Abstract
South-Eastern Brazil experienced a devastating drought associated with significant agricultural losses in austral summer 2014. The drought was linked to the development of a quasi-stationary anticyclone in the South Atlantic in early 2014 that affected local precipitation patterns over South-East Brazil. Previous studies have suggested that the unusual blocking was triggered by tropical Pacific sea surface temperature (SST) anomalies and, more recently, by convection over the Indian Ocean related to the Madden–Julian Oscillation. Further investigation of the proposed teleconnections appears crucial for anticipating future economic impacts. In this study, we use numerical experiments with an idealized atmospheric general circulation model forced with the observed 2013/2014 SST anomalies in different ocean basins to understand the dominant mechanism that initiated the 2014 South Atlantic anticyclonic anomaly. We show that a forcing with global 2013/2014 SST anomalies enhances the chance for the occurrence of positive geopotential height anomalies in the South Atlantic. However, further sensitivity experiments with SST forcings in separate ocean basins suggest that neither the Indian Ocean nor tropical Pacific SST anomalies alone have contributed significantly to the anomalous atmospheric circulation that led to the 2014 South-East Brazil drought. The model study rather points to an important role of remote forcing from the South Pacific, local South Atlantic SSTs, and internal atmospheric variability in driving the persistent blocking over the South Atlantic.
Highlights
Agriculture represents an important part of Brazil’s economy
In addition to a signal arising from the western tropical Pacific, convection over the Indian Ocean associated with the MJO has been suggested to drive a Rossby wave train featuring a phase similar to the 2014 case, unfavorable for the development of South Atlantic Convergence Zone (SACZ) episodes (Rodrigues and Woollings 2017)
Our experiments show that the South Pacific has likely acted as an essential contributor to the increased 500 hPa geopotential height (500GPH) in the study area
Summary
Agriculture represents an important part of Brazil’s economy. Products differ regionally depending on the local climate. The eastward progression of the MJO’s characteristic convective dipole over the western Indian Ocean toward the maritime continent has been associated with a switch from wet to dry conditions in SE Brazil, accompanied by an anticyclonic circulation over the South Atlantic during austral summer Rodrigues and Woollings (2017) link eastward propagating Rossby wave packets initiated by convection over the Indian Ocean with negative precipitation anomalies related to South Atlantic blocking and suppressed SACZ episodes with a time lag of about 6 days. These vertical motions interacted with the meridional Hadley cell, producing a stationary atmospheric Rossby wave that reinforced unusually high pressure throughout the lower and middle troposphere off the east and west coasts of South America (Coelho et al 2016). We use a combination of observational analyses and idealized sensitivity experiments to further investigate the proposed origins of the South Atlantic anticyclonic pattern that caused the 2014 drought in SE Brazil
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