Dominant SST Mode in the Southern Hemisphere Extratropics and Its Influence on Atmospheric Circulation
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The variability in the Southern Ocean (SO) sea surface temperature (SST) has drawn increased attention due to its unique physical features; therefore, the temporal characteristics of the SO SST anomalies (SSTA) and their influence on extratropical atmospheric circulation are addressed in this study. Results from empirical orthogonal function analysis show that the principal mode of the SO SSTA exhibits a dipole-like structure, suggesting a negative correlation between the SSTA in the middle and high latitudes, which is referred to as the SO Dipole (SOD) in this study. The SOD features strong zonal symmetry, and could reflect more than 50% of total zonal-mean SSTA variability. We find that stronger (weaker) Subantarctic and Antarctic polar fronts are related to the positive (negative) phases of the SOD index, as well as the primary variability of the large-scale SO SSTA meridional gradient. During December–January–February, the Ferrel cell and the polar jet shift toward the Antarctic due to changes in the SSTA that could be associated with a positive phase of the SOD, and are also accompanied by a poleward shift of the subtropical jet. During June–July–August, in association with a positive SOD, the Ferrel cell and the polar jet are strengthened, accompanied by a strengthened subtropical jet. These seasonal differences are linked to the differences in the configuration of the polar jet and the subtropical jet in the Southern Hemisphere.
Key wordsextratropical sea surface temperature air–sea interaction Southern Annular Mode
南大洋海表温度变率因其独特的物理特征得到越来越多的关注, 本文分析了南大洋海表温度变率特征及其对南半球热带外大气环流的影响。经验正交函数分解的结果表明, 南大洋海温变率的主模态表现为偶极子结构, 反应了南半球中、高纬度之间海温的反向变化, 称为南大洋偶极子 (SOD)。 SOD具有显著的纬向对称性, 其对南半球热带外纬向平均海温的解释方差在50%以上。当SOD为正 (负) 位相时, 海温经向梯度加强 (减弱)。 在12-2月的南半球夏季, 费雷尔环流和极锋急流位置的向极移动与SOD正位相对应的海温异常有关, 并伴随副热带急流位置的向极移动。在6-8月的南半球冬季, SOD正位相对应费雷尔环流和极锋急流强度的增强, 副热带急流的强度也相应增强。 这种SOD对大气环流影响的季节差异, 与极锋急流和副热带急流在不同季节的不同配置有关。
关键词热带外海温 海气相互作用 南半球环状模
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The authors would like to thank the editor and the anonymous reviewers for their comments and suggestions, which significantly contributed to improving the manuscript. This work was jointly supported by a National Natural Science Foundation of China NSFC project (Grant No. 41405086), the strategic priority research program grant of the Chinese Academy of Sciences (Grant No. XDA19070402), and the NSFC projects (41775090, 41705049). The NCEP/NCAR atmospheric reanalysis datasets are available at http://www.esrl.noaa.gov/psd/. We acknowledge the World Climate Research Programme’s Working Group on Coupled Modelling, which is responsible for CMIP, and we thank the climate modeling groups for producing and making available their model output. We acknowledge the World Climate Research Programme’s Working Group on Coupled Modelling, which is responsible for CMIP, and we thank the climate modeling groups for producing and making available their model output."
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