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| Author(s): |
Igor Stivanelli Custódio
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Instituto Astronômico e Geofísico (IAG/SBD) |
| Defense date: | 2022-12-20 |
| Examining board members: |
Pedro Leite da Silva Dias;
Tercio Ambrizzi;
Cristiano Mazur Chiessi;
Gilvan Sampaio de Oliveira;
Ilana Elazari Klein Coaracy Wainer
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| Advisor: | Pedro Leite da Silva Dias |
| Abstract | |
The South American Monsoon System (SAMS) is the main component of South America\'s summer precipitation. The main objective of this study is to investigate the spatial-temporal variability and the effect of individual climate forcing mechanisms during the last 21,000 years on the SAMS. The results are based on TraCE-21k simulations FULL and Single Forcings experiments and the IPSL transient simulation for the last 6,000 years. The identification of spatial variability patterns associated to the core of monsoon region and the South Atlantic Convergence Zone (SACZ) patterns are based on multivariate EOF analysis (precipitation, humidity, zonal and meridional wind) which produces two main modes: the South American Large Scale Monsoon Index (LISAM) and the SACZ mode. The Atlantic Intertropical Convergence Zone (A-ITCZ) positioning index (wind stress and moisture divergence methods) and the variability modes were identified through EOF analysis. The LISAM and SACZ modes show that the TraCE-21k and IPSL represents the SAMS and SACZ patterns and the comparison to the 20th Century reanalysis EOF analysis show significant agreement. The TraCE-21k LISAM and A-ITCZ time series proved to be an important instrument to identify monsoon precipitation variability, consistent with the regime changes registered in climatic proxies. The freshwater pulses forcing in TraCE-21k is a determining factor for the observed changes in the precipitation regime and A-ITCZ positioning, mainly for the periods between the Heinrich Stadial 1 (H1) and the Younger Dryas (YD). The A-ITCZ pattern presents a double band in the subperiods of the past 21ky, with the secondary band appearing mainly when the A-ITCZ position is southward, during cold periods (H1 and YD). Changes in the hemispheric total radiative flux at the top of the atmosphere are confirmed to be a determining factor for the A-ITCZ changes in the last 21ky, in agreement with recent theories on the ITCZ dynamical control. The results show that the observed and modelled SACZ southward shift in the Late Holocene is mainly modulated by insolation changes, with stronger correlation observed since the Mid-Holocene period. Through wavelet analysis, it was noted that energy was transferred from low to high frequencies in the BøllingAllerød, evidenced in SAMS, SACZ and A-ITCZ modes for the full forcing and freshwater pulse experiments in the Northern Hemisphere. In agreement with the observational studies, the importance in the recent period of the observed multidecadal variability, associated with the Pacific and Atlantic modes, in the LISAM, SACZ and A-ITCZ positioning began in the Middle Holocene period, with direct influences by the orbital forcing and ice cover changes, and these results are consistent with previous studies. (AU) | |
| FAPESP's process: | 17/05285-4 - Influence of the transients on displacement and location of the Atlantic Intertropical Convergence Zone in past climate simulations |
| Grantee: | Igor Stivanelli Custódio |
| Support Opportunities: | Scholarships in Brazil - Doctorate |