Irina Valerievna Gorodetskaya

Atmospheric rivers (ARs) are the conduit for the majority of atmospheric moisture transport to the polar regions and influence the evolution of polar ice sheets and sea ice. Their impacts on the polar cryosphere are expected to intensify as atmospheric moisture content and temperatures increase in a warming climate. Previous Atmospheric River Tracking Method Intercomparison Project (ARTMIP) studies show that quantitative and qualitative conclusions about the global climatology, impacts, and future changes of ARs depend on the choice of AR detection tool (ARDT) used in the analysis. There is a community need for a similar comparison of ARDTs in the polar regions (both the Arctic and Antarctica), where the unique atmospheric conditions require different parameters for AR detection relative to global ARDTs. Here, we present the ARTMIP polar synthesis experiment, a collaborative effort to provide community guidance on best practices for ARDT selection in polar studies. We build upon the existing ARTMIP framework to curate and compare AR catalogues from eleven ARDTs that have been developed for polar AR identification. We first analyze Arctic and Antarctic AR climatology across ARDTs in the historical record using MERRA-2 atmospheric reanalysis, focusing on similarities and differences among ARDTs linked to their algorithm design, and the effect of inter-ARDT differences on AR-attributed ice sheet and sea ice impacts. We then extend our analysis to future AR projections by applying a subset of ARDTs to three representative members of the CESM2 large ensemble under the SSP3-7.0 emissions scenario up to the year 2099. Finally, we use a subset of five ARDTs in a case study to assess the sensitivity of existing ARDTs to changes in detection thresholds. Our results show that polar ARDTs can generally be grouped into two categories based on their detection of AR frequency and impacts: (1) "global heritage" ARDTs that were originally developed for global AR studies and subsequently tuned for polar AR detection; and (2) "Antarctic heritage" ARDTs that were developed from inception for AR detection in the interior of Antarctica. The global heritage ARDTs generally show polar AR frequency and impacts that peak in the oceanic storm tracks of both the Northern and Southern hemispheres and decrease toward the poles, with little to no ARs identified in the interior of the Antarctic Ice Sheet. The Antarctic heritage ARDTs, conversely, show a less pronounced meridional gradient in AR detection in both hemispheres, and attribute a substantial proportion of precipitation in the Antarctic interior to ARs. Global heritage ARDTs show a large spread in future AR projections due to their varied algorithm design parameters, while Antarctic heritage ARDTs show greater cross-algorithm consistency in projecting small increases in AR frequency. Our polar synthesis leads us to recommend that researchers carefully consider their research questions and study region when choosing which ARDT(s) to use, and following the guidance from previous ARTMIP experiments, we recommend using multiple ARDTs to constrain uncertainty related to AR detection where possible.

East Antarctica (EA) experienced an unprecedented atmospheric river (AR)-driven heatwave in March 2022. Using high-resolution model simulations, this study investigates how atmospheric moisture (Q) and sea surface temperature (SST) influence AR development and associated surface impacts through latent heat exchange and circulation evolutions. A 20% increase in Q and an ~1.3°C increase in SST over the target region enhanced area-averaged precipitation over EA by up to 10.25% and 17.23%, respectively, while amplifying Dome C warming by up to 5.38°C and 3.95°C. However, the responses are nonlinear, with AR strength and precipitation responding more strongly to reduced Q and enhanced SST. Increased Q accelerates blocking development and AR intensification, shifting the AR eastward and enhancing oceanic precipitation. In contrast, SST warming enhances evaporation and moisture retention, producing a delayed but stronger precipitation response. Temperature changes show strong spatial variability among sensitivity experiments, likely due to uncertainties in cloud radiative effects.

Antarctic sea ice and its snow cover play a pivotal role in regulating the global climate system through feedback on both the atmospheric and the oceanic circulations. Understanding the intricate interplay between atmospheric dynamics, mixed-layer properties, and sea ice is essential for accurate future climate change estimates. This study investigates the mechanisms behind the observed sea-ice and snow characteristics at a coastal site in East Antarctica using in situ measurements in winter–spring 2022. The observed sea-ice thickness peaks at 1.16 m in mid–late October and drops to 0.06 m at the end of November, following the seasonal solar cycle. On the other hand, the snow thickness variability is impacted by atmospheric forcing, with significant contributions from precipitation, Foehn effects, blowing snow, and episodic warm and moist air intrusions, which can lead to changes of up to 0.08 m within a day for a field that is in the range of 0.02–0.18 m during July–November 2022. A high-resolution simulation with the Polar Weather Research and Forecasting model for the 14 July atmospheric river (AR), the only AR that occurred during the study period, reveals the presence of AR rapids and highlights the effects of katabatic winds from the Antarctic Plateau in slowing down the low-latitude air masses as they approach the Antarctic coastline. The resulting convergence of the two airflows, with meridional wind speeds in excess of 45 m s−1, leads to precipitation rates above 3 mm h−1 around coastal Antarctica. The unsteady wind field in response to the passage of a deep low-pressure system with a central pressure that dropped to 931 hPa triggers satellite-derived pack ice drift speeds in excess of 60 km d−1 and promotes the opening up of a polynya in the Southern Ocean around 64° S, 45° E from 14 to 22 July. Our findings contribute to a better understanding of the complex interactions within the Antarctic climate system, providing valuable insights for climate modeling and future projections.

Atmospheric rivers are episodic events that can advect relatively large quantities of moisture to Antarctica, contributing to both disproportionate precipitation and melting events. The Year of Polar Prediction, an international effort to improve weather prediction over the southern polar region, presents an opportunity to study the clouds and precipitation associated with winter atmospheric river events. This study uses enhanced surface, profile, and remote‐sensing observations from the Antarctic Peninsula (AP) during a Targeted Observing Period around 16 May 2022, when an event occurred with local warming similar to a warm front. We compare regional atmospheric simulations with the polar‐optimized version of the Weather Research and Forecasting Model to various in situ and remote‐sensing observations. The study emphasizes data from three stations: Escudero, Vernadsky, and Rothera. Mixed‐phase clouds were simulated at the three stations, with the precipitation being primarily rain at Escudero and primarily snow at Vernadsky and Rothera. The model produced reasonable simulations of the clouds and precipitation. Furthermore, modeled longwave cloud forcing at Escudero had small errors compared to observed values. A sensitivity test enhancing secondary ice production indicates mixed‐phase cloud sensitivity to the Hallett‐Mossop process, especially at Rothera.

Antarctic sea ice and its snow cover play a pivotal role in regulating the global climate system through feedback on both the atmospheric and the oceanic circulations. Understanding the intricate interplay between atmospheric dynamics, mixed-layer properties, and sea ice is essential for accurate future climate change estimates. This study investigates the mechanisms behind the observed sea-ice and snow characteristics at a coastal site in East Antarctica using in situ measurements in winter–spring 2022. The observed sea-ice thickness peaks at 1.16 m in mid–late October and drops to 0.06 m at the end of November, following the seasonal solar cycle. On the other hand, the snow thickness variability is impacted by atmospheric forcing, with significant contributions from precipitation, Foehn effects, blowing snow, and episodic warm and moist air intrusions, which can lead to changes of up to 0.08 m within a day for a field that is in the range of 0.02–0.18 m during July–November 2022. A high-resolution simulation with the Polar Weather Research and Forecasting model for the 14 July atmospheric river (AR), the only AR that occurred during the study period, reveals the presence of AR rapids and highlights the effects of katabatic winds from the Antarctic Plateau in slowing down the low-latitude air masses as they approach the Antarctic coastline. The resulting convergence of the two airflows, with meridional wind speeds in excess of 45 m s⁻¹, leads to precipitation rates above 3 mm h⁻¹ around coastal Antarctica. The unsteady wind field in response to the passage of a deep low-pressure system with a central pressure that dropped to 931 hPa triggers satellite-derived pack ice drift speeds in excess of 60 km d⁻¹ and promotes the opening up of a polynya in the Southern Ocean around 64° S, 45° E from 14 to 22 July. Our findings contribute to a better understanding of the complex interactions within the Antarctic climate system, providing valuable insights for climate modeling and future projections.

Insufficient understanding of the surface energy and mass budgets of the Southern Ocean and Antarctic Continent (SOAC) fundamentally limits our ability to estimate when, how fast and severely the region will respond to anthropogenic climate change. The recent abrupt sea ice decline raises a red flag. The SOAC surface energy and mass budgets are worryingly-inaccurately represented in predictive models. A key problem is the misrepresentation of aerosol-cloud-precipitation interactions and their impact on radiative feedbacks, systematically leading to gross surface temperature and precipitation biases. To mitigate these important shortcomings, Theme 6 aims at closing five critical knowledge gaps: (i) Quantifying aerosol sources, properties and processes; (ii) Characterizing cloud and precipitation properties; (iii) Understanding the surface energy budget and boundary layer structure; (iv) Constraining cloud-circulation coupling; and (v) Advancing the modelling of clouds and aerosols. Together, these five elements describe both the continuum of atmospheric processes and their impacts on the entire SOAC, as well as the large regional variability of these processes. We recommend an integrated ensemble of in situ and remote sensing observations targeted specifically at improving numerical representation and constraining model uncertainties. We emphasize the need for profile observations from the surface to low-level cloud altitude along latitudinal gradients, i.e., from the marginal sea ice zone towards the Antarctic plateau, while simultaneously covering East and West Antarctica as well as the Peninsula. Observations are categorized into three priority levels, where particularly priority 1 builds on existing long-term observations to build a strong legacy from existing efforts into future activities beyond Antarctica InSync. Priority 2 and 3 focus on process studies. Theme 6 will mitigate the present lack of structured data to constrain aerosol-cloud-precipitation processes and their radiative feedbacks.

Antarctica InSync is a global effort to synchronise research across Antarctica and the Southern Ocean, connecting ice, ocean, land, climate, and life to protect this vital region. This roadmap paper introduces the scientific and technological motivation and action plan to build an international programme for a coordinated field season in Antarctica and its surrounding seas. It lays out the international collaboration that is required to realise an ambitious action plan and the opportunities for the science community to address important scientific themes that identify current knowledge gaps. In the spirit of the Antarctic Treaty Consultative Meeting (ATCM), the planned scientific action mandates free data exchange, facilitates international collaboration, and derives expert scientific advice together with the Scientific Committee on Antarctic Research (SCAR). Aligned with challenges of the United Nation Ocean and Cryosphere Decades, we plan a shared global effort to better understand the role of Antarctica and its surrounding ocean for our global futures, building on decades of achievements in polar and ocean science. As a milestone leading up to the next International Polar Year in 2032/33 (IPY5), the ambition is to achieve a new level of cooperation, with opportunities for the next generation of polar scientists around the world by enhancing practices in sharing of ideas, infrastructure and information.

Antarctica is changing faster than our current observation networks can robustly assess or predict. Recent extreme events – major ice-shelf collapse, unprecedented heatwaves and abrupt, record-low winter sea ice – show that rare extremes can rapidly reshape the Antarctic system. These changes matter well beyond the polar regions: Antarctica influences global sea level, ocean circulation, and the whole climate system. This white paper sets out the case for Antarctica InSync (2027–2030) to deliver a four-year, coordinated observational baseline ahead of the International Polar Year 2031/32, so it is possible to distinguish temporary anomalies from long-term shifts, detect early warning signs of tipping points, and improve the evidence base for risk management. The result is more reliable projections, better attribution of drivers, and earlier detection of destabilising trajectories – directly supporting policy decisions on climate adaptation, coastal planning, and the design of international monitoring commitments, specifically targeting the following four focus areas bridging ocean-atmosphere-ice interactions and climate variability: • Snow, firn and SMB: Fund coordinated field and satellite-calibration measurements to reduce the largest uncertainty in sea-level projections: how snowfall, melt, refreezing and runoff will change. • Atmosphere and water cycle: Expand weather, precipitation and water-isotope observations to track storms and moisture transport inland – essential for forecasting extremes and future snowfall/rainfall shifts. • Ocean–sea ice–atmosphere coupling: Invest in marginal-ice-zone and ice shelves fronts observations to understand how sea-ice loss and ocean warming amplify extremes, alter heat/moisture exchange, destabilise ice shelves and weaken deep-water formation. • Variability and warming detection: Combine new observations and ice-core and marine records to separate human-driven trends from natural variability and identify early warning signals of irreversible change.

Precipitation over the Iberian Peninsula (IP) is highly sensitive to atmospheric rivers (ARs)—long corridors of anomalous horizontal and poleward moisture transport from lower latitudes. This study aims to deepen the understanding of the mechanisms behind Iberian ARs and to quantify their contribution to precipitation over a long‐term period. We identify ARs affecting the IP in the ERA5 reanalysis with a 31‐km horizontal resolution and covering a 42‐year period (1979–2020). Additionally, we explore their association with the fronts of extratropical cyclones. Impact on IP precipitation is evaluated using regional observational gridded products (E‐OBS, IB01) and global reanalysis (ERA5). Three AR events (unnamed storm in October 1979, Storm Gong in January 2013, and Storm Ana in December 2017) were selected as case studies and analyzed in detail. During 1979–2020, the IP was affected by 580 persistent ARs (lasting at least 18 hr) with an annual mean of 13.8 ± 2.8 ARs and the northern IP coast being the most affected region. The year 2013 is marked by the highest total number of persistent ARs (20). Cold fronts were found more often in the vicinity of ARs than warm fronts. Case studies highlight changes in the relationship between ARs and fronts throughout their lifecycle. Precipitation associated with persistent ARs exhibits a strong north‐south gradient in the western IP with the highest contribution to annual precipitation occurring in the northern region (∼30%). Our study demonstrates the important role of ARs in the Iberian precipitation using the latest high‐resolution reanalysis and observational data.

With the ongoing warming trend on the Antarctic Peninsula (AP), the amount, intensity, and frequency of precipitation is projected to increase by the end of the 21st century. The future of precipitation phase—whether rainfall will dominate snowfall over the AP—remains uncertain. Warm weather events occurring over the AP have been showing frequent snowfall to rainfall transitions, particularly during atmospheric rivers (AR) (Chyhareva et al., 2021; Wille et al., 2021; Gorodetskaya et al., 2023).ARs are long corridors of anomalously high water vapour transport, which bring heat and moisture towards polar regions and, notably, can also facilitate the transport of aerosols (Lapere et al., 2021). When the sources of moisture and aerosols co-occur within ARs, aerosols can be scavenged and deposited as precipitation on ice-sheet surfaces.In pristine environments such as Antarctica, aerosols of natural origin play an important role in cloud and precipitation formation (Mallet et al., 2023). Bioaerosols, specifically bacteria, can serve as potent ice-nucleating particles, facilitating the formation of ice and influencing precipitation formation, especially in mixed-phase clouds.This study aims to identify culturable bacteria present in precipitation samples—rainfall, snowfall, and surface snow following precipitation events—collected in the northern AP, on King George Island, in the vicinity of the King Sejong station. Bacterial isolates were identified using 16S rDNA gene sequencing, revealing key differences in culturable biodiversity between rainfall and snowfall samples. Genera known for exhibiting ice-nucleating activity, Pseudomonas and Stenotrophomonas, were predominantly recovered from rainfall. Additionally, potentially novel strains were recovered from rainfall samples. Surface snow samples following precipitation events exhibited high culturable biodiversity, including Spirosoma sp. and Bacillus sp. strains, which are adapted to the extreme conditions of aerial and polar environments.These results highlight a shift from snowfall to rainfall-dominated precipitation in the AP may impact the local biodiversity, and the newly introduced ice-nucleating strains can further impact the Antarctic climate. Bacteria associated with ice nucleating activity were recovered from precipitation, indicating bacteria can impact the polar aerosol budget, cloud dynamics and climate of the AP.Future analysis of AR-associated precipitation is key to determining the atmospheric transport of bioaerosols and is a necessary component for understanding the current warming trend of the AP.Acknowledgements: PROPOLAR (Portuguese Polar Program) projects APMAR/TULIP/APMAR2/APMAR2025 and FCT project MAPS (2022.09201.PTDC) and MicroANT (2023.15890.PEX)References:Chyhareva, A., et al (2021). Precipitation phase transition in austral summer over the Antarctic Peninsula. Ukr. Ant. J., https://doi.org/10.33275/1727-7485.1.2021.664Gorodetskaya, I., et al. (2023). Record-high Antarctic Peninsula temperatures and surface melt in February 2022: A compound event with an intense atmospheric river. npj Clim. Atmos. Sci. https://doi.org/10.1038/s41612-023-00529-6Lapere, S., et al. (2024). Polar aerosol atmospheric rivers: Detection, characteristics, and potential applications. J. Geophys. Res.: Atmospheres, 129(2). https://doi.org/10.1029/2023JD039606Mallet, M., et al. (2023). Untangling the influence of Antarctic and Southern Ocean life on clouds. Elementa: Sci. Anthropocene, 11(1). https://doi.org/10.1525/elementa.2022.00130Wille, J. D., et al. (2021). Antarctic atmospheric river climatology and precipitation impacts. J. Geophys. Res.: Atmospheres, 126(8), e2020JD033788Keywords: Antarctic Peninsula, precipitation, bioaerosols, culturable biodiversity, ice-nucleation