Finke Kathrin, Jiménez-Esteve Bernat, Taschetto Andréa S, Ummenhofer Caroline C, Bumke Karl, Domeisen Daniela I V
Department of Meteorology, Stockholm University, Stockholm, Sweden.
Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland.
Clim Dyn. 2020;55(11):3197-3211. doi: 10.1007/s00382-020-05442-9. Epub 2020 Sep 3.
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.
2014年南半球夏季，巴西东南部遭遇了一场毁灭性干旱，造成了重大农业损失。这场干旱与2014年初南大西洋上一个准静止反气旋的发展有关，该反气旋影响了巴西东南部的局部降水模式。此前的研究表明，这种异常阻塞是由热带太平洋海表面温度（SST）异常引发的，最近则是由与马登-朱利安振荡相关的印度洋对流引发的。对所提出的遥相关进行进一步研究对于预测未来的经济影响似乎至关重要。在本研究中，我们使用理想化的大气环流模型进行数值实验，该模型由不同海洋盆地观测到的2013/2014年SST异常强迫驱动，以了解引发2014年南大西洋反气旋异常的主导机制。我们表明，全球2013/2014年SST异常强迫增加了南大西洋出现正位势高度异常的可能性。然而，在单独海洋盆地进行的SST强迫的进一步敏感性实验表明，印度洋和热带太平洋的SST异常单独对导致2014年巴西东南部干旱的异常大气环流都没有显著贡献。该模型研究反而指出，来自南太平洋的远程强迫、南大西洋局部SST以及大气内部变率在驱动南大西洋持续阻塞方面发挥了重要作用。
