Open Access

Ole Einar Tveito, Radan Huth, Andreas Philipp, Piia Post, Massimiliano Pasqui, Pere Esteban, Christoph Beck, Matthias Demuzere, Christel Prudhomme

• Research on relationships between large scale atmospheric circulation and different climatic and environmental variables has multiplied, and with it the need for a simple description of atmospheric conditions. This has led to renewed interest for weather and circulation type classifications. The objective of cost Action 733 was to develop a classification technique scalable to any European region for a wide range of applications. A necessity to reach this goal was to develop a general numerical approach for assessing and comparing classifications of atmospheric circulation and typical weather situations in European regions. In addition, the action aimed to increase the knowledge of the relationships between atmospheric circulation and responding weather, climate and environmental variables. During five years the Action succeeded to produce an extensive, consistent catalogue of atmospheric circulation type classifications (cost733cat) based on different methodological concepts. TheResearch on relationships between large scale atmospheric circulation and different climatic and environmental variables has multiplied, and with it the need for a simple description of atmospheric conditions. This has led to renewed interest for weather and circulation type classifications. The objective of cost Action 733 was to develop a classification technique scalable to any European region for a wide range of applications. A necessity to reach this goal was to develop a general numerical approach for assessing and comparing classifications of atmospheric circulation and typical weather situations in European regions. In addition, the action aimed to increase the knowledge of the relationships between atmospheric circulation and responding weather, climate and environmental variables. During five years the Action succeeded to produce an extensive, consistent catalogue of atmospheric circulation type classifications (cost733cat) based on different methodological concepts. The resulting catalogue and associated classification types are produced through an open source (GPL) software developed within the Action (cost733class), allowing to generate classifications from a wide number of algorithms and parameter options. Hence it provides a freedom to generate classifications tailored to any location or potential application. Criteria and procedures to systematically evaluate circulation type classifications are defined and tested, and several of these are included in the software. The Action has provided a unique opportunity to systematically evaluate an extensive number of classifications within a coordinated inter-disciplinary environment, and has increased the knowledge on a range of classification approaches, extremely useful for developing any new weather type classification method for European Regions.…