The footprint of COST733

Weather and/or circulation type classification has engaged meteorologists and climatologists for a long time. Classification usually means to group something that can appear as complex and chaotic into something discrete, structured and easy to understand based on characteristic features of the process to be grouped. In atmospheric sciences classifications have a long tradition, and got a renaissance in the 1990’ies as helpful tools to understand the impacts of a changing climate. This required a transition from the traditional manual and subjective classifications such as the German Grosswetterlagen and the British Lamb Weather Types to objective and automatic methods that could run on computers, and a large number of classifications were developed using the opportunities given by computers and tools offered by statistical software. The high number of different methods applied for classification of circulation types implied challenges to the meteorological-climatological communities since most circulation type classifications were adapted to a specific region, and not necessarily easily transferable to another region and they were focused on a specific (environmental) problem, and the spatial and temporal scale are adapted to this purpose. Comparison and evaluation of  the various weather types classifications per se as well as the applications using these classifications was therefore difficult. 

COST Action 733 was initiated aiming to meet the need for a coordinated European effort to produce one or a few standard methods designed to facilitate such comparisons, and to establish a unified, transferable approach to synoptic classifications. COST733 was active between 2005 and 2010, collecting, evaluating and comparing a wide range of synoptic classification methods for various applications. It was a large network of more than 60 scientists. During the course of the actions more than 80 scientific papers were published. 

The main outcome and contribution to the scientific community of the action was however the jointly developed cost733class-software that includes the circulation classification methods selected for evaluation and comparison. This software has been widely used by a large number of scientists world wide over the last 10 years, and has set the standard for  addressing classification of weather types.  During the last 5 years COST733 has been mentioned by more than 300 scientific contributions. In this presentation we will take a short  retrospect of COST733 and look at its role as an inspiration and tool for continued research involving circulation type classifications.