标题：The Arctic Subpolar Gyre sTate Estimate: Description and Assessment of a Data-Constrained, Dynamically Consistent Ocean-Sea Ice Estimate for 2002–2017
期刊名称：Journal of Advances in Modeling Earth Systems
电子版ISSN：1942-2466
出版年度：2021
卷号：13
期号：5
页码：e2020MS002398
DOI：10.1029/2020MS002398
出版社：John Wiley & Sons, Ltd.
摘要：A description and assessment of the first release of the Arctic Subpolar gyre sTate Estimate (ASTE _ R1), a data-constrained ocean-sea ice model-data synthesis, is presented. ASTE _ R1 has a nominal resolution of 1/3° and spans the period 2002–2017. The fit of the model to an extensive (O(10 9 )) set of satellite and in situ observations was achieved through adjoint-based nonlinear least squares optimization. The improvement of the solution compared to an unconstrained simulation is reflected in misfit reductions of 77% for Argo, 50% for satellite sea surface height, 58% for the Fram Strait mooring, 65% for Ice Tethered Profilers, and 83% for sea ice extent. Exact dynamical and kinematic consistency is a key advantage of ASTE _ R1, distinguishing the state estimate from existing ocean reanalyses. Through strict adherence to conservation laws, all sources and sinks within ASTE _ R1 can be accounted for, permitting meaningful analysis of closed budgets at the grid-scale, such as contributions of horizontal and vertical convergence to the tendencies of heat and salt. ASTE _ R1 thus serves as the biggest effort undertaken to date of producing a specialized Arctic ocean-ice estimate over the 21st century. Transports of volume, heat, and freshwater are consistent with published observation-based estimates across important Arctic Mediterranean gateways. Interannual variability and low frequency trends of freshwater and heat content are well represented in the Barents Sea, western Arctic halocline, and east subpolar North Atlantic. Systematic biases remain in ASTE _ R1, including a warm bias in the Atlantic Water layer in the Arctic and deficient freshwater inputs from rivers and Greenland discharge. Plain Language Abstract A 2002–2017 ocean-sea ice reconstruction, ASTE _ R1, is distributed for use in climate studies over the early 21st century in the northern high latitudes. The product is a model-data synthesis, using a numerical model to interpolate approximately a billion satellite and in situ observations. The primary strength of ASTE _ R1 compared to most existing ocean reanalyses is that strict adherence to the equations describing the fluid flow and conservation laws is built into the product, thus making ASTE _ R1 free from artificial un-physical sources or sinks and associated “jumps” in the time-evolving state. Furthermore, the product is consistent with most available observations, both used in the synthesis and retained for independent verification. This indicates good large-scale representation of evolving sea-ice, ocean currents and water properties, including year-to-year variability and decadal trends in heat and freshwater storage in the Arctic and subpolar North Atlantic. Some systematic data-model differences remain in the product and highlight where extra data and/or model development will improve the next release. The product and underlying model configuration are freely available to the research community.
关键词：Arctic Mediterranean;data assimilation;heat and freshwater exchange;ocean-sea ice;state estimate;subpolar north Atlantic
