Дисертації з теми "Thermohaline variability"
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Hughes, Tertia M. C. "Uniqueness and variability of the ocean's thermohaline circulation." Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=28780.
Повний текст джерелаAnother new result is the range of Conveyor equilibria found under mixed boundary conditions. Rare cases with North Pacific sinking are characterized by a very fresh halocline in the Southern Ocean and a reversed pole-to-pole surface density contrast. A more quantitative investigation leads to an approximately linear relationship between the Atlantic overturning and the meridional gradient of zonally-averaged depth-integrated steric height from the northern boundary of the ocean to the southern tip of Africa; on the other hand, the local linear relationships postulated in most two-dimensional plane models of the overturning circulation could not be validated.
In the second part, the climatology of a global ocean model is presented, and the importance in the model of the warm water route of the Conveyor through the Indian Ocean relative to the cold water route through Drake Passage is noted. The implied ocean heat and freshwater transports from the Canadian Climate Centre second generation atmospheric general circulation model are then presented, and are shown to be incompatible with the present-day thermohaline circulation.
Finally, in the third part, a simple new parameterization of the sea surface temperature-evaporation feedback is developed as an extension of the traditional mixed boundary conditions. The positive sign of the feedback for the thermohaline circulation is demonstrated, and three examples featuring decadal, century and millennial timescale variability in one-hemisphere idealized basins are discussed. No fundamental alterations of the mechanisms under mixed boundary conditions are found, although the timescale is altered or the variability interrupted sooner in some cases.
Stuebe, David Allen. "Temperature and salinity variability in thermohaline staircase layers." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/39194.
Повний текст джерелаIncludes bibliographical references (p. 65-67).
A moored profiler record from the western tropical North Atlantic provides the first continuous time series of temperature, salinity and velocity profiles in a thermohaline staircase. Variations in the intensity of layering and the evolution of layer properties are well documented during the 4.3 month record. Such staircases are the result of strong salt fingering at the interfaces between the mixed layers, and these data provide unique insights into the dynamics of salt fingers. In particular, a striking linear correlation between the temperature and salinity of the layers may be interpreted as resulting from vertical salt finger flux divergences. Data from this record allow new interpretations of previous work on this topic by McDougall (1991).
by David Allen Stuebe.
S.M.
Tyner, Robin D. "DECADAL variability of thermohaline structure at the SHEBA site." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1999. http://handle.dtic.mil/100.2/ADA365397.
Повний текст джерела"June 1999". Thesis advisor(s): Timothy P. Stanton. Includes bibliographical references (p. 97-100). Also available online.
Myers, Paul Glen. "Seasonal forcing and low-frequency variability of the thermohaline circulation." Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=60722.
Повний текст джерелаDespite the presence of the forcing on the dominant seasonal timescale, it is found that the system may oscillate at the decadal period or longer. The decadal variability is excited by changes in the net surface density flux which are due to the advection of temperature and salinity anomalies in the model domain. The magnitude of the seasonal cycle also plays an important role in determining the timescale of variability. Violent overturning events may occur on the century timescale under seasonal forcing. The magnitudes of the flushes are reduced compared to those found in similar experiments without the presence of a seasonal cycle.
Bensi, Manuel. "Thermohaline variability and mesoscale dynamics observed at the E2M3A deep-site in the South Adriatic Sea." Doctoral thesis, Università degli studi di Trieste, 2012. http://hdl.handle.net/10077/7387.
Повний текст джерелаContinuous measurements are strictly essential to better understand the deep convection as well as for monitoring the seasonal and interannual thermohaline variability in the ocean. For these reasons, the south Adriatic Sea has been constantly monitored by means of the E2M3A deep observational site, located in its central part (Latitude 41° 50’ N, Longitude 17° 45’ E, maximum depth 1250m) since 2006. Temperature, salinity and current time series collected between 2006 and 2010 are analysed in this thesis and they represent the longest time series available for this region. Moreover, these time series are merged with Conductivity-Temperature-Depth (CTD) profiles obtained from several oceanographic cruises to provide the necessary spatial distribution of data for describing the thermohaline properties in the study area. The analysis of the data presented here shows that winter 2007 was characterized by a weak convection, while winter 2008 and following winters revealed a stronger deep convection able to reach 800-900m in February 2008. Time series highlight the abrupt temperature (T) and salinity (S) decrease, noticeable down to 600-700m depth from March 2008 on. The intermediate layer experienced a maximum decrease in T and S of ~0.4°C and ~0.06 respectively, clearly evident after each strong winter convection phase. The bottom layer (~1200m), instead, shows an opposite behaviour: it suffered a continuous T and S increase (linear trend of ~0.05 °C y-1 and ~0.004 y-1, respectively) during the whole observational period. These changes are discussed in a context of strong relationship between the variability of the Ionian surface circulation recently discovered, and the heat and salt content changes in the South Adriatic presented in this study. The results show that the mechanism triggering the salt content changes in the South Adriatic is based mainly on the winter convection, which transfers surface fresher water towards deeper layers. Nevertheless, current measurements also indicate that the passage of mesoscale eddies in the region can produce sudden thermohaline perturbations along the water column for 10-15 days. Cyclonic eddies seem to be more frequent in the proximity of the observational site than the anticyclonic ones. Interestingly, the comparison between time series and satellite images (Chl-a surface distribution) reveals, for the first time, that the vortices act along the whole water column. Their passage produces a twofold effect: the contribution to the re-stratification of the water column during the post convection phase, by exchanging the buoyancy between the mixed path and the surrounding waters, and the transfer of heat and salt between the deep and the intermediate layers.
Misure oceanografiche in continuo sono essenziali per comprendere meglio il processo di formazione delle acque dense e per monitorare la variabilità termoalina stagionale e interannuale in oceano. Per queste ragioni, a partire dal 2006 il Sud Adriatico è stato costantemente monitorato grazie all’utilizzo del sito di osservazione denominato E2M3A, ancorato nella parte centrale del Sud Adriatico (latitudine 41° 50’ N, longitudine 17° 45’ E, profondità massima 1250m). Le serie temporali di temperatura, salinità e correnti marine raccolte tra il 2006 e il 2010 sono analizzate in questa tesi e rappresentano la serie di dati più lunga mai ottenuta in questa regione. Oltretutto, per fornire la necessaria copertura spaziale dei dati utile a descrivere le proprietà termoaline nell’area di studio, le serie temporali sono state integrate con profili CTD (Conductivity-Temperature-Depth) provenienti da diverse crociere oceanografiche. L’analisi dei dati presentata qui mostra che l’inverno 2007 è stato caratterizzato da una debole convezione, mentre l’inverno 2008 e i successivi hanno mostrato una convezione più intensa, capace di raggiungere 800-900m di profondità a Febbraio 2008. Le serie temporali evidenziano una diminuzione repentina di temperatura (T) e salinità (S), visibile fino a 600-700m a partire da Marzo 2008. Lo strado intermedio ha subito rispettivamente una diminuzione massima di T e S di ~0.4°C e ~0.06, chiaramente evidente a seguito di ogni fase di intensa convezione invernale. Lo strato di fondo (~1200m) ha mostrato invece un comportamento opposto: un inaspettato e continuo aumento di T and S (trend lineare ~0.05 °C y-1 e ~0.004 y-1, rispettivamente) durante tutto il periodo di studio. Questi cambiamenti sono discussi nell’ambito della forte relazione tra la variabilità della circolazione superficiale dello Ionio recentemente scoperta e i cambiamenti nel contenuto di calore e sale del Sud Adriatico presentati in questo studio. I risultati mostrano che il meccanismo in grado di produrre cambiamenti nel contenuto di sale nel Sud Adriatico è principalmente basato sulla convezione invernale, che trasferisce acqua superficiale meno salata verso strati più profondi. Tuttavia, le misure di corrente mostrano che anche il passaggio di vortici a mesoscala può indurre repentine perturbazioni delle proprietà termoaline lungo la colonna d’acqua anche per 10-15 giorni. Vortici di tipo ciclonico sembrano essere più frequenti in prossimità del mooring rispetto a quelli di tipo anticiclonico. È interessante notare che il confronto tra le serie temporali e le immagini da satellite della distribuzione superficiale di clorofilla-a rivela, per la prima volta in questa regione, che i vortici agiscono su tutta la colonna d’acqua. Il loro passaggio produce un duplice effetto: il contributo alla ri-stratificazione della colonna d’acqua a seguito della fase di convezione invernale e il trasferimento di calore e sale tra gli strati intermedio e profondo.
XXIV Ciclo
1978
Hutchinson, Katherine Alessandra. "Thermohaline variability of AAIW in the Atlantic sector of the Southern Ocean investigated using an Altimetry Gravest Empirical Mode." Master's thesis, University of Cape Town, 2013. http://hdl.handle.net/11427/6648.
Повний текст джерелаKuhlbrodt, Till. "Stability and variability of open-ocean deep convection in deterministic and stochastic simple models." Phd thesis, [S.l. : s.n.], 2002. http://pub.ub.uni-potsdam.de/2002/0033/kuhlb.pdf.
Повний текст джерелаHoundegnonto, Odilon Joël. "Analyse des variations thermohalines des échelles intrasaisonnière à saisonnière des panaches d'eau douce du Golfe de Guinée." Thesis, Brest, 2021. http://www.theses.fr/2021BRES0105.
Повний текст джерелаIn the Gulf of Guinea (GG), freshwater originated from river discharges and high precipitation rates contribute to the upper ocean density stratification, and play a key role in modulating air-sea interactions. However, the thermohaline variations of the ocean upper layers within the freshwater plumes in the GG are still poorly known, as they are poorly observed and documented. The main objective of this thesis is therefore to study and document the spatial variability at horizontal mesoscale (10-100 km) and vertical (0-100m), from intra-seasonal to seasonal time scales of the thermohaline 3D structure in the freshwater plume areas of the GG: mainly the Congo and Niger Rivers plumes. First, using SSS SMOS satellite data, our study showed that freshwater plumes in this region extend towards the open ocean following two propagation regimes. During September to January, they propagate northwestward while from January to April they redirect to the southwest, where their maximum extension is observed in April. The rest of the year, from May to August, is marked by a surface salinization episode, where the freshwater plumes dissipate with a minimum extension observed in August. A salinity budget analysis in the surface mixed layer allowed highlighting the main physical processes controlling the seasonal variability of salinity within these freshwater plumes. We showed that horizontal advection processes and freshwater fluxes by precipitation and river discharges are the main contributors of low SSS distribution in this region. In the southeastern Gulf of Guinea, off Congo, the horizontal SSS advection is dominated by Ekman wind-driven currents. Second, we showed that the offshore distribution of the Congo plume on intra-seasonal time scales is associated with salt barrier layers and with thermohaline staircases profiles. In a case study (for 2016/03/31), we showed that the observed thermohaline staircases would result from the shear dynamics between the surface Ekman flow associated with the offshore (North-Westward) distribution of the Congo plume, and the geostrophic (South-Eastward) flow associated with the denser and saltier subsurface water masses of the open ocean to the west. Finally, using a Lagrangian approach, we have highlighted the origin and large-scale structuring of water masses involved in the strong haline stratification observed off Congo. This study showed the strong shear of the currents associated with the vertical salinity gradients within the water column associated with the staircases profiles
Barrier, Nicolas. "Variability of the ocean circulation in the North-Atlantic in response to atmospheric weather regimes." Thesis, Brest, 2013. http://www.theses.fr/2013BRES0064/document.
Повний текст джерелаThe aim of the PhD is to investigate the impacts of the large-Scale atmospheric variability on the North- Atlantic ocean circulation. This question has already been addressed in a large number of studies, in which the atmospheric variability is decomposed into modes of variability, determined by decomposing sea-Level pressure anomalies into Empirical Orthogonal Function (EOFs). These modes of variability are the North-Atlantic Oscillation (NAO), the East-Atlantic Pattern (EAP) and the Scandinavian Pattern (SCAN). EOF decomposition assumes that the modes are orthogonal and symmetric. The latter assumption, however, has been shown to be inadequate for the NAO. Hence, a different framework is used in this study to assess the atmospheric variability, the so-Called weather regimes. These are large-Scale, recurrent and quasi-Stationary atmospheric patterns that have been shown to capture well the interannual and decadal variability of atmospheric forcing to the ocean. Furthermore, they allow to separate the spatial patterns of the positive and negative NAO phases. Hence, these weather regimes are a promising alternative to modes of variability in the study of the ocean response to atmospheric variability. Using observations and numerical models (realistic or in idealised settings), we have shown that the Atlantic Ridge (AR), NAO− and NAO+ regimes drive a fast (monthly to interannual) wind-Driven response of the subtropical and subpolar gyres (topographic Sverdrup balance) and of the meridional overturning circulation (MOC, driven by Ekman transport anomalies). At decadal timescales, the subpolar gyre strengthens for persistent NAO+ and Scandinavian Blocking (BLK) conditions via baroclinic adjustment to buoyancy fluxes and slackens for persistent AR conditions via baroclinic adjustment to wind-Stress curl anomalies. The latter mechanism also accounts for the strengthening of the subtropical gyre for persistent NAO+ conditions and its weakening for persistent AR conditions. The gyres response to persistent NAO− conditions reflects the southward shift of the gyre system (the intergyre gyre). The MOC spins-Up for persistent NAO+ and BLK conditions via increased deep water formation in the Labrador Sea, and conversely for the NAO− and AR regimes. Last, heat budget calculations in the subpolar gyre and the Nordic Seas have been performed using four global ocean hindcasts. The winter averaged heat convergence in the western subpolar gyre is positively correlated with the NAO− winter occurrences, which is due to the intergyregyre circulation, while it is negatively correlated with AR winter occurrences, because of the wind-Driven reduction of both gyres. Downward surface heat flux anomalies are negatively correlated with NAO+ occurrences, and conversely for the NAO−. In the Nordic Seas, they are positively correlated with BLK and to a lesser extent AR occurrences. Furthermore, we suggest that the heat content variability in the western subpolar gyre is the signature of the delayed response (6-Year lag) to the time-Integrated NAO+ forcing, due to the combination of the immediate (0-Lag) response of surface heat flux and the lagged (3 year lag) response of ocean heat convergence
Msadek, Rym. "Rôle de la circulation thermohaline dans la variabilité du climat." Paris 6, 2009. http://www.theses.fr/2009PA066087.
Повний текст джерелаSevellec, Florian. "Variabilité basse fréquence endogène et exogène de la circulation thermohaline." Brest, 2007. http://www.theses.fr/2007BRES2009.
Повний текст джерелаOne of the consequences of the global warming is the modification of the freshwater flux get by the ocean. The thermohaline circulation is able to produce some low frequency variability. We are going to study the impact of the freshwater flux on the thermohaline circulation and mainly on the decadal to millennial variability. In the ocean two paradigms coexist for the explanation of the observed variability: it can be endogenous or exogenous. During the study of endogenous variability in a 2D latitude-depth model, the growth mechanism and the oscillation one of a centennial mode are characterized. This mode, corresponding to a salinity anomaly advected around the circulation, is feed by the positive salinity feedback on the advection. A millennial oscillation cycle which appears through an infinite-period bifurcation is characterized. Thus, we point out that the centennial oscillation is a precursor of millennial oscillation. During the study of the exogenous variability, the optimal perturbations of the sea surface salinity influencing the ocean circulation are performed in three models of the thermohaline circulation: a latitude-depth model, a planetary-geostrophic model and a primitive equation in global realistic configuration. Moreover, by this study et the optimal perturbations, we have fixed modification bound of the ocean circulation at 0. 75 Sv and at 0. 03 PW
Huck, Thierry. "Modélisation de la circulation thermohaline : analyse de sa variabilité inter-décennale." Brest, 1997. http://www.theses.fr/1997BRES2052.
Повний текст джерелаPaillard, Didier. "Modèles simplifiés pour l'étude de la variabilité de la circulation thermohaline au cours des cycles glaciaire-interglaciaire." Paris 11, 1995. http://www.theses.fr/1995PA112168.
Повний текст джерелаBalbon, Estelle. "Variabilite climatique et circulation thermohaline dans l'ocean atlantique nord et en mer de norvege au cours du quaternaire superieur." Paris 11, 2000. http://www.theses.fr/2000PA112132.
Повний текст джерелаManthé, Sandrine. "Variabilité de la circulation thermohaline glaciaire et interglaciaire en Atlantique Nord tracée par les foraminifères planctoniques et la microfaune benthique." Bordeaux 1, 1998. http://www.theses.fr/1998BOR10659.
Повний текст джерелаRuprich-Robert, Yohan. "Variabilité climatique de l'Atlantique Nord aux échelles de temps décennale à multidécennale : mécanismes et prévisibilité." Toulouse 3, 2014. http://thesesups.ups-tlse.fr/3332/.
Повний текст джерелаAt decadal to multidecadal timescale, the North Atlantic Ocean is characterized by a large-scale modulation of its surface temperature and heat/salt content. The latter, known as Atlantic Multidecadal Oscillation or Variability (AMV), is associated with anomalous climate conditions over the adjacent continents, especially over the Sahel, the north American continent and Europe. It is impossible from the sole observations to assess the origin of such a variability because of their short temporal coverage with respect to the involved timescale and because of their critical undersampling of the three dimensional states of the ocean. In this thesis, we have used the CNRM-CM5 climate model as a numerical lab to first investigate the internal mechanisms (as opposed to forced by external factors such as solar, greenhouse gazes etc. ) at the origin of the AMV and second to quantify the associated predictability. The analysis of a 1000-yr control simulation (external climate forcing maintained to a constant level) shows that the model AMV is mainly controlled by the multidecadal evolution of the Atlantic meridional overturning circulation (AMOC) and associated heat/salt transport. The AMOC low-frequency variability is forced by the excitation of wintertime atmospheric modes over the Atlantic, namely the East Atlantic Pattern and the North Atlantic Oscillation. Those kick a chain reaction of oceanic processes leading in fine about 30 years later to an AMOC/AMV event. Such a timescale is controlled by the ocean dynamics and thermodynamics intrinsic properties. More specifically, we insist on the critical role played by the density anomalies of the first 500-meter of the subpolar gyre in controlling a large part of the AMOC fluctuations. We then focus on the estimation of the predictability level of the AMV in CNRM-CM5. To do so, we adopt the so-called perfect model approach that consists in reforecasting the model itself via an ensemblist method. Based on the use of a series of metrics and simple statistical models, we show that the AMOC/AMV in CNRM-CM5 is predictable for leadtimes ranging from 15 to 30 years as a function of the oceanic initial conditions. Such a conditional predictability is linked to the evolution of the density anomalies of the subpolar gyre and more specifically its salinity component, in line with the above-documented proposed mechanism. The oceanic predictability is associated to some predictability over the continents in terms of surface temperature and atmospheric circulation
Somot, Samuel. "Modélisation climatique du bassin méditerranéen : variabilité et scénarios de changement climatique." Phd thesis, Université Paul Sabatier - Toulouse III, 2005. http://tel.archives-ouvertes.fr/tel-00165252.
Повний текст джерелаgrâce au développement d'un modèle régional couplé (AORCM). Il reproduit correctement
ces processus et permet de quantifier et d'étudier leur variabilité climatique. Le couplage
régional a un impact significatif sur le nombre de cyclogénèses intenses en hiver et sur
les flux et précipitations associés. Il simule une variabilité interannuelle plus faible qu'en
mode forcé pour les flux et la convection et permet de comprendre les rétroactions
qui la pilotent. L'impact régional d'un scénario climatique est analysé avec les modèles
non-couplés : le nombre de cyclogénèses diminue, les pluies associées augmentent au
printemps et en automne et diminuent en été. En outre, la Méditerranée se réchauffe,
se sale et sa circulation thermohaline s'affaiblit fortement. Cette thèse conclut de plus à
la nécessité des AORCMs pour étudier l'impact du changement climatique en Méditerranée.
Desprès, Agnès. "Les fronts de méso-échelle dans la mer d'Irminger : origine dynamique et variabilité." Paris 6, 2010. http://www.theses.fr/2010PA066162.
Повний текст джерелаKolbe, Marlen. "Sea level anomalies in the southern ocean due to thermohaline variability." Master's thesis, 2020. http://hdl.handle.net/10400.1/15206.
Повний текст джерелаOceano Antártico é responsável pela maior parte da absorção global de calor oceânico. Ao mesmo tempo, as águas de latitudes mais altas são fortemente estratificadas por salinidade. Esta tese investiga a variabilidade da altura estérica no Oceano Antártico de 2008 a 2017, analisando a temperatura potencial (✓) e os perfis práticos de salinidade (S) obtidos a partir de reanálises oceânicas globais. O trabalho foi realizado utilizando um método inovador denominado Análise de Componentes Principais Funcionais (fPCA). Este procedimento de extração de características foi aplicado nos perfis ✓ e S (profundidade de 2000 m) que foram transformados em funções B-spline previamente. Os modos termohalinos resultantes revelam informações sobre a estrutura geral ✓ e S, e suas variações foram analisadas ao longo do tempo. Ao integrar anomalias de densidade, a altura estérica foi calculada e relacionada às mudanças dos modos usando um modelo de regressão linear múltipla. Por último, as tendências da altura estérica foram comparadas aos dados da altura total da superfície do mar (SSH) da altimetria de satélite. Apesar dos recentes aumentos na água de degelo e nas temperaturas atmosféricas, a altura estérica nas águas da Antártica acima de 2000 m caiu recentemente devido ao maior conteúdo de sal, enquanto as águas subtropicais mais ao norte aumentaram principalmente devido ao aumento do armazenamento de calor. Mudanças de altura estérica interanual são claramente representadas na variabilidade SSH total, mas no momento a causa dominante para o aumento significativo do nível do mar ao sul de 30°S é o aumento da descarga de água doce das geleiras e mantos de gelo.
Meißner, Katrin J. [Verfasser]. "Langfristige Variabilität der thermohalinen Zirkulation in einem gekoppelten Ozean-, Meereis-, Atmosphärenmodell / vorgelegt von Katrin J. Meißner." 1999. http://d-nb.info/959504559/34.
Повний текст джерела