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Abstract A set of surface energy balance observations from Siple Dome in West Antarctica, combined with all-sky imagery and spectral shortwave irradiance data, provides a unique resource for evaluating atmospheric model performance with current mixed-phase cloud microphysical parameterizations. This location is in a region of current concern regarding atmospheric surface melting stress on ice shelves. The Polar Weather Research and Forecasting (PWRF) Model version 4.7.1, equipped with the Thompson aerosol-aware double-moment parameterization, is initialized with ERA5 reanalysis data to simulate hourly surface radiative flux components and cloud microphysical properties matching observations spanning 21 December 2019–19 January 2020. Consistent with earlier studies, the double-moment scheme improves cloud amount, net longwave, and net radiative flux simulations compared with the ERA5 single-moment scheme. However, PWRF with the double-moment scheme produces simulations that are episodic in their realism compared with all available observations. Instances of good agreement, for example, within 20 W m⁻²in radiative fluxes, alternate with days showing larger discrepancies. Additionally, PWRF produces excessive cloud liquid water during a modest storm system intrusion but inadequate cloud liquid and ice water during quiescent conditions when low-level stratus clouds show phase transitions due to precipitation. These results illustrate the value of Siple Dome as a site for fundamental studies in mixed-phase cloud microphysics. Significance StatementWest Antarctica is seeing increasing episodes of surface melt on the floating ice shelves that buttress and moderate the loss of their upstream glaciers. Surface melt at or slightly below freezing temperatures is driven by solar and atmospheric thermal radiation, which is in turn modulated by the region’s pervasive cloud cover. Atmospheric regional or Earth system models generally have difficulty with realistically simulating cloud cover over West Antarctica because the clouds contain complex mixtures of supercooled liquid water and ice particles in various forms. This study uses a unique surface energy balance dataset from West Antarctica to show not only improvements but also remaining discrepancies in one of the current model representations of cloud physics, providing guidance to improve future field work. 

Abstract Recent decades have seen record-high temperatures on the Antarctic Peninsula (AP) due to combined atmospheric rivers (ARs) and föhn warming. While ARs frequently enhance föhn, not all events cause surface warming over the entire Larsen C Ice Shelf (LCIS). Using high-resolution Polar WRF simulations, we examine the relationship between ARs and föhn over the AP during austral summers and identify four distinct AR shapes associated with föhn-induced surface warming over the LCIS: zonal-perpendicular, zonal-like, convex, and concave. Zonal-like ARs associated with coupled low-high-pressure systems and convex ARs linked to blocking highs produce strong föhn warming across the entire LCIS, primarily affecting its northern and southern sectors, respectively. In contrast, zonal-perpendicular and concave ARs generate moderate-to-weak warming, owing to either weaker AR intensity or AR curvature. Although downward shortwave radiation dominates surface warming, enhanced moisture suppresses its increase from föhn-induced cloud clearance while enhancing downward longwave radiation near mountain gaps. Sensible heat flux also contributes substantially along the mountain foothills. As ARs intensify under climate change, their interaction with föhn over the AP can critically influence the future stability of coastal ice shelves. 

Abstract Global reanalyzes are widely used for investigations of Antarctic climate variability and change. The European Centre for Medium‐Range Weather Forecasts 5th generation reanalysis (ERA5) is well regarded and spans 1940 to today. We investigate whether ERA5 reliably represents the 2‐m air temperature trends across the 1940–2022 (83 years) period at seasonal and annual time scales. We compare ERA5 temperatures with an observation‐based temperature reconstruction for Antarctica (RECON) that has monthly resolution for 1958–2022, the period of reliable observational availability. Results for individual stations are also examined. ERA5 anomalously warms Antarctica in relation RECON especially for the period prior to 1979 when satellite observations over the Southern Ocean were sparse. Trend hotspots that are shown to be artifacts are found at three locations and are present until today. The results demonstrate that ERA5 temperature trends can be questionable even today, but variability is well captured after 1979. 

Antarctic land ice stores the majority of Earth’s freshwater and carries substantial uncertainties regarding its future contribution to global sea level rise. While ocean processes associated with basal melting currently dominate ice loss, atmospheric forcing could have an increasing future impact, especially with intensified extreme weather events. For instance, atmospheric rivers, which are key drivers of long-distance moisture transport, introduce significant uncertainties to Antarctica’s ice mass balance, as they are capable of causing both intense snowfall and surface melting. They also impact ocean stratification and mixed-layer depth through freshwater input, ultimately affecting air-sea exchange. Associated interactions among components of the Earth system—atmosphere, ocean, and glacier—are not fully captured by global climate models and observations. This paper assesses Antarctica’s future, highlighting uncertainties stemming from limited understanding of atmospheric and oceanic forcings such as atmospheric rivers, and their consequences for projecting sea-level rise-related hazards. 

Abstract. Atmospheric rivers (ARs) are the primary mechanism for transporting water vapor from low latitudes to polar regions, playing a significant role in extreme weather in both the Arctic and Antarctica. With the rapidly growing interest in polar ARs during the past decade, it is imperative to establish an objective framework quantifying the strength and impact of these ARs for both scientific research and practical applications. The AR scale introduced by Ralph et al. (2019) ranks ARs based on the duration of AR conditions and the intensity of integrated water vapor transport (IVT). However, the thresholds of IVT used to rank ARs are selected based on the IVT climatology at middle latitudes. These thresholds are insufficient for polar regions due to the substantially lower temperature and moisture content. In this study, we analyze the IVT climatology in polar regions, focusing on the coasts of Antarctica and Greenland. Then we introduce an extended version of the AR scale tuned to polar regions by adding lower IVT thresholds of 100, 150, and 200 kg m−1 s−1 to the standard AR scale, which starts at 250 kg m−1 s−1. The polar AR scale is utilized to examine AR frequency, seasonality, trends, and associated precipitation and surface melt over Antarctica and Greenland. Our results show that the polar AR scale better characterizes the strength and impacts of ARs in the Antarctic and Arctic regions than the original AR scale and has the potential to enhance communication across observational, research, and forecasting communities in polar regions.