On the Seasonality of the El Niño Teleconnection to the Amundsen Sea Region

Abstract

The Amundsen Sea low (ASL) is a quasi-stationary low pressure system that affects climate in West Antarctica. Previous studies have shown that El Niño–Southern Oscillation (ENSO) modulates the position and strength of the ASL with the strongest teleconnection found in austral winter despite the amplitude of ENSO events generally being largest in austral autumn/summer. This study investigates the mechanisms behind the seasonality of the El Niño teleconnection to the Amundsen Sea region (ASR) using experiments with the HadGEM3 climate model forced with an idealized fixed El Niño sea surface temperature anomaly present throughout the year. The seasonality of the El Niño–ASR teleconnection is found to originate from seasonal differences in the large-scale zonal winds in the South Pacific sector. In austral winter, the region of strong absolute vorticity near ~30°S associated with the subtropical jet, in combination with the changes to upper-tropospheric divergence due to the El Niño perturbation, acts as an anomalous Rossby wave source that is largely absent in austral summer. Furthermore, in austral summer the poleward propagation of tropically sourced Rossby waves into the ASR is inhibited by the strong polar front jet in the South Pacific sector, which leads to Rossby wave reflection away from the ASR. In austral winter, Rossby waves are able to propagate into the ASR, forming part of the Pacific South America pattern. The lack of the Rossby wave source in the tropical Pacific and the absence of favorable conditions for wave propagation explains the weaker El Niño–ASR teleconnection in austral summer compared to austral winter.

Role of the South Pacific Convergence Zone in West Antarctic Decadal Climate Variability

“…Furthermore, Turner et al (2016) recently showed that over the 1999-2014 negative IPO period, the Antarctic Peninsula cooled, and Clem et al (2018) showed that the negative IPO warmed the Ross Ice Shelf. However, they note that in austral summer when Antarctic Peninsula cooling is strongest, the tropical teleconnection is weak because of unfavorable conditions for Rossby wave propagation into high latitudes (Jin & Kirtman, 2009;Scott Yiu & Maycock, 2019). Moreover, they are not fully consistent with ASL deepening.…”

“…Turner et al () attributed the recent Antarctic Peninsula cooling to increased cyclonic activity in Drake Passage. However, they note that in austral summer when Antarctic Peninsula cooling is strongest, the tropical teleconnection is weak because of unfavorable conditions for Rossby wave propagation into high latitudes (Jin & Kirtman, ; Scott Yiu & Maycock, ). Therefore, while prior studies implicate the IPO as an important driver of West Antarctic decadal climate variability, no consistent explanation links the recent negative IPO event to the reversal in West Antarctic climate trends.…”

Generation of the Amundsen Sea Low by Antarctic Orography

“…However, Raphael et al (2016) found that the seasonal location of the ASL does not always coincide with the center of maximum storm activity. Several other recent studies (e.g., Yiu & Maycock, 2019, 2020 have linked the existence of the ASL to zonal asymmetries in tropical sea surface temperatures (SSTs) via planetary scale Rossby wave activity from the tropics to the southern high latitudes.…”

El Niño Southern Oscillation signal in a new East Antarctic ice core, Mount Brown South

“…RWT result from reduced (enhanced) Walker Cell convection in the tropics in austral winter during El Niño (La Niña) events. This causes the Pacific South American (PSA) pattern of high-low-high (low-high-low) tropospheric pressure anomalies that propagate south-eastward from the equatorial Pacific toward the South Pacific (Yiu and Maycock 2019). Proxy records for the ENSO from tree-ring, coral and ice core records have been used to produce multi-centennial reconstructions of the ENSO (e.g., Braganza et al 2009;Carré et al 2014;Cobb et al 2003;Cobb et al 2013;Dätwyler et al 2019;Emile-Geay et al 2016;Freund et al 2019;Fowler et al 2012;Grothe et al 2019;Stahle et al 1998).…”