Teses / dissertações sobre o tema "Mining pools"

Having identified differentially regulated genes, the final and most labour intensive part of the analysis process is drawing biological conclusions and hypothesises about the data. A novel solution is presented which combines experimental data with a curated annotation sources along with analysis tools to assist the researcher in exploring the information contained within their dataset.

Bitcoin est une crypto-monnaie pionnière qui enregistre les transactions dans un registre public et distribué appelé blockchain. Il est utilisé comme support pour les paiements, les investissements et plus largement la gestion d’un portefeuille numérique qui n’est pas administré par un gouvernement ou une institution financière. Au cours de ces dix dernières années, l’activité transactionnelle de Bitcoin a rapidement et largement augmenté. La volumétrie ainsi que la nature évolutive de ces données posent des défis pour l’analyse et l'exploration des usages ainsi que des activités sur la blockchain. Le domaine de l’analyse visuelle travaille sur la conception de systèmes analytiques qui permettent aux humains d'interagir et d'obtenir des informations à partir de données complexes. Dans cette thèse, j'apporte plusieurs contributions à l'analyse des activités de minage sur la blockchain Bitcoin. Tout d'abord, je propose une caractérisation des travaux passés et des défis de recherche liés à l’analyse visuelle pour les blockchains. À partir de cette étude, j'ai proposé un outil d’analyse visuelle pour comprendre les activités de minage qui sont essentielles pour maintenir l'intégrité et la sécurité des données sur la blockchain Bitcoin. Je propose une méthode pour extraire l’activité des mineurs à partir des données de transaction et tracer leur comportement de bascule d’un pool de minage à un autre. L'analyse empirique de ces données a notamment révélé que les nouveaux pools de minage offraient une meilleure incitation et attiraient davantage de mineurs. Cette analyse a également montré que les mineurs choisissaient stratégiquement leur pool de minage dans le but de maximiser leur profit. Pour explorer l'évolution et la dynamique de cette activité sur le long terme, j'ai développé un outil d’analyse visuelle, appelé MiningVis, qui intègre des données liées au comportement des mineurs avec des informations contextuelles issues des statistiques et de l’actualité de Bitcoin. L'étude avec des utilisateurs démontre que les participants au minage de Bitcoin cherchent à utiliser l'outil pour analyser l'activité globale plutôt que pour étudier les détails d’un pool de minage. Les commentaires des participants prouvent que l'outil les a aidés à mettre en relation plusieurs informations et à découvrir les tendances dans l’activité de minage de Bitcoin
Bitcoin is a pioneer cryptocurrency that records transactions in a public distributed ledger called the blockchain. It has been used as a medium for payments, investments, and digital wallets that are not controlled by any government or financial institution. Over the past ten years, transaction activities in Bitcoin have increased rapidly. The volume and evolving nature of its data pose analysis challenges to explore diverse groups of users and different activities on the network. The field of Visual Analytics (VA) has been working on the development of analytical systems that allow humans to interact and gain insights from complex data. In this thesis, I make several contributions to the analysis of Bitcoin mining activity. First, I provide a characterization of the past work and research challenges related to VA for blockchains. From this assessment, I proposed a VA tool to understand mining activities that ensure data integrity and security on the Bitcoin blockchain. I propose a method to extract miners from the transaction data and trace pool hopping behavior. The empirical analysis of this data revealed that emerging mining pools provided a better incentive to attract miners. Simultaneously, miners strategically chose mining pools to maximize their profit. To explore the evolution and dynamics of this activity over the long term, I developed a VA tool called MiningVis that integrates mining behavior data with contextual information from Bitcoin statistics and news. The user study demonstrates that Bitcoin miner participants use the tool to analyze higher-level mining activity rather than mining pool details. The evaluation of the tool proves that it helped participants to relate multiple information and discover historical trends of Bitcoin mining

Cette thèse propose trois essais contribuant à déterminer les opportunités et les défis des technologies blockchain et des crypto-monnaies, afin de comprendre leur possibilité d’adoption dans le système bancaire et l’économie en général. Tout d’abord, nous avons montré, à travers une revue de littérature, des expérimentations pratiques, et une analyse comparative des différentes plateformes de DLT existantes, que les DLT alternative de consortium sont les prototypes qui devraient prédominer dans le système bancaire à l’avenir. Ensuite, nous avons mis en évidence la résistance et la résilience des principaux systèmes de récompenses utilisés par les pools de minage face aux événements du halving de Bitcoin. Cette comparaison est complétée par des calculs supplémentaires qui enrichissent véritablement l’analyse des décisions et des comportements des mineurs rejoignant un pool. Enfin, nous avons développé une solution de tokenisation adaptée pour le Liban, visant à assurer une reprise économique, tout en abordant le contexte économique tumultueux du pays et en étudiant les défis des solutions numériques existantes
This thesis presents three essays that contribute to determining the opportunities and challenges of blockchain technologies and cryptocurrencies, in order to understand their potential for adoption in the banking system and the economy in general. Firstly, we have demonstrated, through a literature review, practical experiments, and a comparative analysis of different existing DLT platforms, that consortium alternative DLTs are the prototypes likely to predominate in the banking system in the future. Next, we highlighted the resilience and robustness of the main reward systems used by mining pools in the face of Bitcoin halving events. This comparison is complemented by additional calculations that truly enrich the analysis of the decisions and behaviors of miners joining a pool. Finally, we developed a tokenization solution tailored for Lebanon, aimed at ensuring economic recovery, while addressing the country’s tumultuous economic context and examining the challenges of existing digital solutions

La nostra epoca è caratterizzata da forti innovazioni tecnologiche, alcune delle quali rappresentano delle vere e proprie sfide a sistemi esistenti e consolidati. Degno di nota è l'avvento della tecnologia blockchain e, di conseguenza, l'introduzione del concetto di criptovaluta. Una criptovaluta è una moneta digitale che può essere scambiata come quella cartacea ma con modalità differenti, basate sulla crittografia. La crittografia serve a rendere sicure le transazioni e a controllare la creazione di nuove valute. Diversamente da tutte le monete non digitali, le criptovalute sfuggono a qualsiasi autorità, infatti a coniarle non ci pensa la Zecca dello Stato e non c'è alcuna Banca Centrale che ne controlli il valore, non esiste neppure un intermediario finanziario che ne convalidi le transazioni. La vera rivoluzione infatti non è tanto nella digitalizzazione dei pagamenti, a cui tutti ormai nell’era di Internet sono abituati, quanto al fatto che questi siano decentralizzati e non convalidati con i sistemi tradizionali. TurtleCoin è una criptovaluta che nasce da un progetto già esistente, come qualsiasi altra criptovaluta. Questa nello specifico nasce da Monero. TurtleCoin nasce una notte del 9 dicembre 2017, quando due sviluppatori che lavoravano su altri progetti, in mezzo a tanta follia e volatilità del mercato, hanno pensato di progettare una cryptovaluta divertente e ottima per effettuare transazioni veloci (si stimano 20 volte più veloci delle transazioni di Bitcoin o Bitcoin Cash). \newline Nella loro idea di cryptomoneta c’era l’intenzione di garantire la privacy, avere facilità di estrazione e facilità di utilizzo. \newline TurtleCoin si focalizza quindi sulla riservatezza, la decentralizzazione, la scalabilità e sulla fungibilità, prendendo queste caratteristiche da Monero.

Aspect-oriented software design (AOSD) enables better and more complete separation of concerns in software-intensive systems. By extracting aspect code and relegating crosscutting functionality to aspects, software engineers can improve the maintainability of their code by reducing code tangling and coupling of code concerns. Further, the number of software defects has been shown to correlate with the number of non- encapsulated nonfunctional crosscutting concerns in a system. Aspect-mining is a technique that uses data mining techniques to identify existing aspects in legacy code. Unfortunately, there is a lack of suitably-documented test data for aspect- mining research and none that is fully representative of large-scale legacy systems. Using a new technique called concern seeding--based on the decades-old concept of error seeding--a tool called AspectAssay (akin to the radioimmunoassay test in medicine) was developed. The concern seeding technique allows researchers to seed existing legacy code with nonfunctional crosscutting concerns of known type, location, and quantity, thus greatly increasing the pool of available test data for aspect mining research. Nine seeding test cases were run on a medium-sized codebase using the AspectAssay tool. Each test case seeded a different concern type (data validation, tracing, and observer) and attempted to achieve target values for each of three metrics: 0.95 degree of scattering across methods (DOSM), 0.95 degree of scattering across classes (DOSC), and 10 concern instances. The results were manually verified for their accuracy in producing concerns with known properties (i.e., type, location, quantity, and scattering). The resulting code compiled without errors and was functionally identical to the original. The achieved metrics averaged better than 99.9% of their target values. Following the small tests, each of the three previously mentioned concern types was seeded with a wide range of target metric values on each of two codebases--one medium-sized and one large codebase. The tool targeted DOSM and DOSC values in the range 0.01 to 1.00. The tool also attempted to reach target number of concern instances from 1 to 100. Each of these 1,800 test cases was attempted ten times (18,000 total trials). Where mathematically feasible (as permitted by scattering formulas), the tests tended to produce code that closely matched target metric values. Each trial's result was expressed as a percentage of its target value. There were 903 test cases that averaged at least 0.90 of their targets. For each test case's ten trials, the standard deviation of those trials' percentages of their targets was calculated. There was an average standard deviation in all the trials of 0.0169. For the 808 seed attempts that averaged at least 0.95 of their targets, the average standard deviation across the ten trials for a particular target was only 0.0022. The tight grouping of trials for their test cases suggests a high repeatability for the AspectAssay technique and tool. The concern seeding technique opens the door for expansion of aspect mining research. Until now, such research has focused on small, well-documented legacy programs. Concern seeding has proved viable for producing code that is functionally identical to the original and contains concerns with known properties. The process is repeatable and precise across multiple seeding attempts and also accurate for many ranges of target metric values. Just like error seeding is useful in identifying indigenous errors in programs, concern seeding could also prove useful in estimating indigenous nonfunctional crosscutting concerns, thus introducing a new method for evaluating the performance of aspect mining algorithms.

This thesis focuses on the mining of cryptocurrency with emphasis on analysis of communication between miner and server. It describes basic principles of cryptocurrencies, mining and employed communication protocols. The next part of thesis is about design and implement modification of existing system (catalogue). This modification will add temporality to the catalog, what increase reliability of stored metadata. Description, functionality and purpose of existing system is included in the next text.

Doctor of Philosophy
Genetics Interdepartmental Program
Bikram S. Gill
Leaf rust, caused by fungus Puccinia triticina, is an important foliar disease of wheat worldwide. Breeding for race-nonspecific resistant cultivars is the best strategy to combat this disease. Aegilops tauschii, D genome donor of hexaploid wheat, has provided resistance to several pests and pathogens of wheat. To identify potentially new adult plant resistance (APR) genes, 371 geographically diverse Ae. tauschii accessions were evaluated in field with leaf rust (LR) composite culture of predominant races. Accessions from Afghanistan only displayed APR whereas both seedling resistance and APR were common in the Caspian Sea region. Seventeen accessions with high APR were selected for production of synthetic hexaploid wheat (SHW), using ‘TetraPrelude’ and/or ‘TetraThatcher’ as tetraploid parents. Six SHWs were produced and evaluated for APR to LR and resistance to tan spot at seedling stage. Genetic analysis and mapping of APR introgressed from accession TA2474 was investigated in recombinant inbred lines (RIL) population derived from cross between SHW, TA4161-L3 and spring wheat cultivar, ‘WL711’. Genotyping-by-sequencing approach was used to genotype the RILs. Maximum disease severity (MDS) for LR was significantly correlated among all experiments and APR to LR was highly heritable trait in this population. Nine genomic regions significantly associated with APR to LR were QLr.ksu-1AL, QLr.ksu-1BS, QLr.ksu-1BL.1, QLr.ksu-1BL.2, QLr.ksu-2DS, QLr.ksu-2DL, QLr.ksu-5AL, QLr.ksu-5DL and QLr.ksu-6BL. Association of QLr.ksu-1BL.1 with marker Xwmc44 indicated this locus could be slow-rusting APR gene, Lr46/Yr29. QTLs detected on 2DS, 2DL and 5DL were contributed by TA4161-L3 and are novel, along with QLr.ksu-5AL. Tan spot, caused by necrotrophic fungus, Pyrenophora tritici-repentis, has recently emerged as a damaging disease of wheat worldwide. To identify QTLs associated with resistance to Race 1 of P. tritici-repentis, F[subscript]2:3 population derived from cross between SHW, TA4161-L1 and winter wheat cultivar, ‘TAM105’ was used. Two major effect QTLs, QTs.ksu-1AS.1 and QTs.ksu-7AS were significantly associated with tan spot resistance and contributed by TA4161-L1. QTs.ksu-7AS is a novel QTL and explained 17% of the phenotypic variation. Novel QTLs for APR to LR and tan spot identified in SHWs add new variation for broadening the gene pool of wheat and providing resources for breeding of durable resistant cultivars.

Optimized memory management is important for a demanding application to achieve high-performance results. But un-optimized or unwanted memory behaviors can usually be difficult to detect without an overview of how memory is structured during run-time. This thesis explores real-time visualization of dynamic memory allocation for applications using the memory pool allocation technique. In the thesis, technical and graphical challenges are described together with their solutions and the design choices that were made. The final result is a program that can visualize dynamic memory management in real time, with the focus on displaying a detailed and comprehensive memory overview that preserves the level of detail over time.
Optimerad minneshantering är viktig för att uppnå hög prestanda i en krävande applikation. Men att upptäcka icke optimerade eller oönskade minnesbeteenden kan vara svårt utan en visuell översikt över hur minnet är strukturerat under programmets exekvering. Denna avhandling undersöker hur dynamisk minnesallokering kan visualiseras i realtid för applikationer som använder allokeringstekniken minnes\-pool. I avhandlingen beskrivs tekniska och grafiska utmaningar tillsammans med deras lösningar och de designval som gjordes. Slutresultatet är ett program som kan visualisera dynamisk minneshantering i realtid och som fokuserar på att visa en detaljerad och omfattande minnesöversikt som bevarar detaljeringsgraden över tiden.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
The popularity of social networks have attracted attention of companies. The growing amount of connected users and messages posted per day make these environments fruitful to detect needs, tendencies, opinions, and other interesting information that can feed marketing and sales departments. However, the most social networks impose size limit to messages, which lead users to compact them by using abbreviations, slangs, and symbols. Recent works in literature have reported advances in minimizing the impact created by noisy messages in text categorization tasks by means of semantic dictionaries and ontology models. They are used to normalize and expand short and messy text messages before using them with a machine learning approach. In this way, we have proposed an ensemble of machine learning methods and natural language processing techniques to find the best way to combine text processing approaches with classification methods to automatically detect opinion in short english text messages. Our experiments were diligently designed to ensure statistically sound results, which indicate that the proposed system has achieved a performance higher than the individual established classifiers.
A popularidade das redes sociais tem atraído a atenção das empresas. O crescimento do número de usuários e das mensagens enviadas por dia transforma esse ambiente em uma rica fonte de informações para descoberta de necessidades, tendências, opiniões e outras informações que podem auxiliar departamentos de vendas e marketing. Contudo,a maioria das redes sociais impõe limite no tamanho das mensagens, o que leva os usuários a usarem abreviações e gírias para compactarem o texto. Trabalhos na literatura demonstraram avanço na minimização do impacto de mensagens ruidosas nas tarefas de categorização textual através da utilização de dicionários semânticos e modelos ontológicos. Com a aplicação destes, as amostras são normalizadas e expandidas antes de serem apresentadas aos métodos preditivos. Assim, nesta dissertação é proposto um comitê de máquinas de classificação utilizando técnicas de processamento de linguagem natural para detectar opiniões automaticamente em mensagens curtas de texto em inglês. Os resulta-dos apresentados foram validados estatisticamente e indicaram que o sistema proposto obteve capacidade preditiva superior aos métodos preditivos isolados.

碩士
佛光大學
資訊學系
96
The statistical results of public opinion poll often bring important information to politicians to formulate meaningful campaign strategies. However, facing sensitive issues, survey subjects will usually give an answer of “undecided”, which consequently causing the inability to predict correctly the voting outcome. To overcome this difficulty, the first part of this study integrates the clustering, classification and neural network techniques, to design two data mining techniques, which are the Tree-based Predictive Model and Back Propagation Predictive Model, to predict the possible support of the undecided voters separately. It then uses the actual ballot counts to examine the accuracy of the forecast pattern. The second part of this research design is to study the application of the Apriori Association Rule in the advanced analysis of survey, using the degree of support and confidence two parameters to find out the latent knowledge providing and establishing effective decision making. The study then uses the general statistic method to test on the mined Association Rule. The research shows that the forecast pattern designed by this research, applying in the political survey data, indeed can actually be used to estimate the possible support of the undecided voters of certain party, based on to the previous observation of undecided voters’ data. This in turn can learn about the percentage of vote received. Through the help of tree diagram, user can also understand the different characteristics of the interviewed group in the public opinion, providing reference for decision-making. The application of the Apriori Association Rule algorithm on the analysis of political public opinion poll indeed is able to discover the various unique correlations between the variables. The application is also able to excavate the unique voter characteristics and behaviors, which could not be identified through classification technique, such as “majority of the supporters of the Democratic Progressive Party would think that the industry suitable for Ilan to develop is tourism”. This rule is subtlety learned by the experts in public survey through the accumulation of years of experience. Therefore, the Association Rule algorithm is helpful to the surveyors in making related marketing strategy.

Six point sources of potential contamination from gold mine tailings were identified along the Kromdraai/Koekemoerspruit drainage basin. The degree of contamination of the tailings, soils, surface water, stream sediments and plants at each point source, as well as the individual contribution of these point sources to the contamination of downstream localities was determined by means of quantitative indices. These indices include availability percentage, threshold exceedance ratio, geoaccumulation index, bioaccumulation index and hyperaccumation threshold exceedance ratio. Both the total concentration pool as well as the available (soluble) fraction thereof were evaluated relative to pH and plant uptake, and as applicable to the sample type, by using the USEPA 3050b and DIN 19730 (NH4NO3) extraction methods, respectively. The results for the eight selected potentially toxic trace elements (Cr, Co, Ni, Cu, Pb, Zn, As and U) were further categorised under current and potential future contamination statuses and discussed according to a source-pathway-receptor model relative to individual localities. Composite sampling was employed to provide a representative average of each locality for an overall contamination profile of the study area. Plant species were classified according to accumulation degree and hyperaccumulation status in order to derive an indication of accumulation efficiency relative to the geochemical status of soils or tailings. A document was compiled in order to be used as a guideline for rehabilitation purposes specific to a geochemically-contaminated drainage system.
MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015

The most important component of the climate system over the Indian Ocean region is the southwest monsoon, which dictates the life and economy of billions of people in the tropics. Being a phenomena that involves interaction between atmosphere, ocean and land, the southwest monsoon is strongly influenced by upper ocean, primarily through warm sea surface temperature (SST). This is particularly true about the southeastern Arabian Sea (SEAS) and the onset of southwest monsoon over the peninsular India. A localized patch of warm water, known as the Arabian Sea mini warm pool (ASMWP), forms in the SEAS during February–March. It remain as the warmest spot in the northern Indian Ocean till early April. A large region, surrounding the SEAS, attains SST exceeding 30°C during April–May, with often the ASMWP as its core. The ASMWP is believed to have a critical impact on the air-sea interaction during the onset phase of southwest monsoon and on the formation of the onset vortex, during late May or early June. This thesis addresses the formation mechanisms of ASMWP, using a high-resolution Ocean General Circulation Model (OGCM) of the Indian Ocean. In addition to the formation of ASMWP, the SEAS is characterized by several features in its hydrography and circulation, which have been invoked in the past to explain the preferential warming of this oceanic region. During November–January, the prevailing surface currents transport low-salinity water from the Bay of Bengal into the SEAS and leads to strong haline stratification in the upper layer and formation of barrier layer (layer between mixed layer and isothermal layer). The vertical distribution of temperature in the SEAS exhibit inversions (higher subsurface temperature than that at surface) during December–February. A high in sea level and anticyclonic eddies develop in the SEAS during December and they propagate westward. These eddies modify the hydrography through downwelling and play an important role in the redistribution of advected low-salinity water within the SEAS. The seasonally reversing coastal and equatorial currents present in and around SEAS also have a major contribution in setting up the hydrography, through the advection and redistribution of cooler low-salinity water. These features make the SEAS a unique oceanographic region. The first hypothesis on the formation of ASMWP, which has been suggested by diagnostic studies, is based on the barrier layer mechanism. The barrier layer, caused by the influx of low-salinity water at surface, is argued to maintain a shallow mixed layer which can warm more efficiently. In addition, presence of barrier layer can prevent mixed layer cooling, by cutting off the interaction of mixed layer with cooler thermocline water below. However, a coupled model study have shown that there is no significant impact on the ASMWP formation from barrier layer, but only a weak warming effect during it mature phase during April. The second hypothesis, which is based on an OGCM study, has suggested that the temperature inversions present within the barrier layer can heat the mixed layer through turbulent entrainment and in turn lead to the formation of ASMWP during February–March. Both hypotheses rule out the possibility of air-sea heat fluxes being the primary reason in its formation. The strong salinity stratification in the SEAS during December–March is central to the hypotheses about formation of the ASMWP. Observational studies have only limited success in assessing the contribution from barrier layer and temperature inversions, as the ASMWP always form in their presence. OGCMs offer a better alternative. However, modelling processes in the northern Indian Ocean, especially that in the SEAS, is a challenging problem. Previous Indian Ocean models have had serious difficulties in simulating the low-salinity water in the Bay of Bengal and its intrusion into the SEAS. The northward advection of low-salinity water in the SEAS, along the west coast of India, is used to be absent in model simulations. Moreover, the coarse resolution inhibited those models from simulating faster surface currents and vigorous eddies as seen in the observations. In this thesis, we use an OGCM of the Indian Ocean, based on the recent version of Modular Ocean Model (MOM4p0), to study the ASMWP. The model has high resolutions in the horizontal (1/4o x 1/4o) and vertical (40 levels, with 5 m spacing in upper 60 m), and has been forced with daily values momentum, heat and freshwater fluxes. The turbulent (latent and sensible) and long wave heat fluxes have been calculated as a function of model SST. The freshwater forcing consists of precipitation, evaporation and river runoff, and there are no surface restoring or flux adjustments. The river runoff has been distributed over several grid points about the river mouth instead of discharging into a singe grid point, which has resulted in remarkable improvements in salinity simulation. The model simulates the Indian Ocean temperature, salinity and circulation remarkably well. The pattern of model temperature distribution and evolution matches very well with that in the observations. Significant improvements have been made in the salinity simulation, including the Bay of Bengal freshwater plume and intrusion of low-salinity water from the bay into the SEAS. The salinity distribution within the SEAS is also well represented in the model. The use of appropriate horizontal friction parameters has resulted in the simulation of realistic currents. The observed features in the SEAS, including the life cycle of the ASMWP, low-salinity water, barrier layer, temperature inversions, eddies and currents are well represented in the model. Present study has unraveled the processes involved in the life cycle of barrier layer and temperature inversions in the SEAS. Presence of low-salinity water is necessary for their formation. Barrier layer develops in the SEAS during November, after the intrusion of low-salinity water from the Bay of Bengal. The barrier layer is thickest during January–February, and it dissipates during March–April. The variations and peak of barrier layer thickness is controlled by variations in isothermal layer depth, which in turn is dominated by the downwelling effects of anticyclonic eddies. The intense solar heating during March–April leads to the formation of shallow isothermal layer and results in the dissipation of barrier layer. Temperature inversions starts developing in the SEAS during December, reaches its peak during January–February and dissipates in the following months. Advection of cooler low-salinity water over warmer salty water and penetrating shortwave radiation is found to cause temperature inversions within the SEAS, whereas winter cooling is also important to the north and south of the SEAS. There is significant variation in the magnitude, depth of occurrence and formation mechanisms of temperature inversions within the SEAS. Analysis of model mixed layer heat budget has shown that the SEAS SST is mainly controlled by atmospheric forcing, including the life cycle of ASMWP. It has also shown that the heating from temperature inversions do not contribute to the formation of ASMWP. In an experiment in which a constant salinity of 35 psu was maintained over the entire model domain, the ASMWP evolved very similar to that in the standard run, suggesting that the salinity effects are not necessary for the formation of ASMWP. Examination of wind field show that the winds over the SEAS during November–February are low due to the blocking of northeasterly winds by Western Ghats. Several process experiments by modifying the wind and turbulent heat fluxforcing fields have shown that these low winds lead to the formation of ASMWP in the SEAS during February–March. The low winds reduce latent heat loss, resulting in net heat gain by the ocean. This helps the SEAS to keep warmer SST while the surrounding region experience intense cooling under the strong dry northeasterly winds. As the winds are weak over the SEAS, the mixed layer is not able to feel the stratification beneath and the mixed layer depth is determined by solar heating, with or without salinity effects. In addition, the weak winds are not able to entrain the temperature inversions present in the barrier layer. The winds are weak during March–April too, and the air-sea heat fluxes dictate the SST evolution during this period. Therefore, during November–April, the SEAS acts as a low wind heat-dominated regime, where the evolution of sea surface temperature is solely determined by atmospheric forcing. We show that, in such regions, the evolution of surface layer temperature is not dependent on the characteristics of subsurface ocean, including the presence of barrier layer and temperature inversions.

The most important component of the climate system over the Indian Ocean region is the southwest monsoon, which dictates the life and economy of billions of people in the tropics. Being a phenomena that involves interaction between atmosphere, ocean and land, the southwest monsoon is strongly influenced by upper ocean, primarily through warm sea surface temperature (SST). This is particularly true about the southeastern Arabian Sea (SEAS) and the onset of southwest monsoon over the peninsular India. A localized patch of warm water, known as the Arabian Sea mini warm pool (ASMWP), forms in the SEAS during February–March. It remain as the warmest spot in the northern Indian Ocean till early April. A large region, surrounding the SEAS, attains SST exceeding 30°C during April–May, with often the ASMWP as its core. The ASMWP is believed to have a critical impact on the air-sea interaction during the onset phase of southwest monsoon and on the formation of the onset vortex, during late May or early June. This thesis addresses the formation mechanisms of ASMWP, using a high-resolution Ocean General Circulation Model (OGCM) of the Indian Ocean. In addition to the formation of ASMWP, the SEAS is characterized by several features in its hydrography and circulation, which have been invoked in the past to explain the preferential warming of this oceanic region. During November–January, the prevailing surface currents transport low-salinity water from the Bay of Bengal into the SEAS and leads to strong haline stratification in the upper layer and formation of barrier layer (layer between mixed layer and isothermal layer). The vertical distribution of temperature in the SEAS exhibit inversions (higher subsurface temperature than that at surface) during December–February. A high in sea level and anticyclonic eddies develop in the SEAS during December and they propagate westward. These eddies modify the hydrography through downwelling and play an important role in the redistribution of advected low-salinity water within the SEAS. The seasonally reversing coastal and equatorial currents present in and around SEAS also have a major contribution in setting up the hydrography, through the advection and redistribution of cooler low-salinity water. These features make the SEAS a unique oceanographic region. The first hypothesis on the formation of ASMWP, which has been suggested by diagnostic studies, is based on the barrier layer mechanism. The barrier layer, caused by the influx of low-salinity water at surface, is argued to maintain a shallow mixed layer which can warm more efficiently. In addition, presence of barrier layer can prevent mixed layer cooling, by cutting off the interaction of mixed layer with cooler thermocline water below. However, a coupled model study have shown that there is no significant impact on the ASMWP formation from barrier layer, but only a weak warming effect during it mature phase during April. The second hypothesis, which is based on an OGCM study, has suggested that the temperature inversions present within the barrier layer can heat the mixed layer through turbulent entrainment and in turn lead to the formation of ASMWP during February–March. Both hypotheses rule out the possibility of air-sea heat fluxes being the primary reason in its formation. The strong salinity stratification in the SEAS during December–March is central to the hypotheses about formation of the ASMWP. Observational studies have only limited success in assessing the contribution from barrier layer and temperature inversions, as the ASMWP always form in their presence. OGCMs offer a better alternative. However, modelling processes in the northern Indian Ocean, especially that in the SEAS, is a challenging problem. Previous Indian Ocean models have had serious difficulties in simulating the low-salinity water in the Bay of Bengal and its intrusion into the SEAS. The northward advection of low-salinity water in the SEAS, along the west coast of India, is used to be absent in model simulations. Moreover, the coarse resolution inhibited those models from simulating faster surface currents and vigorous eddies as seen in the observations. In this thesis, we use an OGCM of the Indian Ocean, based on the recent version of Modular Ocean Model (MOM4p0), to study the ASMWP. The model has high resolutions in the horizontal (1/4o x 1/4o) and vertical (40 levels, with 5 m spacing in upper 60 m), and has been forced with daily values momentum, heat and freshwater fluxes. The turbulent (latent and sensible) and long wave heat fluxes have been calculated as a function of model SST. The freshwater forcing consists of precipitation, evaporation and river runoff, and there are no surface restoring or flux adjustments. The river runoff has been distributed over several grid points about the river mouth instead of discharging into a singe grid point, which has resulted in remarkable improvements in salinity simulation. The model simulates the Indian Ocean temperature, salinity and circulation remarkably well. The pattern of model temperature distribution and evolution matches very well with that in the observations. Significant improvements have been made in the salinity simulation, including the Bay of Bengal freshwater plume and intrusion of low-salinity water from the bay into the SEAS. The salinity distribution within the SEAS is also well represented in the model. The use of appropriate horizontal friction parameters has resulted in the simulation of realistic currents. The observed features in the SEAS, including the life cycle of the ASMWP, low-salinity water, barrier layer, temperature inversions, eddies and currents are well represented in the model. Present study has unraveled the processes involved in the life cycle of barrier layer and temperature inversions in the SEAS. Presence of low-salinity water is necessary for their formation. Barrier layer develops in the SEAS during November, after the intrusion of low-salinity water from the Bay of Bengal. The barrier layer is thickest during January–February, and it dissipates during March–April. The variations and peak of barrier layer thickness is controlled by variations in isothermal layer depth, which in turn is dominated by the downwelling effects of anticyclonic eddies. The intense solar heating during March–April leads to the formation of shallow isothermal layer and results in the dissipation of barrier layer. Temperature inversions starts developing in the SEAS during December, reaches its peak during January–February and dissipates in the following months. Advection of cooler low-salinity water over warmer salty water and penetrating shortwave radiation is found to cause temperature inversions within the SEAS, whereas winter cooling is also important to the north and south of the SEAS. There is significant variation in the magnitude, depth of occurrence and formation mechanisms of temperature inversions within the SEAS. Analysis of model mixed layer heat budget has shown that the SEAS SST is mainly controlled by atmospheric forcing, including the life cycle of ASMWP. It has also shown that the heating from temperature inversions do not contribute to the formation of ASMWP. In an experiment in which a constant salinity of 35 psu was maintained over the entire model domain, the ASMWP evolved very similar to that in the standard run, suggesting that the salinity effects are not necessary for the formation of ASMWP. Examination of wind field show that the winds over the SEAS during November–February are low due to the blocking of northeasterly winds by Western Ghats. Several process experiments by modifying the wind and turbulent heat fluxforcing fields have shown that these low winds lead to the formation of ASMWP in the SEAS during February–March. The low winds reduce latent heat loss, resulting in net heat gain by the ocean. This helps the SEAS to keep warmer SST while the surrounding region experience intense cooling under the strong dry northeasterly winds. As the winds are weak over the SEAS, the mixed layer is not able to feel the stratification beneath and the mixed layer depth is determined by solar heating, with or without salinity effects. In addition, the weak winds are not able to entrain the temperature inversions present in the barrier layer. The winds are weak during March–April too, and the air-sea heat fluxes dictate the SST evolution during this period. Therefore, during November–April, the SEAS acts as a low wind heat-dominated regime, where the evolution of sea surface temperature is solely determined by atmospheric forcing. We show that, in such regions, the evolution of surface layer temperature is not dependent on the characteristics of subsurface ocean, including the presence of barrier layer and temperature inversions.