Characterisation of convective events in Belgium
In the last years it became clear that typical severe storm features like bow echoes, downbursts or even tornadoes are more frequent than previously thought. As of 2008, scientific research on severe convective storms on the Belgian territory was very limited and a systematic study of convective storms on Belgian territory was needed.
In 2009, our radar group started a research project to characterise the convective storm activity. The results of this project have been published in 2013 in the Journal of Applied Meteorology and Climatology. The paper can be find on the AMS website with this abstract summarising the main results below the link :
High-resolution volumetric reflectivity measurements from a C-band weather radar are used to study the characteristics of convective storms in Belgium. After clutter filtering, the data are processed by the storm-tracking system Thunderstorm Identification, Tracking, Analysis, and Nowcasting (TITAN) using a 40-dBZ reflectivity threshold. The 10-yr period of 5-min data includes more than 1 million identified storms, mostly organized in clusters. A storm is observed at a given point 6 h yr−1 on average. Regions of slightly higher probability are generally correlated with orographic variations. The probability of at least one storm in the study area is 15%, with a maximum of 35% for July and August. The number of storms, their coverage, and their water mass are limited most of the time. The probability to observe a high number of storms reaches a maximum in June and in the early afternoon in phase with solar heating. The probability of large storm coverage and large water mass is highest in July and in the late afternoon. Convective storms are mostly small and weak. Deeper ones are found mainly in the afternoon whereas bigger and more intense ones also appear in the evening. The occurrence of the most intense storms does not vary along the day. Simple tracks have a mean duration of 25 min. Complex tracks, involving splitting or merging, last 70 min on average. Most convective storms move in the northeast direction, with a median speed of 30 km h−1. Their motion is slower in summer and in the afternoon. Regions with slightly higher convective initiation are related to orography.
An example of an interactive analysis of a convective event (16h49UT, 1 Oct 2006) with the "TITAN" software package developed at UCAR (US). The cell marked in blue on the figure caused a tornado in the vicinity of Brussels. The yellow polygons indicate the past locations of this cell, the cyan ones the future locations. The red area is a forecast position of this cell for 1hr ahead, based on its previous locations and size.
Classification of convective storms by their organisation mode.
It can be seen that most storms are of the cellular type while convective systems (with an area bigger than 100 km²) are relatively rare. Convective cells tend to be organized (nearest neighbouring cell at less than 10 km) rather than isolated.
Kinematics of convective storms.
Distribution of storm tracks kinematic properties : (a) number of individual tracks per complex track, (b) duration and (c) mean direction.
Contact person for this topic: Edouard Goudenhoofdt