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<p> Sand levels were monitored at five southern California beaches for periods of 3 to 15 years, spanning a total of 18 km alongshore. Every 3 months, GPS equipped vehicles measured sand elevations on cross-shore transects from the backbeach to 8 m depth, with 100 m alongshore resolution. Subaerial observations were collected monthly above the spring low-tide line. Wave buoys and a numerical model provided hourly wave estimates in 10 m depth at each site. </p><p> These observations show that beach profile shapes (depth versus cross-shore distance) evolve consistent with the equilibrium hypothesis: under steady wave conditions, evolution is toward a unique, wave condition dependent, equilibrium beach profile. Beaches far out of equilibrium change rapidly, and as equilibrium is approached they change ever more slowly. At the sandy regions, a simple equilibrium beach state model has skill >0.5 (Chapter 2, [Ludka et al., 2015]). </p><p> Repeated nourishments over multiple decades, costing hundreds of thousands of dollars, are a primary beach management strategy worldwide, but the wave-driven redistribution of nourishment sand is poorly understood. At four survey sites, 50,000-300,000 m</p><p>3 of imported sand was placed on the subaerial beach overalongshore spans between 300-1300 m. Wave conditions in the months after placement were similar at all sites, but the subaerial nourishment pads eroded and retreated landward at different rates. A pad built with native-sized sand washed offshore in the first few storms. In contrast, nourishments with coarser than native sand remained on the beach face for several years and protected shorelines during the significant wave attack of the 2015&ndash;16 El Ni&ntilde;o (Chapter 3, [Ludka et al., 2016]). These relatively resilient and coarse subaerial pads stretched alongshore in a pattern consistent with seasonally shifting, wave-driven alongshore currents. Natural gains and losses in the total sand volume budget, integrated spatially over each site, are sometimes larger than the nourishment contributions (Chapter 4, in prep for Coastal Engineering). </p>

<p> The Intertropical Convergence Zone (ITCZ) is a feature that results from the ocean-atmosphere interactions in the tropics around the world. The ITCZ is characterized by surface wind convergence, tall storm clouds, and it forms a belt of high time-averaged precipitation around the globe. The ITCZ undergoes seasonal migrations between 5&deg;S and 15&deg;N roughly following the subsolar point on Earth with the seasons, with a mean annual position located slightly above the Equator, between 2&deg; and 5&deg;N. </p><p> This study tested the hypothesis that there was a northward shift in the median position of the ITCZ in the first decade of the 2000&rsquo;s relative to the 1900&rsquo;s. This hypothesis has been posed in the literature given a weakening in the intensity of the Trade Winds observed in the southern Caribbean Sea during the first decade of the 2000&rsquo;s, with concomitant ecological impacts due to weakening in coastal wind-driven upwelling. The hypothesis was tested by analyzing variations in the monthly latitudinal position of the ITCZ over the Atlantic Ocean relative to the median position computed for the period 1987&ndash;2011. The position of the ITCZ was derived from satellite-derived ocean surface wind measurements collected from 1987 to 2011. A Mann-Kendall analysis and a Monte Carlo simulation were used to test for trends in the median cross-basin latitudinal position of the ITCZ. The study included an analysis of regional changes across the tropical central Atlantic (50&deg;W to 15&deg;W), the Western Atlantic (50&deg;W to 30&deg;W), and the Eastern Atlantic (30&deg;W to 15&deg;W) within the tropics. The results show a slight southward trend in the median position of the ITCZ over the central Atlantic and also in the Eastern Atlantic in the first decade of the 2000&rsquo;s relative to the 1990&rsquo;s. While this trend is barely significant, it is likely simply due to interannual variation in the average annual position of the ITCZ. </p><p> The data were also examined for the timing and persistence of a double ITCZ in the Atlantic. The double ITCZ over the Atlantic appeared every year in February or March, with the largest separation between the northern and southern branches of the ITCZ observed in June and July. </p><p> The possible effects of changes in the average latitudinal position of the ITCZ on the upwelling in the Cariaco Basin (southeastern Caribbean Sea off Venezuela) were also examined. Anomalies of the median of the latitudinal position of the ITCZ in the Atlantic were compared with anomalies of in-situ temperature collected during the 1990&rsquo;s and the first decade of the 2000&rsquo;s by the CARIACO Ocean Time-Series program and with anomalies of satellite SST (from the Advanced Very High Resolution Radiometer satellite; AVHRR) from 1995 to 2016. Correlation analysis were performed between anomalies of water temperatures at various depths and anomalies of satellite SST with anomalies of the monthly mean ITCZ position with lags up to 3 months for the time series, and also just for the Cariaco basin upwelling months (December-April). </p><p> For the whole Cariaco time series there were no significant correlations between the anomalies of the ITCZ position and anomalies in subsurface temperatures in the Cariaco Basin. However, during the upwelling period, the central Atlantic and Western Atlantic ITCZ position anomalies were directly correlated with Cariaco Basin temperature anomalies with no-lag (r = 0.20), and the central and Eastern Atlantic ITCZ position anomalies were inversely correlated with Cariaco Basin temperatures (r ~ -0.22 to -0.28) with ITCZ leading Cariaco temperatures by 3 months. However, these correlations were low, indicating that other factors than the position of ITCZ latitudinal position play bigger role on the Cariaco basin upwelling variability. </p><p> Interannual variability in oceanographic and meteorological characteristics of the Atlantic Ocean are expected as a result of large-scale changes in other regions of the world, including due to changes such as the El Ni&ntilde;o Southern Oscillation (ENSO) and the Atlantic Multidecadal Oscillation (AMO). Six oceanic-atmospheric variables are used to monitor ENSO over the tropical Pacific, while the AMO is determined by monitoring SST over the Atlantic. Correlations with lags of up to &plusmn; 6 months were conducted with those climate indices and the anomalies of the median monthly latitudinal position of the ITCZ. Significant direct correlations with ENSO (Multivariate ENSO Index) were seen in the Atlantic and Western Atlantic (r = 0.15), with ENSO leading the position of the ITCZ anomalies by 3 months. This implies that within three months after an El Ni&ntilde;o event (warm ENSO anomaly in the Pacific) the ITCZ over the mid-Atlantic and Western Atlantic Ocean tends to shift to a more northerly position. The AMO also had a direct influence on the anomalies of the ITCZ position (r = 0.13) in the Central and the Western Atlantic, with the AMO leading ITCZ anomalies by 1 month (i.e. a warming of the North Atlantic led to a northward shift in the ITCZ one month later). Correlations between AMO and the ITCZ anomalies in the Eastern Atlantic were also direct but with no lag. Although significant, these correlations were low. </p><p> An inverse correlation (~ -0.35) was found between ENSO and anomalies of water temperature of the Cariaco Basin. ENSO lagged ocean temperature anomalies by 3 to 4 months for both the whole Cariaco time series and for the upwelling months of CARIACO data. Correlations with AMO were direct (~ 0.4); for the whole time series AMO led Cariaco temperature anomalies by 3 months, but for the upwelling months AMO lagged Cariaco temperature anomalies by one month.</p>

Some aspects of the barotropic instability of continental boundary currents are investigated herein. In the first problem, a piecewise linear wall-jet is perturbed by the most unstable linear mode and the nonlinear evolution of the disturbance is computed. It is shown that the eddies in the wall-jet case evolve much differently than those resulting from the instability of a free jet. This simple model illustrates that even without dissipative processes, a rapid diffusion of mean momentum and vorticity occurs. This contrasts with the main result of this study presented in the second problem where it is argued that the use of a classical eddy parametrization in the analysis of continental boundary currents leading to the diffusion of momentum and relative vorticity fails to recognize that the relevant eddies are dominated by the conservation of potential vorticity, which in turn may produce an increase in the mean relative vorticity. To illustrate this effect, we examine a non-inflected barotropic shear flow destabilized by the cross stream variation in the bottom topography of a continental slope. The finite amplitude evolution of the waves is analyzed in a simple model with a steplike bottom topography and with piecewise uniform potential vorticity distribution. The increase in maximum mean vorticity is computed for various values of the Rossby number and the topographic elevation, and it is suggested that a similar effect, taking into account the isopycnal topography as well as the isobaths, could maintain the large inshore shear of the Gulf Stream. Cross shelf transport of different water types (i.e.: potential vorticity and passive tracers) are also computed and suggested to be pertinent to the more realistic oceanic problem involving baroclinic effects. The numerical calculation employs the well known method of contour dynamics, and the Green's function appropriate for the step-like topography is derived. / Source: Dissertation Abstracts International, Volume: 54-07, Section: B, page: 3531. / Major Professor: Melvin E. Stern. / Thesis (Ph.D.)--The Florida State University, 1993.

A high resolution limited area model with realistic bottom topography has been developed for the East China Sea, based upon the primitive-equation GFDL ocean model. Solutions are obtained for an ocean driven by annual mean heat and fresh-water forcing at the surface, and specified advective transports of mass, heat, and salt at the open boundaries. / Analysis of temperature and salinity on various isopycnal surfaces suggests that the mixing was confined to the surface layer, and that the entrainment of cooler and fresher coastal waters into the Kuroshio begins northeast of Taiwan. / Analysis of fluid particle trajectories illustrates that the mixing in the East China Sea is attributable to the convergence of shelf water driven by Taiwan Strait outflow, and of subsurface Kuroshio water driven by shelf break upwelling. Also, the trajectory analysis suggested that a process of bifurcation is occurring southwest of Kyushu, and this process selects the fluid parcels that compose the Tsushima Warm Current. Further analysis showed that the dominant balance following a fluid parcel in the Kuroshio was between advection and horizontal diffusion. / From this experiment a quantitative estimate of 0.085PW of heat transport, and 0.03Sv $\perthous$ of salt transport, representing 5% of the total Kuroshio transport of heat and salt, have crossed 33$\sp\circ$N into the Yellow and Japan Seas. In addition, as this warm and salty water is removed from the large-scale circulation, cooler and fresher coastal water of the order of 1Sv, blends into the Kuroshio as replacement. / Source: Dissertation Abstracts International, Volume: 55-12, Section: B, page: 5261. / Major Professor: Ya Hsueh. / Thesis (Ph.D.)--The Florida State University, 1994.

Axially-symmetric, linear modes of global, primitive equation, ocean-atmosphere models are examined to see if they contain decadal ($\sim$10-30 years) oscillation time scale modes. / A two-layer model of the global ocean and a two-level model of the global atmosphere are formulated. Both models are linearized about axially-symmetric basic states containing mean meridional circulations in the ocean and the atmosphere. The linearized perturbation system is solved as an eigenvalue problem. Uncoupled, axially-symmetric modes of oscillation of the ocean and the atmosphere are calculated. Axially-symmetric modes of the coupled ocean-atmosphere system are also calculated. Sensitivity of the results to various physical processes and parameter values are examined. / The main conclusion of this study is that linearized, uncoupled and coupled ocean-atmosphere systems in the presence of basic states containing mean meridional circulations can generate axially-symmetric modes of variability on decadal time scales. The spatial structures of uncoupled and coupled decadal modes, however, are quite different. Some of the decadal modes have meridional structures that are comparable to the meridional structures of the observed axially-symmetric modes of oscillations of sea level pressure and sea surface temperature over the Pacific Ocean. Families of decadal period, growing modes in the coupled ocean-atmosphere model exist for a number of sensitivity experiments carried out in this study. / It is shown with a scale analysis that the same mechanism operates to generate variability of the axially-symmetric atmospheric modes on time scales of weeks to decades and variability of the axially-symmetric oceanic modes on time scales of years to centuries. The two most important processes in both the systems are the advection of perturbation fields by basic state meridional velocity and the advection of basic state fields by perturbation meridional velocity. The latter is crucial for the existence of the oscillations. / There are axially-symmetric modes in the uncoupled and coupled models on El Nino-Southern Oscillation and intra-seasonal time scales also. / Source: Dissertation Abstracts International, Volume: 51-04, Section: B, page: 1878. / Major Professor: Jon E. Ahlquist. / Thesis (Ph.D.)--The Florida State University, 1990.

The distribution of iron in three different environments has been studied in an attempt to understand what processes control its concentration in the open ocean. In the Ochlockonee Estuary, dissolved Fe concentrations are dominated by a high molecular weight colloidal fraction ($>$10,000 molecular weight) that is also significant in controlling the dissolved organic carbon concentration. These Fe-oxyhydroxides are greater than 80% removed before the salinity reaches open ocean values. In the eastern Atlantic ocean, surface water Fe concentrations are controlled by atmospheric deposition of Saharan dust as evidenced by a strong correlation with Al. The concentration of Fe in the surface waters of the Sargasso Sea show a large variation between spring and fall with the highest concentrations in the fall correlating with a time of high atmospheric deposition. During this period of elevated surface water concentrations, between 60 and 80 percent of the Fe is not truly dissolved but colloidal in size (between 1000 molecular weight and 0.45 $\mu$m). The colloidal size fraction plays a significant role in the dissolved Fe cycle when concentrations greatly exceed saturation ($>$1 nM). / Source: Dissertation Abstracts International, Volume: 56-12, Section: B, page: 6619. / Major Professor: William M. Landing. / Thesis (Ph.D.)--The Florida State University, 1995.