Collaborative Research: An eddy-permitting Arctic & Sub-Polar State Estimate for climate research

点击翻译按钮获取中文摘要

Funds are provided to produce an eddy-permitting Arctic and sub-polar NorthAtlantic state estimate (ASTE) for climate research, using basic tools developed within the Estimating the Circulation and Climate of the Ocean (ECCO) consortium. The coupled ocean/sea-ice general circulation model (MITgcm) will be constrained by as many ocean and sea-ice observations as available and practical. The target period is from 1992 to present. The fit will be achieved through minimization of a least-squares misfit function (adjoint or Lagrange Multiplier method). The coupled ocean/sea-ice adjoint model has been generated by means of automatic differentiation (AD). A similar effort has been successfully accomplished with the production of the Southern Ocean State Estimate (SOSE). The domain of the ASTE covers the Atlantic northward of 26 N and the entire Arctic, with the exception of the Pacific sector southward of Bering Strait (66 N). The horizontal resolution is 7 to 12 km with 50 vertical levels. The control space comprises the initial conditions of the coupled ocean/sea-ice state, the time-varying surface atmospheric state, time-varying open boundary conditions, and spatially varying model parameters.The observational backbone used initially for the ocean consists of: sea surface height from satellite altimetry, daily satellite SST, mean geoid and time-varying bottom pressure from satellite gravity and moorings, Argo float profiles, hydrographic data from WOCE and PHC, available mooring arrays such as Line-W and RAPID/MOCHA, and current meters available via AON/CADIS, PANGEAE (ASOF), and NSIDC (SCICEX). Sea-ice satellite observations used initially will comprise: daily ice concentration, ice drift velocities from passive microwave radiometry, scatterometry, and SAR imagery. In-situ under-ice data will include ice-tethered profilers, ice mass balance buoys, ice draft from submarine-borne upward looking sonar, as well as various buoy and mooring data from the IABP and AON/CADIS archives. Extension to other data sources includes tests of satellite retrievals of ice thickness or freeboard data from combined radar and laser altimetry.Their approach offers strict dynamical consistency of the computed state estimate over the entire integration period, enabling exact time-varying budget calculations relevant for climate studies, such as the assessment of circulation shifts and their associated lateral heat and freshwater changes on seasonal and longer time scales. In this sense, the product differs significantly from what in the atmospheric context are called ?re-analysis? products. Another novelty of the product is its combined treatment of the Arctic and the subpolar gyre, and the synthesis of all available data types. Initial science foci will be on the connection between deep water formation processes and the Atlantic meridional overturning, the freshwater input at high latitudes and its pathways, and the interaction between Atlantic Water, Arctic halocline formation, and sea-ice.