1Dept. de Física de la Atmósfera. Fac. de Ciencias. Universidad de Salamanca - Spain
2 Dept. de Física. Instituto del Medio Ambiente. Universidad de León - Spain
Based on the use of an objective classification scheme of the general atmospheric circulation affecting the Iberian Peninsula between 1990 and 1998, daily circulation has been characterized through the use of a set of indices associated with the direction and vorticity of the geostrophic flow.
The synoptic characteristics and the frequency of circulation weather types (CWTs) are analyzed, obtaining the 5-6 basic situations with the highest statistical frequency. It is shown that the anticyclonic (A) type is the most frequent class in the winter, spring and autumn seasons, while in summer, the pure easterly (E) type followed by the cyclonic (C) type occur predominantly.
Comparisons were made of the frequencies of the daily dominant circulation types and the corresponding daily values of the cloud-to-ground lightning flashes observed over the Iberian Peninsula for the 1992 to1994 period. Each synoptic situation is described by means of a group of characteristics that afford an explanation for the development of the convective processes. The results suggest a high degree of correspondence, especially for the months of May to October, in which stormy activity is the major feature (r = 0.76). The existence of strong links between the variability in cloud-to-ground lightning flashes and the variability in a reduced number of circulation weather types shows that storm activity on long temporal and large spatial domains may be objectively explained as a function of synoptic situations.