Showing papers by "Nova Southeastern University published in 1981"

Array measurements of atmospheric pressure fluctuations above surface gravity waves

Abstract: A joint experiment to study microscale fluctuations of atmospheric pressure above surface gravity waves was conducted in the Bight of Abaco, Bahamas, during November and December 1974. Field hardware included a three-dimensional array of six wave sensors and seven air-pressure sensors, one of which was mounted on a wave follower. The primary objectives of the study were to resolve differences in previous field measurements by Dobson (1971), Elliott (1972b) and Snyder (1974), and to estimate the vertical profile of wave-induced pressure and the corresponding input of energy and momentum to the wave field.Analysis of a pre-experiment intercalibration of instruments and of 30 h of field data partially removes the discrepancy between the previous measurements of the wave-induced component of the pressure and gives a consistent picture of the profile of this pressure over a limited range of dimensionless height and wind speed. Over this range the pressure decays approximately exponentially without change of phase; the decay is slightly less steep than predicted by potential theory. The corresponding momentum transfer is positive for wind speeds exceeding the phase speed. Extrapolation of present results to higher frequencies suggests that the total transfer is a significant fraction of the wind stress (0·1 to 1·0, depending on dimensionless fetch).Analysis of the turbulent component of the atmospheric pressure shows that the ‘intrinsic’ downwind coherence scale is typically an order-of-magnitude greater than the crosswind scale, consistent with a ‘frozen’ turbulence hypothesis. These and earlier data of Priestley (1965) and Elliott (1972c) suggest a horizontally isotropic ‘intrinsic’ turbulent pressure spectrum which decays as k−ν where k is the (horizontal) wave-number and ν is typically −2 to −3; estimates of this spectrum are computed for the present data. The implications of these findings for Phillips’ (1957) theory of wave growth are examined.

A Linear Stratified Ocean Model of the Equatorial Undercurrent

Abstract: A linear stratified ocean model is used to study the wind-driven response of the equatorial ocean. The model is an extension of the Lighthill (1969) model that allows the diffusion of heat and momentum into the deeper ocean, and so can develop non-trivial steady solutions. To retain the ability to expand solutions into sums of vertical normal modes, mixing coefficients must be inversely proportional to the square of the back ground Vaisala frequency. The model is also similar to the earlier homogeneous ocean model of Stommel (i960). He extended Ekman dynamics to the equator by allowing his model to generate a barotropic pressure field. The present model differs in that the presence of stratification allows the generation of a baroclinic pressure field as well. The most important result of this paper is that linear theory can produce a realistic equatorial current structure. The model Undercurrent has a reasonable width and depth scale. There is westward flow both above and below the Undercurrent. The meridional circulation conforms to the ‘classical’ picture suggested by Cromwell (1953). Unlike the Stommel solution, the response here is less sensitive to variations of parameters. Ocean boundaries are not necessary for the existence of the Undercurrent but are necessary for the existence of the deeper Equatorial Intermediate Current. The radiation of equatorially trapped Rossby and Kelvin waves is essential to the development of a realistic Undercurrent. Because the system supports the existence of these waves, low-order vertical modes can very nearly adjust to Sverdrup balance (defined below), which in a bounded ocean and for winds without curl is a state of rest. As a result, higher-order vertical modes are much more visible in the total solution. This property accounts for the surface trapping and narrow width scale of the equatorial currents. The high-order modes tend to be in Yoshida balance (defined below) and generate the characteristic meridional circulation pattern associated with equatorial Ekman pumping.

A linear stratified ocean model of the coastal undercurrent

Abstract: The linear, stratified ocean model of McCreary (1981) is used to study the wind-driven response of the ocean near an eastern coast. The model can be regarded as an extension of the inviscid models of Lighthill (1969) and of Gill & Clarke (1974) that allows the vertical diffusion of heat and momentum into the deep ocean. Solutions are still found as expansions of vertical normal modes. Vertical mixing affects each mode as a linear drag with a drag coefficient that increases rapidly with mode-number, n. A zonally uniform band of steady equatorward winds forces the ocean, and the resulting flow field has many features in common with observations at eastern boundaries. There is a surface equatorward jet and a poleward Coastal Undercurrent confined within 10-20 km of the coast. Both currents extend well poleward of the wind band. Upwelling does not reach great depths, but occurs only above the core of the Undercurrent. Weak downwelling occurs at greater depths. There is offshore Ekman drift in the surface mixed layer and return flow at a depth slightly above the core of the Undercurrent. The baroclinic alongshore pressure gradient field and the vertical mixing of heat and momentum are essential elements of the model dynamics, but the $\beta $ and horizontal mixing are not. Low-order vertical modes (n 6) tend toward a two-dimensional balance. They generate the transverse circulation pattern associated with coastal Ekman pumping.

Analysis of current observations on the Georgia shelf

Abstract: An analysis is made of HF radar measurements of surface currents in shallow water near the Georgia coast, and also of vertical profile measurements of current and density. The dominant structure is found to be a clockwise ellipse of semidiurnal periodicity, the ellipses becoming smaller, narrower and turning clockwise with depth. There is a definite phase lead of the bottom currents with respect to the upper currents, and some evidence of veering of the currents in the non-Ekman sense. In order to explain the observed vertical variations, a simple analytical expression is developed for periodic rotary currents in a barotropic ocean of constant eddy viscosity and depth h, when the free-surface elliptic motion is known. The solution depends on the ratios ω/f and h/hEkman, and also on the sense of turning of the free surface ellipse. The model is able to explain several features of the observed vertical variations as frictional effects.

Growth Characteristics of Reef-Building Corals Within and External to a Naval Ordinance Range: Vieques, Puerto Rico

Abstract: The skeletal growth of reef·building corals is known to be sensitive to the environment. In particular. high levels of sedimentation and turbidity lead to decreased growth rate. suppressed growth variation. and. ultimate· ly. coral death because of reduced illumination necessary to zooxanthellae andJor increased energy expenditure by the coral animal to remove impacted sediments. To assess the effect of Naval Ordnance Range usage at Vieques. Puerto Rico. specimens of Montastrea an· nularis were collected from reefs adjacent to and removed from the range area. Growth was measured from an· nual increments revealed by X·radiography of medial slabs of the coral skeletons. Mean growth rates and growth variances were calculated for each station or station grouping over the common time period 1970-1977. Statistical comparison of the growth data reveals a general similarity between range and control stations. This evidence coupled with quantitative coral abundance and diversity data of others indicate a lack of anomalous and adverse sedimentation/turbidity conditions affecting corals on reefs near the range area. Chronologies of coral band widths compared to historical recorded environmental data indicate that a major natural parameter which controls coral growth in Vieques is annual water temperature variation.

Assessing compliance to home relaxation: A simple technology for a critical problem

Abstract: A simple, low-cost, and reliable technology for assessing compliance with relaxation practice in the natural environment is presented. Brief, audible “cue” tones are overdubbed onto selected client relaxation tapes, which are ordered by the therapist and then played in sequence by the client. The presence/absence or number of cue tones on each tape in the sequence is self-monitored, thereby providing the therapist with a record for objectively assessing whether or not the tapes were used as instructed. A clinical case example is presented to illustrate use of the procedure. Finally, advantages and limitations of the procedure are discussed.

Beach nourishment, a practical method of erosion control

Abstract: Artificial beach nourishment, the placing of sand onto eroded beaches, is increasingly employed by coastal engineers as an alternative to structural control of shoreline erosion. Man-made beaches approximating natural forms and processes offer greater protection against storms than eroded beaches and provide increased recreational opportunities. It is hoped that maintenance nourishment will keep pace with subsidence and eustatic rise in sea level, primary causes of beach erosion. Even though negative impacts of beach restoration may be short-lived and limited in scope, sound ecological engineering practices require careful monitoring of dredging operations.

Forced Shelf Circulation by an Alongshore Wind Band

Abstract: The forced circulation over a continental shelf generated by the alongshore wind stress is studied within the frictional regime. The model alongshore wind stress has a finite extent in the alongshore direction and oscillates monochromatically, resembling a series of anticyclones traveling across the coastline. Both the shelf-wave response and the localized non-wavelike response exist within the wind band. The numerical results show that the interaction of shelf waves with locally wind-forced response generates a large increase in the phase speed within the wind band. Given an alongshore variation in the alongshore wind stress, a right-bounded phase propagation is possible even in the absence of continental shelf waves. Given a reasonable friction currently accepted for the east coast of the United States, the resonance mechanism at the cutoff frequency may not be important, and lower frequency wind events generate larger amplitude continental shelf circulation. By reducing the friction, energy at cutoff fequencies leaks out of the wind band in both directions effectively. It also is shown that non-wavelike response depends only on the local wind stress and is not affected significantly by friction.

The vascular anastomoses of the human heart.

Abstract: Several types of vascular anastomoses were found in the normal human heart which mainly represent the increase in calibre of pre-existing channels in response to certain stimuli such as total or partial occlusion of the coronary arteries, generalized hypoxia, anaemia, bodily exercise, drugs, etc.. The heart circulation though looking rather simple with several types of vessels with different going in and out orifices, is in fact, extremely complex. We could show with this new technique different kind of anastomoses in normal hearts, between the same type of vessels, between vessels and heart chambers and between different types of vessels.