CE01 - Terre fluide et solide

Atmospheric River Climatology in Antarctica – ARCA

Atmospheric River Climatology and impacts in Antarctica

ARCA aims to describe atmospheric rivers (AR) in the polar regions by applying detection algorithms for these events on historical, current and future climate simulations. ARCA will evaluate their impact on the Antarctic surface mass balance. ARCA will also analyze the extent to which moisture transported by ARs has a particular isotopic and chemical signature and assess whether these events can be traced in ice cores.

Links between rivers and climate extremes in Antarctica

Over much of Antarctica, the surface mass balance (SMB) is controlled by a few extreme events, resulting in high natural variability in this variable. In particular, it has recently been shown that extreme moisture intrusions related to atmospheric rivers (AR) from the Southern Ocean are major sources of snow accumulation, warming and surface melting. <br />In the ARCA project, we propose to identify atmospheric rivers in various model outputs and climate reanalyses to understand how natural variability and external forcings control atmospheric river activity.<br />We propose to quantify the moisture and heat transport to Antarctica associated with these events and analyze their impacts on the SMB. Finally, we will establish the past, present and future climatologies of Antarctic ARs and the impact of variations in their frequency and intensity on the Antarctic SMB.<br />We will also describe the impact of ARs on the isotopic and aerosol contents of air masses transported across East Antarctica, and investigate the extent to which ice core records allow us to trace AR activity over the past few centuries. To do this, ARCA will re-examine existing ice core data. <br /><br />The ARCA project will provide products that describe the climatology and variability of ARs (occurrence maps, statistics), their atmospheric moisture signature (isotope time series and aerosol content), and their impacts on Antarctic climate and the SMB (through induced melt and accumulation maps). Results will be presented for the 20th and 21st centuries, aiming in particular to provide observationally constrained projections of AR impacts on the SMB (ice core data). ARCA plans to propose a multi-proxy approach, based on various variables including water stable isotopes, to define how to retrieve past ARs from ice cores, and define qualitatively periods of high and low AR activity over the past millennium. Finally, ARCA will define regions in the Adelie and Wilkes Lands where ice cores should be drilled to better recover ARs and their influence on past climate variability.

ARCA will use recent new numerical methodologies to identify ARs applied to global and regional circulation models (GCM and RCM respectively). To do so, we have developed a detection algorithm based on the climatology of variables describing the intensity of the moisture content of air masses. For a given time step, the detection of an event is obtained when the moisture content exceeds an extreme value continuously over at least 20° of latitude. These simple criteria allow to describe the spatial coherence and the extreme character of the event. The developed algorithm presents two detection schemes; one based on integrated water vapor (IWV) and the other on vertically integrated meridional water vapor transport (vIVT)

one key challenge of the ARCA project is to reconstruct the intensity and frequency of atmospheric rivers in the past using the ice core archive (chemical and water isotope analyses). This is an ambitious goal because it requires ensuring that 1) the air masses associated with atmospheric rivers have a specific isotopic and/or chemical signature and 2) this signature remains identifiable in the ice cores despite all the processes affecting the archiving of events of only a few days.
To this end, ARCA provides new and original field measurements of stable water isotopes and chemical composition of snow precipitation and air masses from Adelie and Wilkes lands (East Antarctica).
To understand the variations in atmospheric signals and in deposited snow, ARCA will develop and apply a regional circulation model with a representation of the cycle of water stable isotopes. This will help to describe the impact of AR on the isotope and aerosol content of air masses transported across East Antarctica, and then analyze how the signal may be transmitted in the ice core record.

Finally, ARCA aims to quantify whether anomalous isotopic and chemical signals associated with AR can be recovered from Antarctic snow and ice core records. This is a challenge whose feasibility remains to be demonstrated. To do this, ARCA will revisit existing ice core data (aerosol, water isotope content) to assess (qualitatively) past AR variability and the resulting bias in current estimates of Antarctic climate over the past millennium.

The systematic analysis of atmospheric river impacts in Antarctica is very recent and relied on the development of systematic detection algorithms for atmospheric rivers adapted to polar regions. These tools were developed during the writing of the ARCA project (Wille et al., 2019) and were used here to analyze the contribution of atmospheric rivers to the surface mass balance of Antarctica. ARs contribute positively and negatively to the Antarctic mass balance by causing both heavy snowfall (Wille et al., 2021; Maclennan et al., 2022) and melting in the different affected regions (Wille et al., 2022 ; Turner et al., 2022). ARs are responsible for a significant portion of the annual snow accumulation on the continent (up to 25% of the total in some areas). The most intense daily precipitation events are associated with the arrival of atmospheric rivers (Wille et al., 2021). Indeed, 70% of precipitation events exceeding the 99th percentile of daily precipitation intensity were associated with ARs. Interannual and decadal variations in Antarctic accumulation since 1980 were also largely controlled by atmospheric river activity (Wille et al., 2021). Wille et al. (2021) demonstrated that AR activity is significantly correlated with variations in the Southern Annular Mode (SAM). Effects of the SAM on subsurface ocean temperature and melt of below the ice shelves was also analyzed by Verfaillie et al. (2022).
Wille et al. (2022) also demonstrated that atmospheric rivers cause the majority of temperature extremes along the Antarctic Peninsula. This was the case for the Antarctic continent-wide temperature record (18.3°C set at Esperanza Station on February 6, 2020). This was also the case for the East Antarctic heat wave that occurred on March 18, 2022 (up to 35°C anomaly). Wille et al. (2022) described that these temperature extremes were leading to the generation of extreme melt and other conditions conducive to the destabilization of Antarctic Peninsula platforms. Indeed, after saturating the snow on the surface of the ice-shelves, meltwater may accumulate in lakes and eventually fill crevasses, contributing to the ice-shelf instability through hydro-fracturing processes. Atmospheric rivers also cause sea ice to disperse around Antarctic Peninsula ice-shelves. Ocean swells can then strike the ice-shelf and generate a flexure, which weakens it. These atmospheric river effects were observed during the collapse of the Larsen A and B ice shelves, and in 60% of large iceberg calving events after 2000.

No one knows today whether or not atmospheric rivers will become more frequent in the future in Antarctica. This will depend on future variations in the climate variability controlling the ultimate activity of atmospheric rivers. Antarctica is known to have particularly strong natural climate variability on different time scales (interannual to multi-decadal). The anthropogenic climate change signal is only expected to emerge from the natural variability around 2020-50 in Antarctica. From then on, variations in the southern ring mode of the location and strength of semi-permanent lows (e.g. in the Amundsen Sea) are expected, which will likely induce changes in the frequency of atmospheric rivers affecting the continent. Other large-scale patterns may also play a role in these events (e.g., the variability associated with the El Niño Southern Oscillation). Without a clear understanding of the processes controlling blocking conditions off the continent, trends in the frequency and intensity of atmospheric rivers will remain pure speculation.
ARCA will now focus on better defining the large-scale factors controlling the evolution and variability of ARs in the past, present and future. Analysis of the atmospheric processes involved in atmospheric river events is already being carried out using a large set of simulations of pre-industrial, present and future climates. The frequency and intensity of atmospheric rivers are analyzed under different climate conditions, including or not anthropogenic and internal climate forcings. We focus on the variability associated with the southern annular mode but also on the potential impacts of ENSO.
In order to know how realistic the future variability proposed by the models is, we are working on the definition of a long-term baseline to assess the natural variability of Antarctic atmospheric rivers. Thus, an additional challenge of the ARCA project will be to reconstruct the intensity and frequency of atmospheric rivers in the past using the ice core archive (chemical and water isotope analyses). This is an ambitious goal as it requires ensuring that 1) the air masses associated with atmospheric rivers have a specific isotopic and/or chemical signature and 2) this signature remains identifiable in the ice cores despite all the processes affecting the archive and the measurement resolutions that are not those of a few days events.

1. Collow, A.B.M., Shields, C.A., Guan, B., Kim, S., Lora, J.M., McClenny, E.E., Nardi, K., Payne, A., Reid, K., Shearer, E.J., Tomé, R., Wille, J.D., Ramos, A.M., Gorodetskaya, I.V., Leung, L.R., O’Brien, T.A., Ralph, F.M., Rutz, J., Ullrich, P.A., Wehner, M. (2022). An Overview of ARTMIP’s Tier 2 Reanalysis Intercomparison : Uncertainty in the Detection of Atmospheric Rivers and Their Associated Precipitation. Journal of Geophysical Research : Atmospheres 127, e2021JD036155. doi.org/10.1029/2021JD036155
2. Pohl, B., V. Favier, J. Wille, D.G. Udy, T. R. Vance ; J. Pergaud ; N. Dutrievoz, J. Blanchet, C. Kittel ; C. Amory, G. Krinner, F. Codron (2021). Relationship between weather regimes and atmospheric rivers in East Antarctica, Journal of Geophysical Research-Atmosphere, 126, e2021JD035294. doi.org/10.1029/2021JD035294
3. Verfaillie, D., C. Pelletier, H. Goosse, N. C. Jourdain, C. Y. S. Bull, Q. Dalaiden, V. Favier, T. Fichefet, and J. Wille, How does the Southern Annular Mode impactice-shelf basal melt in Antarctica ? Communications Earth & Environment, 3, 139 (2022). doi.org/10.1038/s43247-022-00458-x
4. Wille, J.D., V. Favier, N.C Jourdain, C. Kittel, J. V Turton, C. Agosta, I. V Gorodetskaya, G. Picard, F. Codron, C. Leroy-Dos Santos, C. Amory, X. Fettweis, J. Blanchet, V. Jomelli, A. Berchet, Intense atmospheric rivers can weaken ice shelf stability at the Antarctic Peninsula. Commun Earth Environ 3, 90 (2022). doi.org/10.1038/s43247-022-00422-9
5. Wille, J.D., Favier, V., Gorodetskaya, I. V., Agosta, C., Kittel, C., Chowdhry Beeman, J., Jourdain, N., Lenaerts, J.T.M., Codron, F. (2021) Antarctic atmospheric river climatology and precipitation impacts, Journal geophysical Research-Atmosphere, 126 (8), e2020JD033788
6. Shields, C. A., Wille, J. D., Marquardt Collow, A. B., Maclennan, M., & Gorodetskaya, I. V. (2022). Evaluating uncertainty and modes of variability for Antarctic atmospheric rivers. Geophysical Research Letters, 49, e2022GL099577. doi.org/10.1029/2022GL099577
7. Turner, J., Lu, H., King, J. C., Carpentier, S., Lazzara, M., Phillips, T., & Wille, J. (2022). An extreme high temperature event in coastal East Antarctica associated with an atmospheric river and record summer downslope winds. Geophysical Research Letters, 49, e2021GL097108. doi.org/10.1029/2021GL097108
8. Maclennan, M. L., Lenaerts, J. T. M., Shields, C. A., Hoffman, A. O., Wever, N., Thompson-Munson, M., Winters, A. C., Pettit, E. C., Scambos, T. A., and Wille, J. D. (2022). Climatology and Surface Impacts of Atmospheric Rivers on West Antarctica, The Cryosphere Discuss. [preprint], doi.org/10.5194/tc-2022-101, in review.

Outreach:
1. Favier, V., J. Wille, C. Agosta, C. Amory, L. Barthélémy, F. Codron, E. Fourré, I. Gorodetskaya, C. Kittel, G. Krinner, B. Pohl (2022) Des rivières dans le ciel de l’Antarctique. La Météorologie, Météo et Climat, 2022, 117, pp.19-23. ?10.37053/lameteorologie-2022-0032?.

Over a large part of Antarctica, the surface mass balance (SMB) is controlled by a few extreme events, resulting in a high natural variability of this parameter. In particular, extreme moisture intrusions linked to Southern Ocean Atmospheric Rivers (ARs) have been recently demonstrated to be major sources of both snow accumulation, heating and surface melt. Despite their key role, there is a general omission of AR variability, and more broadly of extreme events, in studies of past and future Antarctic climate and SMB.
ARCA will assess the impact of ARs on the surface mass balance of Antarctica and will explore to what extent past AR activity can be recorded in ice cores.

To reach this goal, ARCA is organized in 4 working packages. 1) ARCA will use recent novel numerical methodologies for identifying ARs applied to global and regional circulation models (GCMs and RCMs respectively). New algorithms will be applied to historical, present and future climate simulations. 2) ARCA will provide new field measurements of water stable isotopes and chemistry composition of snow precipitation and air masses from Adelie and Wilkes Lands, and 3) apply a regional scale modeling of water stable isotopes to interpret the signal observed in the field. 4) ARCA will finally revisit data from existing ice cores (aerosol content, e.g. sea salt, insoluble particles, water isotopes).

Following this methodology, ARCA proposes to:
1) understand how natural variability and external forcings control the AR activity.
2) quantify AR moisture and heat transport towards Antarctica and their impacts on the SMB of Antarctica.
3) describe AR impact on the isotopic and aerosol contents of air masses transported through East Antarctica,
4) analyze the processes (e.g., moisture origin, sublimation of hydrometeors) producing characteristic signals in air masses during ARs,
5) estimate the induced bias in ice core records in regards to past temperature reconstructions.
6) Evaluate (qualitatively) past AR variability and the resulting bias in current estimates of past millenium climate in Antarctica.

The ARCA project will deliver products that describe AR climatology and variability (occurrence maps, statistics), their atmospheric moisture signature (time-series of isotopes and aerosol content), and their impacts on Antarctic climate and SMB (through maps of induced melting and accumulation). Results will be presented for the 20th and 21st centuries, aiming in particular at projecting observationally constrained impacts of ARs on the SMB. ARCA will define a multi proxy approach to define how past AR could be retrieved in ice cores and provide a metric using water isotopic composition in ice cores to qualitatively define periods of higher and lower AR activity over the past millennium. Finally, ARCA will define the regions of Adelie and Wilkes Lands where ice cores should be drilled to best capture the AR and their influence in past climate variability.

The ARCA consortium presents recognized experts from the IGE, LSCE and LOCEAN in particular in atmospheric modeling with polar-Regional Circulation Models and General Circulation Models, AR detection and estimation surface mass balance for Antarctica. The project will also rely on the broad expertise of the group in the interpretation of water isotopes and aerosol contents in air samples and ice cores.

Project coordination

Vincent Favier (Institut des Géosciences de l'Environnement)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

UTAS/IMAS University of Tasmania/Institute for Marine and Antarctic Studies
UGA-IGE Institut des Géosciences de l'Environnement
LSCE Laboratoire des Sciences du Climat et de l'Environnement
LOCEAN Laboratoire d'océanographie et du climat : expérimentations et approches numériques
CESAM Universidade de Aveiro / Centre for Environmental and Marine Studies
EPFL-LTE École Polytechnique Fédérale de Lausane - Laboratoire de télédétection environnementale
ULiège Université de Liège / Laboratoire de Climatologie
LOCEAN Laboratoire d'océanographie et du climat : expérimentations et approches numériques

Help of the ANR 492,065 euros
Beginning and duration of the scientific project: December 2020 - 48 Months

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