Decadal Variability of the ENSO Teleconnection to the High-Latitude South Pacific Governed by Coupling with the Southern Annular Mode*

Abstract

Decadal variability of the El Niño-Southern Oscillation (ENSO) teleconnection to the high-latitude South Pacific is examined by correlating the European Centre for Medium-Range Weather Forecasts (ECMWF) 40-yr Re-Analysis (ERA-40) and observations with the Southern Oscillation index (SOI) over the last two decades. There is a distinct annual contrast between the 1980s and the 1990s, with the strong teleconnection in the 1990s being explained by an enhanced response during austral spring. Geopotential height anomaly composites constructed during the peak ENSO seasons also demonstrate the decadal variability.Empirical orthogonal function (EOF) analysis reveals that the 1980s September-November (SON) teleconnection is weak due to the interference between the Pacific-South American (PSA) pattern associated with ENSO and the Southern Annular Mode (SAM). An in-phase relationship between these two modes during SON in the 1990s amplifies the height and pressure anomalies in the South Pacific, producing the strong teleconnections seen in the correlation and composite analyses. The in-phase relationship between the tropical and high-latitude forcing also exists in December-February (DJF) during the 1980s and 1990s.These results suggest that natural climate variability plays an important role in the variability of SAM, in agreement with a growing body of literature. Additionally, the significantly positive correlation between ENSO and SAM only during times of strong teleconnection suggests that both the Tropics and the high latitudes need to work together in order for ENSO to strongly influence Antarctic climate.

Ice cores record significant 1940s Antarctic warmth related to tropical climate variability

“…The positive sea level pressure anomalies in the South Pacific and the equatorward storm track are characteristic features of most El Niño events (8,18). The apparent unusual strength of the circulation anomalies and the isotopic response may be linked to the phasing with the Southern Annular Mode (25). (Table 3).…”

“…However, our results suggest that these mechanisms do not provide complete explanations for Antarctic temperature change over multiple decades. The El Niño connection to West Antarctic climate is intermittent and variable, because it depends on the location and strength of deep convection in the tropics and the interaction of Rossby waves originating from the tropics with the SH zonal flow (8,24,25). The warming is not likely associated with high-latitude atmospheric circulation variability alone, because the positive trend in the Southern Annular Mode over recent decades (36) Future work will need to address more thoroughly the detection and attribution of Antarctic climate trends.…”

Characterizing the zonally asymmetric component of the SH circulation

“…The largest signal is during ASO (Fig. 8d); we note that the ENSO-teleconnections with the SH are strongest in spring (Fogt and Bromwich 2006). Further analysis shows a statistically significant correlation between the PC3 and LONE time series for all seasons (0.6 [ r [ 0.4), but not for the intervals are 10% with minimum contour being 20%; regions where more than 50% of the variance is explained are shaded Fig.…”

“…Additionally, remaining linear trends have been removed from the data prior to analysis unless otherwise stated. Marshall (2003) and Fogt and Bromwich (2006) suggest that the ECMWF 40-year reanalysis (ERA40) is a better representation of the high latitude SH climate, but ERA40 is only available up to 2001 (Uppala et al 2005). To give the longest possible period of analysis with reliable data NRA was chosen as the primary dataset, but the results presented here have been compared with those derived from the ERA40 data, and are found to be insensitive to the choice of reanalysis.…”

Changing distributions of sea ice melt and meteoric water west of the Antarctic Peninsula

“…However, this mode of climate variability has a marked impact on the southeast Pacific sector of the Southern Ocean via both atmospheric and oceanic teleconnections (Meredith et al, 2008b;Turner, 2004;Yuan, 2004 Niño and/or negative SAM conditions result in the greater local preponderance of colder, drier air masses. The coincident phasing of these two atmospheric modes can thus amplify or dampen the atmospheric circulation changes and climatic anomalies at the WAP (Clem and Fogt, 2013;Fogt and Bromwich, 2006;Stammerjohn et al, 2008b).…”