The influence of oceanic and atmospheric large-scale variabilities on the Atlantic Meridional Mode decadal time scale

• Autor(a) principal: Sandro Miguel Ferreira Veiga
• Data de Publicação: 2018
• Tipo de documento: Tese
• Idioma: eng
• Título da fonte: Biblioteca Digital de Teses e Dissertações do INPE
• Texto Completo: http://urlib.net/sid.inpe.br/mtc-m21c/2018/06.19.17.40

The Atlantic Meridional Mode (AMM) is a prominent coupled ocean-atmosphere mode of variability that manifests itself in the tropical Atlantic, mainly in the boreal spring although in some years it maintains itself active throughout the boreal summer and fall. The AMM impacts in continental land regions are due to its modulation of the Intertropical Convergence Zone, which tends to be located over the warmer hemisphere during the AMM peak phase. It also influences the conditions in the Atlantic hurricane Main Development Region. Many AMM features remain to be understood, from what determines its dominant decadal variability to the complex physical processes that sustain it. In this study, it is investigated the influence of the Atlantic Ocean variability and atmospheric large-scale variabilities on the dominant decadal periodicity that characterizes the AMM. Since we are interested in investigating the link between AMM and different phenomena at decadal time scale, observational and reanalysis datasets consisting of long record are used in this study. Through statistical analysis, it is shown that the sea surface temperature decadal variability in the Atlantic Ocean is linked to the AMM by the AMO. The AMO precedes the AMM. To further understand the ocean influence, the ocean heat content (0300m) decadal variability is analyzed. The results show that there is no significant relationship between the ocean heat content and the AMM. Regarding the atmospheric large-scale variabilities, it is concluded that El Niño-Southern Oscillation and the Interdecadal Pacific Oscillation do not significantly impact the AMM on decadal time scale. In this work is shown that the NAO is an important external forcing on the AMM, both at interannual and decadal time scale. In order to reinforce the conclusions, data from CMIP5 models are also used. The new version of the Brazilian Earth System Model (BESM-OA2.5) is one of the models used. Therefore the evaluation of its historical simulation is presented. The last topic studied is related to the potential changes of the AMM in a perturbed climate scenario. To this purpose, the idealized 4×CO2 experiments performed by four models are used. Two models show that the AMM maintains its spatio-temporal pattern under a perturbed climate scenario, while the Atlantic Meridional Overturning Circulation changes profoundly its structure.