For describing the impact of the atmospheric circulation on climate, a considerable number of classifications of weather and circulation types have been developed. These classifications are based on various criteria and methods, and they refer to various atmospheric scales. It is actually not easy to get an overview of all these classifications existing in Europe or even the whole world.
This was the reason to organise a special session of this topic at the 5th European Conference on Applied Climatology (ECAC) in Nice in 2004. The title was 'Synoptic climatology, weather types and downscaling' The presentations demonstrated very clearly that synoptical climatology, which is in fact not a new topic, has not died out, but is still applied to climate phenomena, although the methods and also the applications have been changed throughout the years and decades.
As some of the presenters wished to publish their contribution in a suitable way, and since there were no extended conference proceedings of the ECAC, we were encouraged to set up a special issue for this topic in a dedicated journal. We decided to choose the International Journal of Climatology, since it is a well-known climatological journal, also dealing with circulation pattern analyses and climatological applications. So we were very glad that Glenn McGregor, editor of this journal, was interested and made it possible for us to realise this idea.
The papers of this special issue represent only a small part of the variety of weather and circulation types classifications and their climatological applications, but they are characteristic examples. They refer to different spatial scales from parts of a country within Europe (e.g. north-east Spain) to the large-scale of a region e.g. North Atlantic -Europe. In particular, this issue consists of the following papers: S. M. Vicente-Serrano and J. I. LΓ³pez-Moreno analysed the spatial and temporal variability of winter droughts in north-east Spain and the influence of the frequencies of weather types and North Atlantic circulation patterns. The influence is highly dependent on the region within north-east Spain.
J. Martin-Vide and J.-A. Lopez-Bustins defined a special circulation index for the western Mediterranean basin, the Western Mediterranean Oscillation Index (WeMOi), which is more appropriate for explaining monthly precipitation anomalies in eastern Spain than the North Atlantic Oscillation (NAO). P. Esteban et al. applied Principal Component Analysis and clustering techniques to generate a classification of daily sea-level pressure patterns for western Europe (30-60 Β°N, 30 Β°W -15 Β°N) for the period 1960-2001 using the NCEP/NCAR reanalysis data. The methodology appears to be applicable to other climatic areas of the world also. M. Baldi et al. analysed heat waves in the Central Mediterranean of the last half-century in relation to the position of the Mediterranean jet stream. A circulation configuration with a streak of the Mediterranean jet over the Alps and a strong anti-cyclonality south of it, forcing a strong subsidence and an adiabatic warming over the Mediterranean, is characteristic for anomalous warm spells in this region. J. Bartholy et al. evaluated the number of mid-latitude cyclones, the position of cyclone tracks and the cyclonic intensity over the North Atlantic and Europe for the years 1957-2002. Their results suggest that both the number and the intensity of mid-latitude cyclones increased considerably during this period, especially over the northwestern Atlantic.