Letteratura scientifica selezionata sul tema "Observabilité SWOT"

Abstract. The southwestern tropical Pacific exhibits a complex bathymetry and represents a hot spot of internal-tide generation. Based on a tailored high-resolution regional model, we investigate for the first time the internal-tide field around the New Caledonia islands through energy budgets that quantify the coherent internal-tide generation, propagation, and dissipation. A total of 15.27 GW is converted from the barotropic to the baroclinic M2 tide with the main conversion sites associated with the most prominent bathymetric structures such as continental slopes and narrow passages in the north (2.17 GW) and ridges and seamounts south of New Caledonia (3.92 GW). The bulk of baroclinic energy is generated in shallow waters around 500 m depth and on critical to supercritical slopes, highlighting the limitations of linear semi-analytical models in those areas. Despite the strongly dominant mode-1 generation, more than 50 % of the locally generated energy either dissipates in the near field close to the generation sites or loses coherence. The remaining baroclinic energy propagates within well-defined tidal beams with baroclinic energy fluxes of up to 30 kW m−1 toward the open ocean. The New Caledonia site represents a challenge for SWOT (Surface Water and Ocean Topography) observability of balanced motion in the presence of internal tides with sea surface height (SSH) signatures >6 cm at similar wavelengths. We show for our study region that a correction of SSH for the coherent internal tide potentially increases the observability of balanced motion from wavelengths >160 km to well below 100 km.

Semarang as a city located in the coastal area is dealing with the some problems, such as rising sea level, land subsidence, scarcity of land and illegal settlers. In order to deal with rising sea level, a polder system is developed in Kemijen (northern of Semarang). This polder system depends on dredging, a pumping station and retention basins to store water. To make the polder function well and reduce the floods, the existing retention basins should be expanded. Therefore, people who are living at the borders of these basins should be relocated or floating houses could be a solution.. This study aims to determine the acceptance of the Kemijen inhabitants towards floating houses as alternative residential in coastal areas. Data collecting in this study were obtained through interviews with the Kemijen residents and stakeholders. The data then processed by SWOT analysis. Based on the research result, it can be concluded that the social acceptance of the inhabitants is quite low, but there is potential because they see positive elements in a floating house. According to the survey most inhabitants do have insufficient income to pay for a floating house. Building on water is still not legal in Indonesia and therefore the law should probably be adjusted. Besides the land owner is still reluctant in building legal houses on its land. In order to improve the social acceptance of floating houses, these factors should be strengthening, namely relative advantages, compatibility, complexity, trialability and observability.

Abstract. The processes that contribute to the flat sea surface height (SSH) wavenumber spectral slopes observed in the tropics by satellite altimetry are examined in the tropical Pacific. The tropical dynamics are first investigated with a 1∕12∘ global model. The equatorial region from 10∘ N to 10∘ S is dominated by tropical instability waves with a peak of energy at 1000 km wavelength, strong anisotropy, and a cascade of energy from 600 km down to smaller scales. The off-equatorial regions from 10 to 20∘ latitude are characterized by a narrower mesoscale range, typical of midlatitudes. In the tropics, the spectral taper window and segment lengths need to be adjusted to include these larger energetic scales. The equatorial and off-equatorial regions of the 1∕12∘ model have surface kinetic energy spectra consistent with quasi-geostrophic turbulence. The balanced component of the dynamics slightly flattens the EKE spectra, but modeled SSH wavenumber spectra maintain a steep slope that does not match the observed altimetric spectra. A second analysis is based on 1∕36∘ high-frequency regional simulations in the western tropical Pacific, with and without explicit tides, where we find a strong signature of internal waves and internal tides that act to increase the smaller-scale SSH spectral energy power and flatten the SSH wavenumber spectra, in agreement with the altimetric spectra. The coherent M2 baroclinic tide is the dominant signal at ∼140 km wavelength. At short scales, wavenumber SSH spectra are dominated by incoherent internal tides and internal waves which extend up to 200 km in wavelength. These incoherent internal waves impact space scales observed by today's along-track altimetric SSH, and also on the future Surface Water Ocean Topography (SWOT) mission 2-D swath observations, raising the question of altimetric observability of the shorter mesoscale structures in the tropics.

Abstract Several models are presented for the sea-surface height (SSH) signature of the interior-ocean internal-wave continuum. Most are based on the Garrett-Munk internal-wave model. One is derived from the frequency spectrum of dynamic height from mooring observations. The different models are all plausibly consistent with accepted dynamical and semi-empirical spectral descriptions of the climatological interval-wave field in the interior ocean, but they result in different proportionalities between interior and SSH spectral energy levels. The differences arise in part from differences in the treatment of near-surface stratification, and a major source of uncertainty for all the models comes from inadequately constrained assumptions about the energy in the low-vertical-mode internal-wave field. Most of these models suggest that the SSH signature of the internal-wave continuum will be visible in SSH measurements from the Surface Water and Ocean Topography (SWOT) wide-swath satellite altimeter. Temporal variability of internal-wave energy levels and the internal-wave directional spectrum are less well characterized but will also be consequential for the observability of internal-wave signals in SWOT data.

<p style='text-indent:20px;'>In data assimilation for geophysical problems, the increasing amount of satellite data to analyze makes it more and more challenging to guarantee near real time forecasting. Thus, low time and memory consuming data assimilation methods become very attractive. The back-and-forth nudging (BFN) method is a non-classical data assimilation method that can be seen as a deterministic and smoothing version of the Kalman filter. From a practical point of view, the BFN method is very valuable for its simplicity of implementation (no optimization, no differentiation, ...) and its rapidity of convergence. Under observability conditions, we prove the mathematical convergence of BFN at deep layers for a multi-layer quasi-geostrophic (MQG) ocean circulation model using an infinite dimensional variant of LaSalle's invariance principle. We also extend the BFN to the problem of joint state-parameter identification. The numerical experiments, performed on 120km large swath sea surface height (SSH) simulated data of the Surface Water Ocean Topography (SWOT) satellite, show the high robustness of the algorithm to uncertainties and the few iterations needed to reach convergence, whereas some problems remain due to non-reversibility properties in time. We also give a strategy to improve geophysical model accuracy, considering the large number of uncertain parameters inherent to models and their impacts on state estimation performance. We propose here a joint state-parameter estimation, tested on the baroclinic wavenumber as an unobserved parameter.</p>

L'équilibre énergétique de l'océan traduit des échanges d'énergie entre les termes sources aux échelles planétaires et la dissipation aux micro-échelles. Cette cascade d'énergie, cruciale dans la compréhension du système océanique, demande à être mieux comprise et quantifiée. La plus grande part de l'énergie dans l'océan est associée à la dynamique mésoéchelle. Les échelles spatiales correspondantes sont aussi celles des marées internes et dans les régimes océaniques où l'énergie des ondes internes est suffisamment forte celles-ci représentent un transfert d'énergie majeur vers les échelles dissipatives. La nouvelle mission satellite SWOT (Surface Water Ocean Topography) permettra d'observer globalement pour la première fois ces processus de fines échelles. Une motivation de cette thèse est l'observabilité du niveau de la mer SWOT avec le challenge de comprendre la part respective de la dynamique méso et sous-mésoéchelle et des ondes internes. La région d'étude se situe autour de la Nouvelle Calédonie dans le Pacifique sud-ouest et plus particulièrement dans la région sud survolée par une fauchée SWOT lors de la phase de cal-val du satellite caractérisée par une orbite à 1 jour. La thèse s'appuie sur une simulation régionale dédiée à haute résolution (1/60°) forcée ou pas par la marée barotrope en plus des forçages "classiques". Pour la première fois la dynamique des marées internes autour de la Nouvelle-Calédonie est décrite. Cette région s'avère être un hot spot de génération de marées internes associé aux principales structures bathymétriques,. La marée interne est principalement semi diurne. Elle se caractérise par un premier mode barocline très important et une forte signature dans la SSH (>6cm). Cette énergie de marée interne se propage dans l'océan ouvert à partir de deux zones localisées au nord et au sud de la Nouvelle Calédonie malgré des taux de dissipation d'énergie élevés à proximité des zones de génération. Cette propagation est majoritairement associée à de la marée interne cohérente mais l'activité méso-échelle s'avère être une source potentielle de perte de cohérence de la marée interne (marée incohérente). Cette marée interne incohérente est associée aux interactions avec les tourbillons océaniques soit par la réfraction de la propagation de l'énergie du faisceau de marée par les courants à méso-échelle lors de la propagation de l'énergie de marée, soit par les variations de la conversion de l'énergie barotrope en énergie barocline dues aux changements de stratification induits par les tourbillons à méso-échelle. Des observations in situ obtenues par des planeurs sous-marins autonomes révèlent le réalisme du modèle numérique quant à la simulation des marées internes tout en s'avérant être une plateforme in-situ appropriée pour documenter les marées internes, y compris leur signature de la SSH. Dans les régions de forte marée interne, celle-ci domine la variance de la SSH pour des longueurs d'onde jusqu'à 200 km correspondant. Une attention particulière est accordée à la marée incohérente, qui se manifeste dans la SSH à des échelles inférieures à 100 km. Cette thèse initie également l'étude de l'impact des marées internes sur la circulation à méso-échelle et sous-méso-échelle, avec des voies prometteuses pour les travaux futurs sur les échanges d'énergie entre les échelles et la fermeture du bilan énergétique océanique. Ces travaux participeront à la valorisation des données SWOT dans le cadre de SWOT-AdAC avec la campagne SWOTALIS. Enfin, ils sont une première initiative dans l'implication des marées internes en lien avec l'écosystème marin de la Nouvelle-Calédonie associée à un objectif de mise en place d'aires marines protégées au sein du parc naturel de la mer de Corail
The oceanic energy cascade and the associated redistribution of energy from planetary scales to microscales are crucial to achieve climate equilibrium, yet they remain to be fully understood and quantified. Among the submesoscale flow regime which is characterized by equal contributions from rotational (balanced) and non-rotational (unbalanced) effects, it is internal tides (internal gravity waves at tidal frequency) which have been shown to represent a major energy transfer toward dissipative scales. The Surface Water Ocean Topography (SWOT) satellite mission will push forward global sea surface height (SSH) observations of fine-scale physics of combined balanced and unbalanced motions, and their interactions. Our understanding of these processes will ultimately depend on our ability to disentangle these two different dynamical flow regimes. This thesis aims to tackle SWOT SSH observability of balanced and unbalanced motions around New Caledonia, an area with pronounced internal tide activity alongside elevated level of mesoscale to submescale eddy variability located beneath two swaths of SWOT's fast-sampling phase during which SWOT orbited on a 1-day repeat cycle to collect high-frequency measurements. As an initial step, this thesis provides the first comprehensive description of internal-tide dynamics around New Caledonia, an internal generation hot spot in the southwestern tropical Pacific that has not yet been explored in the literature, based on a tailored regional high-resolution (1/60°) numerical modeling effort. Internal tide generation around New Caledonia is associated with the main bathymetric structures, i.e. continental slope, shelf breaks, small- and large-scale ridges, and seamounts, strongly dominated by the semidiurnal tide and low-vertical modes, with a strong signature in SSH. It is found to be a major source of tidal energy propagation toward the open ocean despite enhanced energy dissipation rates close to the generation sites. Mesoscale eddy variability is shown to be a potential source for the loss of tidal coherence (or tidal incoherence) due to eddy-internal tide interactions, either through the refraction of tidal beam energy propagation by mesoscale currents toward the open ocean or by mesoscale-eddy induced variations of barotropic-to-baroclinic energy conversion. Important insight is provided by in-situ observations of autonomous underwater gliders. They reveal the numerical model's realism of internal-tide dynamics while proving to be a suitable in-situ platform to infer internal tides, including SSH signature. SWOT SSH observability of balanced and unbalanced motions represent a challenge around New Caledonia as the internal tide dominates SSH variance at wavelengths similar to those of balanced motion at scales less than 200~km wavelength. Particular emphasis is given to the incoherent tide, which manifests in SSH at scales less than 100~km, while restricting the observability of mesoscale and submesoscale motions. An outlook is given on the impact of internal tides on the mesoscale to submesoscale circulation with promising routes for future work on cross-scale energy exchanges and the closure of the oceanic energy budget. Finally, the comprehensive description of internal-tide dynamics conducted in this thesis has important implications for the New Caledonia marine ecosystem, with the hope of paving the way for the island's efforts in the conservation of marine protected areas