High-resolution Current Profiler Research Articles

Seasonal variability of tides in the deep northern South China Sea

Tides are the major energy source for ocean mixing, regulating the variation of oceanic circulation and sediment transport in the deep sea. Here twenty months of high-resolution current profiles, which were observed via a mooring system at a water depth of 2100 m in the northern South China Sea (SCS), are used to investigate seasonal variability in deep-sea tides. Spectral analysis shows that tides in this region are dominated by diurnal tide, and both diurnal and semidiurnal tide are vertical mode-1 dominant. Baroclinic diurnal tidal current exhibits pronounced seasonal variability, showing its kinetic energy was the strongest in summer, and the maximum depth-averaged value was up to 86.7 cm2 s−2, which was about 1.5 times of that in winter and twice that in spring and autumn. In contrast, baroclinic semidiurnal tide displays no evident seasonal variability. Such seasonal variability in baroclinic tide was mainly modulated by the barotropic forcing from the Luzon Strait. On the other hand, two anticyclonic eddies and one cyclonic eddy, which originated off southwestern Taiwan in winter, crossed the mooring system. The cyclonic eddy had weak impact on current velocity in the deep sea, but the two deep-reaching anticyclonic eddies enhanced the current velocity through the full-water column by inducing strong subinertial flows. Consequently, the kinetic energy of tides was strengthened and the incoherent variance of baroclinic diurnal tide increased in winter, which contributed ~85% of the variability in diurnal tide. Meanwhile, the velocity of baroclinic diurnal tide was reduced in winter, which was attributed to the weakened stratification induced by the passage of anticyclonic eddies in the deep sea. The seasonal variability of tides in the deep northern SCS can provide a dynamic mechanism for interpreting sediment transport processes in the deep sea on different time scales.

Structure of Turbulent Flow in a Shallow Tidal Estuary

A high-resolution current profiler (HRCP), which belongs to a pulse-to-pulse coherent Doppler sonar, has been used to measure vertical profiles of turbulence parameters, such as the Reynolds stresses, eddy viscosity, production and dissipation rates, etc., and to test the parametrization of dissipation rate and eddy viscosity. The HRCP and automatic ascending/descending CTD are deployed during the autumn of 2001 for 24 h in a tidal estuary. Reliable velocities along the beams with HRCP are collected with 3 s intervals and a vertical resolution as fine as 0.03 m in the range 0.02–0.98 m above the bottom. Density profiles with the CTD are taken nominally every 30 sec. The turbulent velocity variables depend largely on the tidal phase; the variables during the ebb deviate from those in neutral equilibrium boundary layer. This deviation during the ebb presumably arises from the “inactive motion.” The stability function SM in the Mellor–Yamada (M–Y) model is smaller than 0.39 even when the stratification is negligible during the flood. The constant of proportionality B1 in the dissipation model is larger than 16.6 used in M–Y model. There is room for improving some of the mixing parametrizations in estuarine tidal flows.

High Resolution Measurements of Turbulence, Velocity and Stress Using a Pulse-to-Pulse Coherent Sonar

Abstract Considered are the capabilities of a recently developed pulse-to-pulse coherent sonar called the High Resolution Current Profiler (HRCP). Special emphasis is placed on methods whereby reliable and accurate vertical profiles of turbulence parameters, such as turbulent kinetic energy and Reynolds stresses, may be extracted from such sonars. The prototype HRCP has been developed in order to obtain precise and reliable measurements of both the mean and the fluctuating components of the velocity vector profile in the bottom boundary layer (lowermost 10 m). The prototype HRCP developed through the project BSEX is a 307 KHz pulse-to-pulse coherent sonar with four beams mounted 30° off the vertical in 90° azimuthal increments. It has 50 range cells covering a vertical profiling distance of 10 meters. The data collected are radial speeds along the four acoustic beams. Thus, care has to be exercised in interpreting the measurements in terms of turbulence parameters. It is shown, based upon reasonable assum...

High resolution current profiling in the Straits of Florida

A method is described for obtaining high resolution current profiles in areas with moderate and strong flows. Repeated profiling at two-hour intervals was conducted at three locations in the Straits of Florida. The observed profiles reveal rich details in the vertical structure of the Florida Current. The two most pronounced features are transient phenomena: a strong subsurface current maximum 4 miles west of Bimini and the occurence of southward flow in the lower half of the water column at the western side of the Straits of Florida.

Southward Flow under the Florida Current

High-resolution current profiles were obtained in the Florida Straits by means of a new technique. Large temporal variations in the current profiles were observed. At times extensive southward flow, with speeds up to 30 centimeters per second, was recorded in the lower half of the water column.

Evaluation Of M-Y Closure Model In Tidal Estuary With TurbulenceData From High-resolution Current Profiler

A high-resolution current profiler (HRCP), which belongs to a pulse-topulse coherent Doppler sonar, has been used to measure accurate vertical profiles of turbulence parameters, such as the Reynolds stresses, eddy viscosity, production and dissipation rates, etc., and to test the parameterization of dissipation rate and eddy viscosity. The HRCP and automatic ascendingldescending CTD are deployed in a tidal shallow estuary. The current near the bed during the ebb tide is smaller than during the flood tide. Thus, the bed-generated turbulence during the ebb is weak compared with that during the flood. The velocity profiles are almost linear during the ebb, whereas the profiles fit to a logarithmic form during the flood. The rate of TKE production is not balanced by dissipation even near the bottom. The constant of proportionality B1 in the dissipation model is much larger than 16.6 used in M-Y model. The results of numerical simulation using M-Y model are compared with the mean and turbulence data deduced by HRCP. l Introduction Many industrial or domestic wastes are discharged to coastal waters. Since estuaries often lie within regions of high population and industrial activity, the effect of discharged waste on the water quality, biological productivity, and species diversity in estuaries have become a topic of increasing concern. The flow in tidal estuaries is very complex, particularly due to tidal oscillations associated with changes in depth, mean velocity, direction of flow and density gradients affected by salt, heat and suspended particles. Moreover, the flow is very sensitive to the vertical mixing by turbulence. Therefore, it Transactions on the Built Environment vol 70, © 2003 WIT Press, www.witpress.com, ISSN 1743-3509