Circulation weather types and cloud-to-ground flash density over the Iberian Peninsula

摘要

Based on the use of an objective classification method for the general atmospheric circulation observed over the Iberian Peninsula for the 1990-98 period, we have characterized the daily circulation by means of a set of indices associated with the direction and vorticity of the geostrophic flow. We analyse the synoptic characteristics of the types of circulation obtained, gaining statistical information about the most frequent basic situations for the annual and seasonal periods. We show how the anticyclone situation (A) predominates in winter, spring and autumn, whereas in summer the most frequent weather corresponds to pure easterly weather (E) followed by cyclonic weather (C). We report the findings of a comparative study between the frequencies of the daily values of the dominant types of circulation and the corresponding daily values of the number of cloud-to-ground flashes over the Iberian Peninsula between 1992 and 1994. Each synoptic situation is described by a set of characteristics that explains the development of the convective processes. A high degree of correspondence was obtained, especially for the months between May and October, in which major storm activity occurs (Pearson correlation coefficient: 0.76). All the results show that convective processes, which generate storm activity, can be appropriately explained in terms of the variability of a small number of general synoptic situations.