Abstract
AbstractThe Southern Annular Mode (SAM) is the predominant atmospheric variability mode in the Southern Hemisphere. In this paper, we present the spatial variability results of the SAM pattern for the period 1979–2018. The SAM‐intrinsic pattern variability analysis is based on the principal component analysis (PCA), which is carried out for the ERA‐Interim 500 hPa geopotential height (GPH) data set. A spatiotemporally resolved data set of SAM pattern maps (PCA loadings) is derived by projecting monthly shifted sub‐sequences of SAM index values (PCA scores) on the corresponding GPH anomalies. The dominant SAM structure within single pattern fields is mapped automatically and can be interpreted as the Southern Hemisphere polar front. This data set allows an analysis of the geographical positions of the characteristic circumpolar SAM structure over four decades and shows considerable variability over space and time. Five different states of SAM patterns, which are associated with characteristic circulation anomalies during different phases of the study period, are identified. Station‐based Antarctic temperature anomalies can be synoptically explained by these circulation anomalies. The overall latitudinal trend of the SAM pattern indicates an intensification of the meridional structure, especially over the East Antarctic Southern Ocean. Furthermore, we show that the SAM pattern variability is significantly correlated with the Pacific Decadal Oscillation and the Atlantic Multidecadal Oscillation. Composites of 500 hPa GPH anomalies during the positive and negative phases of the respective indices indicate teleconnections with Pacific Decadal Oscillation and Atlantic Multidecadal Oscillation, and this can explain latitudinal trends of the SAM pattern.
Highlights
The Southern Annular Mode (SAM), known as the Antarctic Oscillation, is the dominant atmospheric circulation variability mode in the Southern Hemisphere (SH) (Thompson & Wallace, 2000)
We show that the SAM pattern variability is significantly correlated with the Pacific Decadal Oscillation and the Atlantic Multidecadal Oscillation
The present study has demonstrated that the SAM and its annularity structure varied significantly during the past four decades
Summary
The Southern Annular Mode (SAM), known as the Antarctic Oscillation, is the dominant atmospheric circulation variability mode in the Southern Hemisphere (SH) (Thompson & Wallace, 2000). The Pacific‐South American (PSA) mode describes a Rossby wave train pattern between the tropical western Pacific and the South American region (Ding et al, 2012) The influence of this mode induces a strong zonally asymmetric component in the West Antarctic region, whereas the East Antarctic sector (0–180°) is characterized by a distinct zonal SAM pattern (Ding et al, 2012; Fogt, Jones, et al, 2012). Clem, Renwick, McGregor, and Fogt (2016) provided an estimate of the seasonally varying influence of the SAM and the Southern Oscillation on the temperature variability of the Antarctic Peninsula. We can directly assess the annularity of the SAM pattern, whose spatiotemporal variability shows large variations over the past four decades Based on these initial results, we identified five dominant SAM structures which occur during different periods of the study period.
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