Performance of the ECMWF forecasting system in the Arctic during winter

The performance of the ECMWF forecasting system in the Arctic during boreal winter is investigated. A comparison between different analysis products suggests that synoptic-scale features in the Arctic are relatively well represented by state-of-the-art analysis systems. Furthermore, it is shown that the improvement in deterministic forecast error in the Arctic since the early 1980s closely follows that reported in previous studies for the Northern Hemisphere as a whole. One of the biggest 'jumps' in deterministic forecast skill, both in the troposphere and in the stratosphere, occurred in autumn 2000 when the high-resolution deterministic system (T(L)511, about 40 km) was introduced at ECMWF. Our results suggest that 10-day forecasts of the stratospheric circulation have been very skilful, particularly since the introduction of the high-resolution system. Adjoint computations reveal pronounced flow-dependence of the sensitivity of short-range forecast error to initial perturbations at high northern latitudes (north of 70 degrees N); this highlights the importance of using ensemble prediction systems (EPSs) for weather forecasting in the Arctic. Verification of the ECMWF EPS in the Arctic reveals substantial improvements in probabilistic predictive skill since the mid-1990s. The most pronounced increase in probabilistic forecast skill, particularly on synoptic scales, occurred in autumn 2000 when the high-resolution EPS (T(L)255, about 80 km) was introduced. Finally, it is shown that the observed stratosphere - tropo sphere link ('downward propagation' of stratospheric anomalies), which constitutes a potential source of extended-range predictability in high latitudes, is realistically represented in seasonal integrations with the ECMWF model - even at the relatively low horizontal resolution of T(L)95 (about 180 km). Copyright (C) 2007 Royal Meteorological Society.