Foehn winds link climate‐driven warming to ice shelf evolution in Antarctica

Abstract

Rapid warming of the Antarctic Peninsula over the past several decades has led to extensive surface melting on its eastern side, and the disintegration of the Prince Gustav, Larsen A, and Larsen B ice shelves. The warming trend has been attributed to strengthening of circumpolar westerlies resulting from a positive trend in the Southern Annular Mode (SAM), which is thought to promote more frequent warm, dry, downsloping foehn winds along the lee, or eastern side, of the peninsula. We examined variability in foehn frequency and its relationship to temperature and patterns of synoptic-scale circulation using a multidecadal meteorological record from the Argentine station Matienzo, located between the Larsen A and B embayments. This record was further augmented with a network of six weather stations installed under the U.S. NSF LARsen Ice Shelf System, Antarctica, project. Significant warming was observed in all seasons at Matienzo, with the largest seasonal increase occurring in austral winter (+3.71 ∘ C between 1962-1972 and 1999-2010). Frequency and duration of foehn events were found to strongly influence regional temperature variability over hourly to seasonal time scales. Surface temperature and foehn winds were also sensitive to climate variability, with both variables exhibiting strong, positive correlations with the SAM index. Concomitant positive trends in foehn frequency, temperature, and SAM are present during austral summer, with sustained foehn events consistently associated with surface melting across the ice sheet and ice shelves. These observations support the notion that increased foehn frequency played a critical role in precipitating the collapse of the Larsen B ice shelf.

Identification of Air Masses Responsible for Warm Events on the East Antarctic Coast

“…The isentropic drawdown of this warm air could therefore explain a large part of the foehn warming observed. In Antarctica, this type of foehn warming (nonlinear foehn event) has been observed on the east side of the AP (Elvidge et al 2015Cape et al 2015;Grosvenor et al 2014) and in the McMurdo dry valleys of EA (Speirs et al 2010;Steinhoff et al 2013Steinhoff et al , 2014. We cannot, however, ignore the contribution of the latent heating of precipitation.…”

“…The summer warming of the AP over the last half of the 20th century, for example, is consistent with strengthened westerly marine air advection driven by changes in the Southern Hemisphere Annular Mode (SAM) (e.g., Marshall et al 2006;Turner et al 2016). This warm westerly flow travels over mountain ranges on the AP, causing additional temperature increase by adiabatic warming as the air descends on the east side of the AP that is called a foehn warming (e.g., Elvidge et al 2015Cape et al 2015;Grosvenor et al 2014). The increase in poleward marine air advection is also known to have contributed to summer warming at Byrd Station through most of the late 1980s, though it can not solely explain long-term trends in West Antarctica (Bromwich et al 2012).…”

“…We minimize the effect of initial conditions by discarding the first 6 h forecasts for the model spin-up. The AMPS output has been successfully used to model mesoscale atmospheric dynamics over the Antarctica (e.g., Schlosser et al 2008;Schlosser et al 2010;Speirs et al 2010;Nicolas and Bromwich 2011;Cape et al 2015).…”

Meltwater produced by wind–albedo interaction stored in an East Antarctic ice shelf

“…With a directional constancy exceeding 0.95 ( Supplementary Fig. 2), these downslope winds are far more relentless than the episodic foehn events in the grounding zone of Antarctic Peninsula ice shelves 5 , where directional constancy is lower than 0.7. They generate the atmospheric and surface conditions that are responsible for the meltwater production in the RBIS grounding zone in two ways.…”

Observationally constrained surface mass balance of Larsen C ice shelf, Antarctica

“…1), the firn contains a massive subsurface ice layer (Hubbard et al, 2016), influencing ice-shelf temperatures, density, and potentially, flow properties. The occurrence of föhn winds has increased in recent decades (Cape et al, 2015), contributing to the destabilization of Larsen B ice shelf through increased meltwater production.…”