Central tropical Pacific convection drives extreme high temperatures and surface melt on the Larsen C Ice Shelf, Antarctic Peninsula

Abstract

Northern sections of the Larsen Ice Shelf, eastern Antarctic Peninsula (AP) have experienced dramatic break-up and collapse since the early 1990s due to strong summertime surface melt, linked to strengthened circumpolar westerly winds. Here we show that extreme summertime surface melt and record-high temperature events over the eastern AP and Larsen C Ice Shelf are triggered by deep convection in the central tropical Pacific (CPAC), which produces an elongated cyclonic anomaly across the South Pacific coupled with a strong high pressure anomaly over Drake Passage. Together these atmospheric circulation anomalies transport very warm and moist air to the southwest AP, often in the form of “atmospheric rivers”, producing strong foehn warming and surface melt on the eastern AP and Larsen C Ice Shelf. Therefore, variability in CPAC convection, in addition to the circumpolar westerlies, is a key driver of AP surface mass balance and the occurrence of extreme high temperatures.

Compound drivers behind new record high temperatures and surface melt at the Antarctic Peninsula in February 2022

“…However, the heatwaves in 2015 and 2022 occurred during an El Niño and a neutral ENSO year, respectively, while the February 2022 event was linked to a La Niña. While Clem et al [30] pointed to a lack of ENSO phase preference for causing central Pacific convection, our results show that both positive SST anomalies and transient mid-latitude activity contributed to additional moisture supply over the SPCZ stretching into the subtropics, where moisture feeding the AR originated. The MJO, which was exceptionally strong in the central tropical Pacific during the March 2015 event [59], was much weaker and confined to the Indian Ocean in February 2022, with negative OLR anomalies west of 90ºE.…”

“…The two most recent temperature records in the northeastern AP (in March 2015 and February 2020) were both linked to ARs that combined with an intensified foehn effect [16,37], triggering record warm events in the northeastern AP. Clem et al [30] linked these ARs to enhanced central tropical Pacific convection (and El Niño-like SST anomalies), which triggered a Rossby wave train towards Antarctica. The latter deepened the Amundsen Sea Low and built a record-breaking high-pressure system over the Drake Passage [17], thereby directing the AR towards the AP.…”

Heat Waves: Physical Understanding and Scientific Challenges

“…Recent events such as the 2021 North American HW have also been linked to upwind latent heating and the occurrence of landfalling atmospheric rivers (long narrow corridors of high water vapor transport), which can lead to additional warming through sensible heat convergence and water vapor‐temperature feedbacks (e.g., Mo et al., 2022; Schumacher, Hauser, & Seneviratne, 2022). The co‐occurrence of high temperatures and atmospheric rivers has also been identified as a threat to the ice‐shelf stability in polar regions (e.g., Clem et al., 2022). This suggests that the contribution of processes can substantially vary over small areas and/or across HW events, as found for other regions (e.g., central Africa and Australia; L. Hu et al., 2019; Hirsch & King, 2020).…”

Estimating surface melt in Antarctica from 1979 to 2022, using a statistically parameterized positive degree-day model

“…Projecting Antarctic surface melt is therefore still a challenge, partly because of uncertainties introduced by clouds (Kittel et al, 2022), atmospheric rivers (e.g. Clem et al, 2022), or other localized climate phenomena.…”