Submitted by Lucienne Costa (lucienneferreira@ufcg.edu.br) on 2018-08-28T16:57:40Z No. of bitstreams: 1 MAISSA LUDYMILLA CARVALHO PONTES – DISSERTAÇÃO (PPGMET) 2018.pdf: 4820642 bytes, checksum: e320b4696bcf114846cc43a6004d16a1 (MD5) / Made available in DSpace on 2018-08-28T16:57:40Z (GMT). No. of bitstreams: 1 MAISSA LUDYMILLA CARVALHO PONTES – DISSERTAÇÃO (PPGMET) 2018.pdf: 4820642 bytes, checksum: e320b4696bcf114846cc43a6004d16a1 (MD5) Previous issue date: 2017-06-05 / Capes / A qualidade da estação chuvosa no Nordeste pode ser relacionada com a variabilidade que surge em decorrência do fenômeno El Niño-Oscilação Sul (ENOS) que influencia a estação chuvosa tanto pela alteração na célula de Walker quanto, por padrões de teleconexões, sendo este último responsáveis por causar variabilidades na Temperatura da superfície do Mar (TSM) no Atlântico Norte, através de padrões de trem de onda, que pode influenciar no deslocamento e tempo da permanecia da Zona de Convergência Intertropical (ZCIT) nestas latitudes. O deslocamento mais para norte da ZCIT pode ocasionar a formação de uma célula termalmente direta com seu ramo de subsidência ao sul do equador. A precipitação na estação chuvosa no Nordeste ainda pode ser influenciada pela variabilidade da TSM, pressão ao nível do mar (PNM) e vento sobre a bacia do Atlântico, influenciando também o posicionamento da ZCIT, tanto por influenciar o gradiente inter-hemisférico de TSM quanto pelo posicionamento da convergência dos alísios. Neste trabalhou buscou-se melhorar a compreensão da forma como estes mecanismos se combinam, e se há predominância entre eles. Numa etapa inicial foram analisados compostos de um conjunto de variáveis para situações de El Niño, La Niña e neutralidade no Pacífico, com o intuito de investigar os principais mecanismos controlador da variabilidade do Atlântico nesses diferentes casos. Mostrando assim, que nas fases positiva e negativa do ENOS a grande variabilidade nos extratrópicos se sobressai sobre as pequenas variações na região tropical e que as anomalias de fluxo de calor são influenciadas pelo o mecanismo de retroalimentação positiva, para condições de neutralidade a variabilidade nos trópicos parece ser mais notada e a variação do fluxo de calor ocorre pela variação da temperatura na interface oceano-atmosfera. Tais resultados foram seguidos por analises de alguns estudos de casos, para isto, foram analisados anos específicos com relação às anomalias nas células de Hadley, Walker, fluxos de calor, TSM, pressão ao nível (PNM), vento e precipitação mostrando que os efeitos das teleconexões do ENOS são influenciados de maneiras diferentes dependendo da intensidade do fenômeno. Para os anos estudados um dos principais mecanismos de variabilidade para a TSM na região tropical foi o mecanismo de retroalimentação positiva. Todavia, para o ano em que o gradiente inter-hemisférico foi bem defino, a variação da temperatura na interface oceano-atmosfera foi o principal forçante para as anomalias de fluxo de calor. Mostrando que o mecanismo de variabilidade mudará de ano para ano a depender das anomalias da TSM. As bacias do Atlântico Tropical Norte e Sul tendem a responderem a variabilidade com mecanismos diferentes de um ano para outro. / The quality of the rainy season in the Northeast can be related to the variability that arises in from of the phenomenon El Niño-Southern Oscillation (ENSO). That influences the rainy season by both the change in Walker's cell and by teleconnection patterns. The latter are responsible for causing variability in the sea surface temperature (SST) in the North Atlantic, by means of wave train patterns, which may influence the displacement and time of permanence of the Intertropical Convergence Zone (ITCZ) in these latitudes. This further northward shift of the ITCZ may lead to the formation of a thermally direct cell with its branch of subsidence south of the equator. Precipitation in the rainy season in the Northeast can still be influenced by the variability of SST, sea level pressure (PNM) and wind over the Atlantic basin. This variability also affects the positioning of the ZCIT, both because it influences the inter - hemispheric SST gradient and the positioning of the trade-offs. In this work was sought to improve the understanding of how these mechanisms combine, and whether there is predominance between them. In an initial stage we analyzed compounds of a set of variables for situations of El Niño, La Niña and neutral Pacific. The aim was to investigate the main mechanisms controlling the Atlantic variability in these different cases. It is possible to observe that in the positive and negative phases of the ENSO the great variability in the extratropics stands out for the small variations in the tropical region and that the anomalies of the heat flow were influenced by the positive feedback mechanism. For the neutral Pacific the variability in the tropics seemed to be more noticeable and the variation of the heat flow occurred by the temperature variation at the ocean-atmosphere interface. Some case studies were then made. That is, we analyzed specific years with respect to the anomalies in the cells of Hadley, Walker, heat flows, SST, geopotential, wind and precipitation. Thus, the effects of ENSO teleconnections are influenced in different ways depending on the intensity of the phenomenon. For the years studied, one of the main mechanisms of variability for SST in the tropical region was the positive feedback mechanism. However, for the year in which the inter-hemispher ic gradient was well defined, the temperature variation at the ocean-atmosphere interface was the main force for the heat flow anomalies. Showing that the variability mechanism will change from year to year depending on the SST anomalies. The results show that the North Atlantic and Southern Tropical Atlantic basins tend to respond to variability with different mechanisms from year to year.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Meteorology and Physical Oceanography, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND LINDGREN. / Bibliography: leaves 118-120. / by Randall J. Patton. / M.S.

Submitted by Irvana Coutinho (irvana@ufpa.br) on 2012-09-04T12:58:12Z No. of bitstreams: 2 license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) Dissertacao_EventosExtremosZona.pdf: 4064520 bytes, checksum: 95b3a838f2f0f39eaf1998d54471a484 (MD5) / Approved for entry into archive by Irvana Coutinho(irvana@ufpa.br) on 2012-09-04T13:13:20Z (GMT) No. of bitstreams: 2 license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) Dissertacao_EventosExtremosZona.pdf: 4064520 bytes, checksum: 95b3a838f2f0f39eaf1998d54471a484 (MD5) / Made available in DSpace on 2012-09-04T13:13:20Z (GMT). No. of bitstreams: 2 license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) Dissertacao_EventosExtremosZona.pdf: 4064520 bytes, checksum: 95b3a838f2f0f39eaf1998d54471a484 (MD5) Previous issue date: 2008 / RPCH - Rede Estadual de Previsão Climática e Hidrometeorológica do Estado do Pará / FAPESPA - Fundação Amazônia de Amparo a Estudos e Pesquisas / Este trabalho reporta uma investigação observacional sobre as características climatológicas (período de 1985 a 2007) associadas aos eventos extremos da ZCIT observados sobre o Oceano Atlântico equatorial, procurando estabelecer as influências na variabilidade pluviométrica da Amazônia oriental, durante os meses de fevereiro, março e abril. Tais eventos foram selecionados objetivamente através da análise de Funções Ortogonais Empíricas e os padrões oceano-atmosfera associados aos eventos da ZCIT, bem como seus impactos na precipitação da Amazônia oriental, foram investigados com base em composições mensais. Os resultados evidenciaram algumas diferenças mensais, principalmente no padrão da circulação atmosférica em 200 hPa e na configuração vertical da circulação troposférica meridional associada à célula de Hadley equatorial. Quanto à estrutura dinâmica dos padrões oceano-atmosfera observada nos meses de fevereiro, março e abril, basicamente evidenciou-se que a ZCIT forma-se sobre o Oceano Atlântico equatorial numa região de confluência dos ventos alísios de sudeste e nordeste, coincidente com áreas contendo TSM anomalamente quente, movimento vertical ascendente associado à célula de Hadley, com divergência do vento em altos níveis. Os impactos de tais eventos na variabilidade espacial da precipitação sobre a Amazônia oriental mostrou que os principais estados afetados pela ZCIT são: Amapá, Pará e Maranhão. Adicionalmente, relatam-se alguns impactos sócio-ambientais (enchentes, alagamentos, queda de árvores, proliferação de doenças, entre outros) que ocorreram na Região Metropolitana de Belém, associados a ocorrência dos eventos extremos da ZCIT selecionados neste trabalho. / This work reports an observational analysis of the climatological characteristics (period of 1985-2007) associated with the ITCZ extreme events, observed over the equatorial Atlantic Ocean, establishing its influences on the pluviometric variability over eastern Amazon, during the months of February, March and April. These events were selected objectively through Empirical Orthogonal Functions analysis, and the ocean-atmosphere patterns associated with ITCZ events, as well as, its impacts on eastern Amazon rainfall, were investigated through monthly composites. The results showed some monthly differences in the dynamical pattern related to the 200 hPa atmospheric circulation and configuration of vertical tropospheric motion, associated with the equatorial Hadley cell. Basically, the dynamic structure of the ocean-atmosphere patterns observed in February, March and April, showed that the ITCZ is formed over the equatorial Atlantic Ocean in a region of confluence between northeasterly and southerly winds that is coincident with areas of abnormally hotter SST, upward vertical air motion associated with the Hadley cell, and divergent outflow at high levels. The impacts of such events in the precipitation variability over the eastern Amazon, showed that the states affected by ITCZ are mainly Amapá, Pará and Maranhão. Additionally, it were reported some socio-environmental impacts (floods, falling trees, proliferation of diseases, among others) that occurred in the metropolitan area of Belém, associated with the occurrence of extreme weather events ITCZ selected in this work, associated to the presence of ITCZ over the region.

The shape of the thermocline and the depth of the lysoline in the western tropical Pacific are both influenced by the overlying atmosphere, and both the shape of thermocline and the depth of the lysocline can be reconstructed from foraminifera-based paleo-proxies. Paleoclimate proxy evidence suggests a southward shift of the Intertropical Convergence Zone (ITCZ) during times of Northern Hemisphere cooling, including the Last Glacial Maximum (LGM), 19-23 ka before present. However, evidence for movement over the Pacific has mainly been limited to precipitation reconstructions near the continents, and the position of the Pacific marine ITCZ is less well constrained. In this study, I address this problem by taking advantage of the fact that the upper ocean density structure reflects the overlying wind field. I reconstruct changes in the upper ocean density structure during the LGM using oxygen isotope measurements on the planktonic foraminifera G. ruber and G. tumida in a transect of sediment cores from the Western Tropical Pacific. The data suggest a ridge in the thermocline just north of the present-day ITCZ persists for at least part of the LGM, and a structure in the Southern Hemisphere that differs from today. The reconstructed structure is consistent with that produced in a General Circulation Model with both a Northern and Southern Hemisphere ITCZ. I also attempt to reconstruct the upper ocean density structure for Marine Isotope Stages 5e and 6, the interglacial and glacial periods, respectively, previous to the LGM. The data show a Northern Hemisphere thermocline ridge for both of these periods. There is insufficient data to draw any conclusions about the Southern Hemisphere thermocline. Using the same set of sediment cores, I also attempt to reconstruct lysocline depth over the last 23,000 years using benthic foraminiferal carbon isotope ratios, planktonic foraminiferal masses, and sediment coarse fraction percentage. Paleoclimate proxy evidence and modeling studies suggest that the deglaciation following the LGM is associated with a deepening of the lysocline and an increase in sedimentary calcite preservation. Although my data lack the resolution to constrain the depth of the lysocline, they do show an increase in calcite preservation during the last deglaciation, consistent with lysocline deepening as carbon moves from the deep ocean to the atmosphere.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Meteorology and Physical Oceanography, 1981. / Microfiche copy available in Archives and Science. / Bibliography: leaves 53-54. / by James Che-Ming Chung. / M.S.

The east-west oriented cloud bands in the tropics are called the Inter-tropical Con-vergence Zones (ITCZ). Till recently, the ITCZ has been assumed to have a simple vertical structure with convergence near the surface boundary layer and divergence near the tropopause. Recent work has shown that the ITCZ can have a complex ver-tical structure with multi-level ows. This complex structure has a profound impact on the mass, momentum and energy budget in the ITCZ. This thesis addresses the factors that govern the shallow meridional circulation that occurs in the ITCZ and the mechanisms that govern the abrupt poleward transition and the gradual poleward migration . The shallow meridional circulation forms when the boundary layer ow that con-verges in the ITCZ, rises above the boundary layer and diverges in the lower tropo-sphere. The ow above the boundary layer is in the direction opposite to the direction of the ow within the boundary layer. Some authors have argued that this is caused by the reversal of pressure gradients just above the boundary layer in response to strong sea surface temperature gradients. This hypothesis neglects the eect of plan-etary rotation on the ow and was found to be insucient to explain the formation of shallow meridional circulation. In the east Pacic ocean, the shallow circulation forms only to the south of the ITCZ when the ITCZ forms away from the equator, while it is absent when the ITCZ forms close to the equator. The aqua-planet simulations of the equatorial and the o-equatorial ITCZ were conducted using Community Atmosphere Model (CAM 3.0). The model used the Eulerian dynamical core with T42 horizontal resolution and 26 levels in vertical. Each simulation was run for 3 years and analysis of last six months was presented. The simulations reproduced the contrast in the vertical structure of the equatorial and o-equatorial ITCZ. The shallow circulation was simulated with-out the reversal of pressure gradients and the SST gradients were weakest when the shallow circulation was simulated. We have proposed a new mechanism for the exis-tence of shallow meridional circulation in the ITCZ. We have argued that, in Earth's atmosphere, the mean horizontal ow generally occurs in the direction perpendicular to the direction of applied pressure gradient due to the action of Coriolis force. If the local rotational eects of the ow (relative vorticity) cancels the action of the Coriolis force, then a ow along the pressure gradient is possible. We demonstrated that this condition was satised only to the south of the ITCZ when it forms away from the equator. The ITCZ is characterized by the maximum mass convergence in the boundary layer. The mass convergence is mainly caused by the deceleration of poleward ow in the boundary layer. When the ITCZ forms close to the equator, the ow in the boundary layer is a resultant of vector addition of three forces, a pressure gradient force in the north-south direction (i.e., the ow towards low pressure), a Coriolis force which acts in the east-west direction( perpendicular to the direction of the ow), and surface friction which opposes the resultant ow. When the ITCZ forms away from the equator a three way balance does not capture the dynamics of ow. As the poleward ow is accelerated towards low pressure, it has to advect a considerable amount of zonal momentum with it which acts to retard the poleward ow. This eect of advection of zonal momentum has to be included in the force balance to obtain an accurate estimate of the ow and associated convergence. The ITCZ acts like a heat engine. The energy is gained near the surface, some energy is transported towards pole while some is utilized in driving the meridional circulation. The rest is rejected near the tropopause. The transport within the troposphere occurs through the vertical or horizontal advection of the energy due to vertical and horizontal motions respectively. Our analysis of the ITCZ suggests that; a large amount of transport occurs through horizontal motions that was neglected in the previous studies. The detailed analysis suggests that the latent energy in the form of mass of water vapor is exported out of the ITCZ at dierent levels in association with the multilevel ows. The equatorial and the o-equatorial ITCZ are dierent because, evaporation is larger in the o-equatorial ITCZ when compared to the equatorial ITCZ. The ITCZ shows a strong sub-seasonal variability in its location in the Indian Ocean and the west Pacic Ocean during boreal summer. There are two favorable locations, one near the equator and another away from the equator, for formation of the ITCZ. The equatorial ITCZ either propagates abruptly or gradually to the o-equatorial location. A detailed analysis of moisture and momentum budget of the simulated abrupt and gradual propagations enabled us to separate the role of thermo-dynamic and dynamic processes. We found that, if the equatorial ITCZ would propa-gate abruptly or gradually to the o-equatorial location is decided by the availability of the water vapor in the boundary layer between the two locations of the ITCZ, i.e., by the thermodynamic processes. But, such a transition to the o-equatorial location is allowed only when the constraints imposed by the re-adjustment in the circulation are satised. In simple terms, these constraints emerge due to two processes. 1. The Earth (lower boundary of the atmosphere) spins at maximum eective radius near the equator. As a result, the atmosphere gains maximum angular momentum near the equator (`zonal momentum' in Cartesian co-ordinates) . The ITCZ is one of the primary avenues to transport the zonal momentum from the lower troposphere to the upper troposphere. When the favorable location of ITCZ is near the equator, the location of ITCZ and the location where atmosphere gains maximum zonal momentum are coincident. The ITCZ and associated meridional circulation transports the zonal momentum upwards which is then transported polewards. As the favorable location of ITCZ moves away from the equator, the two locations are die rent. As a result, the atmospheric ow has to re-adjust so that the zonal momentum is transported from the equator to the favorable location of the ITCZ which then transports it upwards and polewards. In summary, this thesis proposes a new mechanism for the generation of shallow meridional circulation, the abrupt transition and the gradual propagations of the ITCZ.

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2016-06-10T19:29:13Z No. of bitstreams: 1 CatiElisaDeAvilaValadao_TESE.pdf: 22074758 bytes, checksum: 702cc3f01b20335c0a4d7438f5c6a479 (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2016-06-13T22:20:59Z (GMT) No. of bitstreams: 1 CatiElisaDeAvilaValadao_TESE.pdf: 22074758 bytes, checksum: 702cc3f01b20335c0a4d7438f5c6a479 (MD5) / Made available in DSpace on 2016-06-13T22:20:59Z (GMT). No. of bitstreams: 1 CatiElisaDeAvilaValadao_TESE.pdf: 22074758 bytes, checksum: 702cc3f01b20335c0a4d7438f5c6a479 (MD5) Previous issue date: 2015-08-14 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / The impacts of the Madden?Julian Oscillation (MJO) on precipitation over Northeast Brazil (NEB, also known as Nordeste) are evaluated based on daily raingauge data from 492 stations over 30-year period (1981-2010). Composites of precipitation, outgoing longwave radiation and moisture-flux anomalies are performed for each phase of the MJO based on the Jones?Carvalho MJO index. To distinguish the MJO signal from other patterns of climate variability, daily data are filtered using a 20 - 90 day band-pass filter; only days classified as MJO events are considered in the composites. A preliminary analysis based on precipitation data was conducted for a small scale area located in NEB?s semiarid interior, in an area known as Serid?. The Serid? is one of the driest regions in NEB, and is recognized by the United Nations Convention to Combat Desertification as particularly vulnerable to desertification. Composites of rainfall anomalies were computed for each of the eight phases of the MJO during February-May, which is Serid??s main rainy season. Results showed that the rainfall patterns in Serid? undergo substantial changes (from enhancement to suppression) as the convective center of the MJO propagates eastward. When combining the MJO signals for wet and dry phases, the difference represents about 50 - 150% modulation of the mean rainfall over Serid?. Then a comprehensive analysis of the role of the MJO in modulating the spatiotemporal variation of NEB?s precipitation was performed, considering all four seasons. The results showed strong seasonality of the MJO impact on precipitation. The most spatially coherent signals of precipitation anomalies occurred in the austral summer, when about 80% of the raingauge stations showed increased precipitation during phases 1 - 2 and suppressed precipitation in phases 5 - 6 of the oscillation. Although the MJO impacts precipitation on intraseasonal timescales in all seasons in most locations, these impacts vary in magnitude and depend on the phase of the oscillation. Precipitation anomalies over NEB are explained by the interaction of convectively coupled Kelvin-Rossby waves with the dominant climatic features in each season. During the austral summer and spring, westerly regimes increased precipitation over most NEB. In the austral winter and fall, precipitation anomalies exhibited more complex spatial variability. In these seasons precipitation anomalies in eastern coastal areas depended on the strength of the South Atlantic anticyclone, which is largely modulated by Rossby waves. The strengthening of the anticyclone intensified the convergence of the trade winds in coastal areas and precipitation windward of the coastal range. Conversely, the intensification of the subsidence was responsible for precipitation deficits in the lee side of the range. These conditions were typically observed when easterly regimes dominate over tropical South America and NEB, decreasing moisture flow from the Amazon. / Este estudo tem como objetivo investigar os impactos da oscila??o de Madden-Julian (OMJ) na precipita??o da regi?o Nordeste do Brasil (NEB). Para tanto foram utilizados dados di?rios de precipita??o baseados em 492 pluvi?metros distribu?dos na regi?o e cobrindo um per?odo de 30 anos (1981 ? 2010). As an?lises atrav?s de composi??es de anomalias de precipita??o, radia??o de onda longa e fluxo de umidade, foram obtidas com base no ?ndice da OMJ desenvolvido por Jones-Carvalho. Para distinguir o sinal da OMJ de outros padr?es de variabilidade clim?tica, todos os dados di?rios foram filtrados na escala de 20 ? 90 dias; portanto somente dias classificados como eventos da OMJ foram considerados nas composi??es. Uma an?lise preliminar baseada apenas nos dados de precipita??o foi feita para uma pequena ?rea localizada no interior semi?rido do NEB, conhecida como Serid?. Essa microrregi?o ? uma das ?reas mais secas do NEB e foi reconhecida pela Conven??o das Na??es Unidas para o Combate ? Desertifica??o e Mitiga??o dos Efeitos das Secas como particularmente vulner?vel ? desertifica??o. Composi??es de anomalias de precipita??o foram feitas para cada uma das oito fases da OMJ durante Fevereiro-Maio (principal per?odo chuvoso da microrregi?o). Os resultados mostraram a exist?ncia de varia??es significativas nos padr?es de precipita??o (de precipita??o excessiva ? deficiente) associados ? propaga??o da OMJ. A combina??o dos sinais de precipita??o obtidos durantes as fases ?midas e secas da OMJ mostrou que a diferen?a corresponde cerca de 50 ? 150% de modula??o das chuvas na microrregi?o. Em seguida, uma investiga??o abrangente sobre o papel da OMJ sobre toda a regi?o Nordeste foi feita considerando-se as quatro esta??es do ano. Os resultados mostraram que os impactos da OMJ na precipita??o intrassazonal do NEB apresentam forte sazonalidade. A maior coer?ncia espacial dos sinais de precipita??o ocorreram durante o ver?o austral, quando cerca de 80% das esta??es pluviom?tricas apresentaram anomalias positivas de precipita??o durante as fases 1 ? 2 da OMJ e anomalias negativas de precipita??o nas fases 5 ? 6 da oscila??o. Embora impactos da OMJ na precipita??o intrassazonal tenham sido encontrados na maioria das localidades e em todas as esta??es do ano, eles apresentaram varia??es na magnitude dos sinais e dependem da fase da oscila??o. As anomalias de precipita??o do NEB observadas s?o explicadas atrav?s da intera??o existente entre as ondas de Kelvin-Rossby acopladas convectivamente e as caracter?sticas clim?ticas predominantes sobre a regi?o em cada esta??o do ano. O aumento de precipita??o observado sobre a maior parte do NEB durante o ver?o e primavera austrais encontra-se associado com o fluxo de umidade de oeste (regime de oeste), o qual favorece a atividade convectiva em amplas ?reas da Am?rica do Sul tropical. Por outro lado, as anomalias de precipita??o durante o inverno e outono austrais apresentaram uma variabilidade espacial mais complexa. Durante estas esta??es, as anomalias de precipita??o observadas nas esta??es localizadas na costa leste do NEB dependem da intensidade do anticiclone do Atl?ntico Sul, o qual ? modulado em grande parte por ondas de Rossby. As caracter?sticas topogr?ficas do NEB parecem desempenhar um papel importante na variabilidade observada na precipita??o, principalmente nestas ?reas costeiras. A intensifica??o do anticiclone aumenta a converg?ncia dos ventos al?sios na costa contribuindo para a ocorr?ncia de precipita??o observada ? barlavento do planalto da Borborema. Por outro lado, o aumento da subsid?ncia parece ser respons?vel pelos d?ficits de precipita??o observados ? sotavento. Tais condi??es mostraram-se t?picas durante o predom?nio do regime de leste sobre a regi?o tropical da Am?rica do Sul e o NEB, durante o qual ocorre uma diminui??o no fluxo de umidade proveniente da Amaz?nia.

Ce travail avait pour but de reconstituer l'évolution de la température et du δ¹⁸O des eaux de surface et des eaux de la thermocline dans la Warmpool indo-pacifique (IPWP) en combinant la thermométrie Mg / Ca et la mesure des isotopes stables de l'oxygène sur des foraminifères planctoniques de surface et de sub-surface prélevés dans des carottes de sédiments situées dans l'océan Indien tropical oriental. Ce travail a permis de ré-évaluer les effets des différentes méthodes de nettoyage et de la dissolution in situ sur la thermométrie Mg/Ca des foraminifères planctoniques, mettant en évidence la nécessité de corrections différentes suivant les espèces. L’évolution de l’IPWP au cours des 270 000 dernières années a été reconstituée. Les résultats indiquent que le δ¹⁸O des eaux de surface reflètent principalement l'advection latérale plutôt que l'historique des précipitations régionales, et suggèrent que l'hydrologie de surface IPWP est contrôlée par la migration latitudinale de la zone de convergence intertropicale aux échelles de temps orbitales mais aussi en réponse aux événements climatiques abrupts de l'hémisphère nord (eg. événements de Heinrich). Les variations de salinité de surface sont étroitement corrélées aux changements d’export vers l’Atlantique au niveau du Courant des Aiguilles (Sud de l’Afrique). Puis, les changements dans le transport des eaux de la thermocline issues de l’ITF vers l'océan Indien ont été étudiés. Les résultats montrent que le transport était plus faible pendant les glaciations (ie. MIS 6 et 4-2) que pendant les périodes interglaciaires (ie. MIS 7, MIS 5 et Holocène) et exerçaient une influence significative sur les changements de la température de la thermocline dans l'Océan Indien. / This work aimed at reconstructing the late Quaternary evolution of surface and thermocline temperature and ocean surface water δ¹⁸O in the Indo-Pacific Warm Pool by combining Mg/Ca-thermometry and stable oxygen isotope analyses on surface and thermocline-dwelling planktonic foraminifers retrieved from sediment cores in the eastern tropical Indian Ocean. This study allowed to re-evaluate the effects of different cleaning methods and in-situ dissolution on the Mg-thermometry of planktonic foraminifers, evidencing the need for species-dependent corrections. Then, the IPWP evolution over the last 270,000 years has been explored. Results indicate that surface water δ¹⁸O chiefly reflects lateral advection rather than local precipitation history, and suggest that surface IPWP hydrology is controlled by the latitudinal migration of the Intertropical Convergence Zone at orbital timescale as well as during abrupt northern hemisphere climatic events (i.e. Heinrich events). Ocean surface salinity in the IPWP and Agulhas leakage region varied synchronously, implying their teleconnection through oceanic and atmospheric circulation. Moreover, changes in the transport of thermocline water to the Indian Ocean by the Indonesian Throughflow (ITF) have been reconstructed. Results show that thermocline water transport was weaker during glacials (i.e. MIS 6 and 4-2) than during interglacials (MIS 7, MIS 5 and Holocene), and exerted significant influence on Indian Ocean TWT change.

Do changes in how cross-equatorial energy transport is partitioned between the ocean and atmosphere impact the hemispheric climate response to forcing? To find out, we alter the cross-equatorial ocean heat transport in a state-of-the-art GCM and ascertain how changes in energy transport and its partitioning impact hemispheric climate and precipitation sensitivity following abrupt CO2-doubling. We further evaluate the applicability our results in CMIP6-class ESMs, where AMOC facilitates the northward cross-equatorial ocean heat transport. In our experiments, changes in ocean cross-equatorial energy transport trigger compensating changes in atmospheric energy transport through changes in the Hadley cells and a shift in the Intertropical Convergence Zone. However, the climate sensitivity in each hemisphere is linearly related to the ocean heat transport convergence, not atmospheric energy transport convergence, due to the impact of ocean heating on evaporation and atmospheric specific humidity. Similarly, we also find that ocean heat transport convergence controls the hemispheric precipitation sensitivity through the impact of ocean heating on surface evaporation. This relationship is also evident in CMIP6 models, where we find differences in hemispheric precipitation sensitivity to be related to the Atlantic Meridional Overturning Circulation (AMOC). Changes in the AMOC control hemispheric differences in upper ocean heat content, which then affect how the hydrologic cycle responds to CO2 forcing in each hemisphere. These results suggest that ocean dynamics impact the hemispheric climate response to CO2 forcing, particularly how much regional precipitation changes with warming. / Graduate