A recent study analyzing data from 1980 to 2020 found that atmospheric rivers (ARs), though infrequent, have accounted for up to 70% of extreme snowfall events in East Antarctica since the 1980s, significantly impacting the continent’s ice sheet mass balance.
A major AR over Antarctic on March 17, 2022. Atmospheric rivers in Antarctica - John D.Wille et al.
The research explored the atmospheric dynamics of antarctic ARs to better understand their net contributions to the ice-sheet mass balance.
To conduct the study, researchers combined data from specialized polar-adapted atmospheric river (AR) detection algorithms with reanalysis datasets (ERA5 and MERRA-2), which provide high-resolution representations of atmospheric conditions over Antarctica. This approach enabled detailed observations and analyses of AR frequency, distribution, and intensity between 1980 and 2020.
The dynamics of a landfalling Antarctic AR. a, Multilevel atmospheric river (AR) dynamics, from the surface, through to the lower troposphere and midtroposphere. Mid-latitude sources of moisture are transported towards the polar latitudes by an AR (grey arrow), resulting in latent heat release of AR moisture. When the latent heat release occurs, it amplifies the polar jet stream (white arrow) and cyclogenesis via potential vorticity (PV) anomalies. b, Mountainous meso-scale dynamics typically observed in coastal regions such as the Antarctic Peninsula, focusing on thermodynamic processes. Mixed-phase clouds along the windward coastline heat the surface through downwelling longwave radiation (red arrows). When the AR airstream crosses mountainous terrain, it descends and warms adiabatically, creating a foehn wind on the leeward side. c, Cyclone (synoptic-scale) dynamics demonstrating the pathway of the AR airstream as it lifted isentropically in the warm conveyer belt (orange arrows) over the warm front and eventually reaches the anticyclone (high-pressure area), causing the cyclone to intensify. ARs, through the poleward transport of moisture and heat, substantially alter the dynamics and thermodynamics of Antarctic weather patterns when reaching the cold, and sometimes mountainous terrain, along the Antarctic coastline. Image credit: Atmospheric rivers in Antarctica – John D. Wille et al.
They found that despite their infrequent nature, ARs significantly contribute to snowfall in Antarctica, accounting for up to 70% of extreme snowfall events in regions such as East Antarctica since the 1980s. The substantial snowfall typically benefits Antarctica’s surface mass balance by enhancing ice sheet accumulation.
However, the study also identified some negative impacts, including AR-induced melting and destabilization of coastal ice shelves. Studying past ARs researchers found a direct connection to ice shelf collapse, notably Larsen A in 1995 and Larsen B in 2002.
AR frequency, trends and projections. a, Atmospheric river (AR) frequency (h per year, 1980–2020; teal shading) derived from the algorithm and MERRA-2 (Modern-Era Retrospective Analysis for Research and Applications, version 2) reanalysis of ref. 7. Interannual variability is shown in white contours (h per year). Coastal (based on ice sheet and shelves) AR frequency is shown by longitude and grouped by season. b, Relative change in AR frequency (%) by individual glacier basin from 1980 to 2020 is shown with shading, also based on the MERRA-2 reanalysis of ref. 7. Hatching indicates a linear fit of AR frequency (horizontal) or AR precipitation (vertical) per basin from 1980 to 2020 that has a P value <0.05. AR precipitation trend values are not shown. Despite being rare events, positive trends in AR frequency are responsible for increased snowfall in West Antarctica and Queen Maud Land during the 1980–2020 period. Image credit: Atmospheric rivers in Antarctica – John D.Wille et al.
Although progress has been made in understanding Antarctic ARs, key gaps still remain. Ongoing research aims to identify the tropical forcing patterns that drive initial moisture export and the Rossby wave amplification that directs moisture transport. Once the moisture reaches the Antarctic Ice Sheet, its influence on mesoscale cyclonic activity remains unclear.
From 15–19 March 2022, an extremely intense atmospheric river (AR) made landfall in East Antarctica that triggered a subsequent heatwave with temperatures 30–40 °C above normal across an area roughly half the size of Europe (see the figure). The origins of this AR were traced back to tropical convection and the occurrence of three successive cyclones across the Indian Ocean and of tropical-temperate troughs over the African landmass, which advected record-high plumes of tropical moisture into the mid-latitudes. This tropical convection helped to initiate a Rossby wave propagation leading to the formation of an intense blocking anticyclone centred south of Tasmania. The block extended poleward, which directed the subtropical moisture towards Antarctica in the form of an AR family event. The AR, coupled with a warm conveyor belt near the coastline, helped to lift the moisture to the tropopause, causing substantial potential vorticity anomalies in the high troposphere, which reinforced the atmospheric blocking deep into East Antarctica. These combined factors pushed a record-shattering moisture flux poleward (an Aqua Moderate Resolution Imaging Spectroradiometer, true colour image from 17 March 2022) (see the figure), where IVT from this AR was 8.7 standard deviations from the mean AR IVT across East Antarctica and the event ranked as an AR category 4 on the polar AR scale. The accompanying upper-level warm air advection into the continent and longwave radiation from liquid-laden clouds eroded the typical surface temperature inversions over the ice sheet. This AR and subsequent heatwave led to an area of 3.3 million km2 in East Antarctic to exceed March monthly temperature records. Meanwhile, a new all-time high temperature record of −9.4 °C was set near Concordia Station on 18 March 2022, despite March typically being a winter transition month. This event accounted for 32% of total Antarctic ice sheet (AIS) precipitation during March, which saw highly anomalous rain (+0.49 Gt) and surface melt (0.5 Gt) along coastal areas, although snowfall vastly counterbalanced the losses due to melt (+42.5 Gt). At Dome C station, isotope measurements revealed a distinct summer-like signature, whereas cosmic ray measurements were attenuated by the anomalous atmospheric moisture; both showing the implications for paleoclimate studies. Finally, an extratropical cyclone west of the AR landfall likely triggered the final collapse of the already critically unstable Conger Ice Shelf, while further diminishing land-fast ice, which was already at a record minimum. Overall, the AR event largely contributed to 2022 being a rare positive mass balance year for the entire AIS, thus slightly mitigating the AIS’s contribution to sea-level rise. However, the temperature extremes also raised concerns of potentially dire consequences for ice sheet stability if a similar magnitude event happens over a sensitive ice shelf in West Antarctica during the summer melt season. Image credit: Atmospheric rivers in Antarctica – John D. Wille et al.
High-resolution, kilometer-scale models are essential for resolving how moisture transport within warm conveyor belts influences cyclone intensity and AR impacts.
Additionally, reducing uncertainties in polar AR detection techniques is essential for improving the understanding of AR impacts. Identifying AR signals in ice core records prior to 1979 could support longer-term climate reconstructions of Antarctic AR activity.
According to the researchers, an important question is how the balance between the positive and negative impacts of ARs on the ice sheet mass balance will shift with climate change, both in the near and long term.
AR impacts. Typical observed impacts from atmospheric river (AR) landfalls in regions of mountainous terrain, such as the Antarctic Peninsula. These include windward snowfall accumulation to leeward foehn wind and downwelling longwave radiation, resulting in intense surface melt. On an ice shelf, these can lead to melt pond formation and eventual hydrofracturing while disintegrating the sea ice buffer along the ice shelf front. Thus, AR events can cause impacts on ice surface mass balance from the margins to the interior. Image credit: Atmospheric rivers in Antarctica – John D. Wille et al.
Atmospheric rivers are relatively long and narrow corridors of concentrated water vapor transport in the atmosphere, responsible for the majority of horizontal moisture movement outside the tropics. While their size and strength can vary significantly, an average atmospheric river carries roughly the same amount of water vapor as the average discharge at the mouth of the Mississippi River. In extreme cases, this transport can reach up to 15 times that volume.
Atmospheric rivers capable of transporting large volumes of water vapor and driven by strong low-level winds can result in extreme precipitation and flooding, especially when they stall over flood-prone watersheds. This can lead to widespread disruptions, including travel delays, landslides, and severe damage to infrastructure and property.
Rishav is a skilled researcher specializing in extreme and severe weather reporting. He combines exceptional research capabilities with scientific precision to deliver clear, data-driven articles. Known for uncovering critical information, Rishav ensures his work is accurate, insightful, and impactful. His passion for both science and literature fuels his dedication to producing high-quality news articles. You can reach him at rishav(at)watchers(.)news.
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