Abstract
The Energy Exascale Earth System Model (E3SM) is a state-of-the-science Earth system model (ESM) with the ability to focus horizontal resolution of its multiple components in specific areas. Regionally refined global ESMs are motivated by the need to explicitly resolve, rather than parameterize, relevant physics within the regions of refined resolution, while offering significant computational cost savings relative to the respective cost of high-resolution (HR) global configurations. In this paper, we document results from the first Arctic regionally refined E3SM configuration for the ocean and sea-ice components (E3SM-Arctic-OSI), while employing data-based atmosphere, land, and hydrology components. Our aim is an improved representation of the Arctic coupled ocean and sea ice state, its variability and trends, and the exchanges of mass and property fluxes between the Arctic and the Subarctic. We find that E3SM-Arctic-OSI increases the realism of simulated Arctic ocean and sea ice conditions compared to a similar low-resolution E3SM simulation without the Arctic regional refinement in ocean and sea ice components (E3SM-LR-OSI). In particular, exchanges through the main Arctic gateways are greatly improved with respect to E3SM-LR-OSI. Other aspects, such as the Arctic freshwater content variability and sea-ice trends, are also satisfactorily simulated. Yet, other features, such as the upper ocean stratification and the sea-ice thickness distribution, need further improvements, involving either more advanced parameterizations, model tuning, or additional grid refinements. Overall, E3SM-Arctic-OSI offers an improved representation of the Arctic system relative to E3SM-LR-OSI, at a fraction (15 %) of the computational cost of comparable global high-resolution configurations, while permitting exchanges with the lower latitude oceans that can not be directly accounted for in Arctic regional models.
Highlights
The Arctic Ocean has been undergoing fundamental changes over the past several decades, which are best exemplified by a drastic year-round, and summer, decline in sea-ice coverage (Perovich et al, 2019)
We find that E3SM-Arctic-OSI increases the realism of simulated Arctic ocean and sea ice conditions compared to a similar low-resolution E3SM simulation without the Arctic regional refinement 10 in ocean and sea ice components (E3SM-LR-OSI)
Seasonal (Jan-Feb-Mar, or JFM, and July-Aug-Sep, or JAS) hydrographic profiles of the E3SM-Arctic-OSI and E3SM-LR-OSI 265 simulations are computed over the Arctic Ocean and over the region of the Canada Basin, and compared with i) Regional Arctic System Model (RASM) model results; ii) Ice-Tethered Profiler (ITP) observations2 (Toole et al, 2011); and iii) the World Ocean Atlas 2018 climatology (WOA18; Locarnini et al, 2018; Zweng et al, 2018)
Summary
The Arctic Ocean has been undergoing fundamental changes over the past several decades, which are best exemplified by a drastic year-round, and summer, decline in sea-ice coverage (Perovich et al, 2019). The above examples and many other Arctic to mid-latitude exchange processes are inherently associated with feedbacks between various components of the Earth System, namely the ocean, cryosphere, atmosphere, and land hydrology, and are better explored using a global, fully coupled Earth System Model (ESM). One such model is the recently developed 40 Energy Exascale Earth System Model (E3SM), sponsored by the United States Department of Energy (Golaz et al, 2019). We utilize the E3SM-MPAS framework to evaluate the first regionally refined E3SM Arctic ocean/sea-ice configuration (E3SM-Arctic-OSI), using 10 km horizontal resolution in the pan-Arctic region and 10 − 60 km resolution elsewhere For this particular effort, we use a databased atmosphere model component to force E3SM-Arctic-OSI.
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