Tropical Connections to Climatic Change in the Extratropical Southern Hemisphere: The Role of Atlantic SST Trends

Abstract

The austral spring relationships between sea surface temperature (SST) trends and the Southern Hemisphere (SH) extratropical atmospheric circulation are investigated using an atmospheric general circulation model (AGCM). A suite of simulations are analyzed wherein the AGCM is forced by underlying SST conditions in which recent trends are constrained to individual ocean basins (Pacific, Indian, and Atlantic), allowing the impact of each region to be assessed in isolation. When forced with observed global SST, the model broadly replicates the spatial pattern of extratropical SH geopotential height trends seen in reanalyses. However, when forcing by each ocean basin separately, similar structures arise only when Atlantic SST trends are included. It is further shown that teleconnections from the Atlantic are associated with perturbations to the zonal Walker circulation and the corresponding intensification of the local Hadley cell, the impact of which results in the development of atmospheric Rossby waves. Thus, increased Rossby waves, forced by positive Atlantic SST trends, may have played a role in driving geopotential height trends in the SH extratropics. Furthermore, these atmospheric circulation changes promote warming throughout the Antarctic Peninsula and much of West Antarctica, with a pattern that closely matches recent observational records. This suggests that Atlantic SST trends, via a teleconnection to the SH extratropics, may have contributed to springtime climatic change in the SH extratropics over the past three decades.

Asymmetry of the winter extra-tropical teleconnections in the Northern Hemisphere associated with two types of ENSO

“…Subsequently, the anomalous upper-level divergence/convergence is formed in the subtropics, which dominantly determines the generation of the extra-tropical anomalous vorticity forcing through producing the vortex stretching effect. This physical process is in accordance with that proposed by Simpkins et al (2014). They analyzed the impacts of the tropical Atlantic SST anomalies on the extra-tropical atmospheric circulation in the Southern Hemisphere.…”

“…This perturbation is crucial for the way the tropical forcing expands its impact to the extra-tropics as demonstrated by Simpkins et al (2014). The modification in the local Hadley circulation is shown in Fig.…”

“…4e, vectors), but it is much weaker compared to that for the EP El Niño. Consequently, the perturbation of the local Hadley cell and the resultant subtropical upper-level divergent/ convergent anomalies provide a bridge that the anomalous tropical forcing extends its influence to the extra-tropics, since these upper-level divergent/convergent anomalies likely play a vital role in determining the extra-tropical vorticity forcing anomalies (Simpkins et al 2014).…”

How much, how fast?: A science review and outlook for research on the instability of Antarctica's Thwaites Glacier in the 21st century

“…The strengthening of the regional westerly winds that have forced warmer waters to the grounding zones can be attributed primarily to remote changes occurring in the tropics (Schneider and Steig, 2008;Ding et al, 2011;Bracegirdle, 2012;Steig et al, 2012;2013;Dutrieux et al, 2014;Simpkins et al, 2014;Clem and Fogt, 2015;Clem and Renwick, 2015;Fogt and Wovrosh, 2015;Li et al, 2014Li et al, , 2015a. However, there is also likely a component of change resulting from larger-scale circulation changes (the Southern Annular Mode, or SAM) owing to stratospheric ozone depletion and increased greenhouse gases (e.g., Thompson et al, 2011;Arblaster et al, 2011).…”

Seasonal sea ice changes in the Amundsen Sea, Antarctica, over the period of 1979–2014

“…Air-ocean-ice interactions in the Amundsen Sea region are thought to be sensitive to large-scale climate variability and tropical teleconnections; e.g., the Southern Annular Mode (SAM) (e.g., Turner et al, 2009), El Niño-Southern Oscillation (ENSO) (e.g., Yuan, 2004), the Atlantic Multi-decadal Oscillation (Li et al, 2014;Simpkins et al, 2014), and warming in the central tropical Pacific (Steig et al, 2012). However, the sensitivity of sea ice in the Amundsen Sea to large-scale climate variability will likely vary between the exposed offshore region and the partially enclosed coastal area.…”