Rapid Summertime Sea Ice Melt in a Coupled Numerical Weather Prediction System.
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| Title: | Rapid Summertime Sea Ice Melt in a Coupled Numerical Weather Prediction System. |
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| Authors: | Barrell, Christopher1 (AUTHOR) c.barrell@uea.ac.uk, Renfrew, Ian A.1 (AUTHOR), Bennett, Miriam1 (AUTHOR), Elvidge, Andrew D.1 (AUTHOR), Weiss, Alexandra2 (AUTHOR), Methven, John3 (AUTHOR), Blockley, Ed4 (AUTHOR), Copsey, Dan4 (AUTHOR), Graham, Tim4 (AUTHOR), Krumpen, Thomas5 (AUTHOR) |
| Source: | Journal of Advances in Modeling Earth Systems. Oct2025, Vol. 17 Issue 10, p1-23. 23p. |
| Subject Terms: | *Sea ice, *Climate feedbacks, *Cyclones, Numerical weather forecasting, Phase transitions, Heat radiation & absorption, Model validation |
| Geographic Terms: | Arctic regions, Fram Strait |
| Abstract: | Coupled Numerical Weather Prediction (NWP) models have only recently been implemented for short‐term environmental prediction and both challenges and benefits are evident in polar regions. Their simulation of surface exchange over sea ice depends on the model's sea‐ice characteristics, however these are hard to constrain due to a lack of in situ and accurate remotely sensed observations. We focus on the Fram Strait region during peak melt conditions and during the passage of an Arctic cyclone: very challenging conditions for coupled NWP. We use in situ aircraft observations from the Arctic Summertime Cyclones field campaign in July‐August 2022, plus satellite products, to evaluate a set of 5‐day forecasts from the Met Office Unified Model. Our model set ups are based on operational GC4 (Global Coupled 4) and developmental GC5 (Global Coupled 5) configurations, which use the CICE5.1 and SI3 sea‐ice models respectively. We find a combination of deficiencies in the simulated sea‐ice field, due to initialization and modeling problems. An initially low concentration of sea ice results in excessive absorption of shortwave radiation by the ocean, leading to excessive basal melting of the sea ice, and further sea‐ice loss; leading to relatively poorly simulated sea‐ice fields in general. In contrast, the passage of an Arctic cyclone and its impact on sea‐ice velocities are captured well. Although we demonstrate several deficiencies in the short‐term forecasts of two state‐of‐the‐art coupled NWP models, we also find promising aspects of model performance and some clear benefits from a fully coupled atmosphere‐ice‐ocean system. Plain Language Summary: Weather prediction in the Arctic requires an accurate representation of sea ice as it plays a key role in the exchange of momentum, heat and moisture between the surface and the atmosphere. We investigate a challenging set of conditions for weather forecasting: the passage of an Arctic cyclone over Fram Strait in the European Arctic during peak summertime sea ice melting. We use observations made during the Arctic Summertime Cyclones field campaign in July‐August 2022 to evaluate forecasts from the Met Office Unified Model that feature ocean and sea ice model components that interact (are "coupled") with the atmosphere. We find discrepancies in the simulated sea ice field that result from issues in the satellite observations fed into the models and model biases. A lack of sea ice results in increased heat absorption by the ocean, after which the warmer water melts the sea ice faster, forming a feedback loop known as the ice‐albedo feedback. The passing cyclone also drives changes in the sea ice cover, but we find that these effects are generally simulated well in the forecasts. Overall, despite the issues discussed, we find that using such coupled models are advancing weather prediction in the Arctic. Key Points: Sea ice melts too fast in 5‐day coupled forecasts from August 2022, verified using in situ aircraft observations and satellite‐based productsThe assimilated sea‐ice fraction product is biased low, leading to accelerated sea ice melt through the ice‐albedo feedback mechanismThe passage of an Arctic cyclone provides a short‐term dynamical forcing of the sea ice that is reasonably well represented in the forecasts [ABSTRACT FROM AUTHOR] |
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| Abstract: | Coupled Numerical Weather Prediction (NWP) models have only recently been implemented for short‐term environmental prediction and both challenges and benefits are evident in polar regions. Their simulation of surface exchange over sea ice depends on the model's sea‐ice characteristics, however these are hard to constrain due to a lack of in situ and accurate remotely sensed observations. We focus on the Fram Strait region during peak melt conditions and during the passage of an Arctic cyclone: very challenging conditions for coupled NWP. We use in situ aircraft observations from the Arctic Summertime Cyclones field campaign in July‐August 2022, plus satellite products, to evaluate a set of 5‐day forecasts from the Met Office Unified Model. Our model set ups are based on operational GC4 (Global Coupled 4) and developmental GC5 (Global Coupled 5) configurations, which use the CICE5.1 and SI3 sea‐ice models respectively. We find a combination of deficiencies in the simulated sea‐ice field, due to initialization and modeling problems. An initially low concentration of sea ice results in excessive absorption of shortwave radiation by the ocean, leading to excessive basal melting of the sea ice, and further sea‐ice loss; leading to relatively poorly simulated sea‐ice fields in general. In contrast, the passage of an Arctic cyclone and its impact on sea‐ice velocities are captured well. Although we demonstrate several deficiencies in the short‐term forecasts of two state‐of‐the‐art coupled NWP models, we also find promising aspects of model performance and some clear benefits from a fully coupled atmosphere‐ice‐ocean system. Plain Language Summary: Weather prediction in the Arctic requires an accurate representation of sea ice as it plays a key role in the exchange of momentum, heat and moisture between the surface and the atmosphere. We investigate a challenging set of conditions for weather forecasting: the passage of an Arctic cyclone over Fram Strait in the European Arctic during peak summertime sea ice melting. We use observations made during the Arctic Summertime Cyclones field campaign in July‐August 2022 to evaluate forecasts from the Met Office Unified Model that feature ocean and sea ice model components that interact (are "coupled") with the atmosphere. We find discrepancies in the simulated sea ice field that result from issues in the satellite observations fed into the models and model biases. A lack of sea ice results in increased heat absorption by the ocean, after which the warmer water melts the sea ice faster, forming a feedback loop known as the ice‐albedo feedback. The passing cyclone also drives changes in the sea ice cover, but we find that these effects are generally simulated well in the forecasts. Overall, despite the issues discussed, we find that using such coupled models are advancing weather prediction in the Arctic. Key Points: Sea ice melts too fast in 5‐day coupled forecasts from August 2022, verified using in situ aircraft observations and satellite‐based productsThe assimilated sea‐ice fraction product is biased low, leading to accelerated sea ice melt through the ice‐albedo feedback mechanismThe passage of an Arctic cyclone provides a short‐term dynamical forcing of the sea ice that is reasonably well represented in the forecasts [ABSTRACT FROM AUTHOR] |
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| ISSN: | 19422466 |
| DOI: | 10.1029/2025MS004945 |
