Dissertations / Theses on the topic 'Variabilita interannuale'
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Schmitt, Carolin. "Interannual variability in antarctic sea ice motion = Interannuelle Variabilität antarktischer Meereis-Drift /." Karlsruhe : Institut für Meteorologie und Klimaforschung, 2006. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=014885627&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
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Mayot, Nicolas. "La saisonnalité du phytoplancton en Mer Méditerranée." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066440/document.
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Le phytoplancton est un élément primordial dans les réseaux trophiques marins et il est un acteur principal dans les cycles biogéochimiques de la planète. Cependant, des incertitudes subsistent autour des facteurs environnementaux influençant sa saisonnalité ainsi que sa capacité à se développer. L’objectif majeur de cette thèse est d’étudier la réponse du phytoplancton à la variabilité interannuelle des facteurs environnementaux en Mer Méditerranée. Plus précisément, il s’agit de déterminer l’influence de ces derniers sur la saisonnalité du phytoplancton.Dans un premier temps, la variabilité interannuelle des cycles annuels de biomasses phytoplanctoniques observables en Méditerranée a été analysée. Certaines régions, tel que les zones de formation d’eau dense, présentent une variabilité interannuelle importante. L’une des régions les plus variables est la zone de formation d’eau dense en Méditerranée Nord-Occidentale. Une approche multi-outils basée sur des observations a été mise en place pour l’étude des variations spatiale et temporelle de la saisonnalité du phytoplancton dans cette région. Le rôle crucial du mélange vertical et de la disponibilité en lumière sur la saisonnalité du phytoplancton a été évalué. Il est démontré qu’une couche de mélange profonde pendant l’hiver augmente l’intensité du bloom phytoplanctonique printanier, due à une présence plus importante dans la communauté phytoplanctonique de micro-phytoplancton. En conséquence, le taux de production primaire printanier augmente. Enfin, ces modifications de la communauté phytoplanctonique et de la production provoquent une augmentation du stock de carbone organique produit au printempsThe phytoplankton are essential for the oceanic trophic webs and for biogeochemical cycles on Earth. However, uncertainties remain about the environmental factors influencing its seasonality, and its growing efficiency. The main objective of this thesis is to characterize the responses of the phytoplankton to the interannual variability of the environmental factors, in the Mediterranean Sea. More precisely, we aim to assess the influence of the environmental factors on phytoplankton seasonality. The interannual variability of the phytoplankton annual cycles are analyzed in the Mediterranean Sea, thus highlighting the regions associated with annual cycle variability, like the ones where deep-water formation events occur recurrently. One of these regions is the North-Western Mediterranean Sea. A multiplatform approach based on in situ observations is implemented to analyze the spatial and temporal variability of the phytoplankton seasonality in this particular region. The influences of mixed layer depth and the light availability on phytoplankton seasonality are assessed. An intense deepening of the mixed layer (related to the deep convection) increases the magnitude of the phytoplankton spring bloom. Moreover, the strong deepening of mixed layer seems to induce favorable conditions for an important accumulation of micro-phytoplankton (composed of diatoms mainly). In turn, the phytoplankton production rate increases, mostly, the primary production rate of diatoms. Finally, at the scale of the North-Western Mediterranean Sea, the shift in the phytoplankton community structure and in production induces an increase of the organic carbon stock produced during spring
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Scaife, Adam A. "Interannual variability of the stratosphere." Thesis, University of Reading, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284451.
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James, Paul Martin. "Interannual variability in a baroclinic atmosphere." Thesis, University of Reading, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.290299.
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Washington, Richard. "Interannual and interdecadal variability of African rainfall." Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.396138.
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Sinclair, James A. "Seasonal and interannual variability in Saturn's stratosphere." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:1ae2289b-a615-4d16-8f01-b13ea10f3bbe.
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The stratosphere of Saturn is highly variable. With an axial tilt of 26.7°, Saturn experiences seasons like Earth and is currently approaching northern summer solstice in 2017. In addition to general seasonal change, previous studies have highlighted that Saturn's stratosphere is host to a range of dynamical phenomena. These processes have an observable effect on the vertical temperature profile and stratospheric concentrations of acetylene (C2H2) and ethane (C2H6), which may be determined or retrieved from thermal infrared observations of Saturn. This thesis presents an analysis of observations of Saturn acquired by Voyager's IRIS (Infrared Interferometer Spectrometer, 180 - 2500 cm-1, Hanel et al.,[1980]) instrument in 1980, Cassini's CIRS (Composite Infrared Spectrometer, 10 - 1400 cm-1, Flasar et al.,[2004]) instrument from 2005 to 2012 and the Celeste spectrometer (400 - 2000 cm-1, Moran et al.,[2007]) on NASA's IRTF (Infrared Telescope Facility) in 2012 in order to track seasonal and interannual changes in Saturn's stratosphere. The concentrations of C2H2 and C2H6 were seen to decrease at 15°S and increase at 25°N from 2005 to 2009/2010. These changes at 15°S and 25°N respectively indicate upward and downward branches associated with cross-equatorial seasonally-reversing Hadley circulation that has been predicted by a general circulation model [Friedson and Moses, 2012]. Strong cooling of up to 17 K at high-southern latitudes from 2005 to 2010 suggests an autumnal weakening of a vortex that appears to form at the pole of the summer hemisphere [Fletcher et al., 2008]. The emergence of a similar northern polar vortex as northern summer solstice approaches was yet to be observed in 2012. Interannual differences in the equatorial temperature structure between 1980 and 2009/2010 suggest Saturn's semiannual oscillation (or SSAO, Fouchet et al. [2008]; Orton et al. [2008]) has been captured in a different phase from one year to the next. This is puzzling since the oscillation would be expected to have undergone two cycles assuming its period is half a Saturn year (14.7 years). This contrast is suggestive that the period of the SSAO is more quasisemiannual.
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Spadone, Aurélie. "Variabilité interannuelle du courant des Malouines." Paris 6, 2009. http://www.theses.fr/2009PA066226.
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Le courant des Malouines est une émanation de la branche nord du courant circumpolaire Antarctique en Atlantique Sud Ouest. Une série temporelle de transport sur les 1500 premiers m de la colonne d’eau de plus de 15 ans a été construite en utilisant les données altimétriques et les informations sur la structure verticale du courant apportées par deux jeux de mesures in situ obtenues à 8 ans d'intervalle. Bien qu’aucune tendance n’ait été révélée par le jeu de données de 2001-2003, les variations interannuelles sont importantes. Un changement marqué dans la composition spectrale de la série de transport est noté : pendant la période de 1992 à 1997, les variations du transport du courant des Malouines ont des périodes relativement courtes (50-90 jours et autour de 180 jours) alors qu’après 2000, elles sont dominées par des périodes plus longues (autour de la période annuelle). Les variations du transport aux échelles de temps supérieures à 120 jours suivent le rotationnel de la tension de vent dans le Pacifique Sud Est (~40-50°S ; 80-110°W) (retards de phase ≤ 20 jours).
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Nortley, Fay. "Interannual variability in a seasonally varying simple GCM." Thesis, University of Reading, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.294613.
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Grignon, Laure. "Causes of the interannual variability of deep convection." Thesis, University of Southampton, 2009. https://eprints.soton.ac.uk/72147/.
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Deep water formation in the Labrador Sea and the Gulf of Lion, for example, results from convection. A cyclonic circulation leads to a doming of the isopycnals at its centre, where stratification is then completely eroded by high surface winter buoyancy loss. This thesis assesses the causes of the interannual variability of deep convection. We first aim to quantify the relative importance of preconditioning, defined as the temperature and salinity structures and contents of the water column before the onset of convection, and of the buoyancy forcing (averaged over one winter) on the final convective mixed layer depth and on the temperature and salinity of the water mass formed. This study focuses on the Mediterranean and uses data from the Medar/Medatlas and Dyfamed data sets. The heat fluxes are studied and characterised. It is shown the the preconditioning is as important as the winter buoyancy fluxes in setting the final depth of convection. At the Dyfamed site (Corsica Strait), the seasonal cycle shows that the stratification frequency reaches a maximum in the intermediate layer in winter. This winter maximum is thought to be of critical importance. The second (and main) part focuses on the effect of the short-term (O(day)) variability of the surface forcing on convection, using an idealised model. The MIT model is integrated over a square box of size 64km x 64 km x 2km initialised with homogeneous salinity and a linear vertical temperature gradient. The configuration of the model is described and validated. A time-periodic cooling is then applied over a disc of radius 20km at the centre of the surface of the box. It is shown that the final mixed layer depth depends little on this short-term time variability because the lateral buoyancy fluxes are very responsive to the surface ones. Our results are compared with traditional parameterisation of the lateral buoyancy fluxes. General characteristics of the patch are also looked at, such as the rim current, the location of the angular momentum surfaces, the potential vorticity and the residual stratification in the mixed layer. The characteristics of the final water mass in each experiment are studied, showing that the short-term time variability of the forcing has an impact on the characteristics of the water mass formed. The last part compares the modelling study to gliders data for the Labrador Sea obtained by Peter Rhines and Charlie Eriksen of the University of Washington, WA, USA, in winter 2004-05. In that part of the real ocean, the variability of the boundary current seems more important than the variability in the surface forcing.
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Price, Martin R. "Processes governing interannual variabililty in Drake Passage." Thesis, University of East Anglia, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.426986.
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Scherrer, Simon Scherrer Simon Scherrer Simon. "Interannual climate variability in the European and Alpine region /." Zürich : ETH, 2006. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=16338.
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Kowalski, P. C. "Models of interannual mid-latitude sea surface temperature variability." Thesis, University College London (University of London), 2013. http://discovery.ucl.ac.uk/1394920/.
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Well established and novel simple mixed layer models are used to investigate some of the factors influencing mid-latitude sea surface temperature variability. This thesis focuses in particular on the re-emergence mechanism and the factors that influence it. The re-emergence mechanism describes the process whereby winter sea surface temperature anomalies can become sequestered below the mixed layer as it reforms in the spring/summer and are entrained into the mixed layer in the following winter, subsequently impacting the sea surface temperature. In chapter 2 the idealized mixed layer column model used in Stevenson [36] and the quasi-geostrophic wind driven ocean model are derived. Chapter 3 investigates how sea surface temperature anomalies are generated and decay through mixed layer processes and in the absence of atmospheric feedback. The e ect of atmospheric feedback on the sea surface temperature and mixed layer is investigated in chapter 4. Two new models of the re-emergence mechanism are presented in chapter 5: the first is a stochastic two season model and the second is an entraining mixed layer model with a fixed mixed layer annual cycle. These models are used to investigate some of the factors, such as the diff erence between the summer and winter mixed layer depth, that influence the re-emergence mechanism. The impact of interannual mixed layer depth variability on the re-emergence mechanism is then investigated using the model of Stevenson [36]. In chapters 6 and 7, the impact of local Ekman pumping and associated Rossby wave induced vertical motion on the sea surface temperature, the mixed layer and the re-emergence mechanism are investigated.
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Peyser, Cheryl, and Jianjun Yin. "Interannual and Decadal Variability in Tropical Pacific Sea Level." MDPI AG, 2017. http://hdl.handle.net/10150/624972.
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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.
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Nguyen, Dac Da. "Variabilité interannuelle de l'upwelling du sud Vietnam : contributions du forçage atmosphérique, océanique, hydrologique et de la variabilité intrinsèque océanique." Thesis, Toulouse 3, 2018. http://www.theses.fr/2018TOU30081/document.
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L'upwelling du Sud Vietnam (SVU) joue un rôle clef dans la dynamique océanique et la productivité biologique en Mer de Chine du Sud. Cette thèse vise à quantifier la variabilité interannuelle du SVU et identifier les facteurs et mécanismes en jeu. Pour cela, un jeu de simulations numériques pluri-annuelles à haute résolution a été utilisé. Le réalisme du modèle a été évalué et optimisé par comparaison aux observations in-situ et satellites. Les résultats montrent que la grande variabilité du SVU est fortement pilotée par le rotationnel du vent estival, et liée à l'oscillation ENSO via son impact sur le vent. Cependant, cette influence du vent est significativement modulée par la variabilité intrinsèque océanique liée aux interactions entre la vorticité associée aux tourbillons océaniques et le vent, et dans une moindre mesure par la circulation océanique de grande échelle et les fleuves. Ces conclusions sont robustes aux choix effectués pour corriger la dérive de surface du modèleThe summer South Vietnam Upwelling (SVU) is a major component of the South China Sea circulation that also influences the ecosystems. The objectives of this thesis are first to quantitatively assess the interannual variability of the SVU in terms of intensity and spatial extent, second to quantify the respective contributions from different factors (atmospheric, river and oceanic forcings; ocean intrinsic variability OIV; El-Niño Southern Oscillation ENSO) to the SVU interannual variability, and third to identify and examine the underlying physical mechanisms. To fulfill these goals we use a set of sensitivity eddy-resolving simulations of the SCS circulation performed with the ROMS_AGRIF ocean regional model at 1/12° resolution for the period 1991-2004. The ability of the model to realistically represent the water masses and dynamics of the circulation in the SCS and SVU regions was first evaluated by comparison with available satellite and in-situ observations. We then defined a group of sea-surface-temperature upwelling indices to quantify in detail the interannual variability of the SVU in terms of intensity, spatial distribution and duration. Our results reveal that strong SVU years are offshore-dominant with upwelling centers located in the area within 11-12oN and 110-112oE, whereas weak SVU years are coastal-dominant with upwelling centers located near the coast and over a larger latitude range (10-14oN). The first factor that triggers the strength and extent of the SVU is the summer wind curl associated with the summer monsoon. However, its effect is modulated by several factors including first the OIV, whose contribution reaches 50% of the total SVU variability, but also the river discharge and the remote ocean circulation. The coastal upwelling variability is strongly related to the variability of the eastward jet that develops from the coast. The offshore upwelling variability is impacted by the spatio-temporal interactions of the ocean cyclonic eddies with the wind stress curl, which are responsible for the impact of the OIV. The ocean and river forcing also modulate the SVU variability due to their contribution to the eddy field variability. ENSO has a strong influence on the SVU, mainly due to its direct influence on the summer wind. Those results regarding the interannual variability of the SVU are robust to the choice of the surface bias correction method used in the model. We finally present in Appendix-A2 preliminary results about the impacts of tides
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Whitesides, Benton W. "Interannual Zonal Variability of the Coupled Stratosphere-Troposphere Climate System." Thesis, Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/11578.
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Understanding the dynamical relationships between low frequency forcings and the interannual variability of the Earths atmosphere is critical for accurate extended-range forecasts and climate prediction. This thesis investigates possible dynamical couplings between the stratosphere and troposphere by implementing lagged multivariate linear regressions. These regressions were chosen to untangle the separate responses of distinct atmospheric forcings upon zonal mean climate variability. The regressions incorporate monthly meteorological data with indices of four dominant forcings of low frequency atmospheric variability: the El Nino Southern Oscillation, the Quasi-Biennial Oscillation, the 11-year solar cycle, and volcanic activity. The analysis uses data from both the NCAR/NCEP and ECMWF reanalyses for two distinct time periods to expose possible satellite measurement influences. One period consists of all data since 1958, while the other period includes only data since 1979, a period of extensive satellite observations. Diagnostic tools include piecewise potential vorticity inversions, an assessment of anomalous Eliassen-Palm fluxes, stream function analyses, and general circulation model diagnoses. The examination reveals robust patterns associated with each forcing, consistent with existing theories in climate dynamics of the coupling mechanisms between the stratosphere and the troposphere. To better predict climate variability, however, the next step is to investigate the nonlinearities known to play an important role in this system.
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Arfeuille, Gilles. "Modelling the interannual variability of the Arctic sea ice cover." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0033/MQ50711.pdf.
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Arfeuille, Gilles. "Modelling the interannual variability of the Arctic sea ice cover." Thesis, McGill University, 1998. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=21505.
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A thermodynamic-dynamic sea ice model based on the granular material rheology of Tremblay and Mysak is used to study the interannual variability of the Arctic sea ice cover during the 41-year period 1958--1998. The sea ice model is coupled to both a mixed layer ocean model and a one-layer thermodynamic atmospheric model. The model is first run with monthly climatology for most of the thermodynamic and dynamic forcing components to obtain a stable periodic seasonal cycle. For the 41-year run, the monthly wind stress forcing is derived from analyzed sea level pressures from the National Centers for Environmental Prediction (NCEP Reanalysis) data. The atmospheric thermodynamic forcings are based on monthly climatology.In this thesis we explore the high-latitude sea ice circulation and thickness changes due to year-to-year variations in the wind field. We focus our study on the interannual variability of the sea ice. volume in the Arctic Basin, and the subsequent changes in the export of sea ice from the Arctic Basin into the northern North Atlantic via Fram Strait. (Abstract shortened by UMI.)
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Ibbotson, Simon David. "A modelling study of interannual variability in the middle atmosphere." Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325487.
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Davis, Andrew Murphy. "The spatial structure and interannual variability of California current system." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/52236.
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The California Current is the Eastern Boundary Current associated with the North Pacific Subtropical Gyre, transporting cold, nutrient-rich water equatorward. It is also an area of strong mesoscale eddy variance, as well as subsurface zonal currents known as striations. This work examines the causes and variability of these transports using a set of eddy-resolving ocean model simulations.
Large-scale meridional transports are found to be driven interannually by the dominant local pattern of wind stress curl variability. This contrasts with earlier work that suggested that these transports were forced principally by tropically-originating coastal- trapped waves.
While mesoscale eddies possess a large fraction of intrinsic variance, there is a deterministic component as well. North of the Southern California Bight this component is driven by the same pattern of wind forcing. To the south, eddies respond nonlinearly to both atmospheric and oceanic forcing.
Striations are found to develop in response to irregularities in the California coastline. They spin up along with the large-scale circulation, and their magnitude is constrained by the shelf.
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Harle, James. "Interannual-to-seasonal variability of the subpolar North Atlantic Ocean." Thesis, University of Southampton, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.418036.
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Hadjinicolaou, Panayiotis. "Modelling the impact of interannual meteorological variability on stratospheric ozone." Thesis, University of Cambridge, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.620188.
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Loisulie, Saiguran. "A model study of the interannual variability of Tanzanian rainfall." Master's thesis, University of Cape Town, 2006. http://hdl.handle.net/11427/6488.
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Includes bibliographical references (leaves 41-46)The ability of the Hadley Centre Atmospheric Model version 3 (HadAM3) to capturerainfall variability patterns over Eastern Africa and the western tropical Indian Oceanduring the rainy seasons (October to December (OND) and March to May (MAM)) isassessed against data derived from National Centre for Environmental Prediction (NCEP)model and Global Precipitation Climatology Project (GPCP). The vector windsclimatology at 850hPa and 200hPa reveals some comparable patterns in both HadAM3 andNCEP. However, there are indications that the Somali Jet appears earlier and the monsooneasterly winds over the western Indian Ocean are weaker in HadAM3 than in NCEP.Empirical Orthogonal Functions (EOF) and Principal Component Analysis (PCA) derivedfrom the GPCP precipitation and NCEP Outgoing Longwave Radiation (OLR) andgeopotential anomalies were also compared to those from the HadAM3 model.
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Munoz, Ernesto. "The Caribbean low-level jet its structure and interannual variability/." College Park, Md.: University of Maryland, 2007. http://hdl.handle.net/1903/7673.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2007.Thesis research directed by: Dept. of Atmospheric and Oceanic Science. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Yu, Xuri. "Dynamics of seasonal and interannual variability in the equatorial Pacific." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/11065.
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Myoung, Boksoon. "Interannual variability of summer precipitation in Texas and its implication to summer drought." Thesis, [College Station, Tex. : Texas A&M University, 2007. http://hdl.handle.net/1969.1/ETD-TAMU-1422.
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DeTracey, Brendan. "Modelling interannual sea ice variability in the Gulf of St. Lawrence." Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=68167.
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An uncoupled, modified Hibler ice model has been applied to the Gulf of St. Lawrence for three different winters of varying severity, in order to examine interannual sea ice variability. The simulation was initialized with observed November sea surface temperatures, and forced by weekly geostrophic winds, monthly averaged meteorological data and model geostrophic surface currents.Results showed a general correlation with observations, reproducing differences in the sea ice cover between the years chosen. Neglecting oceanic effects caused excessive ice formation in the northwest Gulf and produced discrepancies between the observed and modelled ice edge.
Sensitivity studies revealed a high sensitivity to variations in both the forcing fields and the model free parameters. Further modelling studies must include a coupled ocean component, and force the ice component with weekly meteorological data to improve the accuracy of the prediction.
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McKinley, Galen Anile 1973. "Interannual variability of air-sea fluxes of carbon dioxide and oxygen." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/16824.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2002.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 161-169).
The currently observed increase in atmospheric CO2 due anthropogenic emissions is substantially slowed by natural processes that incorporate CO2 into the terrestrial biota and the ocean. Year-to-year changes in the CO2 growth rate that exceed variations in the fossil fuel source indicate a significant variability in these global CO2 sinks. However, the enormous complexity of the terrestrial and oceanic biogeochemical systems that absorb atmospheric CO2 makes these sinks extremely difficult to understand and precisely quantify. Many techniques, including the interpretation of the relative changes in atmospheric CO2 and O2/N2, ocean modeling, and atmospheric data inversions, have been employed to estimate the mean and variability of global CO2 sinks. However, uncertainty remains large. The goal of this thesis is to improve understanding of global CO2 sinks by considering (1) the error in the atmospheric O2/N2 partitioning method due to the neglect of interannual variability in the air-sea fluxes of 02, and (2) the interannual variability of the ocean CO2 sink.
(cont.) A global, high-resolution ocean general circulation model is used to estimate the magnitude and understand the mechanisms of interannual variability in air-sea fluxes of both CO2 and 02. I find that the global variability in the fluxes of both gases are dominantly forced by large-scale physical processes governing upper ocean dynamics, particularly El Nifio / Southern Oscillation (ENSO) and, for 02, the North Atlantic Oscillation (NAO). Estimates of the extremes of CO2 and 02 flux variability for the period 1980-1998 are +/-0.5x1015 grams Carbon/yr (PgC/yr) and -70/+100x1012 mol/yr (Tmol/yr), respectively. Global 02 flux variability implies up to a 1.0 PgC/yr error in estimates of interannual variability in land and ocean CO2 sinks derived from atmospheric 02/N2 observations. This error is significant for estimates of annual sinks, but it is cumulatively negligible for estimates of mean sinks from October 1991 to April 1998. Increasing convergence of estimates of land.
by Galen Anile McKinley.
Ph.D.
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Gutzler, David Scott. "The structure of annual and interannual wind variability in the tropics." Thesis, Massachusetts Institute of Technology, 1986. http://hdl.handle.net/1721.1/54309.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1986.Microfiche copy available in Archives and Science
Bibliography: leaves 218-224.
by David Scott Gutzler.
Ph.D.
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Kaczmarska, Anna Izabela. "Seasonal and interannual sea surface height variability in the Nordic Seas." Thesis, University of Southampton, 2011. https://eprints.soton.ac.uk/336399/.
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Peard, Kathleen Rhona. "Seasonal and interannual variability of wind-driven upwelling at Lüderitz, Namibia." Master's thesis, University of Cape Town, 2007. http://hdl.handle.net/11427/6498.
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Includes bibliographical references (p. 101-108).The aim of this study is to examine the variability in the wind regime at diurnal, seasonal, interannual and interdecadal time scales. Meteorological measurements including wind speed, wind direction and air pressure collected at Dias Point Lighthouse (260 38.094'S 150 05.612'E) at hourly to eight-hourly intervals from 1960 to 2006 are analysed. Known instrument changes in the time series are validated where possible. Predominant winds at Lüderitz blow parallel to the South to North alignment of the coast. Ekman divergence in response to longshore, equatorward wind stress drives coastal upwelling at Lüderitz, the main centre of upwelling in the Benguela Current System. Wind stress is proportional to the square of the wind speed parallel to the coast and is a proxy for upwelling. A diurnal intensification of wind speeds occurred in all seasons at Lüderitz with a concomitant change in wind direction from south in the early morning to southwest in the afternoon. Pressure changes over the continent due to daytime heating and night-time cooling of the land underlie this variability. Southwesterly winds predominate throughout the year at Lüderitz. Maximum wind stress occurs in the austral summer with a fourfold decrease in wind stress during the austral winter. Highest wind stress was recorded from November to January and lowest wind stress from May to July. The wind mixing index, a measure of turbulent mixing calculated from total wind speed cubed, follows the same seasonal pattern indicating the predominance of southerly winds. The wind minimum at Lüderitz is caused by weakened pressure gradients due to the latitudinal northwesterly shift in the position of the South Atlantic Anticyclone in winter combined with a pressure increase over the continent.
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Ronsmans, Gaetane. "Seasonal and interannual variability of stratospheric nitric acid from IASI measurements." Doctoral thesis, Universite Libre de Bruxelles, 2018. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/278938.
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Measuring the composition of the stratosphere, and understanding the processes regulating it, have become,in the last few decades, top priorities in the scientific community, particularly since the discovery ofthe ozone hole in the 1980s. While a lot has indeed been done in monitoring ozone, other constituents also influence the stratosphere’s composition, and interfere namely with ozone, affecting its chemical and dynamical balance. Among these is nitric acid (HNO3 ) which is a reservoir for ozone depleting NOx ,but also a key player in the formation of polar stratospheric clouds which, by turning inert species into active radicals, enhance the ozone depletion further. The nadir-viewing IASI instrument is a very good means of obtaining simultaneous data of nitric acid and ozone. Indeed, it measures the radiation of the Earth’s atmosphere in the thermal infrared spectral range, which allows it to measure even at night. This is crucial to the study of polar processes, since they occur mostly during the polar winter, when no light reaches these latitudes. Thanks to its design and its technical characteristics, the IASI instrument provides data all-year round, for every location on the Earth. The purpose of this work is to use this unique set of IASI data to understand what drives the variability of HNO3 in the stratosphere. No study so far has focused on the factors affecting the time and spatial distributions of nitric acid to the extent and scale we propose here. We aim to identify and quantify these factors, and to compare them with the drivers of ozone variability. Nitric acid data are thus obtained for the 10 years of IASI observation (2008 − 2017), and vertical profiles are retrieved in near-real time thanks to the FORLI algorithm developed at ULB. The first part of the present work provides a detailed characterization of the IASI FORLI-HNO3 data set in terms of vertical sensitivity and errors. We show that the HNO3 maximum is found around 20 km altitude, where we also find the maximum sensitivity of the measurements to the vertical profile. The analysis of the averaging kernels shows us that only one level of information can be extracted from the vertical profile, which constrains the rest of our analyses to the use of a total (or almost total) column. We also find that the IASI measurements tend to overestimate slightly the HNO3 column in the upper troposphere/lower stratosphere region of the profile. The data set is validated against ground-based FTIR measurements at different latitudes: we find good agreement between IASI and the FTIR data, which confirms that IASI manages to reproduce the HNO3 columns and their seasonality accurately. Comparisons with a state of the art atmospheric model data are also shown, and suggest that improvement is still largely needed in models to represent the HNO3 distributions accurately. The use of a data-assimilated model (BASCOE) shows a much better agreement with the IASI observations. The next part of the work describes the geophysical analyses carried out, and details the first time series and global distributions of HNO3 from IASI. After describing the various (mostly polar) processes at play observed in the time series, the question of the formation of the polar stratospheric clouds is raised, and further results are shown about the temperature at which these form. While a fixed threshold (195 K) is usually used for geophysical analyses, we find from the observational IASI data set that this fixed temperature can vary substantially depending on local conditions and on altitude. The last sections use multivariate linear regressions to fit the HNO3 and O3 time series, featuring various chemical and dynamical variables in order to identify what factors are responsible for their respective variability. We include the variables most commonly used in such kind of study, i.e. a linear trend, harmonical terms to account for the annual seasonality, and proxies for the quasi-biennial oscillation, the multivariate ENSO index, and the Arctic and Antarctic oscillations. The novelty of our work resides in the addition of a proxy for the volume of polar stratospheric clouds to account for the strong denitrification observed in the HNO3 time series in polar regions. We find that the annual cycle, encompassing the solar seasonality and the Brewer-Dobson circulation, is the factor explaining most of the variability of both HNO3 and O3 ,at almost all latitudes. In the polar regions, however, the volume of polar stratospheric clouds is a key factor contributing the most to their variability. Globally, the same factors explain the same portion of both HNO3 and O3 variability. In the last part of the thesis, we conclude and provide a preliminary co-analysis of HNO3 and O3 from the 10-year IASI data. The results are encouraging and highlight the potential of the IASI measurements to monitor the polar processes on various scales.Doctorat en Sciences
info:eu-repo/semantics/nonPublished
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Planton, Yann. "Sources de la variabilité interannuelle de la langue d'eau froide Atlantique." Thesis, Toulouse 3, 2015. http://www.theses.fr/2015TOU30364/document.
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La langue d'eau froide Atlantique est un refroidissement saisonnier qui affecte les eaux superficielles au sud de l'équateur entre les côtes africaines et 30°W environ, pendant la " saison froide " (entre mai et octobre). Ce phénomène se produit tous les ans, mais son intensité, sa durée, ainsi que son extension spatiale sont très variables d'une année sur l'autre. En dépit du couplage très marqué qui lie la langue d'eau froide et les premiers stades de la mousson africaine, les causes de cette variabilité interannuelle sont peu connues. Cette thèse a pour objectif de combler cette lacune en améliorant notre compréhension des processus océaniques contrôlant la variabilité interannuelle de la langue d'eau froide. Cette étude se focalise sur les événements " intenses" de la langue d'eau froide, correspondant à des refroidissements anormalement forts (faibles), précédés par des anomalies négatives (positives) de vent zonal. On se focalise ainsi sur les événements dits " canoniques ", les plus nombreux, et potentiellement similaires en terme de mécanisme. Cette classification, appliquée à une dizaine de réanalyses, permet de retenir, avec une robustesse certaine, cinq années dans chacune des classes. Ces événements sont étudiés grâce à des simulations numériques réalistes. L'utilisation de bilans de chaleur nous a permis d'accéder aux processus physiques qui contrôlent la formation des événements froids et chauds. Le mélange vertical à la base de la couche de mélange apparaît comme le processus fondamental de la variabilité interannuelle de la langue d'eau froide. Lors des événements froids, il accroît le refroidissement entre mars et juillet, alors que son rôle reste discret lors des événements chauds. Au milieu de l'été boréal, les anomalies de mélange vertical sont contrebalancées par des anomalies d'advection horizontale de signes opposés. Ainsi les événements froids comme chauds sont atténués en fin de saison. Cette thèse montre qu'il est plus pertinent de s'intéresser au flux d'énergie cinétique qui est plus directement lié à l'activation du mélange vertical, qu'à la tension de vent en surface. Le flux d'énergie cinétique semble d'autant plus pertinent qu'il joue aussi un rôle majeur lors des événements intenses " non-canoniques ", i.e. événements froids (chauds), précédés par des anomalies positives (négatives) de vent zonal. Enfin, la modulation de la vitesse verticale induite par le vent tend à ajuster i) la profondeur de la couche de mélange, ii) la pente de la thermocline, et iii) le cisaillement vertical de courant zonal. Ce sont des paramètres clés du mélange vertical et donc du taux de refroidissement. La vitesse verticale joue donc un rôle indirect dans l'établissement et la variabilité interannuelle de la langue d'eau froideThe Atlantic cold tongue is a seasonal cooling of the sea surface temperature south of the Equator between the African coasts and around 30°W during the " cold season " (from May to October). The cooling occurs every year but its intensity, duration and spatial extent vary strongly from one year to another. In spite of the very strong coupling between the Atlantic cold tongue and the West African monsoon, the origin of the Atlantic cold tongue variability is not well described. This thesis aims at filling this gap by improving our understanding of the oceanic processes controlling the variability of the Atlantic cold tongue. This study focuses on " intense " Atlantic cold tongue events, defined by abnormally strong (weak) cooling, preceded by negative (positive) zonal wind anomalies. Thus " canonical " being studied, that are the most frequent and probably similar in terms of mechanisms. This classification is applied to ten reanalyses and allows to select with good confidence, five events in each group. These events are studied through realistic simulations. The use of on-line heat budget allows to identify the physical processes that control the formation of cold and warm events. Vertical mixing at the base of the mixed-layer is the fundamental process controlling the interannual variability of the cold tongue. During cold events, it increases the cooling between March and July, while it remains weak during warm events. During boreal summer, vertical mixing anomalies are balanced by horizontal advection anomalies of opposite sign. So cold and warm events are weakened at the end of the season. This thesis highlights that it is more appropriate to focus on the wind energy flux because it is more directly related to the activation of vertical mixing, rather than on the surface wind stress. The wind energy flux is relevant since it is also shown to play a major role during intense " non-canonical " events, i.e. cold (warm) events preceded by positive (negative) zonal wind anomalies. Finally, the modulation of the vertical velocity induced by the wind tends to adjust i) the mixed-layer depth, ii) the intensity of the thermocline, and iii) the vertical shear of the zonal current. These are key parameters of vertical mixing and therefore the cooling rate. Thus, vertical velocity plays an indirect role in the establishment and interannual variability of the Atlantic cold tongue
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Zuki, Zabani Md. "The interannual variability of tropical cyclones in the southern South China Sea /." free to MU campus, to others for purchase, 2004. http://wwwlib.umi.com/cr/mo/fullcit?p1426118.
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Lefebvre, Wouter. "Interannual variability and future changes of the Southern Ocean sea ice cover." Université catholique de Louvain, 2007. http://edoc.bib.ucl.ac.be:81/ETD-db/collection/available/BelnUcetd-10302007-092927/.
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The interannual variability of the sea ice in the Southern Ocean and its evolution projected for the end of the 21st century are investigated using observations and different types of models. First of all, none of the known atmospheric modes of variability are able to explain much of the total sea ice extent variability in the Southern Ocean. However, they have large influences on the local and regional scales. In particular, the response of the sea ice to the Southern Annular Mode is characterized by a dipole between the Ross Sea and the region around the Antarctic Peninsula caused by a low pressure anomaly in the Amundsen Sea in high SAM-index years. Secondly, the sea ice extent in the different regions seems to be mostly uncorrelated, showing that the total sea ice cover cannot be seen as a single entity, but merely as a combination of regional covers. Finally, it is shown why the projected distribution of sea ice is not a simple extrapolation of the current sea ice trends. The mechanisms responsible for the regional variability of the future sea-ice extents are discussed.
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Combes, Vincent Emmanuel. "Intrinsic and Forced Interannual Variability of the Gulf of Alaska Mesoscale Circulation." Thesis, Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/14532.
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The response of the Gulf of Alaska (GOA) circulation to large-scale North Pacific climate variability is explored using three high resolution (15 km) regional ocean model ensembles over the period 1950-2004. On interannual and decadal timescales the mean circulation is strongly modulated by changes in the large scale climate forcing associated with PDO and ENSO. Intensification of the model gyre scale circulation occurs after the 1976-1977 climate shift, as well as during 1965-1970 and 1993-1995. From the model dynamical budgets we find that when the GOA experiences stronger southeasterly winds, typical during the positive phase of the PDO and ENSO, there is net large-scale Ekman convergence in the central and eastern coastal boundary. The geostrophic adjustment to higher sea surface height (SSH) and lower isopycnals lead to stronger cyclonic gyre scale circulation. The opposite situation occurs during stronger northwesterly winds (negative phase of the PDO).
Along the eastern basin, interannual changes in the surface winds also modulate the seasonal development of high amplitude anticyclonic eddies (e.g. Hada and Sitka eddies). Large interannual eddy events during winter-spring, are phase-locked with the seasonal cycle. The initial eddy dynamics are consistent with a quasi-linear Rossby wave response to positive SSH anomalies forced by stronger downwelling favorable winds (e.g. southwesterly during El Nio). However, because of the fast growth rate of baroclinic instability and the geographical focusing associated with the coastal geometry, most of the perturbation energy in the Rossby wave is locally trapped until converted into large scale nonlinear coherent eddies. Coastally trapped waves of tropical origin may also contribute to positive SSH anomalies that lead to higher amplitude eddies. However, their presence does not appear essential. The model ensembles, which do not include the effects of equatorial coastally trapped waves, capture the large Hada and Sitka eddy events observed during 1982 and 1997 and explain most of the variance of tidal gauges along the GOA coast.
In the western basin, interannual eddy variability located south of the Alaskan Stream is not correlated with large scale forcing and appears to be intrinsic. A comparison of the three model ensembles forced by NCEP winds and a multi-century-long integration forced only with the seasonal cycle, shows that the internal variability alone explains most of the eddy variance. The asymmetry between the eddy forced regime in the eastern basin, and the intrinsic regime in the western basin, has important implications for predicting the GOA response to climate change. Eastern boundary eddies transport important biogeochemical quantities such as iron, oxygen and chlorophyll-a into the gyre interior, therefore having potential upscale effects on the GOA high-nutrient-low-chlorophyll region.
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Ding, Hui [Verfasser]. "Annual to interannual equatorial Atlantic variability : mechanisms and tropical impacts / Hui Ding." Kiel : Universitätsbibliothek Kiel, 2010. http://d-nb.info/1020003529/34.
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Li, Yongxiang 1962. "Intraseasonal and interannual variability of sea ice in the Gulf of St.Lawrence." Thesis, McGill University, 2000. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=36640.
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Intraseasonal and interannual variability of sea-ice cover (SIC) in the Gulf of St. Lawrence, including the time of first ice presence (TFIP), time of last ice presence (TLIP), and sea-ice duration (SID), were investigated, using weekly sea ice observations from 1963--1996. For the intraseasonal variations of sea ice, it was found that SIC in different sub-regions displays contrasting features. The largest intraseasonal variations of SIC occur in the Strait of Belle Isle region and in the southwestem Gulf, where the mean SIC is largest and SID is longest. For the interannual variability of sea ice, the largest variability of SIC occurs in the area off mid-Newfoundland, where the mean SIC is small. For the TFIP and TLIP, the largest interannual variability occurs in the area off western Newfoundland and along coasts in the northeast sector of the Gulf, respectively. In addition, sea ice appeared earlier in the coastal regions and disappeared later over the entire Gulf in severe ice years; while sea ice appeared later in the central and eastern Gulf and disappeared earlier over the entire Gulf in light ice years.Several of the forcing factors influencing sea ice variability in the Gulf of St. Lawrence were examined and mechanisms controlling this variability were discussed. It was found that surface air temperature (SAT), the eastward wind component (u-wind), sea surface temperature (SST), sea surface salinity (SSS), mixed layer depth (MLD), total river runoff, the ocean circulation pattern, and sea-ice advection from the Labrador Sea, all play important roles in explaining sea ice variability in the Gulf. However, the relative contributions of these factors to the observed sea ice variability differ in different subregions. Quantitative relationships between sea ice variability and various forcing factors were investigated using statistical analysis and a simplified Hibler's sea-ice model. Both approaches indicated that the December--April averaged SAT, u-wind, and November SST all contribute to the variability of December--June SIC in the Gulf, with SAT playing the most important role. The analysis also indicated that the dependence of SIC on various forcing factors varies with geographical location. For example, SAT influences sea ice variability mainly in the central Gulf, while the u-wind component effects SIC mainly in the eastern Gulf. In addition, statistical analyses also suggest that SSS values present in the previous November play an important role in determining SIC variability. The linear regression between SIC and three independent variables: December--April SAT, November SST and SSS, accounts for 81% of the total SIC variance.
The statistical analysis and model study also indicated that December SAT, u-wind, November SST, and MLD control the time of first ice presence, with SAT and SST playing the dominant role. The linear regression between TFIP and three independent variables (u-wind, SST, and SSS) accounts for 76% of the total TFIP variance. For TLIP, both SAT and u-wind play an important role.
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Navarro-Perez, Eleuteria. "Physical oceanography of the Canary current : short term, seasonal and interannual variability." Thesis, Bangor University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318561.
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Hampson, J. "Interannual variability in stratospheric dynamics : interaction between the QBO and the extratropics." Thesis, University of Cambridge, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.603634.
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This thesis is concerned with interannual variability in the stratosphere, in particular the tropical oscillation called the Quasi-Biennial Oscillation (QBO) and its interaction with the extratropical circulation. A three dimensional mechanistic model is used to investigate interannual variability, with a tropical QBO being forced in the model by either a relaxation scheme or a simple gravity wave parameterisation scheme. The tropospheric forcing of large-scale planetary waves is represented by imposing a geopotential perturbation at the artificial lower boundary of the model. The influence of the QBO on the extratropics is examined to see if there is a preferred mode of variability in the extratropics, and how the extratropical response to the QBO is affected by the strength of extratropical wave forcing in the model. The influence of other details of the QBO, specifically its phase relationships with the annual cycle, its height structure and its time structure are investigated. The correlation between the QBO and the extratropical circulation is seen to be consistent with the Holton-Tan mechanism for the extratropical QBO; this correlation is modulated by the amplitude of extratropical geopotential wave forcing. The extratropical dynamics are seen to affect phase preference relative to the annual cycle, irregularity in period and asymmetry between different phases of the QBO simulated in the three dimensional model. It is hypothesised that this effect comes about through the extratropical wave driving of a seasonally varying equatorial upwelling. This is investigated further in a one dimensional (equatorial) model and a simple zero dimensional model, by imposing the equatorial upwelling as a function of time. The one dimensional model exhibits phase preference, irregularity and asymmetry, consistent with the hypothesis, though cannot explain all equatorial features of the three dimensional model model. The occurrence of "stalled" descents in the parameterised QBO in the three dimensional model is noted and examined.
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Ringer, Mark Adam. "Interannual variability of the earth's radiation budget and cloudiness : a satellite view." Thesis, University of Reading, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319652.
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Brugler, Eric T. "Interannual variability of the Pacific water boundary current in the Beaufort Sea." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/85389.
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Thesis: S.M., Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2013.Includes bibliographical references (pages 133-141).
Between 2002 and 2011 a single mooring was maintained in the core of the Pacific Water boundary current in the Alaskan Beaufort Sea near 152° W. Using velocity and hydrographic data from six year-long deployments during this time period, we examine the interannual variability of the current. It is found that the volume, heat, and freshwater transport have all decreased drastically over the decade, by more than 80%. The most striking changes have occurred during the summer months. Using a combination of weather station data, atmospheric reanalysis fields, and concurrent shipboard and mooring data from the Chukchi Sea, we investigate the physical drivers responsible for these changes. It is demonstrated that an increase in summertime easterly winds along the Beaufort slope is the primary reason for the drop in transport. The intensification of the local winds has in turn been driven by a strengthening of the summer Beaufort High in conjunction with a deepening of the summer Aleutian Low. Since the fluxes of mass, heat, and freshwater through Bering Strait have increased over the same time period, this raises the question as to the fate of the Pacific water during recent years and its impacts. We present evidence that more heat has been fluxed directly into the interior basin from Barrow Canyon rather than entering the Beaufort shelfbreak jet, and this is responsible for a significant portion of the increased ice melt in the Pacific sector of the Arctic Ocean.
by Eric T. Brugler.
S.M.
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Gravelle, Andrew. "Vertical mixing and interannual variability of primary production in the North Atlantic." Thesis, University of Southampton, 2016. https://eprints.soton.ac.uk/404273/.
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It is widely held that as the ocean becomes more intensely stratified with anthropogenic-driven climate change, marine primary productivity (PP) will decline within mid-to-low latitude nutrient-limited waters, and increase within higher latitude light-limited waters. This is consistent with projections from Earth-system models, which predict a decline in global PP over the next century for ‘business-as-usual’ and high-mitigation warming scenarios. However, interannual and longer-term relationships between stratification and PP are more ambiguous in observational studies. Underlying the projected changes in PP are assumptions as to the response of phytoplankton to changes in stratification and vertical mixing at these time scales. This thesis focuses upon the identification and analysis of interannual relationships between phytoplankton biomass and vertical mixing in the North Atlantic. Satellite-derived chlorophyll (Chl) data are divided into regions of similar variability in order to assess the spatial dependence of interannual relationships with vertical mixing. A large-scale bimodal pattern represents the Chl response to the tri-pole pattern of climatic variability associated with the NAO in the North Atlantic. This Chl pattern is related to similar patterns in satellite-derived sea surface temperature (SST), wind speed, and Argo float-derived mixed layer depth (MLD) and stratification. Relationships with these proxies for vertical mixing are found to be spatially heterogeneous. However, it is general to this analysis that relationships are also spatial-scale dependent: localised variability may dominate the local-scale, but tends to cancel-out within regions of similar Chl response to reveal larger-scale relationships that dominate overall variability. Thus, while observational data tend to be noisier at the local-scale, they are consistent with Earth-system models in revealing an overall dependence of phytoplankton upon vertical mixing at larger scales. These large-scale patterns and relationships are in good agreement with output from a hindcast biogeochemical model (NEMO MEDUSA), which is analysed to determine how indirect-relationships with vertical mixing are mediated. Interannual Chl variability is shown to depend upon nutrient-availability throughout the mid-to-low latitude North Atlantic; relationships within the subpolar North Atlantic are undetermined, presumably due to a seasonal-dependence of relationships that are poorly represented by yearly-averaged/yearly-metric time series at these latitudes. Lastly, the bimodal pattern of Chl variability is assessed for stability and continuity of relationships against climate warming. In the projected output of NEMO MEDUSA, under a relative concentration pathway (RCP) 8.5 ‘business-as-usual’ warming scenario, this bimodal pattern in Chl variability is shown to weaken over the next century. While relationships with vertical mixing appear to continue unabated, the dominance of this bimodal pattern upon Chl, SST and MLD variability in the North Atlantic appears to decline over this time.
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Schoenefeldt, Rena [Verfasser]. "Interannuale und dekadische Variabilität der flachen meridionalen Zelle im Indischen Ozean / Rena Schoenefeldt." Kiel : Universitätsbibliothek Kiel, 2008. http://d-nb.info/1019754206/34.
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Pierre, Caroline. "Variabilité interannuelle des émissions d'aérosols minéraux en zone semi-aride sahélienne." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2010. http://tel.archives-ouvertes.fr/tel-00921688.
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Les aérosols minéraux constituent une des plus importantes sources en masse des aérosols atmosphériques. Ces particules ont différents impacts sur l'environnement : elles exercent un forçage radiatif, et peuvent intervenir dans la chimie hétérogène atmosphérique, ainsi que dans la dynamique des nuages. Elles jouent aussi un rôle dans la redistribution de matière à l'échelle globale, notamment par leur dépôt loin des zones sources. L'estimation des quantités d'aérosols minéraux présents dans l'atmosphère, et donc de leurs flux d'émission, qui se font sous l'action du vent en zones arides et semi-arides, demeure l'objet de fortes incertitudes. Si les émissions de particules minérales en zones arides sont relativement bien contraintes à l'heure actuelle, les processus d'érosion éolienne en zones semi-arides sont plus complexes, en raison notamment de la dynamique des états de surface. L'objectif de cette étude est de quantifier les émissions d'aérosols minéraux par érosion éolienne en zone semi-aride sahélienne, et plus précisément d'estimer l'impact de la végétation saisonnière sur ces émissions, sans prendre en compte à ce stade les perturbations induites par l'action de l'homme. Nous avons mis en œuvre des outils de modélisation pour simuler le couvert végétal saisonnier et l'émission d'aérosols par érosion éolienne. La zone d'étude est la ceinture sahélienne, de 10°N à 20°N et de 20°W à 35°E. Les résolutions spatiales retenues sont de 0.10° à 0.25° et 0.5°, et la résolution temporelle de 1 à 10 jours. Afin de pouvoir tenir compte de la variabilité interannuelle des phénomènes observés, la couverture temporelle de l'étude est de 4 ans, sur la période 2004-2007. En régions semi-arides, la disponibilité en eau est le principal facteur limitant le développement de la végétation. Trois produits d'estimation des précipitations issus d'observations satellitaires (CMORPH, RFE2.0 et TRMM3B42) ont donc été comparés entre eux et comparés à des mesures de pluviomètres spatialement interpolées (AGHRYMET), au cours de la saison des pluies au Sahel. Trois critères de comparaisons ont été définis pour qualifier leur pertinence en termes de dynamique de la végétation (distribution spatiale, fréquence journalière et quantités des précipitations). Les trois produits sélectionnés montrent un bon accord sur la ceinture sahélienne, et ce pour les trois critères. De plus, le niveau d'accord est stable au cours du temps, de l'échelle intrasaisonnière à l'échelle interannuelle. La végétation est simulée avec le modèle STEP, conçu spécifiquement pour reproduire la dynamique de la végétation sahélienne. Les simulations sont réalisées en utilisant en entrée les trois champs de pluie issus de l'étape précédente. Les résultats sont comparés à des observations régionales issues de mesures satellitaires (LAI MODIS). Les critères de comparaisons sont déterminés pour leur pertinence en termes de caractérisation de l'état de la surface (limite nord, dates de démarrage et de maximum, et valeurs du maximum de végétation). Ces comparaisons montrent la capacité du modèle utilisé à reproduire la dynamique régionale annuelle. Les différentes phases du cycle végétatif sont bien restituées, avec toutefois des réserves sur le démarrage précis de la pousse. Les émissions d'aérosols désertiques sont simulées en utilisant le modèle DPM, qui repose sur la description explicite des processus physiques mis en jeu. Les caractéristiques des états de surface en l'absence de végétation (rugosité, types de sol) sont décrites en se basant sur des produits de surface satellitaires et de données issus de d'analyses géomorphologiques. En période végétative, les caractéristiques du couvert végétal simulé (hauteur, taux de couverture) sont converties en termes de rugosité dynamique de la surface. L'effet de l'humidité gravimétrique de la couche superficielle du sol est également pris en compte. L'impact de ces différents facteurs est alors illustré, notamment les différences dues à la présence du couvert végétal, en termes d'émissions d'aérosols minéraux, dans une zone définie comme la " frange émissive saisonnièrement végétalisée ", et dont l'étendue varie selon l'année et le produit de pluie utilisé en forçage. Pour la période 2004 à 2007, la strate herbacée saisonnière présente ainsi une capacité d'inhibition des émissions de l'ordre de 8 à 28% en masse du flux total annuel de cette frange, qui lui peut varier de 1 à 30 Mt environ.
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Duchiron, Bertrand. "Variabilité interannuelle de la pluviométrie dans l'espace riverain de l'océan indien." Paris 7, 2002. http://www.theses.fr/2002PA070022.
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La variabilité pluviométrique interannuelle dans l'espace riverain de l'océan indien a été étudiée, sur la période 1946-1975, dans le but d'établir une régionalisation de cet espace puis d'établir des modèles de prévision de la pluviométrie à partir d'indicateurs océano-atmosphérique. A partir d'une base de données pluviométriques, un ensemble de 130 postes, répartis de façon la plus homogène possible dans l'espace d'étude, a été sélectionné. Les valeurs des précipitations lacunaires ont été restituées et l'ensemble du réseau validé. Des analyses multivariées (Analyses en Composantes Principales et des Classifications Ascendantes Hiérarchiques) ont été utilisées pour définir 21 régions pluviométriquement homogènes. Les chroniques de ces zones sont corrélées avec des indices d'anomalies de la circulation océano-atmosphérique sur les fuseaux Indien et Pacifique, avec des décalages de 1 à 3 mois. Pour trois régions, le sens des écarts à la moyenne de la chronique a été estimé au moyen de modèles Logit sur un pas de temps mensuel au coeur des saisons pluvieuses. Les résultats à une échéance d'un mois sont pertinents avec des taux d'erreurs inférieurs à 10%. A une échéance de deux et trois mois, le pourcentage de bonne prévision est supérieur à 80 pour les trois régions. Ces résultats valident le concept de l'utilisation des modèles Logit dans la prévision à moyen terme des tendances pluviométriques dans les régions tropicalesThe interannual variability of rainfall in the coastal areas of the Indian ocean was analysed for the period 1946-1975 and regionalized then we establish statistical forcasting models of rainfall from oceano-atmospheric circulation indicators. A set of 130 well-spatially-distributed stations were selected from a pluviometric database. Missing values were statistically replaced and the output dataset was validated. Multivariate analyes (PCA and clustering analysis) were applied on these data to extract 21 homogeneous pluviometric regions. Times series are strongly correlated over a lag period ranging from 1 to 3 months with some atmospheric and oceanic anomaly indices recorded over the Indian and Pacific oceans. .
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Elia, Letizia. "PCA study of the interannual variability of the GPS height and environmental parameters." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/20438/.
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The objective of this study is to investigate a large network of GPS stations to identify and analyze spatially coherent signals present in the Up coordinate time series of the stations and, at the same locations, to identify and analyze common patterns in the series of environmental parameters and climate indices. The study is confined to Europe and the Mediterranean area, where 107 GPS sites were selected from the archive of the Nevada Geodetic Laboratory (NGL) on the basis of the completeness and length of the data series. The parameters of interest the Up coordinate of the GPS stations, the surface pressure (SP), the terrestrial water storage (TWS) and various climate indices: NAO (North Atlantic Oscillation), EA (East Atlantic), AO (Artic Oscillation), SCAND (Scandinavia), TNA (Tropical North Atlantic) and MEI v2 (Multivariate ENSO Index version 2). The Principal Component Analysis (PCA) is the methodology adopted to extract the main patterns of the space/time variability of these parameters. The work also focused on the coupled modes of space/time interannual variability between pairs of variables using the Singular Value Decomposition (SVD) methodology. The coupled variability between all the aforementioned parameters is investigated.
This study has identified, over Europe and the Mediterranean, main modes of variability in the time series of the GPS Up coordinate, SP and TWS. The SVD analysis of coupled parameters, namely GPS Up-SP and GPS Up-TWS, showed that most of the common variability is explained by the first 3 modes. Moreover, the correlation between the GPS Up coordinate and the climate indices was estimated to investigate the possible influence of climate variability on the GPS Up behaviour. More than 30 stations, over the total of 107, show significant correlations with the AO, TNA and SCAND indices. The correlation coefficients with MEI v2 turn out to be significant and up to 0.5 for about half of the stations.
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Li, Yongxiang. "Intraseasonal and interannual variability of sea ice in the Gulf of St. Lawrence." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/NQ64606.pdf.
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Haylock, Malcolm. "Interannual variability of mean and extreme rainfall and relationship with large-scale circulation." Thesis, University of East Anglia, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.427078.
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Hassanzadeh, Smaeyl. "Interannual variability in the ocean and atmosphere in the 1980s and early 1990s." Thesis, University of Liverpool, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367005.
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Chen, Yijian. "Storm tracks, baroclinic waves propagation and their interannual variability in the northern hemisphere." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/53035.
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