Two bottom-mounted ADCPs were deployed in the coastal waters off the National Museum of Marine Biology and Aquarium at southwestern Taiwan coast from June 5, 2004 to December 20, 2005. The long-term observational dataset of wind, currents, water level and drifters were analyzed here to investigate the mechanism and seasonal variations of tidal and subtidal flows. Diurnal tidal constituent of K dominates the tidal energy in this area. The calculated form ratio is 1.53, indicating that the tide is of the diurnal type. Tidal current direction is consistent with the local coastal line, with the principal axis in the NNE-SSW orientation. The tidal waves of two major constituents¡]K an M ¡^are found to exist in the form of propagating waves in this region, rather than the form of standing waves as was found in the east coast of central Taiwan Strait. The subtidal currents flow toward the south with a speed of about 20-50 cm/s during the winter northeastern monsoon. On the other hand, subtidal flow speed is smaller but still toward the south during the summer southwestern monsoon. Current speed in the surface layer is larger than that in the mid and bottom layers. The persistent southward flow in this region is also found to correlate with the wind stress curl. When the wind stress curl reaches a maximum negative value in winter, an anticyclonic eddy develops and the flow in the study area is toward the south. Analysis of Argos drifter data reveal the existence of anticyclone off the southwestern Taiwan coast. Surface drifters were also deployed in this area, and the trajectories indicate that general flow patterns are toward the south. This finding is consistent with the progressive vector diagram from the moored ADCP current data. To summarize, a persistent southward flow exists in the study region all year round. However, the flow intensifies in winter and decays in summer. The southward flow is also associated with the anticyclonic eddy driven by the negative wind stress curl in winter. The intrusion of Kuroshio water from the Luzon Strait into the northern South China Sea is the possible source of water mass for this phenomenon.

The aim of this study is to investigate how well the wind stress is described in the regional climate model RCA (Rossby Centre Atmospheric model). The model data is compared with measurements taken at Östergarnsholm, an island located east of Gotland in the Baltic Sea. The investigation covers the period October 1997 to September 2000. Compared with the measurements RCA underestimates the wind speed over ocean in most cases. When the wind speed is studied in monthly mean it was found that the wind speed is consistently underestimated in the model, especially during summer and early winter. The wind stress is also underestimated during the year except during late winter and in October when it is overestimated. When wind speed from the model and measurements were studied it was found that lower wind speed is overestimated in the model. This contributes to overestimation of the wind stress for lower wind speeds. For higher wind speeds both wind speed and wind stress is underestimated in RCA. If the model would have a correct wind speed the wind stress would be overestimated with 20-30 % for all wind speeds compared to the measured. This is probably due to miscalculations of wind stress in the model. RCA fail to capture the stability in a satisfactory way. The model describes most of the times a different stratification than the measurements do. Separate studies over modeled and measured wind speed and wind stress was made. RCA is found to represent stable condition well. During unstable stratification modeled wind speed and wind stress are underestimated. Investigation of the measured wave age shows that the model underestimates both wind speed and wind stress for growing sea and mature sea. For the situations when the measured wave age was defined as swell the model overestimated wind speed and wind stress.2 / Den här studien tar upp hur väl friktionen över havsytan beskrivs i den regionala klimatmodellen RCA (Rossby Centre Atmospheric model). Modelldata jämförs med mätningar gjorda på Östergarnsholm, en ö belägen öster om Gotland i Östersjön. Studien spänner över tidsperioden oktober 1997 till september 2000. RCA underskattar i många fall vindhastigheten på 10 m över havsytan jämfört med mätningarna. Då månadsmedelvärden studeras visar det sig att modellen genomgående underskattar vindhastigheten, särskilt på sommaren och på vintern. Friktionen överskattas under sen vinter och för oktober månad. För alla andra månader underskattas friktionen. Studier över vindhastigheterna visar på att de lägre vindhastigheterna överskattas i modellen. Detta bidrar till överskattning av friktionen för de lägre vindhastigheterna. För högre vindhastigheter underskattar RCA vindhastigheterna och därmed även friktionen. Om modellen skulle ge en korrekt vindhastighet skulle resultatet istället visa på en överskattning av friktionen med 20-30 % för alla vindhastigheter. Detta beror troligen på felaktigheter i beräkningen av friktionen i modellen. Stabiliteten visar sig vara dåligt beskriven i RCA. I de flesta fall är skiktningen i modellen och mätningarna helt olika. Jämförelser mellan separata studier mellan modelldata och mätningar visar att vindhastigheten och friktionen beskrivs bra under stabila förhållanden, men i samband med instabil skiktning underskattas vindhastigheten och friktionen i modellen. Studier över den uppmätta vågåldern visar att modellen underskattar både vindhastigheten och friktionen för växande och fullvuxen sjö. Då det råder dyning överskattar modellen både vindhastigheten och friktionen.

This dissertation investigates wind-wave-current interaction, wave breaking detection and the analysis of breaking characteristics at the air-sea interface. In-situ data measured during the Shoaling Waves Experiment (SHOWEX) and Baltic Sea Swell Experiment (BASE) are applied in the studies and analysis. Wind, wind stress and wave data were obtained from several Air Sea Interaction Spar (ASIS) buoys. Surface currents were measured by a High-Frequency Ocean Surface Current Radar. Two distinct types of wave-current-wind interaction were observed in the presence of a strong along-coast current. First, the horizontal current shear resulted in wind-sea waves shifting away from the wind direction. This motion resulted in a steering of the stress away from the mean wind direction. Second, short wind waves on a uniform current are shifted to the current direction, and the wind stress is steered toward the current direction by the short waves. The wind stress veering has been confirmed by data from the SeaWind scatterometer on board the QuikSCAT satellite. This finding is in agreement with the results from some recent studies. The present study also describes an experimental investigation of breaking wave detection by ASIS buoys. A method, developed from the laboratory, and using local wave parameters to provide a detailed description of breaking, is applied to wave data from ASIS buoys. One the basis of these data, the relation between breaking probability and wind speed shows characteristics similar to those from several field experiments with different conditions. Furthermore, additional parameters, wave age and wave steepness, are also shown to affect the breaking probability during our in-situ measurements. Upper ocean shear, which can modulate wave breaking as predicted by both theory and laboratory work, are also observed to change the breaking properties. This characteristic is rarely reported by in-situ experiment.

Thesis (Ph. D.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution. / Includes bibliographical references (p. 186-188).

O trabalho tem o objetivo geral de estudar os efeitos transientes de alta frequência do regime de ventos na ressurgência de Cabo Frio, utilizando para este fim dados oceanográficos e saídas do modelo oceanográfico HYCOM. Para atingir este objetivo utilizou-se um conjunto de dados oceanográficos bem como de ventos obtidos junto ao Banco Nacional de Dados Oceanográficos (BNDO) do Centro de Hidrografia da Marinha (CHM). Estes dados são provenientes de duas comissões realizadas pelo ex-Navio Oceanográfico Almirante Saldanha, uma no período de 16 a 23 de janeiro de 1986 e outra no período de 09 a 22 de setembro de 1972. Os dados mostram uma flutuação na estrutura termohalina da região de Cabo Frio, presumivelmente, associada aos eventos de ressurgência ocorridos devido à variação no campo de ventos predominantes na região, mais especificamente, perturbações de alta frequência como a brisa do mar (BM) e a passagem de sistemas frontais na região. Com os resultados preliminares do presente trabalho podemos inferir a existência de uma correlação entre a atuação da BM no regime de ventos com uma intensificação da ressurgência em Cabo Frio já que a circulação local tem o efeito de alterar tanto a intensidade quanto a direção dos ventos predominantes naquela região fazendo com que o vento resultante se torne mais intenso e com uma tendência de ficar paralelo à costa o que favorece à ocorrência do fenômeno da ressurgência. Com os dados de setembro de 1972 observamos também um comportamento interessante da profundidade da isoterma de 16ºC, que é um bom indicador da intensidade da ressurgência, quando a mesma altera sua profundidade em torno de 50m, passando de 70m para 20m, fato este visivelmente associado à alteração no campo de ventos devido à passagem de um sistema frontal na região. / The overall objective of this work is to study the transient hight-frequency effects of the wind regime on the Cabo Frio upwelling. For this, oceanography data and outputs of the oceanographic model HYCOM were used. In order to obtain this objective, a set of oceanographic and wind data, obtained by means of the National Bank of Oceanographic Data (BNDO) of the Hydrographic Center of the Navy (CHM), was used. This data is a result of two commissions carried out by the ex-oceanographic vessel Almirante Saldanha, one between January 16th and 23rd, 1986, and the other from September 9th to 22rd, 1972. The data showed a fluctuation in the thermohaline structure in the Cabo Frio region, presumably associated to the upwelling events which occur due to variations in the predominant wind fields in the region, specifically high frequency disturbances such as the sea breeze (SB) and the passing of frontal systems in the region. Based on preliminary results of this work, we may infer the existence of a correlation between the role of the SB on the wind regime and an intensification of the Cabo Frio upwelling since the local circulation has the effect of altering the intensity as well as the direction of the predominant winds in the region. Consequently, the resulting wind is intensified and has a tendency of becoming parallel to the coast which, in turn, favors the occurance of the upwelling phenomenon. Based on the September 1972 data, we observed an interesting behavior of the depth of the 16ºC isotherm, which is a good indicator of the intensity of the upwelling process. The depth of this isotherm is altered in approximately 50 m going from 70 m to 20 m, which in noticeably associated to the alteration in the wind field due to the passing of a frontal system in the region.

O trabalho tem o objetivo geral de estudar os efeitos transientes de alta frequência do regime de ventos na ressurgência de Cabo Frio, utilizando para este fim dados oceanográficos e saídas do modelo oceanográfico HYCOM. Para atingir este objetivo utilizou-se um conjunto de dados oceanográficos bem como de ventos obtidos junto ao Banco Nacional de Dados Oceanográficos (BNDO) do Centro de Hidrografia da Marinha (CHM). Estes dados são provenientes de duas comissões realizadas pelo ex-Navio Oceanográfico Almirante Saldanha, uma no período de 16 a 23 de janeiro de 1986 e outra no período de 09 a 22 de setembro de 1972. Os dados mostram uma flutuação na estrutura termohalina da região de Cabo Frio, presumivelmente, associada aos eventos de ressurgência ocorridos devido à variação no campo de ventos predominantes na região, mais especificamente, perturbações de alta frequência como a brisa do mar (BM) e a passagem de sistemas frontais na região. Com os resultados preliminares do presente trabalho podemos inferir a existência de uma correlação entre a atuação da BM no regime de ventos com uma intensificação da ressurgência em Cabo Frio já que a circulação local tem o efeito de alterar tanto a intensidade quanto a direção dos ventos predominantes naquela região fazendo com que o vento resultante se torne mais intenso e com uma tendência de ficar paralelo à costa o que favorece à ocorrência do fenômeno da ressurgência. Com os dados de setembro de 1972 observamos também um comportamento interessante da profundidade da isoterma de 16ºC, que é um bom indicador da intensidade da ressurgência, quando a mesma altera sua profundidade em torno de 50m, passando de 70m para 20m, fato este visivelmente associado à alteração no campo de ventos devido à passagem de um sistema frontal na região. / The overall objective of this work is to study the transient hight-frequency effects of the wind regime on the Cabo Frio upwelling. For this, oceanography data and outputs of the oceanographic model HYCOM were used. In order to obtain this objective, a set of oceanographic and wind data, obtained by means of the National Bank of Oceanographic Data (BNDO) of the Hydrographic Center of the Navy (CHM), was used. This data is a result of two commissions carried out by the ex-oceanographic vessel Almirante Saldanha, one between January 16th and 23rd, 1986, and the other from September 9th to 22rd, 1972. The data showed a fluctuation in the thermohaline structure in the Cabo Frio region, presumably associated to the upwelling events which occur due to variations in the predominant wind fields in the region, specifically high frequency disturbances such as the sea breeze (SB) and the passing of frontal systems in the region. Based on preliminary results of this work, we may infer the existence of a correlation between the role of the SB on the wind regime and an intensification of the Cabo Frio upwelling since the local circulation has the effect of altering the intensity as well as the direction of the predominant winds in the region. Consequently, the resulting wind is intensified and has a tendency of becoming parallel to the coast which, in turn, favors the occurance of the upwelling phenomenon. Based on the September 1972 data, we observed an interesting behavior of the depth of the 16ºC isotherm, which is a good indicator of the intensity of the upwelling process. The depth of this isotherm is altered in approximately 50 m going from 70 m to 20 m, which in noticeably associated to the alteration in the wind field due to the passing of a frontal system in the region.

This study analyzed historical hydrographic data consist of 95 years of NODC data and 18 years of NCOR data. Variations of upper-layer current in Luzon Strait and its neighboring Northern South China Sea are investigated by the method of dynamical topography. On the other hand, higher salinity characteristic of the North Pacific Tropical Water (NPTW) is used to trace the water mass distribution and its seasonal variations in the studied area. The result shows that the maximum of x-component velocity (along 120.25˚E, relative to 400 m ) in the Luzon Strait occurs in the middle of the strait, the flow direction is westward and the speed increases toward the surface. At the north and south ends of the strait flows are eastward and the maximum speed core is at the depth of 0~50 m. Horizontal distribution of flow fields indicates that intrusion of the north Pacific waters into the South China Sea through the Luzon Strait in the whole year. Westward bifurcation of the intrusion flows occurs at 20~21˚N. A cyclonic eddy exists in the South China Sea all year-round, and its core is located at about 18˚N, 118˚E. This eddy strengthens as the monsoon prevails with its speed reached in January and February. Annual mean upper-layer transport (0~ 400 m) of the Luzon Strait is estimated to be about 3.5 Sv (positive value means westward) with a maximum value of about 6.5 Sv in December and a minimum value of 1.1 Sv in June. The Upper-layer current of the SCS is dominated by the monsoon. When the northeast monsoon prevails, the currents are affected by the Ekman effect to form high sea surface height in the north and low sea surface height in the south to produce a westward current. On the other hand, strong two coexistent wind stress curls with reversing signs during the northeast monsoon produce a westward current along the line of zero curl in the middle of the strait. The distribution of the NPTW(£m£c=23.5¡ã25.5 kg/m3,S >34.5 psu) is mostly at a depth of 120¡ã130 m in the South China Sea. NPTW were traced at 125 m depth, and the result indicates that this water mass enters the South China Sea through the Luzon strait all year-round. The intrusion path is along the continental slope of south China. The extent of intrusion reaches the maximum between December and February, and the water mass can spread into the South China Sea basin.

The response of the tropical Atlantic Ocean to wind stress forcing on seasonal and interannual time scales is examined using an ocean data assimilation product from the Geophysical Fluid Dynamics Laboratory (GFDL), and an ocean general circulation model which incorporates a three dimensional flux correction technique to correct biases of the mean state of the ocean. On a seasonal time scale, we investigated the impact of the annual migration of the ITCZ on the exchange pathways of the northern tropical Atlantic. The results indicate that seasonal variation of the zonal slope of the thermal ridge along the boundary between the north equatorial countercurrent and north equatorial current in response to changes in the ITCZ controls, to a large extent, the amount of water participating in the equatorial circulation. These changes can be explained in terms of a simple dynamical model where local Ekman pumping dominates thermocline variation in the western part of the basin, and Rossby wave adjustment comes into play in the eastern basin. On an interannual time scale, we examined the upper heat budget of the equatorial Atlantic in order to identify the key mechanisms by which wind-driven ocean dynamics control SST variability during the onset and peak phases of the Atlantic zonal mode. It is found that, in contrast with Pacific ENSO, both Bjerknes and Ekman feedbacks act together to force the zonal mode, although their relative importance and dominance depend on season and location.

The location of fronts has a direct influence on both the physical and biological processes in the Southern Ocean. However, until recently fronts have been poorly resolved by available data and climate models. In this thesis we utilise a combination of high resolution satellite data, model output and ARGO data to improve our basic understanding of fronts. A method is derived whereby fronts are identified as local maxima in sea surface height gradients. In this way fronts are defined locally as jets, rather than continuous-circumpolar water mass boundaries. A new climatology of Southern Ocean fronts is presented. This climatology reveals a new interpretation of the Subtropical Front. The currents associated with the Subtropical Front correspond to the western boundary current extensions from each basin, and we name these the Dynamical Subtropical Front. Previous studies have instead suggested that the Subtropical Front is a continuous feature across the Southern Ocean associated with the super gyre boundary. A comprehensive assessment of the relationship between front locations and wind stress is conducted. Firstly, the response of fronts to a southward shift in the westerly winds is tested using output from a 100 year climate change simulation on a high resolution coupled model. It is shown that there was no change in the location of fronts within the Antarctic Circumpolar Current as a result of a 1.3° southward shift in the westerly winds. Secondly, it is shown that the climatological position of the Subtropical Front is 5-10° north of the zero wind stress curl line, despite many studies assuming that the location of the Subtropical Front is determined by the zero wind stress curl. Finally, we show that the nutrient supply at ocean fronts is primarily due to horizontal advection and not upwelling. Nutrients from coastal regions are entrained into western boundary currents and advected into the Southern Ocean along the Dynamical Subtropical Front. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Submitted.</p>

A notable feature in the first 20-year satellite altimetry records is an anomalously fast sea level rise (SLR) in the western Pacific impacting island nations in this region. This observed trend is due to a combination of internal variability and external forcing. The dominant mode of dynamic sea level (DSL) variability in the tropical Pacific presents as an east-west see-saw pattern. To assess model skill in simulating this variability mode, we compare 38 Coupled Model Intercomparison Project Phase 5 (CMIP5) models with 23-year satellite data, 55-year reanalysis products, and 60-year sea level reconstruction. We find that models underestimate variance in the Pacific sea level see-saw, especially at decadal, and longer, time scales. The interannual underestimation is likely due to a relatively low variability in the tropical zonal wind stress. Decadal sea level variability may be influenced by additional factors, such as wind stress at higher latitudes, subtropical gyre position and strength, and eddy heat transport. The interannual variability of the Nino 3.4 index is better represented in CMIP5 models despite low tropical Pacific wind stress variability. However, as with sea level, variability in the Nino 3.4 index is underestimated on decadal time scales. Our results show that DSL should be considered, in addition to sea surface temperature (SST), when evaluating model performance in capturing Pacific variability, as it is directly related to heat content in the ocean column.