A climatology of mesoscale convective systems over Europe using satellite infrared imagery. II: Characteristics of European mesoscale convective systems

Abstract

AbstractAn automated method for mesoscale convective system (MCS) identification and tracking (described in part I) is applied in order to derive a sound European MCS database using Meteosat infrared channel (IR10.8) images centred over Europe, the western Mediterranean and north Africa. The database covers five warm seasons, from April to September, for the years 1993 to 1997 and includes more than 6000 MCSs reaching at least an area of 10 000 km2.First results of the derived climatology of European MCSs are presented. They mainly address the MCS geographical location, general MCS characteristics (maximum extent, eccentricity, duration) and the diurnal cycle of the MCS.MCSs are shown to be mainly continental, but some MCS triggering is observed during the second half of August and September over the western Mediterranean Sea. Furthermore, MCS triggering is strongly correlated with orography and local maxima of MCS triggering are observed near all mountain ranges. Regions near the Alps which favour MCS triggering are described in detail. The monthly distributions of occurrence of warm‐season European MCSs are also presented.Distributions of maximum extent, eccentricity, direction of propagation, life duration and triggering and dissipation times are also derived. On average, a theoretical ‘typical European MCS’ moves to the east‐north‐east, triggers near 3 p.m. Local Solar Time (LST), lasts around 5.5 hours and dissipates near 9 p.m. LST. It typically has an eccentricity at the time of maximum extent of 0.53.The diurnal cycle is also studied and proved to be in phase with the diurnal radiative heating, except for around 20% of the MCSs.A detailed analysis of the maximum‐extent distribution shows that it can be fitted by a log‐normal distribution which leads to an average value of the MCS maximum extent of around 9000 km2. This approximation is statistically meaningful and it is independent of the choice to study only MCSs reaching at least 10 000 km2.Finally, a section of this article is devoted to indirect verifications of the discrimination method (see part I) for the whole geographical domain. Copyright © 2002 Royal Meteorological Society