Sensitivity Experiments

Arctic sea-ice extent decrease Decreasing trend in Arctic sea-ice extent (~8 % per decade), maximizing in late summer, superposed on a large inter-annual variability The summertime inter-annual variability is influenced by a variety of factors: oceanic (influx of Atlantic & Pacific warm waters), meteorological (Arctic circulation patterns), radiative (cloud feedbacks) and cryospheric (pre-conditioning by winter ice thinning) Key issue: Atmospheric response to the summer decrease in Arctic sea-ice extent Does the reduced sea-ice extent at end of summer impact the weather and climate in following autumn and winter months? Does this influence extend beyond boundaries of Arctic Ocean? Here, we focus on autumn when accumulated heat in upper ocean due to lowered albedo is released to the atmosphere, and the year 2007 with record low summer extent Here, we use a high-resolution, global forecast model to resolve regional aspects of sea ice forcing. Seasonal forecast model from ECMWF High horizontal resolution (T159;l62) coupled ocean-atmosphere model (IFS HOPE V3 – cy31r1) The operational ensemble prediction system contains no dynamic sea-ice module; rather, the sea ice albeit realistically initialised from ocean analyses is persisted for ~10 days, then relaxed to seasonal climatology. We have adapted the model to be forced by realistic, observed sea-ice throughout the simulation. Ensemble runs with prescribed sea-ice have been made for the autumn-early winter 2007, and additional ensembles with “erroneous ” sea-ice from 6 previous years have been for sensitivity and potential predictability studies