Analysis of a complex rainfall episode in Catalonia on May 2005

A convective-stratiform rainfall episode occurred in Catalonia (in the North-East of the Iberian Peninsula) on 16-17 May 2005 has been examined, focusing our attention on radar information. The more interesting feature of this storm was the mesoscale vortex developed at 00 UTC 17 May, which could be related to the precipitation processes themselves. Its initial radius was 100 km but it expanded developing to a synoptic scale vortex six hours later.

This mesoscale vortex induced new convection, modified low and midlevel flows and conditioned the dimensions, motion and, therefore, the persistence of the rainfall field.

The analysis of the NWP model operational at the Meteorological Service of Spain (INM) (with two horizontal resolutions: 0.5º and 0.2º) were not able to reproduce this mesoscale cyclonic circulation although it generated a mesolow over the Catalonia-Balearic sea (200 km eastward/southeastward of the observed vortex) with its associated circulation, which could be linked to the main synoptic depression located 1000 km westward.

Hourly and daily rainfall accumulations of this event have been derived from radar information. A significant improvement could be observed from the comparison between raw and QC accumulation fields (especially, after correcting for radome attenuation). However, the effects of bright band contamination and path attenuation by rain remain in corrected fields and limit the quality of rainfall estimates from radar.