Heuristic considerations pertaining to hailstone size distributions in theplain of Friuli-Venezia Giulia

In this work, the hailstone size distributions at the ground in the plain o f Friuli-Venezia Giulia are presented, as revealed through a network of pol ystyrene pads (hailpads), managed by volunteers, which has been active sinc e 1988. The aim of this work is to highlight possible differences in the di urnal and seasonal behavior of hail at the ground, both from Friuli-Venezia Giulia and other countries, in order to improve the knowledge of this mete orological phenomenon. In the comparison between different countries, differences are found betwee n the yearly size distributions of Friuli-Venezia Giulia and those of North -East Colorado, measured during the National Hail Research Experiment (NHRE ). The size distributions obtained in South West France and in Friuli-Venez ia Giulia are quite similar and they are slightly different from those of t he Grossversuch experiment. In the comparison between different periods of the year, relevant differenc es an found between April and May and the other months. In particular, thun derstorms are less efficient in producing big hailstones during the former months. The most prolific month in producing hailstones is June, followed b y September. This feature is interpreted as due to a form of synergy betwee n the frequency of the synoptic forcing of storms and the amount of availab le energy at the ground. Analyzing the size distributions at different times of the day, the greates t differences are found in the intervals [00-06] and [06-12] in local time (respectively, [22-04] and [04-10] in UTC). These differences cannot be asc ribed to the melting of the hailstones during their fall. (C) 2001 Elsevier Science B.V. All rights reserved.