April 15 Ian Fenty MIT - EAPS Dynamical Reconstruction of the Ocean-Sea Ice State in the Labrador Sea
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Three decades of satellite observations of sea ice extent in the Labrador Sea and Baffin and Baffin Bay reveal significant annual and Interannual variability. This variability mainly occurs across a thermohaline front, where cold fresh buoyant waters of Arctic origin meet warmer saltier waters of subtropical origin. Despite being thermodynamically and dynamically coupled to both the ocean and atmosphere, sea ice variability is commonly rationalized as primarily owing to regional atmospheric anomalies, such as the NAO. This reflects a severe observational bias; the ocean is far less well observed, especially in regions with seasonal sea ice. Recent interest in deep convection in the Labrador Sea has led to a large increase in the number of available in situ ocean observations. Building on the state-estimation framework of the ECCO group, dynamical reconstructions of the ocean-sea ice state, an ocean-ice state estimate, have been generated by combining observations of the ocean and sea ice in a coupled ocean-sea ice model using the adjoint method. These state estimates permit analysis of the ocean-ice processes which led to the observed evolution of the ice pack. In this talk, I discuss theories of sea ice variability in the Labrador Sea, some technical issues pertaining to practical sea ice-ocean state estimation, and analyze a dynamical reconstruction of the ocean-ice state for the sea ice annual cycle spanning September 1996-August 1997. In the analysis, emphasis is placed on the energy and mass budgets which establish the ice pack’s wintertime quasi-equilibrium position.