The 2014 southeast Brazil austral summer drought: regional scale mechanisms and teleconnections
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The southeast region of Brazil experienced in austral summer 2014 a major drought event leading to a number of impacts in water availability for human consumption, agricultural irrigation and hydropower production. This study aims to perform a diagnostic analysis of the observed climate conditions during this event, including an inspection of the occurred precipitation anomalies in the context of previous years, and an investigation of possible relationships with sea surface temperatures and atmospheric circulation patterns. The sea surface temperature analysis revealed that the southwestern South Atlantic Ocean region near the coast of southeast Brazil showed strong negative association with precipitation over southeast Brazil, indicating that increased sea temperatures in this ocean region are consistent with reduced precipitation as observed in summer 2014. The circulation analysis revealed prevailing anti-cyclonic anomalies at lower levels (850 hPa) with northerly anomalies to the west of southeast Brazil, channeling moisture from the Amazon towards Paraguay, northern Argentina and southern Brazil, and drier than normal air from the South Atlantic Ocean towards the southeast region of Brazil. This circulation pattern was found to be part of a large-scale teleconnection wave train linked with the subsidence branch of the Walker circulation in the tropical east Pacific, which in turn was generated by an anomalous tropical heat source in north/northeastern Australia. A regional Hadley circulation with an ascending branch to the south of the subsidence branch of the Walker circulation in the tropical east Pacific was identified as an important component connecting the tropical and extratropical circulation. The ascending branch of this Hadley circulation in the south Pacific coincided with an identified Rossby wave source region, which contributed to establishing the extratropical component of the large-scale wave train connecting the south Pacific and the Atlantic region surrounding southeast Brazil. This connection between the Pacific and the Atlantic was confirmed with Rossby ray tracing analyses. The local circulation response was associated to downward air motion (subsidence) over Southeast Brazil, contributing to the expressive negative precipitation anomalies observed during summer 2014, and leading to a major drought event in the historical context. The analysis of atmospheric and oceanic patterns of this event helped defining a schematic framework leading to the observed drought conditions in southeast Brazil, including the involved teleconnections, blocking high pressure, radiative and humidity transport effects.
KeywordsDrought Teleconnections Sea surface temperature Austral summer Precipitation Southeast Brazil
The research leading to these results has received funding from the SPECS project (Grant Agreement No. 308378) funded by the European Commission’s Seventh Framework Research Programme. C.A.S.C. and T.A. were supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) processes 306863/2013-8 and 300976/2010-0, respectively. T.A. also had the support from FAPESP (Proc. No. 2008/58101-9) and Vale Technological Institute. The National Meteorological Service (INMET) and regional meteorological centres in Brazil are acknowledged for making available the observed precipitation data used in this study. We thank Simone T. Ferraz and Ana Carolina V. Freitas for their help with Figs. 8 and 9. Two anonymous reviewers are thanked for providing constrictive criticisms that helped improved the quality of the paper.
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