Vertical mixing is an important process that relates surface fluxes to concentrations of pollutants and other chemical species in the atmosphere. Errors in vertical mixing have been identified as a major source of uncertainties in various atmospheric modeling efforts including tracer transport, weather forecasting, and regional climate simulation. This thesis aims to quantify uncertainties in model-derived mixed layer heights (zi) over North America through direct comparisons between radiosonde observations and four models at different months of the year 2004 through the bulk Richardson number method. Results of this study suggest that considerable errors in zi exist throughout the region with the spatial and temporal variations of the errors differ significantly among the selected models. Over all, errors in zi were larger in global models than in the limited area mesoscale models, and the magnitude of the random error was two times larger than the bias. Notably, spatial regions of with extremely large positive biases correspond to those with especially large random errors. The biases and random errors, however, were not correlated linearly nor can be easily used to predict each other. Uncertainties in model-derived zi were attributed, through errors in the bulk Richardson number, to temperature and horizontal winds. Errors in both horizontal winds and temperatures were found contributing more or less the same to uncertainties in zi, with relative errors in both variables being the greatest in the lowest part of the troposphere. Lastly, independent observations from the cooperative profiler network suggest that data assimilation did not add qualitative advantages for the comparisons presented in this study. The mixed layer height uncertainties demonstrated in this study may provide a guide for selecting a model to simulate regional scale atmospheric transport and for interpreting flux estimation and inversions studies.

The subject of this thesis is the application of optical backscatter measurements to locate a special property of the lowest part of the atmosphere -- the mixing height. Mixing height is the altitude of the top of the layer where all the fluxes emitted at the ground become well mixed. Since Holzworth in 1967, the knowledge of this altitude is considered relevant when modeling transport of pollutants or general fluxes originating at the ground. Indirect estimations of the mixing height are possible using atmospheric models, but its accuracy is quite low. Since several institutions are attempting to estimate precise ground fluxes, networks of measurement stations are being created. The correct use of the measured fluxes, in order to estimate the evolution of the air masses, is limited by the accuracy of the localization of this layer. It can be detected in several different ways. Most are related to a direct sounding, performed with meteorological balloons. Remote sensing techniques are also attempted with acoustical or optical instruments. Both optical and acoustical methods have advantages and disadvantages. This work is focused on optical instruments like lidar and ceilometers, which are basically small cost-effective lidar systems.

Approved for public release, distribution is unlimited / This thesis study focuses on understanding the dissipation processes of the stratocumulus deck after sunrise. This objective is met through careful analyses of observational data as well as model simulations. Measurements from the Marine Atmosphere Measurement Lab (MAML) of the Naval Postgraduate School (NPS) are used in this study. In particular, the half-hourly wind profiler/Radio Acoustic Sounding System (RASS) measurements were used to determine the boundary layer top and the evolution of the boundary layer mean thermodynamic properties during the cloud breakup period. Measurements from a laser ceilometer and the routine surface measurements are also used to detect the variation of cloud base height, the evolution of the cloud deck, and the onset of sea breeze. These measurements revealed the increase of the boundary layer depth after sunrise followed by a decrease of the boundary layer depth after the onset of the sea breeze, which points to the role of surface heating and sea breeze development in modulating cloud evolution. The effects of surface heating and sea breeze are further tested using a 1-dimensional mixed layer model modified for coastal land surfaces. / Lieutenant Commander, United States Navy

Ocean submesoscales are the subject of increasing focus in the oceanographic literature; with instrumentation now more capable of observing them in situ and numerical models now able to reach the resolution required to more fully capture them. Submesoscales are typified by horizontal spatial scales of O(1 − 10) km, vertical scales O(100) m and time-scales of O(1) day and are known to be associated with regions of high vertical velocity and vorticity. Occurring most commonly at density fronts at the ocean surface they can control mixed layer restratification and provide an important control on fluxes between the atmosphere and the deep ocean. This thesis sets out to better understand the fundamental physical processes underpinning submesoscale instabilities using a number of idealised process models. Linear stability analysis complemented by non-linear, high-resolution simulations will be used initially to explore the ways in which submesoscale instabilities in the mixed layer may compete and interact with one another. In particular, we will investigate the way in which symmetric and ageostrophic baroclinic instabilities interact when simultaneously present in a flow, with focus on the growth rates and energetic pathways of previously unexplored dynamic instabilities that arise in this paradigm; three-dimensional, mixed symmetric-baroclinic instabilities. Further, these non-linear simulations will allow us to investigate the transition to dissipative scales that can occur in the classical Eady model via a multitude of small-scale secondary instabilities that result from primary submesoscale instabilities. Finally, observational data, taken aboard the SMILES project cruise to the Southern Ocean, helps to motivate the consideration of a new dynamical paradigm; the Eady model with superimposed high amplitude barotropic jet. Non-linear simulations investigate the extent to which the addition of such a jet is capable of damping submesoscale growth. The causes of this damping are then investigated using linear analysis. With this approach eventually demonstrated as being unable to fully explain growth rate reductions, we introduce a new framework combining potential vorticity mixing by submesoscale instabilities with geostrophic adjustment, which relaxes the flow back to a geostrophic balanced state. This framework will help to explain, conceptually, how non-linear eddies control the linear stability of the flow.

L'océan Austral est une région clé pour la compréhension de la circulation océanique globale et du climat. C'est dans cette région qu'une large majorité des eaux de la planète est ventilée dans la couche de surface avant d'être réexpédiée dans l'océan profond. Ainsi la couche de surface de l'océan Austral est un élément central pour la compréhension de la circulation océanique planétaire. Malgré leur rôle fondamental dans la circulation océanique globale et dans le climat, la structure et les caractéristiques de la couche de mélange sont encore mal comprises dans la région Antarctique en raison d'un manque important d'observations in-situ. Cependant, le programme international MEOP (2004) a conduit au déploiement de milliers de capteurs hydrologiques sur des éléphants de mer, et offre une couverture spatiale de données inédites couvrant l’ensemble du cycle saisonnier. Dans cette thèse, nous exploitons ce jeu de données ainsi que d'autres plus conventionnels, afin de décrire les propriétés climatologiques et la dynamique de la couche de mélange sous la glace de mer en Antarctique. Les transferts verticaux entre la couche de mélange et l’océan plus profond, associés à la circulation de retournement y sont décrits aux échelles de temps saisonnières et inter-annuelles. Les résultats soulignent et quantifient le rôle primordial des flux d’eau douce, issus de la glace de mer et des précipitations, sur la transformation de masses d’eau sous la banquise. Nos conclusions suggèrent que des changements dans l’intensité de ces flux d’eau douce pourraient directement affecter les budgets de densité de la couche de mélange et impacter la circulation de retournement globale. / The Southern Ocean is a key region for the understanding of the global ocean circulation and for the climate as a whole. In this region, a large majority of the ocean’s water masses are ventilated in the surface layer, before being sent back to the deep ocean. The surface layer of the Southern Ocean is therefore a central element for understanding the global ocean circulation. Despite their fundamental role in the global ocean circulation and climate, the structure and characteristics of the mixed-layer are still poorly understood in the Antarctic Polar Region due to a significant lack of in-situ observations.However, the international MEOP program (2004) has led to the deployment of thousands of hydrological sensors on Elephant Seals and offers a unique spatial coverage of new data that cover the entire seasonal cycle. In this thesis, we exploit this dataset and other more conventional data, to bring a new perspective on this unknown region. Based on these observations, we describe the climatological properties and dynamics of the mixed-layer under Antarctic sea-ice. The vertical transfers between the mixed-layer and the deep ocean, associated with the meridional overturning circulation, and the hydrographic variations of the water masses in the mixed-layer, are described at seasonal and inter-annual time scales. The results highlight the critical role of freshwater fluxes, induced by sea-ice and precipitations, on the transformation of water masses under the sea-ice. Our findings suggest that changes in the intensity of these freshwater fluxes would directly affect the buoyancy budgets of the mixed-layer and impact the large-scale overturning circulation.

Deep ventilation of the Black Sea is inhibited by a sharp salinity gradient within the upper water column, resulting in a shallow anoxic interface at around 100 &ndash / 200 m depth. Understanding biological and chemical processes within the boundary region between oxic and anoxic waters is fundamental to comprehend the biogeochemical response of the Black Sea to climate forcing. The structure and depth of the chemocline is largely determined by the physical processes which transport surface waters to depth. Here we investigate how the structure and stability of the upper water column responds to changes in climatic forcing over interannual to multidecadal time-scales. We report results from two hydrodynamic model reanalysis. The first, extending from 1971-1993 assimilates CTD data. The second, extending from 1992-2001, assimilates altimetry data. Model results are validated against CTD and satellite data and consistency between modeled surface properties and observations is demonstrated. A problem with the data assimilation scheme of the 1992 -2001 model run is identified, which results in model drift and an unrealistic water column structure at intermediate depths. Model results indicate a warming trend of 0.7 &deg / C in sea surface temperature and a freshening trend of 0.4 in sea surface salinity between 1971 and 2001, with an associated increasing trend in the stability of the seasonal thermocline and a declining trend in surface mixed layer depth of 6.3 m. Trends are superimposed on a distinct multiannual variability characterized by relatively warm and saline conditions between 1971 and 1984, relatively cool and fresh conditions between 1985 and 1993 and warm and fresh conditions post-1993. The period between 1985 and 1993 corresponds to higher NAO and EA/WR index values although these indices do not exhibit a similar ~decadal scale variability. Higher frequency interannual variability in water column characteristics is related to the NAO and EA/WR atmospheric indices. Despite the cool conditions prevalent during the 1990s, the persistent freshening trend caused a reduction in the density of mixed layer waters throughout the study period. A positive feedback is proposed between increasing SSTs, reduced vertical mixing and freshening of the surface layer which further increases the stability of the upper water column. CIL characteristics typically mirrored surface temperature characteristics and varied considerably between the relatively warm period during the early part of the study and the subsequent cool period. The mean thickness and temperature of the CIL between 1971 and 1981 were ~39 m and ~7.5 &deg / C respectively, as compared to ~47 m and ~7.4 &deg / C between 1982 and 1993. Freshening of the upper water column also resulted in an increase in the stability maxima that exists at the base of the CIL, suggesting reduced ventilation of the upper water column during winter.

Cette thèse vise à explorer l'influence des températures de surface de l'océan (TSO) sur les vents de surface en Atlantique tropical aux échelles saisonnière et intrasaisonnière. Nous avons commencé par étudier les bilans de moment cinétique et de convergence des vents de surface, avec un modèle simple de couche de mélange atmosphérique et des réanalyses, afin d'identifier les processus liés à l'influence des TSO sur le vent de surface. La comparaison de ces résultats avec les observations montre que les réanalyses souffrent de problèmes communs à tous les modèles de climat, couplés ou non : nous proposons donc au final d'appliquer notre méthode pour évaluer la capacité d'un modèle d'atmosphère à répondre correctement aux fluctuations de la TSO, et à indiquer quelles paramétrisations sont potentiellement à l'origine de défauts dans le modèle. Dans la deuxième partie de la thèse, nous avons mis en évidence les structures et les périodes où les variabilités océaniques et atmosphères sont maximales, à l'aide de différentes techniques d'analyse spectrale. Nous nous sommes ensuite focalisés sur les zones de fort gradient de la TSO (zones de front) afin d'étudier les caractéristiques des structures spatio-temporelles de la réponse atmosphérique liées aux fluctuations de ce front. Contrairement à la région équatoriale (ou on retrouve des résultats déjà évoqués dans des études antérieures), les deux fronts côtiers au large de l'Angola-Namibie et du Sénégal-Mauritanie ne montrent pas de signe de couplage actif avec l'atmosphère. / The main goal of this thesis is to explore the influence of sea surface temperature (SST), on surface wind at seasonal and intraseasonal timescales. At seasonal timescales, momentum and convergence budget were first documented by using a simple atmospheric mixed layer model, and two reanalyses. This approach allows us to identify the main processes that control the surface wind dynamics, in order to explore their sensitivity to the SST. Results show that these processes vary strongly in different regions of the tropical Atlantic. In addition, the comparison of the representation of theses processes in observations and reanalyses show that, as in all climate models (coupled or not), the reanalyses have the same flaws. Eventually, this work proposes a method to better assess the capacity of an atmospheric model to answer the SST fluctuations, and investigate potential wrong atmospheric parameterizations, such as boundary layers. The second part of this study focuses on tropical Atlantic regions of strong SST gradients, where SST intraseasonal variability is the largest. Several technics of spectrum and statistical analysis were performed in order to investigate the atmospheric patterns associated to these fluctuations of oceanic fronts. Except in the equatorial region (where we found a clear coupling already described in previous studies), no clear hint of a surface wind response to the SST fluctuations was observed in the two coastal upwelling fronts. In addition, the oceanic patterns associated to the SST indexes were also investigated. In all three upwelling fronts, as expected for such upwelling regimes, the vertical oceanic mixing clearly dominates the mixed-layer heat budget. In the equatorial band, as found in previous studies, the horizontal advection is equally important, while it appears surprisingly weak in the coastal fronts. Eventually, potential signals of equatorial and coastal Kelvin waves were also followed to these coastal fronts.

Tropical cyclones (TCs) often change intensity as they move over mesoscale oceanic features, as a function of the oceanic mixed layer (OML) thermal response (cooling) to the storm's wind stress. For example, observational evidence indicates that TCs in the Gulf of Mexico rapidly weaken over cyclonic cold core eddies (CCEs) where the cooling response is enhanced, and they rapidly intensify over anticyclonic warm features such as the Loop Current (LC) and Warm Core Eddies (WCEs) where OML cooling is reduced. Understanding this contrasting thermal response has important implications for oceanic feedback to TCs' intensity in forecasting models. Based on numerical experimentation and data acquired during hurricanes Katrina and Rita, this dissertation delineates the contrasting velocity and thermal response to TCs in mesoscale oceanic eddies. Observational evidence and model results indicate that, during the forced stage, the wind-driven horizontal current divergence under the storm's eye is affected by the underlying geostrophic circulation. Upwelling (downwelling) regimes develop when the wind stress vector is with (against) the geostrophic OML velocity vector. During the relaxation stage, background geostrophic circulations modulate vertical dispersion of OML near-inertial energy. The near-inertial velocity response is subsequently shifted toward more sub-inertial frequencies inside WCEs, where rapid vertical dispersion prevents accumulation of kinetic energy in the OML that reduces vertical shears and layer cooling. By contrast, near-inertial oscillations are vertically trapped in OMLs inside CCEs that increases vertical shears and entrainment. Estimates of downward vertical radiation of near-inertial wave energies were significantly stronger in the LC bulge (12.1X10 super -2 W m super -2) compared to that in CCEs (1.8X10 super -2 W m super -2). The rotational and translation properties of the geostrophic eddies have an important impact on the internal wave wake produced by TCs. More near-inertial kinetic energy is horizontally trapped in more rapidly rotating eddies. This response enhances vertical shear development and mixing. Moreover, the upper ocean temperature anomaly and near-inertial oscillations induced by TCs are transported by the westward-propagating geostrophic eddies. From a broader perspective, coupled models must capture oceanic features to reproduce the differentiated TC-induced OML cooling to improve intensity forecasting.

The aim of the thesis has been to evaluate and understand the effect of caustic alkali solution of varying composition on the behaviour of expansive soil containing mixed layered minerals. Mixed layered minerals are formed of two or more kinds of inter grown layers, not physical mixtures. Illite - smectite is the most abundant and wide spread of the mixed layered clay minerals in sedimentary rocks and soils and also more common than either discrete illite or smectite. In geotechnical engineering much attention has not been paid to the behaviour of soils containing mixed layered minerals. Much less is known about the behaviour of these soils in polluted environment. Mixed layered minerals are more susceptible to environmental changes as the structural linkages between the layer minerals are weak compared to normal layered phyllosilicates. One important pollutant that can have considerable effect on the behaviour of soils is the caustic alkali contamination released from various industries. Recent studies have shown that the behaviour of even stable minerals is affected by alkali contamination. However, the effect of caustic alkali contamination on the behaviour of soils containing mixed layered minerals is not known and has been chosen for detailed study. Also to understand the mechanism of their interaction with alkali, it is necessary to study the effect of alkali solutions on the constituent clay minerals viz., montmorillonite and illite under similar conditions. To elucidate the mechanism of soil alkali interaction limited tests were conducted with simple electrolyte solution, as the alkali solution also acts as electrolyte apart from being alkaline. To confirm the mechanism of interaction, tests are also conducted on these soils with industrial spent liquor containing high caustic alkali and suspended alumina obtained from an alumina extraction plant treating bauxite with high alkali solutions at high temperatures. The results obtained in the laboratory are compared with the soil samples contaminated with leaking industrial Bayer's liquid in the field. Studies are also conducted to suggest remedial measures to control the adverse effects of alkali solutions on soil containing mixed layer minerals. The content of the thesis is broadly divide into 8 Chapters - viz., Introduction, Background and overview, Experimental program and procedures, Behaviour of soils containing mixed layer mineral illite - smectite (BCSI), Behaviour of montmorillonite and illite, Influence of Bayer's liquor and study on the field contaminated soils, Measures to control the influence of alkali contamination on BCSI and Summary and conclusions. The broad outline of these chapters is given in Chapter 1. A review of literature on the behaviour of soils containing different types of clay minerals with emphasis on mixed layer minerals has been presented in Chapter 2. The influence of different inorganic contaminants on the properties of soils in terms of their physical and chemical characteristics as well as their concentration has been summarized. The importance of changes in surface characteristics of soil particles and the changes in the thickness of diffuse double layer in altering the property of soils at low concentration of contaminants and changes in the mineralogy with high concentrated contaminants such as acids and alkalis has been highlighted. This forms the background information necessary to bring out the scope of the study. Four soils having different mineralogy have been used in this study. These soils are, black cotton soil containing predominantly mixed layer mineral illite - smectite mineral called rectorite, illite, montmorillonite (common smectite) and black cotton soil containing predominantly montmorillonite. The properties of the soils used are described in Chapter 3. Caustic alkali solutions of 1N, 4N concentration prepared in the laboratory and industrial alkali-spent liquor are used as contaminants. The spent Bayer's liquor had about 4N alkali concentration and 10% alumina in suspension. To simulate the effect of suspended alumina, two more caustic alkali solutions of 1N and 4N solutions containing 10% alumina by weight of solutions are also prepared. To isolate the effect of electrolyte solutions from that of alkali solution, two electrolyte solutions of 1N and 4N sodium chloride solutions are also used. Test procedures for conducting various tests such as pH, water adsorption characteristics, X-ray diffraction studies, SEM studies, thermal characteristics and geotechnical properties such as Atterberg limits, Oedometer tests and Shear Strength are given in this chapter. The test procedures are modified, wherever necessary, to bring out the effect of contaminants, particularly the effect of duration of interaction on the properties of soils. The source and properties of black cotton soil are presented in Chapter 4. Detailed x-diffraction studies have confirmed the presence of inter layered illite-smectite mineral viz., rectorite, which is uncommon in Indian expansive soils, and is classified as CH (Clay of high compressibility) as per ASTM soil classification. Effect of alkali and salt solutions of 1N and 4N concentration on all physico chemical and geotechnical properties are studied in this chapter. As it is known that presence of certain elements such as aluminium influence the soil alkali interaction, the effect of suspended alumina along with alkali solution has also been investigated. The effect of contaminating fluids such as 1N NaOH, 4N NaOH with and without alumina, 1N NaCl and 4N NaCl on the geotechnical properties of the soil has been studied. Mineralogical changes were observed by XRD and thermal studies in the soil treated with 4N NaOH solution and 4N NaOH + 10% alumina. The interlayer potassium of illite is released and potassium hydroxide is formed in soil treated with 4N NaOH. Swelling compounds such as sodium aluminium silicate hydroxide hydrate (SASH) has formed due to attack of 4N NaOH + 10% alumina on silica rather than on rectorite. Thus the studies clearly bring out that the rectorite present in the soil is dissociated only in the presence of strong alkali solutions of concentration of about 4N. The liquid limit of soil decreased with increase in the electrolyte concentration in the case of NaCl solutions. With 1N NaOH, the liquid limit of soil increased due to increase in the thickness of diffuse double layer due to increased pH. However, Proctor's maximum dry density increased and optimum moisture content decreased with 1N NaOH. With increase in the concentration of alkali solution to 4N, the rectorite dissociates into constituent minerals with the formation potassium hydroxide. The liquid limit of soil decreased probably due to the dominating influence of electrolyte nature of hydroxide solution over the effect of increased negative charge on clay particles due increase in the pH on the constituent minerals. Proctor's maximum dry density decreased and optimum moisture content increased with 4N NaOH. Sediment volume and oedometer free swell at seating/nominal surcharge load of 6.25 kPa of soil increased in 1N and 4N caustic alkali solutions, though by different mechanisms. The increase with 1N solution is essentially due to increased negative charges on clay mineral surface. However, the increase in swelling with 4N solution is associated with the dissociation of rectorite mineral and occurs in two distinct phases unlike in the case of 1N solution. While the first phase can be attributed to the effect of alkaline nature of the solution after reduction in its concentration due to reaction with rectorite and the consequent reduction in its electrolyte nature. The second phase is due to the swelling of the separated constituent minerals in the presence of excess of alkali and occurs after much delay. Consolidation behaviour of rectorite in 1N and 4N alkali solutions has been studied in two ways: 1). Loading without waiting for the second stage of swelling to occur, as in standard consolidation procedure and 2). Loading after completion of second stage of swelling which is occurring after considerable delay as explained earlier. Normally one would initiate loading after equilibrium is reached at the end of first stage of swelling and second stage of swelling is not suspected. As there is no second stage of swelling with 1N solutions, these two types of consolidation tests produced the same results. Abnormal rebound is observed during unloading with 4N solution in which loading cycle is initiated without waiting for second stage of swelling to complete. It is interesting to note that while the liquid limit of soil decreased with increase in the concentration of alkali solution, the swelling increased. The testing procedure and period of interaction as well as the concentration of alkali solution during the test in these two tests are different. The effects of alkali solution are more severe in case of liquid limit because of thorough mixing and consequent effective reaction during testing. Similarly, the volume changes in soil that has already reacted with 4N alkali solution when exposed to further to alkali contamination are considerably less compared to uncontaminated soil exposed to fresh contamination. The shear strength of soil treated with 4N-alkali solution has increased particularly after long period of interaction. This indicates that the soil after mineralogical changes posses good strength. Chapter 5 presents the effect of alkali and salt solutions on the physico chemical and geotechnical properties of component minerals of mixed layered illite/smectite. For this study, commercially obtained montmorillonite (bentonite), naturally occurring black soil containing montmorillonite and commercially pure illite are used. It was observed that montmorillonite alkali reactions would not produce significant mineralogical changes where as illite is dissociated into smectite with the formation of potassium silicate by the interaction of released potassium with soluble silica. This confirms that the ultimate products of rectorite with alkali solutions would be smectite and compounds of potassium. In the absence of mineralogical alterations the liquid limit of montmorillonite decreases due to suppression of diffuse double layer thickness due to dominating influence of alkali solutions on this highly active clay. However a small increase in liquid limit is observed in illite with alkali solutions. Thus the net effect of alkali on rectorite is to decrease the liquid limit with increase in alkali concentration. While the free swell and oedometer swelling of montmorillonite generally decreases with increase in the alkali concentration, they increase in illite. However, in both the minerals the swelling occurs only in one phase. Thus the second phase of swelling that has been observed in rectorite can be attributed to delayed swelling of montmorillonite that has been released by the attack of alkali on rectorite. The behaviour of black soil containing mixed layer mineral contaminated in the field and laboratory by leaking Bayer's spent liquor in an alumina extraction plant has been studied in Chapter 6. The Atterberg limits of the samples treated with liquor are reduced and sediment volume increased. Similarly the swelling at seating load in consolidation test is higher in sample compacted with water and inundated with liquor. X-ray diffraction studies showed that the mineralogical changes are similar to those occurred with 4N caustic alkali solution. The mineralogical and micro structural changes in the soil samples that are contaminated by leaked spent liquor in the field are relatively more marked. Also the behavior of highly montmorillonite clay, bentonite, has been studied contaminated with liquor in the laboratory. The study on the effect of high concentrated alkali solutions on montmorillonite can be useful to study the effect of interaction on the dissociated montmorillonite. These studies are helpful to suggest some possible remedial measures to control the adverse effect of alkali on soils. Possible Remedial schemes that can be adopted before and after contamination of the soil to control the adverse effect of alkali solutions on the black cotton soil containing mixed layered mineral are listed and their effectiveness examined in Chapter 7. The suggested remedial measures include flushing with water to dilute the effect of alkali, neutralisation with dilute hydrochloric acid, stabilisation of soil with lime and calcium chloride and use of impervious membrane to separate the foundation soil from alkali solution. The effectiveness of different measures as well as the method of their application has been described. Efforts are made to understand the mechanism of remedial action. Consolidation tests conducted on soil contaminated with 4N alkali solution and inundated with water showed increased swelling due to dilution of the alkali concentration. Though the swelling of contaminated soil can be controlled by passing dilute hydrochloric acid (1N), the method is not advocated as it can lead to ground water contamination. Mixing the soil with solutions containing up to 5% by weight of calcium compound in water could not prevent the alkali induced heave in the long run when inundated with 4N alkali solution. This was due to dissolution of silica by the strong alkali solutions and formation of swelling compounds such as sodium aluminium silicate hydroxide hydrate (SASH). The formation of sodium aluminates occurred only when the alkali solution contained alumina or soil contained calcium compounds. There are no significant variations in the effects of calcium chloride or calcium hydroxide on contaminated soil. Replacing the foundation soil with soil thoroughly contaminated with 4N alkali solutions and controlling the migration of contaminants into the foundation soil using high-density polyethylene (HDPE) geosynthetic membranes can be an effective measure to control the heaving in alkali contaminated foundation soil containing interstratified illite – smectite. Summary and the major conclusions of the thesis are presented in Chapter 8.

Les évènements de convection profonde sont importants car ils forment les masses d'eau intermédiaires et profondes qui nourrissent la circulation globale. La mer du Labrador, qui forme la Labrador Sea Water (LSW), est le site le plus documenté de l'océan Atlantique Nord. La mer d'lrminger a également été citée mais n'est pas entièrement reconnue à cause du manque d'observations directes. Cette thèse fournit la première description de la convection profonde en mer d'lrminger à l'échelle du bassin grâce aux données Argo. Trois évènements de convection se sont produits en mer d'lrminger depuis 2010. Au cours de l'hiver 2O11-2O12, la convection atteint 1000 m et est expliquée par la séquence d'apparition des tip jets groenlandais.La convection de l'hiver 2O13-2O14, qui atteint 1300 m, est caractérisée par un préconditionnement particulièrement important et un forçage par les tip jets faible. La convection de l'hiver 2O14-2O15, qui atteint 1700 m, montre des tip jets très nombreux et persistants. L'advection de LSW provenant de la mer du Labrador explique les profondeurs exceptionnelles observées au cours de ces deux derniers hivers. Les résultats montrent que la convection n'est pas rare en mer d'lrminger et qu'elle joue un rôle non négligeable sur l'équilibre climatique. / The deep convection events are important because they form the intermediate and deep water masses feeding the global circulation. The Labrador Sea is the main site of deep convection in the North Atlantic Ocean and produces the intermediate Labrador Sea Water (LSW). The lrminger Sea was also cited but was forgotten during decades because of the lack of direct observations. This thesis provides the first description of the lrminger Sea deep convection at basin scale, thanks to the Argo data. Three convective events occurred in the lrminger Sea since 2010. During the 2011-2012 winter, the convection reached 1000 m and is explained by the sequence of the Greenland tip jets. The event of the 2O13-2O14 winter, reaching 130O m, is characterized by a strong preconditioning and a weak forcings by the Greenland tip jets.The convection event of the 2O14-2015 winter, reaching 1700 m, shows many of persistant tip jets. The advection of LSW from the Labrador Sea explains the deepest mixed layers observed during the last two winters. The results show that deep convection in the lrminger Sea is not a rare isolated event and plays a significant role on the climate balance.