Bibliography of the Phd dissertations written by the students of Dr. James J. O'Brien

El Niño Resources

Other Bibliographies

Comprehensive El Niño Bibliography

PhD Students

Dr. Jacob Padro
Dr. John Lee
Dr. Harley Hurlburt
Dr. J. Dana Thompson
Dr. John Kindle
Dr. Joseph Wroblewski
Dr. Richard Grotjahn
Dr. Benoit Cushman-Roisin
Abstracts are included in the following Dissertations.
Dr. George Heburn
Dr. Alex Camerlengo
Dr. Antonio J. Busalacchi
Dr. Richard Rood
Dr. Sirpa Hakkinen
Dr. Ruth Preller

ENERGY SOURCES FOR SOME TROPICAL WAVES
PADRO, JACOB
112 p., 1971

NUMERICAL SIMULATION OF THE PLANETARY BOUNDARY-LAYER OVER BARBADOS, WEST INDIES
LEE, JOHN DENIS
111 p., 1973

THE INFLUENCE OF COASTLINE GEOMETRY AND BOTTOM TOPOGRAPHY ON THE EASTERN OCEAN CIRCULATION
HURLBURT, HARLEY ERNEST
116 p., 1974

THE COASTAL UPWELLING CYCLE ON A BETA-PLANE: HYDRODYNAMICS AND THERMODYNAMICS
THOMPSON, JAMES DANA, JR.
154 p., 1974

EQUATORIAL PACIFIC OCEAN VARIABILITY--SEASONAL AND EL NINO TIME SCALES
KINDLE, JOHN CLIFTON
148 p., 1979

A MODEL OF THE SPATIAL STRUCTURE AND PRODUCTIVITY OF PHYTOPLANKTON POPULATIONS DURING VARIABLE UPWELLING OFF THE COAST OF OREGON
WROBLEWSKI, JOSEPH STANLEY
133 p., 1976

THE INFLUENCE OF THERMAL FRONTS UPON THE SOLUTIONS OF AN ANALYTICAL MODEL OF A MID-LATITUDE WAVE-CYCLONE
GROTJAHN, RICHARD DONALD
171 p., 1979

MIXING, CONVECTION, AND ADVECTION IN THE UPPER OCEAN
CUSHMAN-ROISIN, BENOIT
212 p., 1980

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A NUMERICAL MODEL OF COASTAL UPWELLING OFF PERU--INCLUDING MIXED LAYER DYNAMICS
HEBURN, GEORGE WASHINGTON
140 p., 1980
Two versions of an x-y-t, two-layer, numerical model with realistic coastline and bottom topography on a rotated (beta)-plane are used to study the upwelling system off the Peruvian coast. A hydrodynamic version of the model with two homogeneous layers is used to examine the interaction between the bottom topography and coastal trapped waves. The fluctuations in the undercurrent off the Peruvian coast have been shown (Smith, 1978) to be uncorrelated with the local winds. The hypothesis proposed by Smith is that these fluctuations are the result of coastal trapped Kelvin waves. A parameterization scheme, based on Kelvin wave dynamics is introduced to simulate these coastal trapped waves. The relationship between bottom topographic features and the pycnocline height anomalies for a longshore current event is then examined. The principle of conservation of potential vorticity is used to explain the interactions between the waves and the bottom topography. The results of the hydrodynamic model shows that the interaction between a propagating waves and the bottom topography can play a significant role in determining the location of the centers of enhanced upwelling. A thermodynamic version of the model, one in which the layer averaged densities are predicted variables, it used to extend the information available from the hydrodynamic models. A parameterization scheme for the interfacial mixing is introduced. There is a twofold reason for introducing thermodynamic and mixing into the model. The first is to include physics normally neglected in upwelling models. The second is to provide a physical mechanism to keep the interface from surfacing. The locations of the centers of enhanced upwelling as indicated by the interface displacement and sea surface temperature are examined and compared to observed data. The results of the thermodynamic model show that a positive heat flux is required to balance the large scale wind induced upwelling in order to observe the centers of enhanced upwelling due to internal waves/bottom topography interaction. The local wind forcing for both versions of the model are derived from meteorological buoy wind observations. The time series of wind observations from Pacific Marine Environmental Laboratory's (PMEL) PSS-mooring during March, April, May (MAM) 1977 are used to construct the time- dependent amplitudes for the wind function.

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ON THE DYNAMICAL RESPONSE OF THE SUBARCTIC FRONT TO MOMENTUM TRANSFER
CAMERLENGO, ALEJANDRO LIVIO
102 p., 1981
Theoretical studies and numerical experiments of the subarctic front are conducted. The theoretical side of this research encompasses the determination of a stability criterion and the role friction plays as a dissipative mechanism. In the first case study, it is established that if the difference between the phase speed of the perturbation and the mean long-front geostrophic flow is greater than a certain value, the subarctic front is stable everywhere. In the other case study, it is proved that the time scale of dissipation is sufficiently large to neglect horizontal friction. While the effect of the westerly winds causes a southward shift of the front, the effect of a negative curl shows convergence at the front. This convergence strongly favors frontogenesis. It is established that the phase speed of the first baroclinic mode is larger in a numerical model where a constant density jump between layers is employed. Thus, a smaller time scale is required to avoid the numerical instability caused by the violation of the CFL criterion. A numerical four-layer hydrodynamical model is implemented to investigate the role the atmosphere exerts on the dynamics of the subarctic front. The salient features at the wake of a strong cyclone can be summarized as follows: (i) upwelling of 20 meters of the four interfaces occurs; (ii) the water remains upwelled for several weeks; (iii) the e-folding time scale of the vertical oscillations induced by the storm's passage is of the order of 10 days; (iv) a region of relative maximum convergence is observed in the lower layers below a region of relative maximum upwelling in the upper layer; and (v) the long and cross-front velocity fields are in quadrature in time, with the cross front velocity lagging the long front velocity. With the exception of the cyclone's case, it is established that the effects of the atmospheric wind forcing are confined to the upper layer. These results are supported by oceanic observations. Finally, it is also proved that the response of the front to the atmospheric momentum transfer is independent of the initial form of the subarctic front.

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WIND-DRIVEN VARIABILITY OF THE TROPICAL PACIFIC AND ATLANTIC OCEANS
BUSALACCHI, ANTONIO JAMES, JR.
149 p., 1982
Models incorporating a single baroclinic mode and realistic coastline geometry are used to analyze the linear, dynamic response to estimates of the interannual wind field over the tropical Pacific and the seasonally varying winds of the tropical Atlantic. The interannual variability of the tropical Pacific is studied for the period January, 1961 to December, 1978. Model pycnocline variations at several locations are similar to the observed sea level fluctuations. El Nino events are depicted as periods when the pycnocline is persistently deep along the eastern boundary. Remotely forced equatorial Kelvin waves are responsible for this response. The character of each simulated El Nisno is strongly dependent on the relation between zonal wind stress changes in the western an central equatorial Pacific. A rapid shoaling of the pycnocline in the western tropical Pacific during each El Nino is caused by westward-propagating Rossby waves. Interannual pycnocline displacements in the central equatorial Pacific are determined by the superposition of Kelvin waves excited to the west and first-mode Rossby waves generated to the east. The forced periodic response to the seasonal wind field of the tropical Atlantic is a spatially dependent combination of a locally forced response, Kelvin waves, Rossby waves, and multiple wave reflections. The seasonal displacements of the model pycnocline are compared with observed dynamic height. Annual and semiannual fluctuations dominate the seasonal signal throughout the basin. In general, the distribution of amplitude and phase are similar for annual changes in dynamic height and pycnocline depth. Major features of the seasonal response are reproduced, e.g. an east-west tilting of the equatorial pycnocline about a pivot point, the seasonal pycnocline movement along the northern and southern coast of the Guinea Gulf, and a significant change of phase in the ocean variability north and south of the ITCZ. The relative importance between local and remote forcing is determined for several parts of the basin. The wind-driven annual signal in the Gulf of Guinea is due to zonal wind stress fluctuations west of the gulf. The seasonal response in the western equatorial and northernmost parts of the basin are primarily local.

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MECHANISMS OF STRATOSPHERIC OZONE TRANSPORT
ROOD, RICHARD BENTON
224 p., 1982
Two (beta)-plane planetary wave models are used to study ozone transport in the stratosphere. In the first model, ozone transport is calculated for steady, dissipative planetary waves using the Eulerian, Lagrangian-mean, and residual circulations. A Lagrangian model of parcel dynamics is used to interpret planetary wave-photochemistry interaction. In chemically active regions the mean field ozone changes are found to be significant only where there are large gradients in chemical sources and sinks along particle trajectories. The largest changes in the mean field are found in the lower stratosphere and are due to the Lagrangian-mean advection. In the second model, ozone transport is calculated for the combined diabatic and time dependent planetary wave circulations. Both circulations are instrumental in the formation of the polar spring ozone maximum. The diabatic circulation transports ozone into the lower stratosphere, and planetary waves transport large amounts of ozone northward during sudden and final warmings. Using the transport mechanisms revealed in these models, a scenario is deduced to explain observed large scale ozone transport phenomena.

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DYNAMICS OF THE COUPLED ICE-OCEAN SYSTEM IN THE MARGINAL ICE ZONE: STUDY OF THE MESOSCALE PROCESSES AND OF CONSTITUTIVE EQUATIONS FOR SEA ICE
HAKKINEN, SIRPA MARJA
107 p., 1984
This study is aimed at the modelling of mesoscale processes such as up/downwelling and ice edge eddies in the marginal ice zones. A 2-dimensional coupled ice-ocean model is used for the study. The ice model is coupled to the reduced gravity ocean model (f-plane) through interfacial stresses. The constitutive equations of the sea ice are formulated on the basis of the Reiner-Rivlin theory. The internal ice stresses are important only at high ice concentrations (90- 100%), otherwise the ice motion is essentially free drift, where the air-ice stress is balanced by the ice-water stress. The model was tested by studying the upwelling dynamics. Winds parallel to the ice edge with the ice on the right produce upwelling because the air-ice momentum flux is much greater than air-ocean momentum flux, and thus the Ekman transport is bigger under the ice than in the open water. The upwelling simulation was extended to include temporally varying forcing, which was chosen to vary sinusoidally with 4 day period. This forcing resembles successive cyclone passings. In the model with thin oceanic upper layer, ice bands were formed. The up/downwelling signals do not disappear in wind reversals because of nonlinear advection. This leads to convergences and divergences in oceanic and ice velocities which manifest themselves as ice banding. At least one wind reversal is needed to produce one ice band. A constant wind field exerted on a varying ice cover will generate vorticity leading to enhanced up/downwelling regions, i.e., wind forced vortices. Steepening and strengthening of the vortices are provided by the nonlinear terms. As in the case of ice band formation, the wind reversals will separate the vortices from the ice edge, so that the upwelling enhancements are pushed to the open ocean and the downwelling enhancements underneath the ice.

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A NUMERICAL MODEL STUDY OF CIRCULATION IN THE ALBORAN SEA
PRELLER, RUTH HELEN
139 p., 1985
Reduced gravity and two-layer numerical models have been used to study the circulation in the westernmost basin of the Mediterranean Sea, the Alboran Sea. Circulation is forced by flow through a 20 km wide port in the western boundary representing the Strait of Gibraltar. The reduced gravity model domain is a rectangle measuring 600 km x 160 km with 10km x 5 km grid resolution. When forced by an eastward or northeastward inflow, the model solutions evolve to a steady state which exhibits a meandering current. The first meander of the current forms the northern boundary of an anticyclonic gyre. Horizontal dimensions of the gyre are strongly dependent up on the inflow angle, vorticity associated with the incoming current, magnitude of the incoming transport and the north- south extent of the basin. The meandering current is considered a standing Rossby wave with a highly distorted vorticity trajectory due to the interaction of the current with the northern and southern boundaries. When velocity (transport) is increased, the wavelength increases approximately as SQRT.(v). As a result the anticyclonic gyre shifts east as velocity increases and west as velocity decreases. These solutions show that bottom topography, winds and coastline features are not necessary mechanisms for the formation of the gyre. Two-layer model solutions were obtained using realistic topography, geometry and a westward moving lower layer. The addition of the lower layer flow and topography slightly distorted the circulation in the upper layer, particularly in the southern half of the basin. With topography included, the lower layer flow followed a path similar to that observed for the Mediterranean Deep Water. When topography was removed, the flow followed the path taken by the Levantine Intermediate Water. Experiments using climatological wind to force the model show that a strong wind driven circulation from the Balearic Sea causes cyclonic circulation to form in the location of the Alboran gyre. This cyclonic circulation, however, is very weak and when combined with the Atlantic water inflow serves only to slightly weaken the anticyclonic gyre.

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THE EFFECT OF THE BENTHIC BOUNDARY LAYER ON THE PHYSICS OF INTENSE MESOSCALE EDDIES
PEGGION, GERMANA
152 p., 1985
The Benthic Boundary Layer is a region close the ocean bottom with features distinct from the oceanic interior. Near the bottom the ocean is turbulent and the resultant mixing leads to a neutrally stratified bottom layer. Turbulent closure models have been applied to investigate how the structure of the Benthic Boundary Layer is affected by the flow and the stratification above the layer. The object of the present research is to analyze how the benthic region affects the dynamics of the forcing flow. More specifically, a numerical model based on the level 2 1/2 closure scheme of Mellor and Yamada is developed to examine the decay of deep mesoscale eddy-like flows. It is found that the decay of the flow occurs through conversion of kinetic to potential energy and through dissipation by bottom friction. The relative importance of both processes is expressed by the Rossby number (epsilon) = U/fR and by the stratification parameter s = N('2)H('2)/f('2)R('2) (where H is the total depth of the eddy, R the radius, U the velocity scale, N the Brunt- Vaiasala frequency, and f the Coriolis parameter). A larger Rossby number and stratification parameter lead to a larger conversion of kinetic to potential energy, but a smaller mechanical dissipation of the same energy. Examination of the structure of the Benthic Boundary Layer indicates that a clear distinction should be made between the mixed layer, or the region neutrally stratified, and the Bottom Boundary Layer, or the region where most of the turbulent activity occurs. It is found that the structure of the Bottom Boundary Layer depends also on the magnitude of the flow above the benthic region, but the mixed layer depends also on the sign of the mesoscale activity. Under a cyclonic flow, the mixed layer is defined by vertical advection and it is usually much thicker than the Bottom Boundary Layer. The mixed layer of an anticyclonic flow is the result of both vertical advection and near bottom turbulence, and the ambiguity between the mixed layer and Bottom Boundary Layer is notably reduced.

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A NUMERICAL STUDY ON THE INFLUENCE OF THE MID-ATLANTIC RIDGE ON NON-LINEAR BAROTROPIC AND FIRST MODE BAROCLINIC ROSSBY WAVES GENERATED BY SEASONAL WINDS
BARNIER, BERNARD JEAN
155 p., 1986
A numerical model simulation investigates the influence of the mid-Atlantic ridge on non-linear barotropic and first- mode baroclinic Rossby waves generated by seasonal wind fluctuations. The north Atlantic is simulated by a square- box, two-layer quasi-geostrophic model. The bottom topography is ridge-like and compromises the QG approximation and the actual shape of the ridge. Sponge layers protect all boundaries except the eastern one from wave reflexion. The model is forced by a purely fluctuating wind stress curl derived from the most significant EOF's of the FGGE winds. A flat bottom and a ridge experiment are compared. The topography is an important source of barotropic variability for the eastern basin. The topographic Rossby waves generated over the ridge, either by wave reflexion or by direct wind forcing, account for at least 50% of the barotropic variability of that basin. Their frequencies range from 0.01 to 0.05 cpd. In both experiments the eastern boundary is an important source of annual-period baroclinic Rossby waves. Wavetrains having a wavelength of about 1060 km and a westward phase speed around 3.4 cm sec('-1) propagate energy westward at 3 cm sec('-1). In the flat bottom experiment a source of directly wind-forced baroclinic waves of annual period is found in the middle of the basin. Their amplitude is smaller and they have a noticeable northward phase propagation resulting in a southward group velocity component. The topography blocks the waves coming from the eastern boundary but generates new wavetrains whose phase vector is almost normal to the ridge crest. Those waves propagate energy mostly westward at 2.9 cm sec('-1). The northern waves are out of phase with the southern ones because of the structure of the dominant wind pattern over the ridge region where they are generated. All waves have a small group velocity component in the meridional direction. It is northward (at 0.34 cm sec('- 1)) for the northern waves and southward (at 0.32 cm sec('- 1)) for the southern waves.

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INTERANNUAL VARIABILITY OF THE CALIFORNIA CURRENT SYSTEM: A NUMERICAL MODEL
PARES-SIERRA, ALEJANDRO
146 p., 1987
A reduced gravity model that incorporates the geometry of western North America has been used to study the dynamics of the California Current System (CCS). Three experiments were implemented: first the model was run using 19 years of wind stress from the Comprehensive Ocean-Atmosphere Data Set (local model); a second experiment (remote model) consisted of forcing the model through its southern boundary using the results of a similar reduced gravity equatorial model; in a third experiment, both forcings were used simultaneously (local + remote model). The main objective of this work was to analyze the low frequency variability on the CCS in terms of its contributions from remote and local forcing. Away from the coast, the basic state of the model is determined by the predominantly negative wind curl through an Sverdrup balance. The general seasonal cycle (eg. set- up of Davidson Current, formation and position of Southern California eddy, etc.) is in agreement to what has been described by other authors. Through cross correlation and cross spectral analysis between the model results and observed sea-level data, it was established that most of the interannual variability in sea-level height at the coast is due to disturbances of equatorial origin that propagate into the region in the form of coastally trapped Kelvin waves. For the annual frequency variability, on the other hand, it was found that both local, as well as remotely forced variability, contribute to the total variance.

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DATA ASSIMILATION AND PARAMETER ESTIMATION IN OCEANOGRAPHIC MODELS
SMEDSTAD, OLE MARTIN
137 p., 1989
A variational data assimilation method for a reduced gravity model is developed. The method is applied to the equatorial Pacific Ocean. In the variational formalism a cost function measuring the "distance" between the model solution and the observations is minimized. The phase speed of the model is used as a control parameter and the optimal spatial structure giving the best fit of the model to the observations is determined. In the minimization algorithm a conjugate gradient descent direction is used. The method is computationally effective, and for the experiments considered convergence is achieved in ten iterations or less. Several experiments are performed using the model solutions as observations. It is shown that the assimilation algorithm is able to determine the spatial structure of the phase speed, even if observations are available at only three stations. The estimated phase speed is not sensitive to errors in the observations, and the algorithm gives a unique solution to the problem. Real sea level observations from three stations are assimilated for two different periods. The year 1979 was chosen to represent a year without an El Nino, while 1982/83 was chosen to represent an El Nino year. For 1979 the assimilation gave a phase speed with higher values in the west and lower values in the east compared to the initial guess of a constant phase speed. Assimilation of observations in 1982/83 gave the opposite picture, with lower values in the west and higher values in the east. This result is consistent with observations. The phase speed is proportional to the depth of the thermocline, and during normal conditions the basic stratification consists of a deep thermocline in the west and a shallow thermocline in the east. During an El Nino the picture is reversed. Calculating the correlation coefficient between the model results and the observations shows that the correlation increased for all the stations during the assimilation, even at stations which were not a part of the assimilation.

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A NUMERICAL STUDY OF THE SEASONAL VARIABILITY OF THE SOMALI CURRENT
JENSEN, TOMMY GERT
137 p., 1989
A new numerical ocean model with multiple isopycnal layers has been used to model the Indian Ocean. Normal vertical modes are used for initialization and in a new open boundary formulation. A 21 year integration with the Hellerman-Rosenstein wind stress is made with a 3.5 layer and a 1.5 layer version of the model. The solution with three active layers reproduces the observed general circulation and variability of the Indian Ocean, for instance the semi-annual equatorial undercurrent and Yanai wave field in the west. The seasonal changes in the Somali Current system is studied in more detail. It is found that barotropic instability is likely to cause the generation of the Great Whirl in early June. We find a very good agreement between the observed undercurrents and the simulations in the model. Equatorial onshore flow below the thermocline in June is associated with the disappearance of the undercurrent below the Somali current. The return of this undercurrent in the fall is caused by instability of the Great Whirl. Experiments where the duration of the summer monsoon is extended show that the initial decrease in the magnitude of the Great Whirl is due to eastward and downward energy transfer rather that due to relaxation of the wind. The solutions of the model indicate that baroclinic instability plays an important role in the decay of the Great Whirl. The solution with a single active layer is essentially the same for the upper layer until in the late summer monsoon, when the flow becomes unstable. Different decay patterns of the whirl and associated eddies leads to different flows during the winter monsoon.

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THE DESIGN AND IMPLEMENTATION OF A THREE-DIMENSIONAL, PRIMITIVE EQUATION OCEAN CIRCULATION MODEL
MCCALPIN, JOHN D.
150 p., 1990
The development and implementation of a new, primitive equation ocean circulation model is described. The model employs finite-difference discretization in the horizontal directions and a linear, Galerkin finite-element discretization in the vertical direction. A novel coordinate transformation is employed to retain fourth- order accuracy in the vertical. The main emphasis of this work is an extensive discussion of the decisions concerning physical, numerical, and computational issues, including discussions of several competitive (and currently interesting) numerical schemes which were not chosen. The model is compared and contrasted with the current generation of ocean circulation models. The performance of the model is tested in several simple cases. Finally, some future applications of the model are outlined. A series of high-resolution experiments with the barotropic part of the code are used to discuss the flow along a seamount chain, modelled after the Fieberling Guyot and its neighbors. The basic features of the flow are described and the numerical convergence of the model is demonstrated. The full three-dimensional code is applied to a single- seamount geometry with a variety of amplitudes. Other specific results of this work include: (1) An analysis of the incomplete cancellation of the pressure terms in the transformed coordinate system, with a simple estimate for the spurious acceleration. (2) An analysis of the semi- Lagrangian advection scheme used in some atmospheric models. The damping of the scheme is described in terms of an equivalent Laplacian or biharmonic viscosity coefficient, and formulae are derived for calculating the resolution required to obtain damping below a desired threshold. (3) A discussion of the three-dimensional semi- implicit scheme. It is shown that the scheme becomes physically ill-posed as the stratification of the fluid goes to zero.

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A COUPLED ATMOSPHERE-OCEAN MODEL IN THE TROPICS WITH VARIOUS CLIMATOLOGICAL BACKGROUNDS (PACIFIC OCEAN, EL NINO)
YANG, JIAYAN
149 p., 1991
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.

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ANALYSIS OF AIR AND SEA PHYSICAL PROPERTIES AND SURFACE FLUXES USING A COMBINATION OF IN SITU AND SEASAT DATA
LEGLER, DAVID M.
149 p., 1992
An objective technique which produces regularly spaced fields of winds, temperatures, humidity, wind stress and sensible and latent heat fluxes is developed. It combines in-situ Volunteer Observing Ship (VOS) data and remotely sensed data from SEASAT during the analysis period, July 7-October 10, 1978 for the north Atlantic. The objective technique is a variational method which reduces a set of several constraints expressing closeness to input data, climatology and kinematics. Analysis results are presented for monthly and 5-day periods during the analysis period. Seasonal (3 month) means of temperature, humidity, and flux determined by the monthly and 5-day results are comparable. However, 5-day wind results had much smaller errors than the monthly mean winds averaged over the 3-month period. Variability of the 5-day results indicates high variability of temperatures, humidity, and heat fluxes in the vicinity of the Gulf Stream. Sea surface temperature (SST) variability is high in the eastern Atlantic and is coupled to wind driven ocean variability in the region. Heat fluxes are coupled to and determined by various parameters. The variations for both sensible and latent heat fluxes in the extra-tropics are determined by the position and strength of the circulation of the semi- permanent high pressure system. Some evidence is also found to indicate dependence of SST on latent heat. In the tropics, the heat fluxes are determined by a combination of factors, including zonal wind and SST. Estimates of errors due to insufficient sampling and random data are presented for the monthly results. The sampling and random errors in wind stress are in the range of 10%- 20% of the mean values. For the sensible and latent heat fluxes, the sampling errors are about half of those attributable to random errors. Because of the difference operator used in diagnosing heat fluxes, these fluxes are found to be more sensitive to the accuracies of temperatures and humidity than accuracies of winds.

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ON THE GENERATION AND DISPERSION OF YANAI WAVES WITH A SPECTRAL CHEBYSHEV-COLLOCATION REDUCED-GRAVITY OCEAN MODEL
KELLY, BRIAN GERARD JOSEPH
129 p., 1992
A spectral Chebyshev-collocation method is devised for the 1- 1/2 layer non-linear reduced-gravity equations. Following a general description of spectral methods with their application to meteorological and oceanographic problems the implementation of the numerical technique is described. A bicharacteristic scheme is applied to solve the equations at the boundaries incorporating the boundary conditions. This treatment enables stable time integrations (spectral methods in general are very sensitive to boundary errors). A simple transfinite grid generation method is used to construct grids over irregular (non-rectangular) simply-connected domains. The model is used in a study of the dynamics of Yanai (or mixed Rossby-gravity) wave packets. These are of interest because of the observations of equatorial instability waves (which have the characteristics of Yanai waves) and their role in the momentum and heat budgets in the tropics. A series of experiments is performed to investigate the generation of the waves by simple cross-equatorial wind stress forcings in various configurations and the influence of a western boundary on them. They may be generated in the interior ocean as well as from a western boundary. The observations from all the oceans indicate that the waves have a preferential period and wavelength of around 26 days and 1000 km respectively. This is seen in the model results too and a plausible explanation is provided as being due to the dispersive properties of Yanai waves.

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DETERMINING THE SURFACE HEAT FLUX DISTRIBUTION OVER THE TROPICAL PACIFIC OCEAN BY THE ADJOINT METHOD (SEA TEMPERATURE)
YU, LISAN
178 p., 1992
The parameter optimization problem in oceanography is studied, in which an oceanic model with thermodynamics is used to determine the surface thermal forcing field by the adjoint technique. Two datasets are chosen, the climatological monthly-mean sea surface temperature (SST) and winds. The seasonal variability of the surface heat flux distribution over the tropical Pacific ocean is investigated. The use of a priori information is investigated in the formulation of the cost function. Experimental evidence has verified that adding a priori information of the estimated parameters can increase the probability for the solution to be unique. The a priori information also plays the role of bogus data. It serves not only to increase the number of observations but to improve the conditioning of the Hessian. The results are very promising. It has been possible, for the first time, to calculate the seasonal surface heat flux patterns which are consistent with both the ocean's physics and the observations.

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INTERDECADAL VARIABILITY OF THE EQUATORIAL PACIFIC OCEAN AND ATMOSPHERE: 1930-1989
SHRIVER, JAY FRANCIS
105 p., 1993
Interannual and interdecadal variability of the equatorial Pacific are examined using a new 60-year monthly historical pseudo-stress data set. The monthly mean pseudo-stress fields (1930-1989) are assembled from Comprehensive Ocean- Atmosphere Data Set pseudo-stresses using a variation of Cressman's (1959) objective analysis scheme, climate basis functions obtained from the FSU pseudo-stress product (1966-1990) and a technique called Vector Group Renormalization. The new wind fields are used to force an ocean model (Kubota and O'Brien, 1984). Model estimates of tropical Pacific current and model upper layer thickness (ULT) variability are then obtained for the period of interest. Observed sea level and spatially averaged sea surface temperature (SST) anomalies are used to validate the hindcasts. Interannual fluctuations in modeled and observed sea level fluctuations are compared at Galapagos and Truk, yielding Correlation (r) values of 0.73 and 0.71, respectively. The comparison of the interannual fluctuations in modeled ULT and observed SST anomalies, which were both spatially averaged over a subdomain in the eastern Pacific basin, yielded a correlation (r) value of 0.64. Interdecadal fluctuations in eastern Pacific model ULT are found to be qualitatively consistent with those in the spatially averaged observed SST anomalies. Interdecadal variations are shown to play a significant role in modulating the amplitude of El Nino events. Comparison of interdecadal fluctuations in global mean land air temperature and eastern Pacific ULT suggests a connection between eastern Pacific and global mean land air temperature warming for interdecadal time scales.

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Liu, Ming

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An abstract of the PhD Dissertation of Rodrigo H. Nuñez
College of Oceanography - Florida State University
December, 1996

This study presents the results of an ambitious oceanographic program carried out as the Chilean contribution to the World Ocean Circulation Experiment (WOCE).
Data collected during the WOCE PR-14 cruises has been used to describe and study, for the first time, the structure and variability of the eastern boundary current system of the South Pacific Ocean. In the region where the Antarctic Circumpolar Current (West Wind Drift) bifurcates, forming the Humboldt Current and the Cape Horn Current, transport calculations have been carried out to estimate the transport into each branch and the temporal variability of the transport. The results obtained from the hydrographic data show that the eastward transport into the WOCE PR-14 Sampling Region is almost constant.
The WOCE PR-14 cruises contain information of a short period of time every year, leaving unresolved an important part of the seasonal variability. Therefore, a numerical model, developed at the Naval Research Laboratory (NRL), has been used to complement the results derived from the analysis of the hydrographic data. The NRL finite-depth model yields a realistic representation of the temporal and spatial variability of the eastern boundary current system of the South East Pacific Ocean. Bottom topography is shown to produce a considerable steering effect on the currents of the region, exerting a controlling influence on the main features of the South Pacific Eastern Boundary System, such as the turning point of the Antarctic Circumpolar Current into the Humboldt Current.
The results of this study show that the goals of the WOCE PR-14 cruise have been achieved. A useful description of the ocean behavior of the transition zone (circulation and transport) has been made using the data collected during 1993, 1994 and 1995. The location of the bifurcation of the Antarctic Circumpolar Current has been found and some of the physical processes involved have been described and studied.

COPY OF THE DISSERTATION IS AVAILABLE AS COAPS TECHICAL REPORT 96-4. Contact Gwen Scott at reprints for a copy.

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INTERANNUAL VARIABILITY OF ATMOSPHERIC CARBON DIOXIDE FLUX IN THE EQUATORIAL PACIFIC OCEAN
VERSCHELL, MARK ALAN
A high-resolution biogeochemical model is developed to examine the flux of carbon dioxide from the equatorial Pacific Ocean, the major oceanic source of atmospheric carbon. The model is run for the thirty year period from 1965 to 1994 to investigate interannual variability in the carbon dioxide flux and the mechanisms leading to this variability. The model is forced by upper layer velocities and upwelling from a non-linear high- resolution hydrodynamical model of the tropical Pacific Ocean, the Florida State University Wind Stresses, and the Reynolds sea surface temperatures. The two data sets consist of tens of millions of individual real world observations. The model demonstrates the link between the interannual variations of the carbon dioxide flux and the El Nino/Southern Oscillation (ENSO), and identifies the responsible mechanisms. In particular, ENSO warm events are associated with decreased carbon dioxide flux because of the reduced upwelling of deep, carbon rich water into the surface layer and the weakening of the equatorial trade winds that drive the flux. In contrast, during ENSO cold events enhanced upwelling of deep, carbon rich water and stronger trade winds cause increased carbon dioxide flux from the equatorial Pacific Ocean. Carbon dioxide flux from the biogeochemical model compares well with the limited long- term observational data available. Interannual variations of the flux and proxy ENSO indices of sea surface temperature and thermocline depth also indicate good agreement. Replacing one input forcing field of either upper layer velocities and upwelling, wind stresses, or sea surface temperatures with six-day climatologies of the respective field indicates that both winds and upper layer physics are essential to reproduce the interannual flux variability. Sea surface temperature is less important in determining the variability. Results from a box model forced by zonally averaged input fields demonstrates that modeling the carbon dioxide flux from the equatorial Pacific requires an accurate representation of the critical horizontal spatial scales in the region.

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An abstract of the PhD Dissertation of Rodrigo H. Nuñez College of Oceanography - Florida State University December, 1996

An abstract of the PhD Dissertation of Rodrigo H. Nuñez
College of Oceanography - Florida State University
December, 1996