Does a dipole mode really exist in the South Atlantic Ocean?

Abstract

[1] This study investigates the existence of a dipole mode in the sea surface temperatures (SST) over the South Atlantic Ocean (SAO), using observational and reanalysis data sets from 1950 to 2008. Our results demonstrate that an opposite SST mode, the SAO dipole (SAOD) occurs in the SAO as the anomalous surface waters in the northeastern part; that is, the Atlantic Niño sector and the southwestern part off the Argentina-UruguayBrazil coast are consistently anticorrelated in all months. A typical SAOD episode has a life cycle of about eight months, although the peak intensity in which the SST anomalies are evidently coupled to atmospheric circulation and precipitation anomaly fields lasts for four months during the austral winter (May-August). This coupled atmosphere-ocean interaction mechanism appears to be unique, distinct from the classical Atlantic Niño and independent of the direct influence of the Pacific Ocean-based El Niño or global SST variability. The SAOD may provide a useful framework for investigating climate variability and for improved predictions especially over parts of Africa and the Americas, and some preliminary results are already indicated, e.g., the SAOD is widely related to precipitation anomalies in these regions particularly during the austral winter.

Tropical atmospheric response to decadal changes in the Atlantic Equatorial Mode

“…This mode has a structure similar to the South Atlantic Ocean Dipole (SAOD) described by Nnamchi et al (2011), both in its boreal summer configuration ( Figure 1a) and its seasonal evolution (not shown).…”

“…This mode is similar to the one that Rodriguez-Fonseca et al The question about the opportunity of referring to these two patterns as the Equatorial Mode can be controversial. In this way, Nnamchi et al (2011) argue that the SAOD and the EM are different modes of variability in which different dynamics operate, especially in the subtropical South Atlantic. Nevertheless, we have obtained the two patterns only by looking at the Atlantic variability over the equatorial region, and they also appear as the first mode of variability in the tropical Atlantic for each of the sub-periods of the study (not shown), as well as the SST pattern of the first modes of co-variability between tropical Atlantic SST and summer Mediterranean precipitation computed before and after the 1970's (Losada et al, 2012b).…”

“…Nevertheless, we have obtained the two patterns only by looking at the Atlantic variability over the equatorial region, and they also appear as the first mode of variability in the tropical Atlantic for each of the sub-periods of the study (not shown), as well as the SST pattern of the first modes of co-variability between tropical Atlantic SST and summer Mediterranean precipitation computed before and after the 1970's (Losada et al, 2012b). Also, as Nnamchi et al (2011) have acknowledged, the evolution and peak of both the SAOD and the canonical EM occur during the same season (boreal summer) and the two events share similar equatorial aspects. In the light of all this, we think that is plausible to think that the EM and the SAOD are two different configurations of just one mode that describes the equatorial variability of the tropical Atlantic, and that shows multidecadal variations in its spatial pattern.…”

“…Nnamchi et al (2011) differentiate two different modes of variability characterized by strong loadings of SST anomalies in the tropical Atlantic in summer, the EM and the South Atlantic Ocean Dipole (SAOD), with different dynamics involved. For its part, Richter et al (2012) divide the Atlantic Niños in "canonical" and "non-canonical" events, also depending on their driving mechanisms.…”

Decadal-scale teleconnection between South Atlantic SST and southeast Australia surface air temperature in austral summer

“…1 displays the strongest decadal change over the region (25°-50°S, 50°-10°W), which is a little bit north to the box used in Latif et al (2006). Thus, to better characterize the decadal change in South Atlantic, we define the SAMV index over the region (25°-50°S, 50°-10°W) in southwest South Atlantic, similar to the location of southwest pole of the interannual South Atlantic Ocean dipole (SAOD) (Morioka et al 2011;Nnamchi et al 2011). Because the SAMV indices defined based on datasets ERSSTv4 and HadISST2.1 are highly correlated (r = 0.92, significant at the 99% confidence level), so we will only show the results based on dataset ERSSTv4 in the remainder of this paper unless otherwise stated.…”