1Lab. Física de la Atmósfera. Instituto de Medio Ambiente. Universidad. de León - Spain
2Instituto Nacional de Meteorología. Centre Meteorològic de les Illes Balears - Spain
3Sistemas Lógicos. León - Spain
4ADV Terres de Ponent. Lleida - Spain
5Grup de Meteorologia Departament de Física. U. de les Illes Balears - Spain
It is a well-known fact that the formation of convective systems depends heavily on the atmospheric conditions. The meteorological radar is a tool that provides the necessary data in order to describe the characteristics of these systems. In the case of severe precipitation the radar plays an important role in the characterization of the intensity of the precipitation. It is not easy to determine when a storm has produced rain or hail, since hail generally falls over extensions of only a few hundred km2. In order to distinguish the storm cells that produce rain from those that produce hail, it is necessary to take into account what is known as the 'ground truth'. Then, we may establish the relationship between the reflectivity values registered by the radar and the characteristics of the precipitation.
A project called PAIRAGRA is being carried out in the Ebro Valley, in the NE of the Iberian Peninsula. The project makes also use of a C-band radar that provides images every 3 and a half minutes, approximately. The TITAN software determines the values of the radar variables. The ground truth is determined by means of:
• A network of 166 hailpads located every 4 x 4 km.
• A dense network of observers who register where and when there has been a hailfall.
The first network provides quantitative data about the hailfall, while the second one provides qualitative information. It is necessary to point out here that the damages caused by hail in this area of the Iberian Peninsula amount to approximately 50 M€ annually.
The characteristics of the storms are related to the meteorological conditions in which they develop. Taking into account the huge cost of the damages caused by hailfalls in the Ebro Valley, the main aim of this study is to analyse the hail events in order to determine the atmospheric conditions in which the hailstorms developed. We have established the relationships between two groups of variables:
• The meteorological variables that characterize the preconvective conditions.
• The radar variables.
The results show that not all the indices of atmospheric stability present a statistically significant correlation with the radar variables. The CAPE and the Lifted Index are among the ones that show a good correlation. Others variables have also been studied.