A tropical atmosphere-ocean coupled model is used to study the effects of a zonally sloping thermocline on the coupled oscillatory modes in the tropics. A two and one half layer oceanic model is coupled with the steady state Gill's atmospheric model. A constant depth mixed layer is included in the upper layer. The SST is calculated in the mixed layer. The interface of the two upper layers is sloping and prescribed as the observed 20$\sp\circ$C isotherm in the Pacific Ocean. The formula of Seager et al. (1988) is used to compute the entrained water temperature. / The unstable waves behave like the propagating modes with much larger SST anomalies observed in the eastern Pacific Ocean. It is found that the coupled instabilities are very sensitive to the steepness of the tilted thermocline in the central Pacific Ocean. A series of numerical experiments have been performed, with different thermocline profiles, in the Pacific Ocean. An interannual oscillation is self sustained when a realistic thermocline profile is specified. The initial disturbance slowly decays and comes back to the equilibrium state of rest when the thermocline slope becomes steeper. The oscillation amplitude becomes much larger when a flatter thermocline is used. An additional numerical experiment is conducted to investigate the role of the western boundary reflection. It is found that the reflection does not change the oscillatory period although it affects the amplitude. A simpler conceptual model is also used to explain the physics. / Source: Dissertation Abstracts International, Volume: 52-12, Section: B, page: 6296. / Major Professor: James J. O'Brien. / Thesis (Ph.D.)--The Florida State University, 1991.

An experimental study was carried out on Rayleigh-Benard convection in Couette flow in a horizontal annulus of water. Measurements of heat and momentum fluxes and observations of plan form were made in the low Rayleigh number (Ra) range from 5 $\times$ 10$\sp3$ to 8 $\times$ 10$\sp4$, and in the Reynolds number (Re) range of 10 to 90 to study the effect of shear on plan form and fluxes. Measurements of heat and momentum fluxes were made in the turbulent range of Rayleigh number from 2 $\times$ 10$\sp5$ to 5 $\times$ 10$\sp7$, and for Reynolds numbers in the range of 40 to 350 to study the effect of shear on momentum flux at high Rayleigh numbers. / In the low Rayleigh number range, with Reynolds numbers in the range from 35 to 86, longitudinal rolls are observed at low Rayleigh numbers and they become unstable as the Rayleigh number is increased. A previously unknown result is that the wave number of these longitudinal rolls increases as the Reynolds number is increased. Instabilities of longitudinal rolls are found to be both wavy and cross-roll. Wavy rolls with cross-roll disturbances are found to be stable in most of the parameter space for $Ra > 4\times 10\sp4$. Discrete slope increases in both the heat and momentum flux curves are observed at the transitions where the longitudinal rolls become unstable. / At high Rayleigh and Reynolds numbers, the Nusselt number (Nu) is observed to depend on Rayleigh number to the 0.33 $\pm$ 0.04 power. Curves of Nu vs Ra at high Re lie slightly below corresponding curves at lower Re. The dimensionless momentum flux (Mo) is observed to have different linear dependence upon Nusselt number in different parts within the parameter space. Curves of Mo vs Nu at high Re are well below curves at lower Re. Slopes of these curves decrease with increased Nusselt number and at the highest range of Rayleigh and Reynolds number, the slope becomes negative. / Source: Dissertation Abstracts International, Volume: 52-10, Section: B, page: 5170. / Major Professor: Ruby Krishnamurti. / Thesis (Ph.D.)--The Florida State University, 1991.

A three layer, wind driven, general circulation model involving both subtropical and subpolar gyres has been developed to study intergyre exchange. Following Schopp and Arhan (1986), the present work allows flow to cross the intergyre boundary baroclinically in a model with three active layer. Solutions with deep southward baroclinic exchange are emphasized. The two principal objectives of this work are to clarify the structure and maintenance of the permanent thermocline and to aid in understanding the distribution of deep water masses. / A class of thermocline structures at the zero Ekman pumping line has been constructed which permit intergyre exchange, or communication. These so-called 'windows', which are where the communication occurs at the intergyre boundary, have several unique properties relative to those computed by Schopp and Arhan, and have richer structure due to the additional baroclinic degree of freedom. This study has successfully generalized Schopp's model to three active layers and fully describes the regime of dynamically consistent, continuous solutions in the entire basin. Analytical solutions with deep southward flow, as well as northward flow with outcrop in the subpolar region, have been found. The study shows that the addition of an active third layer has introduced qualitatively new structure to the solution, namely a second baroclinic 'window' is opened. This new window is physically and dynamically distinct from the first window, and most of the intergyre baroclinic transport can occur through it. It also supports the conjecture that the number of communication windows increases with the number of active layers. / In addition to the model results, observed tracer distributions have been reexamined within the context of this model. Possible explanations for the potential vorticity contours in the North Atlantic Ocean, which connect the northern and southern gyres (McDowell et al. (1982)), and for some of the observed subtropical water anomalies found in the Local Dynamic Experiment (Ebbesmeyer et al. (1986)), which appeared to have sources in the subpolar gyre, are proposed. / Source: Dissertation Abstracts International, Volume: 52-08, Section: B, page: 4099. / Major Professor: William K. Dewar. / Thesis (Ph.D.)--The Florida State University, 1991.

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<p>Strengthened stratification of the upper ocean, associated with either anthropogenic warming trends or natural climate oscillations, is generally expected to inhibit marine primary productivity at low and mid latitudes, based on the supposition that increased water column stability will decrease vertical mixing and consequently the upward entrainment of deep nutrients into the euphotic zone. Herein, we examine the local stratification control of productivity over the subtropical and equatorial Pacific by directly comparing a wide range of contemporaneous metrics, drawn from the modern observational record, for interannual stratification and productivity variability. We find no correlation between the two in the subtropical North Pacific. In the equatorial Pacific we do observe a correlation, but find no evidence of a strong causal connection between the two- instead, our analysis suggest that both biomass and stratification in this region are impacted by changes in the westward transport, via surface currents, of relatively cold, nutrient-rich waters that have been upwelled in the eastern Equatorial Pacific. The importance of horizontal nutrient supply is further evidenced by an analysis of seasonal variability in the subtropical North Atlantic, where the annual contraction and expansion of the oligotrophic region appears to be strongly influenced by the waxing and waning, respectively, of lateral nutrient transfers from neighboring, nutrient rich waters of the subpolar gyre and the West African upwelling zone.</p> / Dissertation

An eddy-resolving upper ocean model is developed to study the dynamics and thermo-dynamics of Baie des Chaleurs (BdC, 47.5-48.5N, 65.5-66.5W), Gulf of St. Lawrence (GSL), Canada. The model has primitive equation dynamics with two active layers embedded with a Kraus-Niiler type mixed layer model at the top. / Forced by observed wind, atmospheric heat fluxes, river runoff and appropriate remote forcing (in particular, the Gaspe Current, GC), the model demonstrates that the mean cyclonic general circulation pattern in the bay is a consequence of the intrusion of the GC. In the mixed layer, atmospheric heat fluxes and horizontal thermal advection play a key role in the thermal balance at the eastern part of the bay. The local mixed layer fluctuations are controlled by wind and GC induced divergence. The entrainment (and its corresponding heat flux) is important at the western part of the bay and changes the mean mixed layer depth on a time scale of more than a week. Varying GC intensified the flow variations induced by the wind in the bay and improved simulation results as compared with observations. / Sensitivity runs are conducted to study the effects of external forcing, important physical processes and the internal physical parameterisation on the model results and to compare these with the main model run. Experiments show that nonlinearity is very important in determining the circulation pattern in the bay. Changing external thermal forcing also modifies dynamical processes in the BdC. The fluctuations in the near surface temperature are mainly due to latent and sensible heat changes. The parameter study indicates that, the model is not overly sensitive to changes in most of the parameters, but suggests that sensitivity of the mixed layer physical parameters depends on the dynamical and thermodynamic system applied. / Hydrographic and current meter data are used first to study the variability of both the dynamics and thermodynamics in the BdC and its relation to the separation/intrusion of the unsteady GC. A numerical model is then applied to gain insight into the problem. The time scales of interest range from tidal to seasonal. / The results show that the kinetic energy in the BdC is dominated by the semi-diurnal tide (M$ sb2$) and periods of 5-10 days for high and low frequency bands, respectively. Most of the energy in the low frequency band is found to be induced by wind-related forcing. / Both observations and model results indicate that seasonal variations in the BdC are strongly related to the characteristics of separation/intrusion of the GC, which is mainly controlled by its transport magnitude as well as phase, duration and strength of its acceleration (or deceleration). The separation occurs when (adverse) vorticity having an opposite sign from that existing upstream is generated near the separation area. Although the separation can be generated in a decelerating GC, it can also occur in an accelerating GC when the GC is strong enough to advect upstream vorticity necessary to form a recirculation and the related adverse vorticity downstream. Nonlinearity is critical to the separation. Nevertheless, separation can be generated in a linear current with strong deceleration. The GC intrudes either along the coastline (attachment) into the bay by a non-separated GC or following the separation of the GC (reattachment). Effects of various physical processes on the separation/intrusion and variability of eddies in the BdC are examined.

One of the most difficult tasks of modeling spatial and spatiotemporal random fields is that of deriving an accurate representation of the dependence structure. In practice, the researcher is faced with selecting the best empirical representation of the data, the proper family of parametric models, and the most efficient method of parameter estimation once the model is selected. Each of these decisions has direct consequence on the prediction accuracy of the modeled random field. In order to facilitate the process of spatial dependence modeling, a general class of covariogram estimators is introduced. They are derived by direct application of Bochner's theorem on the Fourier-Bessel series representation of the covariogram. Extensions are derived for one, two and three dimensions and spatiotemporal extensions for one, two and three spatial dimensions as well. A spatial application is demonstrated for prediction of the distribution of sediment contaminants in Galveston Bay estuary, Texas. Also included is a spatiotemporal application to generate predictions for sea surface temperatures adjusted for periodic climatic effects from a long-term study region off southern California.

An idealized box model of the Indian Ocean is used to examine the hypothesis proposed by Godfrey and Weaver (1991) that the buoyancy-forced Leeuwin Current off the west coast of Australia is a manifestation of a basinwide thermohaline circulation driven by the Indonesian throughflow. / The stronger Sverdrup circulation dominates the thermohaline circulation in most of the model ocean except near the eastern boundary. / The western boundary currents apparently play a very minor role in this basinwide thermohaline circulation. This differs from the warm water route proposed by Gordon (1986), and supports the alternative hypothesis that the heat from the equatorial Pacific is returned to the South Atlantic via the eastward-flowing Antarctic Circumpolar Current rather than past the Agulhas Retroflection. / The Indonesian throughflow is shown to significantly affect the surface heat fluxes and the meridional heat transport in the Indian Ocean. The role of the throughflow in maintaining the very warm climate of the Indian Ocean (a net exporter of heat) is described. / Large-scale, fairly long period ($>$100 days) barotropic eddies are found in the western portion of the basin for some solutions.