Enhancing seasonal-to-decadal Prediction Of Climate for the North Atlantic Sector and Arctic (EPOCASA)

During the last decade global surface temperatures rose less rapidly than in the preceding decades. The northern hemisphere saw a spate of harsh winters, exemplified by the last one with extremely cold temperatures and high snowfalls across Europe and eastern North America, and one of the driest March in Western Norway since reliable observations started around 1900. At the same time the Arctic experienced extreme warming and accelerated sea ice loss, culminating in the record-low of September 2012. While anthropogenic global warming may explain much of the recent changes, the northern hemisphere climate fluctuates strongly on timescales of several decades. EPOCASA aims to assess the extent to which these changes are predictable, by developing and applying a dynamical climate prediction system, focusing on the North Atlantic Sector and Arctic. EPOCASA is motivated by several recent advances: the demonstration that subpolar North Atlantic sea surface temperature (SST) are predictable on seasonal-to-decadal timescales, with observed links to the Nordic Seas and Arctic; potential role of stratosphere-troposphere interactions in the atmospheric response to tropical and extra-tropical SST, sea ice, and snow cover variations; as well as the need to reduce model systematic error and develop more advanced initialisation techniques. We will analyse observations and perform extensive model simulations to assess the potential of these factors to enhance climate prediction in the region. The EPOCASA prediction system couples an advanced data assimilation method (the Ensemble Kalman Filter) to the current version of the Norwegian Earth System Model, building upon developments initiated at the Center for Climate Dynamics at the Bjerknes Center. It will be first seasonal-to-decadal climate prediction capability in Norway, paving the way for operational climate prediction that will be of direct benefit to Norwegian Society and Economy.