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Abstract
AbstractTwo variants of sea‐surface temperature (SST) dipole indices for the South Atlantic Ocean (SAO) has been previously described representing: (1) the South Atlantic subtropical dipole (SASD) supposedly peaking in austral summer and (2) the SAO dipole (SAOD) in winter. In this study, we present the analysis of observational data sets (1985–2014) showing the SASD and SAOD as largely constituting the same mode of ocean–atmosphere interaction reminiscent of the SAOD structure peaking in winter. Indeed, winter is the only season in which the inverse correlation between the northern and southern poles of both indices is statistically significant. The observed SASD and SAOD indices exhibit robust correlations (P ≤ 0.001) in all seasons and these are reproduced by 54 of the 63 different models of the Coupled Models Intercomparison Project analysed. Their robust correlations notwithstanding the SASD and SAOD indices appear to better capture different aspects of SAO climate variability and teleconnections.
Highlights
A dipole structure in sea-surface temperature (SST) anomalies represents the dominant mode of ocean–atmosphere fluctuations in the South Atlantic
The dipole structure is typically oriented in the southwest–northeast direction, and two major variants have been described in the literature – the South Atlantic subtropical dipole (SASD) and the South Atlantic Ocean (SAO) dipole (SAOD)
We further investigate the similarity in temporal evolution of the SASD and SAO dipole (SAOD) by calculating their month-by-month correlations with EC1 (which has a constant value for each year; Figure 3(a))
Summary
A dipole structure in sea-surface temperature (SST) anomalies represents the dominant mode of ocean–atmosphere fluctuations in the South Atlantic. The empirical orthogonal function (EOF) analysis of seasonally stratified data sets shows opposite structure of SST anomalies between the equatorial and southwest Atlantic peaking in austral winter (Nnamchi et al, 2011). This dipole pattern is referred to as the SAOD. While the northernmost part of the SAOD extends to the equator and coincides with the Atlantic Niño (ATL3) in both space and time, leading to the notion that the two may represent the same mode of variability (Nnamchi et al, 2016); by definition, the southern part of the SASD (30∘N–40∘S, 10∘ –30∘W) falls within that of the SAOD (25∘N–40∘S, 10∘ –40∘W). The ATL3|SAOD correlation has been described elsewhere (Nnamchi et al, 2016) but that of the SASD and SAOD remains unclear and is the focus of the present study
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