17:15 〜 18:45
[ACG42-P14] Comparison of the Arctic sea ice budget using climate and ice-ocean models with different resolution settings
キーワード：北極海、海氷収支、数値モデリング、大気海氷海洋相互作用
The Arctic is one of the regions where global climate change is most evident. Sea ice symbolizes this change and has been on a clear downward trend for the past few decades, with a further decrease expected at least in the near future. Numerical models are helpful in understanding such sea ice changes, and studies have been conducted using various models in different configurations. However, it still needs to be clarified how the reproducibility of sea ice formation and melting processes, in which sea ice interacts with the atmosphere and ocean in a complex manner, depends on the model setting.
In this study, we conducted historical simulations using a global climate model under several different settings and compared the sea ice budget and other characteristics of the Arctic region. Specifically, we performed experiments using the MIROC6 global climate model, which was jointly developed by the Atmosphere and Ocean Research Institute (AORI), the University of Tokyo, the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), and the National Institute for Environmental Studies (NIES), and its sea ice-ocean component, COCO4.9, at two ocean resolution settings of approximately 1 and 0.25 degrees. In addition, a coupled nested model was also used, in which the Arctic region of the 0.25-degree ocean version of MIROC6 is extended to a resolution of about 5 km using the nesting method. Note that the atmospheric resolution of MIROC6 was fixed to the original T85 in all coupled model cases. The MIROC6 and COCO models were forced by the boundary conditions of the CMIP6 historical experiment and the JRA55-do dataset, respectively, and the results were compared using the end of the 20th century as the analysis period.
The analysis of the sea ice balance shows that the following processes dominate the sea ice budget regardless of the model configurations used: frazil ice formation from open water, basal ice growth from pre-existing sea ice, melting from above the ice, basal and lateral melting below the sea surface, and advection of sea ice. This result is consistent with previous studies of the CMIP6 multi-model analysis. Next, we examined the spatial distribution of terms in the thermodynamic process. Frazil ice formation and basal and lateral ice melting show a distribution with localized peaks at the edges of the sea ice distribution and along the coastline. Comparison between the different settings indicates that these terms are sensitive to the oceanic resolution, especially in winter. This result suggests that the reproducibility of the ocean structure due to different ocean resolutions can strongly influence these processes in the model. On the other hand, the basal ice growth and top ice melting terms have a broader spatial distribution. These terms depend on the spatial distribution of sea ice thickness and albedo parameters, but are also sensitive to whether the model is coupled to the atmosphere. This result suggests that the atmosphere-sea-ice interaction may be more important for the reproducibility of these processes.
In this study, we conducted historical simulations using a global climate model under several different settings and compared the sea ice budget and other characteristics of the Arctic region. Specifically, we performed experiments using the MIROC6 global climate model, which was jointly developed by the Atmosphere and Ocean Research Institute (AORI), the University of Tokyo, the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), and the National Institute for Environmental Studies (NIES), and its sea ice-ocean component, COCO4.9, at two ocean resolution settings of approximately 1 and 0.25 degrees. In addition, a coupled nested model was also used, in which the Arctic region of the 0.25-degree ocean version of MIROC6 is extended to a resolution of about 5 km using the nesting method. Note that the atmospheric resolution of MIROC6 was fixed to the original T85 in all coupled model cases. The MIROC6 and COCO models were forced by the boundary conditions of the CMIP6 historical experiment and the JRA55-do dataset, respectively, and the results were compared using the end of the 20th century as the analysis period.
The analysis of the sea ice balance shows that the following processes dominate the sea ice budget regardless of the model configurations used: frazil ice formation from open water, basal ice growth from pre-existing sea ice, melting from above the ice, basal and lateral melting below the sea surface, and advection of sea ice. This result is consistent with previous studies of the CMIP6 multi-model analysis. Next, we examined the spatial distribution of terms in the thermodynamic process. Frazil ice formation and basal and lateral ice melting show a distribution with localized peaks at the edges of the sea ice distribution and along the coastline. Comparison between the different settings indicates that these terms are sensitive to the oceanic resolution, especially in winter. This result suggests that the reproducibility of the ocean structure due to different ocean resolutions can strongly influence these processes in the model. On the other hand, the basal ice growth and top ice melting terms have a broader spatial distribution. These terms depend on the spatial distribution of sea ice thickness and albedo parameters, but are also sensitive to whether the model is coupled to the atmosphere. This result suggests that the atmosphere-sea-ice interaction may be more important for the reproducibility of these processes.