The variability of results from different automated methods of detection and tracking of extratropical cyclones is assessed in order to identify uncertainties related to the choice of method. Fifteen international teams applied their own algorithms to the same dataset—the period 1989–2009 of interim European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERAInterim) data. This experiment is part of the community project Intercomparison of Mid Latitude Storm Diagnostics (IMILAST; see www.proclim.ch/imilast/index.html). The spread of results for cyclone frequency, intensity, life cycle, and track location is presented to illustrate the impact of using different methods. Globally, methods agree well for geographical distribution in large oceanic regions, interannual variability of cyclone numbers, geographical patterns of strong trends, and distribution shape for many life cycle characteristics. In contrast, the largest disparities exist for the total numbers of cyclones, the detection of weak cyclones, and distribution in some densely populated regions. Consistency between methods is better for strong cyclones than for shallow ones. Two case studies of relatively large, intense cyclones reveal that the identification of the most intense part of the life cycle of these events is robust between methods, but considerable differences exist during the development and the dissolution phases.

We investigate the relationship between large‐scale atmospheric flow and the evolution of the most extreme windstorms affecting Western Continental Europe. The 25 most destructive Western Continental European wind storms are selected from a 43‐year climatology. 22 of these storms are grouped as having a similar trajectory and evolution. We show that these storms typically occur during particularly strong and persistent positive NAO anomalies which peak approximately 2 days before the storms' peak intensity; the NAO pattern then shifts eastward to a position over the European continent when the storms strike Europe. A temporal composite of potential temperature on the 2‐PVU surface suggests that this NAO shift is the result of simultaneous cyclonic and anticyclonic wave breaking penetrating further to the east than during a typical high‐NAO event. This creates an extremely intense, zonally‐orientated jet over the North Atlantic whose baroclinicity favours explosive intensification of storms while steering them into Western Continental Europe.

Recent work using both simplified and comprehensive GCMs has shown that poleward moisture transport across midlatitudes follows Clausius-Clapeyron scaling at temperatures close to modern, but that ...

We present a novel cyclone identification and tracking method that explicitly recognizes multicentre cyclones (MCCs), defined as a cyclonic system with two or three sea-level pressure minima within its outermost contour. The method allows for the recognition of cyclone merger and splitting events in a natural way, and provides a consistent measure of the cyclone extent. Using the ERA-Interim reanalysis dataset, we compute a climatology using this method and show that MCCs occur in about 32 of all cyclone tracks and are much more prevalent in more intense storms. We also show that the method permits reconnection of tracks that would have been spuriously split using a conventional method. We present spatial maps of cyclone mergers, splitting, genesis and lysis using the method and also compute statistics of precipitation falling within cyclones, showing that it is strongly concentrated in the most intense cyclones. Copyright (c) 2011 Royal Meteorological Society