On the crucial role of atmospheric rivers in the two major Weddell Polynya events in 1973 and 2017 in Antarctica

Abstract

This study reports the occurrence of intense atmospheric rivers (ARs) during the two large Weddell Polynya events in November 1973 and September 2017 and investigates their role in the opening events via their enhancement of sea ice melt. Few days before the polynya openings, persistent ARs maintained a sustained positive total energy flux at the surface, resulting in sea ice thinning and a decline in sea ice concentration in the Maud Rise region. The ARs were associated with anomalously high amounts of total precipitable water and cloud liquid water content exceeding 3 SDs above the climatological mean. The above-normal integrated water vapor transport (IVT above the 99th climatological percentile), as well as opaque cloud bands, warmed the surface (+10°C in skin and air temperature) via substantial increases (+250 W m−2) in downward longwave radiation and advection of warm air masses, resulting in sea ice melt and inhibited nighttime refreezing.

Atmospheric extremes caused high oceanward sea surface slope triggering the biggest calving event in more than 50 years at the Amery Ice Shelf

“…The variability of the polar jet front in the Southern Hemisphere and whether behavior similar to the polar jet in the Northern Hemisphere is underway around Antarctica need to be investigated in future work. Several studies have shown evidence for a wavier jet stream in response to rapid Arctic warming and reported a weakening of the polar jet as a result of a reduced temperature gradient between high and mid latitudes due to the increased temperatures in the Arctic (e.g., Francis and Vavrus, 2015;Coumou et al, 2015;Mann et al, 2017). Such a change in the polar jet, which acts as an isolation boundary between high and mid latitudes, would lead to more interactions and spark feedback mechanisms between the Antarctic system and mid latitudes as happened to be the case in the Arctic (Francis et al, 2018(Francis et al, , 2019b.…”

“…3a). The moisture and heat carried by the atmospheric river over the ice sheet may have caused warming at the surface due to con- densation (released heat) as well as an increase in downward longwave radiation (e.g., Francis et al, 2020).…”

“…In fact, weather systems (i.e., cyclones and blocks) resulting from the larger-scale circulation (e.g., Pope et al, 2017) are identified as the main driver of the observed trends in sea ice variability (Matear et al, 2015;Schemm, 2018;Turner et al, 2017;Eayrs et al, 2019). Furthermore, cyclones and their associated atmospheric rivers can induce sea ice melt (Francis et al, 2020) and ice shelf surface melt (Wille et al, 2019) by virtue of their associated anomalous moisture and heat transport to high latitudes which increase the downward longwave radiation at the ice surface (Woods and Caballero, 2016;Lee et al, 2017;Grieger et al, 2018;Francis et al, 2020). Additionally, cyclones can cause significant sea ice drift (Kwok et al, 2017;Francis et al, 2019a) due to the strong surface winds they carry (Schemm, 2018).…”

“…Another aspect of the ZW3 pattern is the impact of the ridges on the propagation speed of the cyclones. In the troughs, the extratropical cyclones and the associated moisture and heat fluxes are directed poleward; once they reach the Antarctic coast they are blocked by the ridges to their east (Francis et al, 2019a(Francis et al, , 2020. This results in stationary cyclones over the same region for 1-2 d, which in turn induces pronounced impact on the sea ice (e.g., Francis et al, 2019a) and waves (Vichi et al, 2019).…”

Recent observations of superimposed ice and snow ice on sea ice in the northwestern Weddell Sea

“…A number of studies have related these negative ice extent anomalies to various atmospheric and oceanic processes, often related to large, negative anomalies of the Southern Annual Mode (SAM), corresponding increases of cyclonic activity, and warm anomalies of several degrees Celsius at the Antarctic Peninsula and over the Weddell Sea (e.g., Francis et al, 2020;Schlosser et al, 2018;Turner et al, 2020;Wang et al, 2019). Together, these studies concluded that these processes contributed to warmer air, increased cloud-radiation feedbacks, increased liquid precipitation, and increased turbulent heat fluxes into the ice (e.g., Francis et al, 2020). In addition, earlier seasonal sea ice retreat, anomalous surface winds, and strong atmosphere-ocean coupling caused stronger heat absorption by the upper ocean, more southward Ekman transport of warmer surface waters, and thus the warming of the Ocean Mixed Layer, amplifying the sea-ice loss (Meehl et al, 2019;Turner et al, 2020).…”