https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2024JD041412
*Authors* Alistair Duffey, Robbie Mallett, Victoria R. Dutch, Julia Steckling, Antoine Hermant, Jonathan Day, Felix Pithan First published: *07 June 2025* https://doi.org/10.1029/2024JD041412 *Abstract* The Arctic winter atmospheric boundary layer often features strong and persistent low-level stability (LLS), which arises from longwave radiative cooling of the surface during the polar night. This stable stratification results in a positive lapse rate feedback, which is a major contributor to Arctic amplification. A second state, with cloudy conditions, weaker stability, and near-zero net surface longwave flux is also observed. Previous work has shown that many CMIP5 models fail to appropriately partition water between liquid and ice phases in mixed-phase clouds, leading to a lack of this cloudy state. In this study, we assess the representation of the Arctic winter atmospheric boundary layer over sea ice in global climate models contributing to the latest phase of the Coupled Model Intercomparison Project (CMIP6). We compare boundary layer process relationships in these models to those in surface-based and radiosonde observations collected during the MOSAiC (2019–2020) and SHEBA (1997–1998) expeditions, and by North Pole drifting stations (1955–1991). The majority of CMIP6 models fail to realistically represent the cloudy state over winter Arctic sea ice. Despite this, CMIP6 multimodel mean LLS falls within the observational range, and models mostly capture the observed dependence of LLS on near-surface air temperature and wind speed. CMIP6 models predict a decline in winter LLS with Arctic warming, with mean stability falling below zero by 2100 under the SSP2-4.5 scenario. Our results highlight the failure to accurately simulate mixed-phase clouds as an important limitation on representing a realistic Arctic winter boundary layer in many CMIP6 models. *Key Points* A cloudy state, without strong low-level stability (LLS), is often observed over winter Arctic sea ice but is absent in most Coupled Model Intercomparison Project (CMIP6) models CMIP6 models show a realistic representation of the dependence of LLS on near-surface air temperature and wind speed Observations show a decreasing trend in Arctic winter LLS, which CMIP6 models project will continue under warming *Plain Language Summary* The atmospheric boundary layer is the lowest part of the atmosphere, directly influenced by contact with the Earth's surface. In the Arctic winter, this layer of the atmosphere is often coldest nearest the surface, making it stable against vertical mixing. This feature of Arctic climate is part of the explanation for the much more rapid warming seen in the Arctic than elsewhere, known as Arctic amplification. In this study, we compare the winter Arctic boundary in climate models against that which has been observed in field campaigns. We assess the latest generation of climate models and the most recent major overwinter Arctic field campaign, MOSAiC, as well as earlier and often underexploited observations: the SHEBA campaign and the North Pole drifting stations. We show that cloudy conditions are underrepresented in many of these models. However, these models mostly succeed in representing how stability varies with temperature and wind speed. As the Arctic warms, low-level stability is expected to decrease and models project that the stable state will no longer be dominant in the Arctic winter before the end of the century under a medium emissions scenario. *Source: AGU* -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion visit https://groups.google.com/d/msgid/geoengineering/CAHJsh9_cGdF7LNvPxt%2BOF3-71jN4%3Df66nR9EyxMygZ741ArKpg%40mail.gmail.com.
