This dissertation discusses a linkage between the Southern Ocean (SO) winds and the global ocean circulation in the framework of a coarse-resolution global ocean general circulation model coupled to a sea-ice model. In addition to reexamination of the conventional linkage that begins with northward Ekman transport and extends to the North Atlantic (NA) overturning, the author investigates a new linkage that begins with the Southern Hemisphere (SH) sea-ice – ocean interaction perturbed by the anomalous SO winds and extends to the SH overturning, the response of the NA overturning, and the long-term baroclinic adjustment of the Antarctic Circumpolar Current (ACC). How the above two linkages will interact with each other in a warming world is also investigated. An interactive momentum flux forcing, allowing for the strength of momentum flux between atmosphere and sea ice to vary in response to the simulated sea-ice conditions, enhances wind-driven ice divergence to increase the fraction of leads and polynyas, which increases dense water formation, and thus intensifies convection. Within three experimental frameworks, this increased dense water consistently increases the Antarctic Bottom Water formation, which directly intensifies the SH overturning and indirectly weakens the NA overturning. As a result of the hemispheric change in overturning circulations, the meridional density gradient across the ACC appears to increase, ultimately increasing the baroclinic part of the ACC via an enhanced thermal wind shear. Subsequently, impacts of the poleward shifted and intensified SH subpolar westerly winds (SWWs) on the global ocean circulation are investigated in phases. When the SWWs are only shifted poleward, the effect of the anomalous winds is transmitted to the northern NA, decreasing both the NA overturning and the North Atlantic Deep Water (NADW) outflow. However, when the SWWs are shifted poleward and intensified, this effect is cut off by the intensified Deacon cell overturning, and is not transmitted to the northern NA, and instead increases the NADW outflow substantially. To sum up, with respect to the SO winds perturbed by the global warming, the SH overturning cell and the NADW outflow increase, leading to an increase in the volume transport of the ACC.

Les radars à synthèse d'ouverture (SAR) spatioportés ont fait la preuve de leur valeur inestimable dans l'observation des vents et des vagues océaniques mondiaux. Les images SAR acquises par plusieurs capteurs sont utilisées, notamment Sentinel-1 (S-1), Envisat/ASAR, Gaofen-3 et Radarsat-2. Cette thèse passe en revue les paramètres SAR couramment utilisés dans la première partie. Une série d'étapes d'étalonnage sont nécessaires pour obtenir un NRCS approprié et une évaluation du NRCS est effectuée pour le mode d'onde S-1 (WV). Il s'avère que WV est mal calibré et est donc recalibré pour obtenir un NRCS précis. Il a été démontré que la coupure de l'azimut est complémentaire du NRCS et peut expliquer l'impact de l'état de la mer sur l'extraction du vent. D'après les produits SAR entièrement polarimétriques disponibles, la coupure de l'azimut varie considérablement en fonction des polarisations. La transformation actuelle de la cartographie SAR est suffisante pour interpréter la coupure azimutale copolarisée, mais pas pour la polarisation croisée. Compte tenu des limites de l'imagerie SAR, un nouveau paramètre est proposé et défini en fonction du spectre croisé de l'image SAR, appelé MACS. La partie imaginaire de MACS est une quantité signée par rapport à la direction du vent. Compte tenu de cette dépendance, on s'attend à ce qu'un algorithme indépendant de récupération du vent en bénéficie. L'ampleur du MACS peut aider à estimer la fonction de modulation de la cartographie SAR. De plus, la MACS donne également des résultats prometteurs en ce qui concerne les études globales sur les vagues. Les signatures globales du MACS à différentes longueurs d'onde sont bien représentatives de la distribution spatiale et saisonnière des vents. Les MACS des vagues longues montrent des valeurs plus élevées sur les trajectoires des tempêtes alors que les vagues plus courtes sont principalement dans les vents des trader. Ces résultats devraient aider à évaluer les résultats du modèle et compléter les études ultérieures sur le climat spectral global des vagues. / Spaceborne synthetic aperture radar (SAR) has been demonstrated invaluable in observing the global ocean winds and waves. SAR images acquired by multiple sensors are employed, including Sentinel-1(S-1), Envisat/ASAR, Gaofen-3 and Radarsat-2. This thesis reviews the commonly used SAR parameters (NRCS and azimuth cutoff) in the first part. A series of calibration steps are required to obtain a proper NRCS and assessment of NRCS is carried out for S-1wave mode (WV). It turns out that WV is poorly calibrated and is thus re-calibrated to obtain accurate NRCS. Azimuth cut off is demonstrated to be complementary to NRCS and can account for the sea state impact on the wind retrieval. Based on the available fully polarimetric SAR products, azimuth cut off is found to vary greatly with polarizations. The present SAR mapping transformation is sufficient to interpret the co-polarized azimuth cut off, while not for the cross-polarization. With the limitations of SAR imaging in mind, a new parameter is proposed and defined based on the SAR image cross-spectra, termed as MACS. The imaginary part of MACS is found to be a signed quantity relative to the wind direction. Given this dependence, an independent wind retrieval algorithm is expected to benefit. The magnitude of MACS is able to aid for estimate of modulation function of SAR mapping. In addition, MACS also gives promising results regarding the global wave studies. The global signatures of MACS at various wave lengths are well representative of the winds distributions, spatially and seasonally. MACS of long waves shows greater values over the storm tracks while the shorter waves are mostly within the trader winds. These results are expected to help evaluate the model outputs and complement further studies of the global wave spectral climate. Data continuity in the coming 10 years shall extend the study towards longer duration.

The standard L2B ocean wind product from the Advanced Scatterometer (ASCAT) is retrieved as a 25 km product on a 12.5 km grid. Ultra-high resolution (UHR) processing allows ASCAT wind retrieval on a high-resolution 1.25 km grid. Ideally, such a high-resolution sample grid provides wind information down to a 2.5 km scale, allowing better analysis of winds with high spatial variability such as those in near-coastal regions and storms. Though the wind field is sampled on a finer grid, the actual data resolution needs to be validated. This thesis provides an analysis and validation of ASCAT UHR wind estimates in order to determine the improvement in resolution compared to the L2B product. This is done using analysis tools such as statistics, the power spectrum, and derivative fields, and through comparison to other high-resolution data such as synthetic aperture radar (SAR). The improvement of UHR wind retrieval is also explored by reducing ambiguity selection errors and correcting for contamination of wind vectors near land. Results confirm that ASCAT UHR winds contain high-resolution information that is not present in the L2B product. The resolution improvement is difficult to quantify due to a lack of truth data. Nevertheless, there is evidence to suggest that the resolution is improved by at least a factor of three to 10 km, and perhaps down to 3 or 4 km. It is found through comparison of UHR and SAR winds that (1) both products have common fine-scale features, (2) their comparative statistics are similar to that of L2B and SAR, suggesting that the high resolution content agrees just as well as the low resolution content because the comparison is performed at a finer scale (3) both products have derivative fields that match well, (4) the UHR product benefits from high-resolution direction information, and (5) the UHR product matches better the expected spectral properties of ocean winds. For the UHR processing improvement methods, the model-based improvement of UHR ambiguity selection allows obvious ambiguity errors to be found and corrected, increases the self-consistency of the wind field, and causes the spectrum to better follow a power law at high wavenumbers. The removal of land-contamination from near-coastal wind vectors allows accurate wind retrieval much closer to land and greater visibility of high-resolution wind features near the coast.

Field-wise wind estimation (also known as model-based wind estimation) is a sophisticated technique to derive wind estimates from radar backscatter measurements. In contrast to the more traditional method known as point-wise wind retrieval, field-wise techniques estimate wind field model parameters. In this way, neighboring wind vectors are jointly estimated, ensuring consistency. This work presents and implementation for field-wise wind retrieval for the SeaWinds scatterometer on the QuikSCAT satellite. Due to its sophistication, field-wise wind retrieval adds computational complexity and intensity. The tradeoffs necessary for practical implementations are examined and quantified. The Levenberg-Marquardt algorithm for minimizing the field-wise objective function is presented. As the objective function has several near-global local minima, several wind fields represent ambiguous wind field estimates. A deterministic method is proposed to ensure sufficient ambiguities are obtained. An improved method for selecting between ambiguous wind field estimates is also proposed. With a large set of Sea-Winds measurements and estimates available, the σ° measurement statistics are examined. The traditional noise model is evaluated for accuracy. A data-driven parameterization is proposed and shown to effectively estimate measurement bias and variance. The parameterized measurement model is used to generate Cramer-Rao bounds on estimator performance. Using the Cramer-Rao bound, field-wise and point-wise performances are compared.

Spaceborne scatterometer instruments are important tools for the remote sensing of the Earth's environment. In addition to the primary goal of measuring ocean winds, data from scatterometers have proven useful in the study of a variety of land and cryopshere processes as well. Several satellites carrying scatterometers have flown in the last two decades. These previous systems have been "fan-beam" scatterometers, where multiple antennas placed in fixed positions are used. The fan-beam scatterometer approach, however, has disadvantages which limit its utility for future missions. An alternate approach, the conically-scanning "pencil-beam" scatterometer technique, alleviates many of the problems encountered with earlier systems and provides additional measurement capability. Due to these advantages, the pencil-beam approach has been selected by NASA as the basis for future scatterometer missions. Whereas the fan-beam approach is mature and well understood, there is need for a fundamental study of the unique aspects of the pencil-beam technique. In this dissertation, a comprehensive treatment of the design issues associated with pencil-beam scatterometers is presented. A new methodology is established for evaluating and optimizing the performance of conically-scanning radar systems. Employing this methodology, key results are developed and used in the design of the SeaWinds instrument - NASA's first pencil-beam scatterometer. Further, the theoretical framework presented in this study is used to propose new scatterometer techniques which will significantly improve the spatial resolution and measurement accuracy of future instruments.