Monitoring and automatic detection of the cold-ring patterns atop deep convective clouds using Meteosat data

This paper presents a newly established database of deep convective storms that exhibit a cold ring at their cloud top, as observed in enhanced infrared (IR) window satellite imagery. The database consists of cold-ring patterns as seen on the Meteosat data over the summer period between 2006 and 2010 for Slovenia and parts of Italy, Austria, Hungary and Croatia. It includes 139 cold rings at different stages, where typically large hail was reported on the ground and as such it serves as an important source of information for any quantitative analysis of the cold rings in this region. The typical characteristics of cold rings in this database are presented and discussed. It was found that the median of the difference between the minimum brightness temperature in the cold ring and the maximum brightness temperature in the central warm spot is 7.1 K, and that the median distance between such pair is 27 km. In addition, the paper presents in detail a new objective satellite-based method for cold-ring or cold-U/V pattern detection on storm tops in infrared imagery. This method uses a combination of infrared brightness temperature from the Meteosat Spinning Enhanced Visible and Infrared Imager (SEVIRI) and the tropopause temperatures from radiosonde measurements. The method was built and evaluated on the cold-ring patterns from the presented database.