publications

2024

1. Polar Aerosol Atmospheric Rivers: Detection, Characteristics, and Potential Applications

   Rémy Lapere, Jennie L. Thomas, Vincent Favier, and 8 more authors

   Journal of Geophysical Research: Atmospheres, Jan 2024

   Publisher: John Wiley & Sons, Ltd

   Abs

   Abstract Aerosols play a key role in polar climate, and are affected by long-range transport from the mid-latitudes, both in the Arctic and Antarctic. This work investigates poleward extreme transport events of aerosols, referred to as polar aerosol atmospheric rivers (p-AAR), leveraging the concept of atmospheric rivers (AR) which signal extreme transport of moisture. Using reanalysis data, we build a detection catalog of p-AARs for black carbon, dust, sea salt and organic carbon aerosols, for the period 1980?2022. First, we describe the detection algorithm, discuss its sensitivity, and evaluate its validity. Then, we present several extreme transport case studies, in the Arctic and in the Antarctic, illustrating the complementarity between ARs and p-AARs. Despite similarities in transport pathways during co-occurring AR/p-AAR events, vertical profiles differ depending on the species, and large-scale transport patterns show that moisture and aerosols do not necessarily originate from the same areas. The complementarity between AR and p-AAR is also evidenced by their long-term characteristics in terms of spatial distribution, seasonality and trends. p-AAR detection, as a complement to AR, can have several important applications for better understanding polar climate and its connections to the mid-latitudes.

2. Synoptic and planetary-scale dynamics modulate antarctic atmospheric river precipitation intensity

   Rebecca Baiman, Andrew C. Winters, Benjamin Pohl, and 3 more authors

   Communications Earth & Environment, Mar 2024

   Abs

   Although rare, atmospheric rivers substantially influence the interannual variability of Antarctic surface mass balance. Here we use MERRA-2 reanalysis to identify characteristics unique to atmospheric river environments by comparing (1) Analog (environments that feature high-low pressure couplets, similar to Atmospheric River environments, but no Atmospheric River), (2) Atmospheric River, and (3) Top Atmospheric River (highest precipitation) timesteps during 1980–2019 around Antarctica. We find significant differences between Atmospheric River and Analog environments including more intense and poleward-shifted mid-tropospheric geopotential height couplets as well as larger atmospheric moisture anomalies. We find similar significant enhancement in synoptic-scale dynamic drivers of Top Atmospheric Rivers compared to all Atmospheric River environments, but no significant difference in local integrated water vapor anomalies. Instead, our results highlight the importance of large-scale dynamic drivers during Top Atmospheric River timesteps, including amplified Rossby waves excited by tropical convection.

3. Winter Targeted Observing Periods during the Year of Polar Prediction in the Southern Hemisphere (YOPP-SH)

   David H. Bromwich, Irina V. Gorodetskaya, Scott Carpentier, and 34 more authors

   Bulletin of the American Meteorological Society, Mar 2024
4. Examining Atmospheric River Life Cycles in East Antarctica

   Jonathan D. Wille, Benjamin Pohl, Vincent Favier, and 10 more authors

   Journal of Geophysical Research: Atmospheres, Apr 2024

   Publisher: John Wiley & Sons, Ltd

   Abs

   Abstract During atmospheric river (AR) landfalls on the Antarctic ice sheet, the high waviness of the circumpolar polar jet stream allows for subtropical air masses to be advected toward the Antarctic coastline. These rare but high-impact AR events are highly consequential for the Antarctic mass balance; yet little is known about the various atmospheric dynamical components determining their life cycle. By using an AR detection algorithm to retrieve AR landfalls at Dumont d’Urville and non-AR analogs based on 700 hPa geopotential height, we examined what makes AR landfalls unique and studied the complete life cycle of ARs reaching Dumont d’Urville. ARs form in the mid-latitudes/subtropics in areas of high surface evaporation, likely in response to tropical deep convection anomalies. These convection anomalies likely lead to Rossby wave trains that help amplify the upper-tropospheric flow pattern. As the AR approaches Antarctica, condensation of isentropically lifted moisture causes latent heat release that?in conjunction with poleward warm air advection?induces geopotential height rises and anticyclonic upper-level potential vorticity tendencies downstream. As evidenced by a blocking index, these tendencies lead to enhanced ridging/blocking that persist beyond the AR landfall time, sustaining warm air advection onto the ice sheet. Finally, we demonstrate a connection between tropopause polar vortices and mid-latitude cyclogenesis in an AR case study. Overall, the non-AR analogs reveal that the amplified jet pattern observed during AR landfalls is a result of enhanced poleward moisture transport and associated diabatic heating which is likely impossible to replicate without strong moisture transport.

5. The Extraordinary March 2022 East Antarctica “Heat” Wave. Part I: Observations and Meteorological Drivers

   Jonathan D. Wille, Simon P. Alexander, Charles Amory, and 51 more authors

   Journal of Climate, Apr 2024

   Place: Boston MA, USA Publisher: American Meteorological Society
6. The Extraordinary March 2022 East Antarctica “Heat” Wave. Part II: Impacts on the Antarctic Ice Sheet

   Jonathan D. Wille, Simon P. Alexander, Charles Amory, and 51 more authors

   Journal of Climate, Apr 2024

   Place: Boston MA, USA Publisher: American Meteorological Society
7. Spatiotemporal Variability of Extreme Precipitation Events and Associated Atmospheric Processes Over Dronning Maud Land, East Antarctica

   Sibin Simon, John Turner, Meloth Thamban, and 2 more authors

   Journal of Geophysical Research: Atmospheres, Apr 2024

   Publisher: John Wiley & Sons, Ltd

   Abs

   Abstract We investigate the spatial and temporal variability of extreme precipitation events (EPEs) in the Dronning Maud Land (DML) sector of Antarctica using high-resolution ECMWF ERA5 reanalysis data. This study examines the spatial occurrence of EPEs across DML, focusing particularly on six locations spanning the coastal and interior parts of the area. The largest snowfall amounts are usually found on eastward-facing slopes in the coastal zone. EPEs occur predominantly in north-easterly to easterly flows, leading to enhanced precipitation on the windward side of the orographic features with a steep gradient. Wind during EPEs was found to be more directionally consistent in the coastal area than in the interior. An east-west couplet of a mid-tropospheric ridge and low-pressure center is essential for steering warm moist maritime airmasses into the DML region before EPEs. Approximately 40% of EPEs result from atmospheric rivers (ARs), narrow bands of moist air originating at subtropical latitudes, which provide the greatest daily precipitation amounts. From 1979 to 2018, much of the DML experienced a statistically significant (p \textless 0.05) increase in the number of EPEs per year, along with increased precipitation from the EPEs. These trends were associated with significant changes in moisture availability and poleward meridional winds in the Atlantic sector of the Southern Ocean. The inter-annual variability in the number of EPEs is primarily dictated by regional atmospheric variability, while the influence of the Southern Oscillation Index and Southern Annular Mode is limited.

2023

1. Increasing extreme melt in northeast Greenland linked to foehn winds and atmospheric rivers

   Kyle S. Mattingly, Jenny V. Turton, Jonathan D. Wille, and 4 more authors

   Nature Communications, Mar 2023

   Abs

   The Greenland Ice Sheet has been losing mass at an increased rate in recent decades. In northeast Greenland, increasing surface melt has accompanied speed-ups in the outlet glaciers of the Northeast Greenland Ice Stream, which contain over one meter of sea level rise potential. Here we show that the most intense northeast Greenland melt events are driven by atmospheric rivers (ARs) affecting northwest Greenland that induce foehn winds in the northeast. Near low-elevation outlet glaciers, 80–100% of extreme (\textgreater 99th percentile) melt occurs during foehn conditions and 50–75% during ARs. These events have become more frequent during the twenty-first century, with 5–10% of total northeast Greenland melt in several recent summers occurring during the ~1% of times with strong AR and foehn conditions. We conclude that the combined AR-foehn influence on northeast Greenland extreme melt will likely continue to grow as regional atmospheric moisture content increases with climate warming.

2. Climatology and surface impacts of atmospheric rivers on West Antarctica

   M. L. Maclennan, J. T. M. Lenaerts, C. A. Shields, and 7 more authors

   The Cryosphere, Mar 2023
3. Impact of the atmospheric river occurring in March 2022 on east Antarctica on Cosmic-Rays measurements

   Guillaume Hubert, Philippe Ricaud, Vincent Favier, and 1 more author

   In Proceedings of 38th International Cosmic Ray Conference — PoS(ICRC2023), Jul 2023
4. Atmospheric Rivers and Weather Types in Aotearoa New Zealand: A Two-Way Story

   Benjamin Pohl, Hamish D. Prince, Jonathan Wille, and 3 more authors

   Journal of Geophysical Research: Atmospheres, Aug 2023

   Publisher: John Wiley & Sons, Ltd

   Abs

   Abstract Here, we analyze the inter-relationships between weather types (WTs) and atmospheric rivers (ARs) around Aotearoa New Zealand (ANZ), their respective properties, as well as their combined and separate influence on daily precipitation amounts and extremes. Results show that ARs are often associated with 3?4 WTs, but these WTs change depending on the regions where ARs landfall. The WTs most frequently associated with ARs generally correspond to those favoring anomalously strong westerly wind in the mid-latitudes, especially for southern regions of ANZ, or northwesterly anomalies favoring moisture export from the lower latitudes, especially for the northern regions. WTs and ARs show strong within-type and inter-event diversity. The synoptic patterns of the WTs significantly differ when they are associated with AR occurrences, with atmospheric centers of actions being shifted so that moisture fluxes toward ANZ are enhanced. The location, angle, and persistence of ARs appear strongly driven by the synoptic configurations of the WTs. Although total moisture transport shows weaker WT-dependency, it appears strongly related to zonal wind speed to the south of ANZ, or the moisture content of the air mass to the north. Finally, WT influence on daily precipitation may completely change depending on their association, or lack thereof, with AR events. WTs traditionally considered as favorable to wet conditions may conceal daily precipitation extremes occurring during AR days, and anomalously dry days or near-climatological conditions during non-AR days.

5. Strong Warming Over the Antarctic Peninsula During Combined Atmospheric River and Foehn Events: Contribution of Shortwave Radiation and Turbulence

   Xun Zou, Penny M. Rowe, Irina Gorodetskaya, and 9 more authors

   Journal of Geophysical Research: Atmospheres, Aug 2023

   Publisher: John Wiley & Sons, Ltd

   Abs

   Abstract The Antarctica Peninsula (AP) has experienced more frequent and intense surface melting recently, jeopardizing the stability of ice shelves and ultimately leading to ice loss. Among the key phenomena that can initiate surface melting are atmospheric rivers (ARs) and leeside foehn; the combined impact of ARs and foehn led to moderate surface warming over the AP in December 2018 and record-breaking surface melting in February 2022. Focusing on the more intense 2022 case, this study uses high-resolution Polar WRF simulations with advanced model configurations, Reference Elevation Model of Antarctica topography, and observed surface albedo to better understand the relationship between ARs and foehn and their impacts on surface warming. With an intense AR (AR3) intrusion during the 2022 event, weak low-level blocking and heavy orographic precipitation on the upwind side resulted in latent heat release, which led to a more deep-foehn like case. On the leeside, sensible heat flux associated with the foehn magnitude was the major driver during the night and the secondary contributor during the day due to a stationary orographic gravity wave. Downward shortwave radiation was enhanced via cloud clearance and dominated surface melting during the daytime, especially after the peak of the AR/foehn events. However, due to the complex terrain of the AP, ARs can complicate the foehn event by transporting extra moisture to the leeside via gap flows. During the peak of the 2022 foehn warming, cloud formation on the leeside hampered the downward shortwave radiation and slightly increased the downward longwave radiation.

6. Record-high Antarctic Peninsula temperatures and surface melt in February 2022: a compound event with an intense atmospheric river

   Irina V. Gorodetskaya, Claudio Durán-Alarcón, Sergi González-Herrero, and 22 more authors

   npj Climate and Atmospheric Science, Dec 2023

   Abs

   The Antarctic Peninsula (AP) experienced a new extreme warm event and record-high surface melt in February 2022, rivaling the recent temperature records from 2015 and 2020, and contributing to the alarming series of extreme warm events over this region showing stronger warming compared to the rest of Antarctica. Here, the drivers and impacts of the event are analyzed in detail using a range of observational and modeling data. The northern/northwestern AP was directly impacted by an intense atmospheric river (AR) attaining category 3 on the AR scale, which brought anomalous heat and rainfall, while the AR-enhanced foehn effect further warmed its northeastern side. The event was triggered by multiple large-scale atmospheric circulation patterns linking the AR formation to tropical convection anomalies and stationary Rossby waves, with an anomalous Amundsen Sea Low and a record-breaking high-pressure system east of the AP. This multivariate and spatial compound event culminated in widespread and intense surface melt across the AP. Circulation analog analysis shows that global warming played a role in the amplification and increased probability of the event. Increasing frequency of such events can undermine the stability of the AP ice shelves, with multiple local to global impacts, including acceleration of the AP ice mass loss and changes in sensitive ecosystems.

7. Antarctica and the Southern Ocean

   Kyle R. Clem, Susheel Adusumilli, Rebecca Baiman, and 58 more authors

   Bulletin of the American Meteorological Society, Dec 2023

   Place: Boston MA, USA Publisher: American Meteorological Society

2022

1. Les rivières atmosphériques de l’Antarctique

   Vincent Favier, Jonathan Wille, Cécile Agosta, and 7 more authors

   La Météorologie, Dec 2022

   Abs

   Sur une grande partie de l’Antarctique, le bilan de masse (c’est-à-dire de neige) de surface est dominé par quelques événements de précipitations extrêmes. Ces événements dépendent d’intrusions de masses d’air très humide associées à des phénomènes dénommés rivières atmosphériques en provenance de l’océan Austral. Ces rivières atmosphériques influencent fortement le climat ; pourtant, les caractéristiques, les mécanismes et les impacts associés restent mal connus en Antarctique. Nous résumons ici l’état des connaissances sur la mise en place de ces événements extrêmes et leurs impacts à la fois sur l’accumulation de neige, le réchauffement et la fonte en surface de la calotte. Over much of Antarctica, the surface mass balance (i.e. the resultant of snow fluxes at the surface of the ice sheet) is dominated by a few extreme precipitation events. It has recently been shown that these events are linked to intrusions of highly humid air masses related with atmospheric rivers traversing the Southern Ocean. These atmospheric rivers strongly influence the climate, yet their meteorological characterization and associated impacts remain poorly understood in Antarctica. We summarize here the latest research regarding the development of these extreme events and their impacts on snow accumulation, warming, and surface melt on the Antarctic ice sheet.

2. Antarctica and the Southern Ocean

   Kyle R. Clem, Marilyn N. Raphael, Susheel Adusumilli, and 38 more authors

   Bulletin of the American Meteorological Society, Dec 2022

   Place: Boston MA, USA Publisher: American Meteorological Society
3. Contribution of Atmospheric Rivers to Antarctic Precipitation

   Michelle L. Maclennan, Jan T. M. Lenaerts, Christine Shields, and 1 more author

   Geophysical Research Letters, Sep 2022

   Publisher: John Wiley & Sons, Ltd

   Abs

   Abstract Atmospheric rivers (ARs) are efficient mechanisms for transporting atmospheric moisture from low latitudes to the Antarctic Ice Sheet (AIS). While AR events occur infrequently, they can lead to extreme precipitation and surface melt events on the AIS. Here we estimate the contribution of ARs to total Antarctic precipitation, by combining precipitation from atmospheric reanalyses and a polar-specific AR detection algorithm. We show that ARs contribute substantially to Antarctic precipitation, especially in East Antarctica at elevations below 3,000 m. ARs contribute substantially to year-to-year variability in Antarctic precipitation. Our results highlight that ARs are an important component for understanding present and future Antarctic mass balance trends and variability.

4. The circum-Antarctic ice-shelves respond to a more positive Southern Annular Mode with regionally varied melting

   Deborah Verfaillie, Charles Pelletier, Hugues Goosse, and 6 more authors

   Communications Earth & Environment, Jun 2022

   Abs

   The Southern Hemisphere cryosphere has recently shown regionally-contrasted responses to climate change, in particular to the positive phases of the Southern Annular Mode. However, the understanding of the impacts of this mode on ice-shelf basal melt at a circum-Antarctic scale is still limited. Here, we performed idealized experiments with a pan-Antarctic regional ice-shelf cavity-resolving ocean—sea-ice model for different phases of the Southern Annular Mode. We show that positive phases lead to increased upwelling and subsurface ocean temperature and salinity close to ice shelves, while the opposite occurs for negative phases. A one-standard-deviation increase of the Southern Annular Mode leads to a net basal mass loss of 40 Gt yr−1, with strong regional contrasts: increased ice-shelf basal melt in the Bellingshausen and Western Pacific sectors and the opposite response in the Amundsen sector. Estimates of 1000–1200 and 2090–2100 ice-shelf basal melt changes due to the Southern Annular Mode are −86.6 Gt yr−1 and 55.0 to 164.9 Gt yr−1, respectively, compared to the present.

5. An Overview of ARTMIP’s Tier 2 Reanalysis Intercomparison: Uncertainty in the Detection of Atmospheric Rivers and Their Associated Precipitation

   A. B. Marquardt Collow, C. A. Shields, B. Guan, and 17 more authors

   Journal of Geophysical Research: Atmospheres, Apr 2022

   Publisher: John Wiley & Sons, Ltd

   Abs

   Abstract Atmospheric rivers, or long but narrow regions of enhanced water vapor transport, are an important component of the hydrologic cycle as they are responsible for much of the poleward transport of water vapor and result in precipitation, sometimes extreme in intensity. Despite their importance, much uncertainty remains in the detection of atmospheric rivers in large datasets such as reanalyses and century scale climate simulations. To understand this uncertainty, the Atmospheric River Tracking Method Intercomparison Project (ARTMIP) developed tiered experiments, including the Tier 2 Reanalysis Intercomparison that is presented here. Eleven detection algorithms submitted hourly tags–binary fields indicating the presence or absence of atmospheric rivers–of detected atmospheric rivers in the Modern Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2) and European Centre for Medium-Range Weather Forecasts’ Reanalysis Version 5 (ERA5) as well as six-hourly tags in the Japanese 55-year Reanalysis (JRA-55). Due to a higher climatological mean for integrated water vapor transport in MERRA-2, atmospheric rivers were detected more frequently relative to the other two reanalyses, particularly in algorithms that use a fixed threshold for water vapor transport. The finer horizontal resolution of ERA5 resulted in narrower atmospheric rivers and an ability to detect atmospheric rivers along resolved coastlines. The fraction of hemispheric area covered by ARs varies throughout the year in all three reanalyses, with different atmospheric river detection tools having different seasonal cycles.

6. Intense atmospheric rivers can weaken ice shelf stability at the Antarctic Peninsula

   Jonathan D. Wille, Vincent Favier, Nicolas C. Jourdain, and 12 more authors

   Communications Earth & Environment, Apr 2022

   Abs

   The disintegration of the ice shelves along the Antarctic Peninsula have spurred much discussion on the various processes leading to their eventual dramatic collapse, but without a consensus on an atmospheric forcing that could connect these processes. Here, using an atmospheric river detection algorithm along with a regional climate model and satellite observations, we show that the most intense atmospheric rivers induce extremes in temperature, surface melt, sea-ice disintegration, or large swells that destabilize the ice shelves with 40% probability. This was observed during the collapses of the Larsen A and B ice shelves during the summers of 1995 and 2002 respectively. Overall, 60% of calving events from 2000–2020 were triggered by atmospheric rivers. The loss of the buttressing effect from these ice shelves leads to further continental ice loss and subsequent sea-level rise. Under future warming projections, the Larsen C ice shelf will be at-risk from the same processes.

7. An Extreme High Temperature Event in Coastal East Antarctica Associated With an Atmospheric River and Record Summer Downslope Winds

   John Turner, Hua Lu, John C. King, and 4 more authors

   Geophysical Research Letters, Apr 2022

   _eprint: https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2021GL097108

   Abs

   Abstract High surface temperatures are important in Antarctica because of their role in ice melt and sea level rise. We investigate a high temperature event in December 1989 that gave record temperatures in coastal East Antarctica between 60° and 100°E. The high temperatures were associated with a pool of warm lower tropospheric air with December temperature anomalies of \textgreater14°C that developed in two stages over the Amery Ice Shelf. First, there was near-record poleward warm advection within an atmospheric river. Second, synoptically driven downslope flow from the interior reached unprecedented December strength over a large area, leading to strong descent and further warming in the coastal region. The coastal easterly winds were unusually deep and strong, and the warm pool was advected westwards, giving a short period of high temperatures at coastal locations, including a surface temperature of 9.3°C at Mawson, the second highest in its 66-year record.

8. Atmospheric Rivers and Weather Types in Aotearoa New Zealand: a two-way story

   Benjamin Pohl, Hamish D. Prince, Jonathan D. Wille, and 3 more authors

   Jun 2022

   Publisher: Wiley
9. Evaluating Uncertainty and Modes of Variability for Antarctic Atmospheric Rivers

   Christine A. Shields, Jonathan D. Wille, Allison B. Marquardt Collow, and 2 more authors

   May 2022

   Publisher: Wiley

2021

1. El Niño–Southern Oscillation signal in a new East Antarctic ice core, Mount Brown South

   C. K. Crockart, T. R. Vance, A. D. Fraser, and 14 more authors

   Climate of the Past, May 2021
2. Antarctic Atmospheric River Climatology and Precipitation Impacts

   Jonathan D. Wille, Vincent Favier, Irina V. Gorodetskaya, and 6 more authors

   Journal of Geophysical Research: Atmospheres, May 2021

   _eprint: https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2020JD033788

   Abs

   Abstract The Antarctic ice sheet (AIS) is sensitive to short-term extreme meteorological events that can leave long-term impacts on the continent’s surface mass balance (SMB). We investigate the impacts of atmospheric rivers (ARs) on the AIS precipitation budget using an AR detection algorithm and a regional climate model (Modèle Atmosphérique Régional) from 1980 to 2018. While ARs and their associated extreme vapor transport are relatively rare events over Antarctic coastal regions (∼3 days per year), they have a significant impact on the precipitation climatology. ARs are responsible for at least 10% of total accumulated snowfall across East Antarctica (localized areas reaching 20%) and a majority of extreme precipitation events. Trends in AR annual frequency since 1980 are observed across parts of AIS, most notably an increasing trend in Dronning Maud Land; however, interannual variability in AR frequency is much larger. This AR behavior appears to drive a significant portion of annual snowfall trends across East Antarctica, while controlling the interannual variability of precipitation across most of the AIS. AR landfalls are most likely when the circumpolar jet is highly amplified during blocking conditions in the Southern Ocean. There is a fingerprint of the Southern Annular Mode (SAM) on AR variability in West Antarctica with SAM+ (SAM−) favoring increased AR frequency in the Antarctic Peninsula (Amundsen-Ross Sea coastline). Given the relatively large influence ARs have on precipitation across the continent, it is advantageous for future studies of moisture transport to Antarctica to consider an AR framework especially when considering future SMB changes.

3. Relationship Between Weather Regimes and Atmospheric Rivers in East Antarctica

   Benjamin Pohl, Vincent Favier, Jonathan Wille, and 9 more authors

   Journal of Geophysical Research: Atmospheres, Dec 2021

   Publisher: John Wiley & Sons, Ltd

   Abs

   Abstract Here, we define weather regimes in the East Antarctica?Southern Ocean sector based on daily anomalies of 700 hPa geopotential height derived from ERA5 reanalysis during 1979?2018. Most regimes and their preferred transitions depict synoptic-scale disturbances propagating eastwards off the Antarctic coastline. While regime sequences are generally short, their interannual variability is strongly driven by the polarity of the Southern Annular Mode (SAM). Regime occurrences are then intersected with atmospheric rivers (ARs) detected over the same region and period. ARs are equiprobable throughout the year, but clearly concentrate during regimes associated with a strong atmospheric ridges/blockings on the eastern part of the domain, which act to channel meridional advection of heat and moisture from the lower latitudes towards Antarctica. Both regimes and ARs significantly shape climate variability in Antarctica. Regimes favorable to AR occurrences are associated with anomalously warm and humid conditions in coastal Antarctica and, to a lesser extent, the hinterland parts of the Antarctic plateau. These anomalies are strongly enhanced during AR events, with warmer anomalies and dramatically amplified snowfall amounts. Large-scale conditions favoring AR development are finally explored. They show weak dependency to the SAM, but particularly strong atmospheric ridges/blockings over the Southern Ocean appear as the most favorable pattern, in which ARs can be embedded, and to which they contribute.

2020

1. Interannual variability of summer surface mass balance and surface melting in the Amundsen sector, West Antarctica

   Marion Donat-Magnin, Nicolas C. Jourdain, Hubert Gallée, and 7 more authors

   The Cryosphere, Jan 2020

   Abs

   Abstract. Understanding the interannual variability of surface mass balance (SMB) and surface melting in Antarctica is key to quantify the signal-to-noise ratio in climate trends, identify opportunities for multi-year climate predictions and assess the ability of climate models to respond to climate variability. Here we simulate summer SMB and surface melting from 1979 to 2017 using the Regional Atmosphere Model (MAR) at 10 km resolution over the drainage basins of the Amundsen Sea glaciers in West Antarctica. Our simulations reproduce the mean present-day climate in terms of near-surface temperature (mean overestimation of 0.10 ∘C), near-surface wind speed (mean underestimation of 0.42 m s−1), and SMB (relative bias \textless20 % over Thwaites glacier). The simulated interannual variability of SMB and melting is also close to observation-based estimates. For all the Amundsen glacial drainage basins, the interannual variability of summer SMB and surface melting is driven by two distinct mechanisms: high summer SMB tends to occur when the Amundsen Sea Low (ASL) is shifted southward and westward, while high summer melt rates tend to occur when ASL is shallower (i.e. anticyclonic anomaly). Both mechanisms create a northerly flow anomaly that increases moisture convergence and cloud cover over the Amundsen Sea and therefore favors snowfall and downward longwave radiation over the ice sheet. The part of interannual summer SMB variance explained by the ASL longitudinal migrations increases westward and reaches 40 % for Getz. Interannual variation in the ASL relative central pressure is the largest driver of melt rate variability, with 11 % to 21 % of explained variance (increasing westward). While high summer SMB and melt rates are both favored by positive phases of El Niño–Southern Oscillation (ENSO), the Southern Oscillation Index (SOI) only explains 5 % to 16 % of SMB or melt rate interannual variance in our simulations, with moderate statistical significance. However, the part explained by SOI in the previous austral winter is greater, suggesting that at least a part of the ENSO–SMB and ENSO–melt relationships in summer is inherited from the previous austral winter. Possible mechanisms involve sea ice advection from the Ross Sea and intrusions of circumpolar deep water combined with melt-induced ocean overturning circulation in ice shelf cavities. Finally, we do not find any correlation with the Southern Annular Mode (SAM) in summer.

2019

1. West Antarctic surface melt triggered by atmospheric rivers

   Jonathan D. Wille, Vincent Favier, Ambroise Dufour, and 4 more authors

   Nature Geoscience, Nov 2019
2. The Dominant Role of Extreme Precipitation Events in Antarctic Snowfall Variability

   John Turner, Tony Phillips, Meloth Thamban, and 10 more authors

   Geophysical Research Letters, Mar 2019

2017

1. January 2016 extensive summer melt in West Antarctica favoured by strong El Niño

   Julien P. Nicolas, Andrew M. Vogelmann, Ryan C. Scott, and 11 more authors

   Nature Communications, Jun 2017
2. A Self-Organizing-Map-Based Evaluation of the Antarctic Mesoscale Prediction System Using Observations from a 30-m Instrumented Tower on the Ross Ice Shelf, Antarctica

   Melissa A. Nigro, John J. Cassano, Jonathan Wille, and 2 more authors

   Weather and Forecasting, Jun 2017

   Place: Boston MA, USA Publisher: American Meteorological Society
3. Evaluation of the AMPS Boundary Layer Simulations on the Ross Ice Shelf, Antarctica, with Unmanned Aircraft Observations

   Jonathan D. Wille, David H. Bromwich, John J. Cassano, and 3 more authors

   Journal of Applied Meteorology and Climatology, Aug 2017

   Abs

   Accurately predicting moisture and stability in the Antarctic planetary boundary layer (PBL) is essential for low-cloud forecasts, especially when Antarctic forecasters often use relative humidity as a proxy for cloud cover. These forecasters typically rely on the Antarctic Mesoscale Prediction System (AMPS) Polar Weather Research and Forecasting (Polar WRF) Model for high-resolution forecasts. To complement the PBL observations from the 30-m Alexander Tall Tower! (ATT) on the Ross Ice Shelf as discussed in a recent paper by Wille and coworkers, a field campaign was conducted at the ATT site from 13 to 26 January 2014 using Small Unmanned Meteorological Observer (SUMO) aerial systems to collect PBL data. The 3-km-resolution AMPS forecast output is combined with the global European Centre for Medium-Range Weather Forecasts interim reanalysis (ERAI), SUMO flights, and ATT data to describe atmospheric conditions on the Ross Ice Shelf. The SUMO comparison showed that AMPS had an average 2–3 m s−1 high wind speed bias from the near surface to 600 m, which led to excessive mechanical mixing and reduced stability in the PBL. As discussed in previous Polar WRF studies, the Mellor–Yamada–Janjić PBL scheme is likely responsible for the high wind speed bias. The SUMO comparison also showed a near-surface 10–15-percentage-point dry relative humidity bias in AMPS that increased to a 25–30-percentage-point deficit from 200 to 400 m above the surface. A large dry bias at these critical heights for aircraft operations implies poor AMPS low-cloud forecasts. The ERAI showed that the katabatic flow from the Transantarctic Mountains is unrealistically dry in AMPS.

2016

1. Evaluation of the AMPS Boundary Layer Simulations on the Ross Ice Shelf with Tower Observations

   Jonathan D. Wille, David H. Bromwich, Melissa A. Nigro, and 4 more authors

   Journal of Applied Meteorology and Climatology, Aug 2016

   Place: Boston MA, USA Publisher: American Meteorological Society