Abstract
El Niño Southern Oscillation (ENSO) drives interannual variability in West Antarctic climate through altering atmospheric circulation in the Amundsen Sea region (ASR). The El Niño–ASR teleconnection is known to be strongest in austral winter and spring, but its variation with El Niño amplitude is underexplored. This study uses experiments from the HadGEM3‐A climate model to investigate the El Niño–ASR teleconnection for a range of imposed SST perturbations spanning weak (0.75 K) to strong (3 K) amplitudes. In austral winter, the El Niño–ASR teleconnection behaves linearly for El Niño amplitudes up to 2.25 K, but is found to weaken for stronger forcing (3 K). The anomalous Rossby wave source in the subtropical South Pacific increases monotonically with El Niño amplitude. However, a Rossby wave reflection surface originally located in the western South Pacific sector extends progressively eastward with increasing El Niño amplitude, reducing wave propagation into the ASR. The wave reflection surface is associated with curvature in the upper tropospheric zonal winds which intensifies as the subtropical jet strengthens under El Niño forcing. In contrast, the El Niño–ASR teleconnection in austral summer, which more closely resembles the Southern Annular Mode, is found to increase linearly for El Niño amplitudes up to 3 K. The results explicitly demonstrate that a linear approximation of the El Niño teleconnection to the ASR is reasonable based on the range of El Niño amplitudes observed in recent history.
Highlights
The Amundsen Sea low (ASL) is a quasi–stationary climatological low pressure centre found in the South Pacific sector of the Southern Ocean between the Antarctic Peninsula and the Ross Sea (Hosking et al, 2013; Turner et al, 2013; Raphael et al, 2016)
This study examines how the El Niño teleconnection to the Amundsen Sea region (ASR) varies as a function of El Niño amplitude
In austral winter (JJA) the teleconnection behaves approximately linearly for El Niño amplitudes up to 2.25 K, but for a stronger El Niño forcing of 3 K the teleconnection in the ASR weakens despite the larger sea surface temperatures (SSTs) forcing
Summary
The Amundsen Sea low (ASL) is a quasi–stationary climatological low pressure centre found in the South Pacific sector of the Southern Ocean between the Antarctic Peninsula and the Ross Sea (Hosking et al, 2013; Turner et al, 2013; Raphael et al, 2016). YIU and MAYCOCK in tropical sea surface temperatures (SSTs), which generate planetary-scale Rossby waves that impact the Southern Hemisphere storm track (Inatsu and Hoskins, 2004), and the topography of Antarctica which causes asymmetries in synoptic activity (Lachlan-Cope et al, 2001). The ASL exhibits some of the highest circulation variability in the Southern Hemisphere (Lachlan-Cope et al, 2001) and has a strong impact on West Antarctic climate (Hosking et al, 2013; Turner et al, 2013; Raphael et al, 2016). It is important to understand the factors that affect the behaviour of the ASL on interannual and longer time-scales
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