The Antarctic Peninsula (AP) is warming faster than most regions in the Southern Hemisphere, exhibiting polar warming amplification. This warming trend, most pronounced in the northern and northwestern AP, has been observed since the 1950s. While some stations recorded short-term cooling or no warming between 1999 and 2016, the long-term warming trend remains undeniable. This warming trend is linked to anthropogenic greenhouse gas increases and is causing an increase in the frequency and intensity of warm extremes. These warm extremes significantly impact the cryosphere by inducing positive feedbacks that accelerate warming (e.g., via the ice/snow-albedo feedback). Previous record-high temperatures in the northeastern AP (March 2015 and February 2020) were linked to atmospheric rivers (ARs) combined with an intensified foehn effect. These ARs were connected to enhanced central tropical Pacific convection, triggering a Rossby wave train towards Antarctica, deepening the Amundsen Sea Low and creating a high-pressure system over the Drake Passage, directing the AR towards the AP. This study focuses on the extreme warm event in February 2022, examining its similarities to and differences from the 2015 and 2020 events, combining multi-scale atmospheric circulation drivers with moisture sources and path diagnostics to enhance understanding of the processes responsible for major AP extreme warm periods and surface melt. The analysis uses observational and modeling data, including near-surface observations, radiosonde data, satellite microwave observations, ERA5 reanalysis, MAR (Modèle Atmosphérique Régional) simulations, and Polar WRF (Weather Research and Forecasting model) simulations.

The literature review section extensively cites previous research on Antarctic Peninsula warming, atmospheric rivers, and their impacts on the cryosphere. Studies highlighting the rapid warming trend on the AP since the 1950s, the role of extratropical cyclones and fronts in Southern Ocean freshwater fluxes, and the connection between atmospheric rivers and extreme weather events in Antarctica are reviewed. The influence of blocking high-pressure systems in directing moisture and heat towards Antarctica is discussed, and past studies linking record-high temperatures on the AP to atmospheric rivers are examined. The studies on the teleconnections between tropical convection anomalies and Antarctic extreme weather events via Rossby wave trains are also reviewed, setting the stage for the current study's investigation into the February 2022 event.

This study employed a multi-faceted approach combining various datasets and models. Ground-based temperature and precipitation data from multiple Antarctic Peninsula stations were used, with precipitation data also obtained from a Doppler micro rain radar at the Vernadsky station. ERA5 reanalysis data provided synoptic and climatological analyses, including calculations of integrated vapor transport (IVT) and integrated water vapor (IWV) to characterize atmospheric rivers. The Atmospheric River scale was calculated following Ralph et al. (2019). The regional climate model MAR (Modèle Atmosphérique Régional) at 7.5-km resolution was used for simulations from 1980 to 2022, forced by ERA5 reanalysis data. Snow melt estimates were obtained from MAR, ERA5-Land reanalysis, and satellite microwave observations. High-resolution (1.2-km) Polar WRF simulations were used for local drivers analysis and to study the foehn effect. FLEXPART Lagrangian particle dispersion model was employed with ERA5 input to determine moisture sources and pathways. A circulation analog analysis was performed using ERA5 data to assess the unprecedented nature of the event and quantify the role of climate change. The analysis involved calculating analogs based on the 500-hPa geopotential height and examining 2-m air temperature anomalies in the region. Return periods of temperature anomalies were estimated for several stations using extreme value theory, examining Generalized Pareto Distribution (GPD) fits.

The February 2022 event set record high near-surface temperatures at several Antarctic Peninsula stations, surpassing previous records established since continuous measurements began. Extremely high hourly temperatures were observed for more than two days at some stations. The event had a significant spatial extent and intensity, with widespread temperature anomalies exceeding the 99th percentile. The event also brought significant snowfall over inland areas and intense rainfall along the coast. Daily total rainfall averaged over the AP reached record levels. The event caused widespread and intense surface melt, reaching record-high values for both the area covered by melt and the total daily amount. Surface melt affected the entire areas of several ice shelves, with the daily melt values exceeding 80 mm w.e. over multiple days. The atmospheric river (AR) that caused this extreme event reached category 3 on the AR scale and brought significant heat and moisture advection, particularly affecting the northern and northwestern Antarctic Peninsula. A foehn effect further enhanced the temperature anomalies on the lee side of the Antarctic Peninsula’s mountains. The AR was linked to anomalously deep extra-tropical cyclones, a strong surface high-pressure system, and Rossby wave breaking. This AR drew moisture from the subtropical South Pacific Ocean, where warm SSTs and high evaporation rates occurred. Analysis of circulation analogs showed that the probability of such an extreme event occurring is significantly increased in the present period (1991–2021) compared to the past (1960–1990), highlighting the role of global warming in the event. The event was associated with extreme conditions in the upper troposphere-lower stratosphere, resulting in the increased shear-generated clear-air turbulence over the Drake Passage region.

The findings demonstrate that the February 2022 event was a multivariate and spatial compound event, involving extreme temperatures, precipitation, and surface melt, all linked to an intense atmospheric river. The event's occurrence was amplified by global warming, with a significantly increased probability in the recent period compared to the past. This highlights the potential impact of climate change on the frequency and intensity of such events. The study also notes significant disruptions to local operations, including flight cancellations and delays in scientific projects due to the extreme weather conditions. The high-resolution Polar WRF model highlighted the role of radiative and turbulent heat fluxes, and the foehn effect. The findings have important implications for understanding ice shelf stability and future sea level rise projections, emphasizing the need for improving operational forecasting tools for Antarctica. The results showed the role of tropical convection, Rossby wave propagation, and the Amundsen Sea Low-Weddell Sea High couplet in directing the AR towards the AP. While the event demonstrated similarities to previous heatwaves in 2015 and 2020, there were differences, including the ongoing La Niña conditions and a less pronounced foehn warming effect compared to previous events.

The February 2022 extreme warm event in the Antarctic Peninsula was a record-breaking event, characterized by record-high temperatures and widespread surface melt. The event's intensity and spatial extent were linked to an intense atmospheric river, influenced by a complex interplay of large-scale atmospheric circulation patterns, tropical convection, and Rossby wave activity. Global warming amplified the probability of such an event, highlighting the vulnerability of the Antarctic Peninsula to climate change. This study emphasizes the need for improved understanding of the processes involved in such events and highlights the implications for ice shelf stability and future sea level projections. Future research should focus on improving the representation of extremes in climate models and refining operational forecasting tools for Antarctica.

The study acknowledges that some limitations affect the results and their interpretation. The spatial resolution of some datasets and models might not adequately capture the fine-scale variability of precipitation in complex terrain. The reliance on reanalysis data introduces uncertainties related to the accuracy of the atmospheric data. The circulation analog method, while useful for assessing the role of climate change, doesn't fully capture the complex dynamical interactions that contribute to the event. The study primarily focuses on the February 2022 event and thus, the long-term implications of such events might need additional research.