinity, and velocity in reversing tidal currents on a shallow inner shelf and in rotating tidal flows over a deeper sloping bottom of the outer shelf. These two regimes of barotropic tide affect small-scale dynamics in the lower part of the water column differently. The reversing flow was superimposed by seiches of ∼2.3 h period generated in semienclosed Jiaozhou Bay located nearby. As the tidal vector rotates over the sloping bottom, the height of the near-bottom logarithmic layer is subjected to tidal-induced variations. A maximum of horizontal velocity Umax appears at the upper boundary of the log layer during the first half of the current vector rotation from the minor to the major axis of tidal ellipse. In rotating tidal flow, vertical shear generated at the seafloor, propagated slowly to the water interior up to the height of Umax, with a phase speed of ∼5 m/h. The time-shifted shear inside the water column, relative to the shear at the bottom, was associated with periodically changing increases and decreases of the tidal velocity above the log layer toward the sea surface. In reversing flows, the shear generated near the bottom and the shear at the upper levels were almost in phase.  相似文献   

6.
The south-flowing waters of the Kamchatka and Oyashio currents are key components of the western subarctic Pacific gyre. The dissipation of tidal energy in shallow and coastal regions of these currents and the attendant mixing are the important processes that affect the upper layer temperature and salinity. Examples of the impact of tidal currents on water temperature and salinity are the persistent tide-driven mixing around the Kashevarov and Kruzenshtern banks. The Kruzenshtern Bank is a shallow submarine bank stretching along the eastern continental slope of the Kuril Islands with the minimum depth of 86 m. Surface drifters observations are used to determine the characteristics of tidal currents and the circulation over these banks. New software that allows more versatility in the harmonic analysis is used for drifter’s data. The two banks have similar features. The variations in current velocities are dominated by the diurnal signals. The K1 and O1 tidal ellipses over the banks are the largest and clockwise. The enhanced tidal currents suggest that the formation of cold and saline water in summer is due to mixing of water column over the banks with intermediate waters. Variations of tidal ellipses over the bank may explain the formation of polynya at the western end of the Kashevarov Bank. We found that the 18.6-year lunar nodal cycle is a significant characteristic of salinity variation at the temperature minimum in the eddies eastward of the Boussole Strait over the period 1990–2015.  相似文献   

7.
A high-resolution three-dimensional model of the Clyde Sea and the adjacent North Channel of the Irish Sea is used to compute the major diurnal and semidiurnal tides in the region, the associated energy fluxes and thickness of the bottom boundary layer. Initially, the accuracy of the model is assessed by performing a detailed comparison of computed tidal elevations and currents in the region, against an extensive database that exists for the M2, S2, N2, K1 and O1 tides. Subsequently, the model is used to compute the tidal energy flux vectors in the region. These show that the major energy flux is confined to the North Channel region, with little energy flux into the Clyde Sea. Comparison with the observed energy flux in the North Channel shows that its across-channel distribution and its magnitude are particularly sensitive to the phase difference between elevation and current. Consequently, small changes in the computed values of these parameters due to slight changes of the order of the uncertainty in the open-boundary values to the model, can significantly influence the computed energy flux. The thickness of the bottom boundary layer in the region is computed using a number of formulations. Depending upon the definition adopted, the empirical coefficient C used to determine its thickness varies over the range 0.1 to 0.3, in good agreement with values found in the literature. In the North Channel, the boundary layer thickness occupies the whole water depth, and hence tidal turbulence produced at the sea bed keeps the region well mixed. In the Clyde Sea, the boundary layer thickness is a small fraction of the depth, and hence the region stratifies.Responsible Editor: Phil Dyke  相似文献   

8.
The tropospheric zenith total delay (ZTD) derived from very long baseline interferometry (VLBI) is an important parameter of the atmosphere, reflecting various atmosphere-related processes and variations. In this paper, ZTD time series of the IVS rapid combined tropospheric product (2002–2006) with a 1-h resolution are used for the first time to investigate the diurnal and semidiurnal oscillations. Significant diurnal and semidiurnal variations of ZTD are found at all VLBI stations. The amplitude of the diurnal cycle S1 is 0.6–1.2 mm at most of the VLBI stations, and the amplitude of the semidiurnal cycle S2 is 0.2–1.9 mm, which nearly accord with the surface pressure tides S1/S2 and co-located GPS estimated S1/S2. The results indicate that the S1 and S2 behaviors are mainly dominated by the hydrostatic component, namely pressure tides. In general, the semidiurnal S2 amplitudes are slightly larger than the diurnal S1. While S1 shows no clear dependency on site altitude, S2 has a regular distribution with VLBI site altitude. The results are in accordance with predictions of the classic tidal theory [Chapman, S., Lindzen, R.S., 1970. Atmospheric Tides, Gordon and Breach, New York].  相似文献   

9.
The tides and tidal energetics in the Indonesian seas are simulated using a three-dimensional finite volume coastal ocean model. The high-resolution coastline-fitted model is configured to better resolve the hydrodynamic processes around the numerous barrier islands. A large model domain is adopted to minimize the uncertainty adjacent to open boundaries. The model results with elevation assimilation based on a simple nudge scheme faithfully reproduced the general features of the barotropic tides in the Indonesian Seas. The mean root-mean-square errors between the observed and simulated tidal constants are 2.3, 1.1, 2.4, and 1.5 cm for M2, S2, K1, and O1, respectively. Analysis of the model solutions indicates that the semidiurnal tides in the Indonesian Seas are primarily dominated by the Indian Ocean, whereas the diurnal tides in this region are mainly influenced by the Pacific Ocean, which is consistent with previous studies. Examinations of tidal energy transport reveal that the tidal energy for both of the simulated tidal constituents are transported from the Indian Ocean into the IS mainly through the Lombok Strait and the Timor Sea, whereas only M2 energy enters the Banda Sea and continues northward. The tidal energy dissipates the most in the passages on both sides of Timor Island, with the maximum M2 and K1 tidal energy transport reaching about 750 and 650 kW m–1, respectively. The total energy losses of the four dominant constituents in the IS are nearly 338 GW, with the M2 constituent dissipating 240.8 GW. It is also shown that the bottom dissipation rate for the M2 tide is about 1–2 order of magnitudes larger than that of the other three tidal components in the Indonesian seas.  相似文献   

10.
Abstract

Tidal pressures and currents were measured with self‐contained capsules dropped to the sea floor for one month at distances of 175, 190, and 500 nautical miles from San Diego. These observations, together with a one‐week bottom pressure record by Filloux at 750 n miles, and three half‐week bottom current records by Isaacs et al, at intermediary distances, were analyzed for tidal components by cross‐correlation with a noise‐free reference time series. (For short records this method has some merit over classical tide analysis.) It was found that the tide decays seaward to e‐1 times the coastal amplitude over a distance of order 1000 km for the semidiurnal species, slower for the diurnal species. Tidal currents turn counterclockwise, and are polarized with maximum flow parrallel to shore in the direction of tidal propagation (320°T) at local high tide. The current amplitude is roughly 2 cm/sec for the semidiurnal component, 1 cm/sec for the diurnal component. Superimposed baroclinic tidal currents lead to poor signal: noise ratios (between 1:1 and 10:1) for the barotropic currents. In contrast, the ratio is typically 1000:1 for the bottom pressures and generally exceeds that for coastal tide stations of comparable duration. Published I.H.B. tidal constants for exposed California coastal stations indicate “upshore” (towards 320°T) propagation at 140 m/sec for semidiurnal tides. 214 m/sec for diurnal tides.

To interpret these diverse observations, we have computed the dispersion laws for all possible rotationally‐gravitationally trapped waves against a straight coast with shelf. Trapped solutions are conveniently portrayed in terms of a parameter μ such that ? = sin μ = iu/v and f = ‐ cos μ = η/v define the ellipticity and impedance of the wave motion, η, u and v being off‐shelf dimensionless elevation, normal‐to‐shore and longshore components of velocity, respectively. We then attempt to fit the observations by a superposition of the possible wave classes, all of the same tidal frequency: (a) a free Kelvin‐like edge wave with small μ (mostly trapped by rotation, but somewhat slowed by the shelf); (6) a free Poincare‐like leaky wave; and (c) a forced wave (the distortion of the sea bottom by the tide producing forces plays a significant role). The mod el can account for the main features of the observed tidal heights, and gives relative amplitudes at the coast of 54:16:4 cm for components a:b:c in the case of the semidiurnal tides, 21:24:9 cm for the diurnal tides. The results place a semidiurnal amphidrome about midway between San Diego and Hawaii. Tidal currents are not well fitted by the model, and there are problems associated with the separation of barotropic and baroclinic modes, and with the benthic boundary layer. Coastal energy dissipation is small in the sea under investigation, but a “ capacitive “ phase delay appears to be associated with Northern California harbors and inland waters.  相似文献   

11.
Near-inertial currents in the DeSoto Canyon region are described using current and wind observations taken between April 1997 and March 1998 for the “DeSoto Canyon Eddy Intrusion Study”. Distinct energy peaks are present at near-inertial frequencies for the clockwise spectrum and there is little energy at the same frequencies for the counterclockwise current spectrum. In this region, amplitudes of the near-inertial currents can be as high as 40 cm s−1. These currents are surface-intensified and display an increase in amplitude from the shelf break to offshore. Between November 1997 and March 1998, they were effectively generated by shifting winds accompanying passages of cold fronts. For this time period, near-inertial currents are reasonably well-simulated by a mixed-layer model forced by observed winds. During summer 1997, however, enhanced near-inertial motions often resulted from resonance between winds and existing currents.  相似文献   

12.
A three-dimensional shelf circulation model is used to examine the effect of seasonal changes in water-column stratification on the tidal circulation over the Scotian Shelf and Gulf of St. Lawrence. The model is driven by tidal forcing specified at the model’s lateral open boundaries in terms of tidal sea surface elevations and depth-averaged currents for five major tidal constituents (M2, N2, S2, K1, and O1). Three numerical experiments are conducted to determine the influence of baroclinic pressure gradients and changes in vertical mixing, both associated with stratification, on the seasonal variation of tidal circulation over the study region. The model is initialized with climatological hydrographic fields and integrated for 16 months in each experiment. Model results from the last 12 months are analyzed to determine the dominant semidiurnal and diurnal tidal components, M2 and K1. Model results suggest that the seasonal variation in the water-column stratification affects the M2 tidal circulation most strongly over the shelf break and over the deep waters off the Scotian Shelf (through the development of baroclinic pressure gradients) and along Northumberland Strait in the Gulf of St. Lawrence (through changes in vertical mixing and bottom stress). For the K1 constituent, the baroclinic pressure gradient and vertical mixing have opposing effects on the tidal circulation over several areas of the study region, while near the bottom, vertical mixing appears to play only a small role in the tidal circulation.  相似文献   

13.
This study examines connections between mean sea level (MSL) variability and diurnal and semidiurnal tidal constituent variations at 17 open-ocean and 9 continental shelf tide gauges in the western tropical Pacific Ocean, a region showing anomalous rise in MSL over the last 20 years and strong interannual variability. Detrended MSL fluctuations are correlated with detrended tidal amplitude and phase fluctuations, defined as tidal anomaly trends (TATs), to quantify the response of tidal properties to MSL variation. About 20 significant amplitude and phase TATs are found for each of the two strongest tidal constituents, K1 (diurnal) and M2 (semidiurnal). Lesser constituents (O1 and S2) show trends at nearly half of all gauges. Fluctuations in MSL shift amplitudes and phases; both positive and negative responses occur. Changing overtides suggest that TATs are influenced by changing shallow water friction over the equatorial Western Pacific and the eastern coast of Australia (especially near the Great Barrier Reef). There is a strong connection between semidiurnal TATs at stations around the Solomon Islands and changes in thermocline depth, overtide generation, and the El Niño Southern Oscillation (ENSO). TATs for O1, K1, and M2 are related to each other in a manner that suggests transfer of energy from M2 to the two diurnals via resonant triad interactions; these cause major tidal variability on sub-decadal time scales, especially for M2. The response of tides to MSL variability is not only spatially complex, it is frequency dependent; therefore, short-term responses may not predict long-term behavior.  相似文献   

14.
On the basis of the current measurements from the moored Long Ranger ADCP in the upper 450 m layer and the deep current measurements at 2000 and 2300 m from the moored cur-rent meters with the time series data of about 7 months at the mooring station in the northeastern South China Sea, the spectral analyses and calculation have been made. The major results are as follows: (ⅰ) From the progressive vector diagrams of the observed daily currents at the water lev-els from 50 m to 400 m, its temporal variation of velocity rotated counterclockwise in most of the observing time. This agrees basically with the result from the qualitative analysis of the sea surface height data, which was obtained from TOPEX/ERS-2 altimeter data by CCAR. The daily and monthly average velocities are both the largest in November, next in October and minimum in Au-gust. (ⅱ) At the 2000 and 2300 m levels, the daily and monthly average velocities are both the largest in January, next in September and minimum in August. From the seasonal change of cur-rents, the current velocity is the strongest in winter (January-March), next in autumn, and weak in summer. (ⅲ) There exists the variation of tidal current with the change of depth. In the upper layer, the height of diurnal peak is higher than that of semidiurnal peak. However, the semidiurnal peak is higher than the diurnal peak at the levels from 200 m to 400 m. In the layers above 450 m the clockwise component is dominant in their fluctuations. In the layers below 1500 m the diurnal peak is again higher than the semidiurnal peak. (ⅳ) There is the prominent periodic fluctuation of more than two months in the layer from 50 m to 2300 m. The period of this prominent peak is 75 d and its fluctuation is counterclockwise in the upper 450 m layers, and is 68 d and 69 d at the depths of 2000 and 2300 m, respectively, and the counterclockwise component is dominant in their fluctua-tions. (ⅴ) There are the variations of periods fluctuating with the change of depth in the upper 450 m layers. For example, when f＞0, there are the prominent fluctuations of about 22 d and 15 d pe-riods at the 50 and 100 m levels. However, there are no such periods at the layer from 200 m to 400 m, where only the fluctuation of about 13 d period occurs. (ⅵ) There are the fluctuations with periods of more than one month, 23 d and 15 d at the 2000 m and 2300 m levels. (ⅶ) In the layer from 50 m to 2300 m there are the following prominent peaks: ⅰ) the fluctuation in the period range of about 4-8 d, which occurs in the weather process; ⅱ) the fluctuation with inertial period, the fluctuation is clockwise; and ⅲ) the fluctuations with short periods of about 8 h and 6 h. (ⅷ) From the cross spectral estimates between two time series, it is shown that there are significant coherence peaks with the periods of more than two months (T = 68.3 d) and more than one month between the two time series of currents at 2000 m and 2300 m depths, and also those with periods of about half a month (15.5 d), 2 d and so on between two time series of currents at 100 m and 2300 m depths.  相似文献   

15.
High-frequency (HF) radar observations of surface currents were conducted for 3 months during summer 2002 in the Keum River estuary. A comparison between HF radar-derived currents and directly measured ones form a buoy showed that the regression slope is close to 1 and the correlation coefficient greater than 0.86, with an RMS difference less than 13 cm/s which is less than 17% of the tidal current. This fairly good agreement allows us to use HF radar observation in investigating the surface flow and circulation in this tidal-current-dominant coastal-plume area. To examine the spatial variation in tidal current characteristics, as well as currents associated with non-tidal forcing, the HF radar-derived currents were separated into tidal and sub-tidal frequency currents. The overall pattern of M2-current ellipse distribution in the study area showed a counterclockwise rotation, with the offshore maximum current direction to the northeast. Eccentricity, the direction of maximum current, and the phase of net motion of the ellipse changed near the estuary mouth and near the gap of the Saemangeum reclamation tide dyke due to the complex coastal geometry and the out-flowing jet during the ebb period.  相似文献   

16.
The tidal circulation patterns in the Terminos Lagoon were studied based on the analysis of 1 year of measurements and numerical simulations using a baroclinic 3D hydrodynamic model, the MARS3D. A gauging network was installed consisting of six self-recording pressure–temperature sensors, a tide gauge station and two current profilers, with pressure and temperature sensors moored in the main lagoon inlets. Model simulations were validated against current and sea level observations and were used to analyse the circulation patterns caused by the tidal forcing. The numerical model was forced with eight harmonic components, four diurnal (K 1, O 1, P 1, Q 1) and four semi-diurnal (M 2, S 2, N 2, K 2), extracted from the TPX0.7 database. The tidal patterns in the study area vary from mixed, mainly diurnal in the two main inlets of the lagoon, to diurnal in its interior. The tidal residual circulation inside the lagoon is dominated by a cyclonic gyre. The results indicate a net flux from the southwest Ciudad del Carmen inlet (CdC) towards the northeast Puerto Real inlet (PtR) along the southern side of the lagoon and the opposite in the northern side. The results indicate two areas of strong currents in the vicinity of the inlets and weak currents inside the lagoon. The area of strong currents in the vicinity of the CdC inlet is larger than that observed in the PtR inlet. Nevertheless, the current analysis indicates that the highest current speeds, which can reach a magnitude of 1.9 m s?1, occurred in PtR. A further analysis of the tide distortion in the inlets revealed that both passages are ebb dominated.  相似文献   

17.
Observations are presented of currents, hydrography and turbulence in a jet-type tidally forced fjord in Svalbard. The fjord was ice covered at the time of the experiment in early spring 2004. Turbulence measurements were conducted by both moored instruments within the uppermost 5 m below the ice and a microstructure profiler covering 3–60 m at 75 m depth. Tidal choking at the mouth of the fjord induces a tidal jet advecting relatively warmer water past the measurement site and dominating the variability in hydrography. While there was no strong correlation with the observed hydrography or mixing and the phase of the semidiurnal tidal cycle, the mean structure in dissipation of turbulent kinetic energy, work done under the ice and the mixing in the water column correlated with the current when conditionally sampled for tidal jet events. Observed levels of dissipation of turbulent kinetic energy per unit mass, 1.1×10−7 W kg−1, and eddy diffusivity, 7.3×10−4 m2 s−1, were comparable to direct measurements at other coastal sites and shelves with rough topography and strong forcing. During spring tides, an average upward heat flux of 5 W m−2 in the under-ice boundary layer was observed. Instantaneous (1 h averaged) large heat flux events were correlated with periods of large inflow, hence elevated heat fluxes were associated with the tidal jet and its heat content. Vertical heat fluxes are derived from shear-probe measurements by employing a novel model for eddy diffusivity [Shih et al., 2005. Parameterization of turbulent fluxes and scales using homogeneous sheared stably stratified turbulence simulations. Journal of Fluid Mechanics 525, 193–214]. When compared to the direct heat flux measurements using the eddy correlation method at 5 m below the ice, the upper 4–6 m averaged heat flux estimates from the microstructure profiler agreed with the direct measurements to within 10%. During the experiment water column was stably, but weakly, stratified. Destabilizing buoyancy fluxes recorded close to the ice were absent at 5 m below the ice, and overall, turbulence production was dominated by shear. A scaling for dissipation employing production by both stress and buoyancy [Lombardo and Gregg, 1989. Similarity scaling of viscous and thermal dissipation in a convecting boundary layer. Journal of Geophysical Research 94, 6273–6284] was found to be appropriate for the under-ice boundary layer.  相似文献   

18.
The relation between tidal flow asymmetry and net transport of sediment in the semidiurnal regime has been extensively described. This study reveals that in the diurnal regime, the direction of long-term net bed-load transport and resulting morphologic changes is partly determined by the phase-angle relationship of O1, K1, and M2. Simple analytical formulations of time-averaged bed-load transport were derived which separate the relative contributions of tidal asymmetry from that of residual flow with tidal stirring. In this particular case, the Red River Delta in Vietnam, transports related to tidal asymmetry are larger than those induced by the monsoon currents, and are an order of magnitude larger than those associated with topographic residual flow around the delta. Tide-induced morphologic changes dominate at water depths between 10 and 25 m, of which the patterns of erosion and deposition overlap with observed bathymetric changes. Additional observed changes that occur in more shallow water cannot be explained by tidal asymmetry and are probably related to wave action and to deposition from the buoyant river plume.Responsible Editor: Jens Kappenberg  相似文献   

19.
《Continental Shelf Research》2006,26(12-13):1469-1480
The generation of internal waves in the partially mixed estuaries is examined. The numerical experiments consider the barotropic tidal currents interacting with isolated obstacles in an open channel. The bottom boundary layer and longitudinal salinity gradient are included. Internal lee (arrested) waves are excited when the accelerating barotropic tidal current approaches the first-mode internal wave speed. The arrested waves are amplified, and are subsequently released when the decelerating tidal current falls below the first-mode internal wave speed. The power input from the barotropic tidal energy into internal wave energy is calculated. It is on the order of 10−2 W/m2, and is comparable to the estimated interior dissipation rate. This suggests that the tidally generated internal waves could be a significant energy source for mixing in the halocline.  相似文献   

20.
Terrain-following ocean models are being used to simulate baroclinic tides and provide estimates of the tidal fields for circulation and mixing studies. These models have successfully reproduced elevations with most of the remaining inaccuracies attributed to topographic errors; however, the replication of barotropic and baroclinic velocity fields has not been as robust. Part of the problem is the lack of an adequate observational dataset in the simulated regions to compare the models. This problem was addressed using a dataset collected during the Flow over Abrupt Topography initiative at Fieberling Guyot. To evaluate the capability of the Regional Ocean Model System (ROMS) to simulate baroclinic tidal velocities, the combined tides for four constituents, M2, S2, K1, and O1, were modeled over Fieberling Guyot. Model inputs, numerical schemes, and parameterizations were varied to improve agreement with observations. These included hydrography, horizontal resolution, and the vertical mixing parameterization. Other factors were evaluated but are not included in this paper. With the best case, semidiurnal baroclinic tides were well replicated with RMS differences between the model estimates and the observations of 1.85 and 0.60 cm s−1 for the major axes of the tidal ellipses for M2 and S2, respectively. However, diurnal K1 baroclinic tides were poorly simulated with RMS differences of 4.49 cm s−1. In the simulations, the K1 baroclinic tides remained bottom-trapped unlike the observed fields, which had free waves due to the contribution of the mean velocity to the potential vorticity. The model did not adequately simulate the mean velocity, and the K1 tides remained trapped. A resolution of 1 km most accurately reproduced the major axes and mean velocities; however, a 4-km resolution was sufficient for a qualitative estimate of where baroclinic tidal generation occurred. Nine vertical mixing parameterizations were compared. The vertical mixing parameterization was found to have minor effects on the velocity fields, with most effects occurring over the crown of guyot and in the lower water column; however, it had dramatic effects on the estimation of vertical diffusivity of temperature. Although there was no definitive best performer for the vertical mixing parameterization, several parameterizations could be eliminated based on comparison of the vertical diffusivity estimates with observations. The best performers were Mellor–Yamada and three generic length scale schemes.  相似文献   

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