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The life cycle of convective‐shower cells under post‐frontal conditions

Seventeen days with post‐frontal shower precipitation are analysed by means of radar data obtained from the German Weather Service's C‐band radar network. The life cycle of clusters—defined here as contiguous rain areas including one or more radar‐reflectivity peaks (i.e. convection cells)—is investigated. To allow for the continuous tracking of clusters, sometimes over a time period of more than an hour, a new, specially adapted tracking algorithm has been developed. The life cycle of convective clusters comprises five different stages: genesis; growth (including merging); stagnation; decay (including splitting); and dissolving. The transition likelihoods from a cluster with n maxima to one with m maxima are determined (the case m > n corresponding to growth and m < n to decay). It is found that, predominantly, clusters grow or decay by one cell. Results relating to the temporal evolution of post‐frontal showers are presented, and a conceptual growth model is proposed. Although single cells are the most frequent cluster type, the spatial structure of the post‐frontal precipitation field is dominated by multi‐celled clusters. Their life cycle is essentially affected by cell merging and splitting. Although the transitions of all (about one million) identified clusters have been analysed and quantified, more research is necessary in order to understand the underlying principles of cluster growth. Copyright © 2008 Royal Meteorological Society