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Pascual
CONVECTIVE STORM INITIATION IN WESTERN CATALONIA:
CHARACTERISTICS AND UNCERTAINTIES OF THE METHODOLOGY
USED.
R. Pascual
Instituto Nacional de Meteorologia, Barcelona (Spain), [email protected]
Spanish Instituto Nacional de Meteorología (INM) 2-km resolution radar reflectivity data at 10 min
intervals have been examined to determine location and timing of storm initiation occurring over western
Catalonia and eastern Aragon plains. To carry out this analysis 27 hailstorms occurred between April and
October, from 2000 to 2003, have been selected. For each day, areas of convective initiation have been
registered by identifying and tracking 2D convective cells on the first PPI (0.5º elevation) using an
operational automated software.
A further careful subjective analysis have been carried out to discriminate the radar-detected storm
initiation locations associated to meteorological phenomena (including splits) from those associated to a
number of effects related to the observational method and the specific characteristics of the particular
algorithms included in the operational software. Attenuation, orographic screening, anaprop and other
inherent radar measurement limitations and the specific thresholds and tracking technique included in the
algorithms used introduce some uncertainties in determination of the preferred areas, times and
mechanisms to develop new convective cells.
A set of different artifacts (false storm initiation locations) have been appeared when examining the 27
radar image loops: splitting (false), old cells rebirthing, ground clutter enhancement (anaprop) and
alternation in the characterization of a storm as a single cell or a multicell storm. It is necessary to extract
these artifacts from the total set of storm initiation locations before to establish some conclusions about
the main characteristics of storm initiation in this area.
Finally this paper presents, as an example of application of the methodology proposed, these locations
stratified according to the synoptic and mesoscale pattern and shows that the specific locations are linked
to the presence of convergence lines, identified from a detailed examination of the radar images.
The development of such a methodology to determine storm initiation locations and times using an
operational 2D convective cell detection and tracking automated software allows to obtain spatial and
temporal distributions over other radar domains that have potential benefits on convective storm
nowcasting and short range forecasting.