The COST 733 circulation type classification software : An example for 1 surface ozone concentrations in Central Europe 2

In the framework of the COST733 Action “Harmonisation and Applications of Weather Types 6 Classifications for European Regions” a new circulation type classification software (hereafter referred to 7 as cost733class software) is developed. The cost733class software contains a variety of (European) classifi8 cation methods and is flexible towards to choice of domain of interest, input variables, time step, number of 9 circulation types, sequencing and (weighted) target variables. This work introduces the capabilities of the 10 cost733class software in which the resulting circulation types (CTs) from various circulation type classifi11 cations (CTCs) are applied on observed summer surface ozone concentrations in Central Europe. First, the 12 main characteristics of the CTCs in terms of circulation pattern frequencies are addressed using the baseline 13 COST733 catalogue (cat 2.0), at present the latest product of the new cost733class software. In a second 14 step, the probabilistic Brier skill score is used to quantify the explanatory power of all classifications in 15 terms of the maximum 8 hourly mean ozone concentrations exceeding the 120 μg/m threshold, this based 16 on ozone concentrations from 130 Central European measurement stations. Evaluation results averaged 17 over all stations indicate generally higher performance of CTCs with a higher number of types. Within the 18 subset of methodologies with a similar number of types, the results suggest that the use of CTCs based 19 on optimisation algorithms are performing slightly better than those based on other algorithms (prede20 M. Demuzere Earth and Environmental Sciences, Katholieke Universiteit Leuven (K.U.Leuven), Celestijnenlaan 200E, 3001 Heverlee (Leuven), Belgium Tel. : +32 16 32 64 24 Fax: +32 16 32 29 80 E-mail: matthias.demuzere@ees.kuleuven. be P. Kassomenos Department of Physics, Laboratory of Meteorology, University of Ioannina, 45110 Ioannina, Greece A. Philipp University of Augsburg, Institute of Geography, Physical Geography and Quantitative Methods, 8 Universittsstr. 10, D-86135 Augsburg, Germany 2 M. Demuzere et al. fined thresholds, principal component analysis and leader algorithms). The results are further elaborated 21 by exploring additional capabilities of the cost733class software. Sensitivity experiments are performed us22 ing different domain sizes, input variables, seasonally-based classifications and multiple-day sequencing. As 23 an illustration, also CTCs conditioned towards temperature with various weights are derived and tested 24 similarly. All results exploit a physical interpretation by adapting the environment-to-circulation approach, 25 providing more detailed information on specific synoptic conditions prevailing on days with high surface 26 ozone concentrations. This research does not intend to bring forward a favourite classification methodology 27 or construct a statistical ozone forecasting tool but should be seen as an introduction to the possibilities 28 of the cost733class software. It this respect, the results presented here can provide a basic user support for 29 the cost733class software and the development of a more useror application-specific CTC approach. 30