Much effort is expended on GCM (and higher resolution) simulations of present climate and the projection of future climates. Across Europe, impact studies are dependent on climate scenarios generated by "downscaling" from such models. The assumptions upon which such scenarios are based are too rarely tested at the regional and sub-regional scales. A prime reason for the inadequate testing of these assumptions is the current absence of robust, automated, methodologies for classifying circulation patterns.
The ACCORD objectives are to evaluate existing methodologies for classifying atmospheric circulation patterns, to automate them and to develop new automated schemes. These automated schemes will be used to further understand climatic variability since the late nineteenth century, and the physical links between circulation at different space-scales and between circulation modes and synoptic features. The importance of the North Atlantic Oscillation will be determined with respect to the variability of surface temperature and precipitation across Europe.
It will be determined whether or not circulation changes both at the supra-regional scale (for example, the NAO) and the sub-regional scale (for example, over southern Scandinavia) can explain both the long term and the recent increases in precipitation in many regions of northwest Europe.
Attempts will be made to improve the potential of the circulation classification approach for downscaling (for example, from the regional scale (European) to the sub-regional scale (for example, Iberian Peninsula, Scandinavia), and from the sub-regional scale to the catchment scale (Greece)) by optimising the discrimination of observed surface weather variables, and assessing stationarity of relationships. Various methods will be used, including multivariate stochastic models, weather generators, mutiple regression models, and non-linear techniques. Particular attention will be paid to the extent to which the schemes are able to capture the full range of climatic variability, especially extreme events, and to the question of time stationarity of observed circulation/surface weather relationships.