Teleconnections between Tropical Pacific SST Anomalies and Extratropical Southern Hemisphere Climate

Abstract

Teleconnections from tropical Pacific sea surface temperature (SST) anomalies to the high-latitude Southern Hemisphere (SH) are examined using observations and reanalysis. Analysis of tropical Pacific SST anomalies is conducted separately for the central Pacific (CP) and eastern Pacific (EP) regions. During the austral cold season, extratropical SH atmospheric Rossby wave train patterns are observed in association with both EP and CP SST variability. The primary difference between the patterns is the westward displacement of the CP-related atmospheric anomalies, consistent with the westward elongation of CP-related convective SST required for upper-level divergence and Rossby wave generation. Consequently, CP-related patterns of SH SST, Antarctic sea ice, and temperature anomalies also exhibit a westward displacement, but otherwise, the cold season extratropical SH teleconnections are largely similar. During the warm season, however, extratropical SH teleconnections associated with tropical CP and EP SST anomalies differ substantially. EP SST variability is linked to largely zonally symmetric structures in the extratropical atmospheric circulation, which projects onto the southern annular mode (SAM), and is strongly related to the SH temperature and sea ice fields. In contrast, CP SST variability is only weakly related to the SH atmospheric circulation, temperature, or sea ice fields and no longer exhibits any clear association with the SAM. One hypothesized mechanism suggests that the relatively weak CP-related SST anomalies are not able to substantially impact the background flow of the subtropical jet and its subsequent interaction with equatorward-propagating waves associated with variability in the SAM. However, there is currently no widely established mechanism that links tropical Pacific SST anomalies to the SAM.

Pacific Influences on Tropical Atlantic Teleconnections to the Southern Hemisphere High Latitudes

“…5c, hatching), have moved toward the central Pacific. Consistent with the observational analyses of Ciasto et al (2015), such shifts may explain the more eastward location of South Pacific Z 200 anomalies.…”

“…In both cases, significant geopotential height anomalies are observed over the Atlantic and Pacific Oceans, but with enhanced magnitudes in the respective basin. Atlantic anomalies are characterized by contrasting pressure centers between the subtropics and midlatitudes, while Pacific anomalies represent the high-latitude response to ENSO; a wave train that appears as positive pressure anomalies over the subtropical Pacific, negative pressure anomalies over the ASL, and positive pressure anomalies over Antarctica, resembling the seasonal teleconnections observed in several studies (e.g., Simpkins et al 2012;Ciasto et al 2015). This Pacific-centered pattern shall be termed ''ENSO-like.''…”

“…Although annular by definition, the SAM possesses a significant nonannular component, expressed as locally enhanced pressure anomalies over the ASL region (Simpkins et al 2012). Numerous studies have also connected the Antarctic circulation to Pacific sea surface temperature (SST) (e.g., Karoly 1989;Turner 2004;Simpkins et al 2012;Ciasto et al 2015). Driven by tropical heating and associated deep convection during El Niño events, upper-level vorticity anomalies excite a pattern of stationary Rossby waves that propagate to the SH high latitudes in a great arc (Hoskins and Karoly 1981;Rasmusson and Mo 1993;Trenberth et al 1998).…”

The Early 1990s Change in ENSO–PSA–SAM Relationships and Its Impact on Southern Hemisphere Climate

“…The positive phase of the PSA is known to be related to La Niña and the negative phase of the PSA is related to El Niño (e.g., Mo 2000). Previous studies showed that ENSO, together with various phases of the SAM and the PSA, can influence the Southern Ocean SSTs (e.g., Ciasto and Thompson 2008;Lee et al 2010;Yeo and Kim 2015), Antarctic sea ice concentrations (e.g., Liu et al 2004;Stammerjohn et al 2008;Yuan and Li 2008), and Antarctic surface air temperatures (e.g., Kwok and Comiso 2002;Ding et al 2011). Fogt and Bromwich (2006) found that the ENSO influences on the SH strengthened from the 1980s to the 1990s.…”

“…Lee and McPhaden (2010) suggested that the more frequent occurrence of CP El Niño has contributed to the SST warming trend in the tropical central Pacific. Several recent studies have begun to examine the possible different impacts of the two types of ENSO on the SH climate using observations (Hurwitz et al 2011;Song et al 2011;Sun et al 2013;Ciasto et al 2015) and model simulations (Zubiaurre and Calvo 2012;Hurwitz et al 2013;Lim et al 2013;Wilson et al 2014).…”